ISSUE II - JUNE 2017
GOLD EDITION
Featuring: The Eleven Body Systems
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CONTENTS Page A Message From The Editor …………………………………………………………………………4 The Publishing Team…………………………………………………………………………………...5 The Skeletal System…………………………………………………………………………………….7 The Muscular System…………………………………………………………………………………10 The Endocrine System……………………………………………………………………………….12 The Cardiovascular System ……………………………………………………………………...15 The Respiratory System…………………………………………………………………………...19 The Integumentary System……………………………………………………………………...21 The Immune System…………………………………………………………………………………..25 The Digestive System………………………………………………………………………………..28 The Urinary System…………………………………………………………………………………….30
The Reproductive System………………………………………………………………………….33 The Nervous System……………………………………………………………………………………35 A Closing Message……………………………………………………………………………………..37
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A message from the edi tor The Medical Diary is a student run initiative, founded by Akila Wickramathilaka. It endeavours to develop interest in the diverse field that is medicine.
Our writers have the liberty to decide what area of medicine they wish to write about, and so the articles in this magazine were written in their own interests. We try to write our articles in a way which makes it accessible for all audiences, but is more focused towards scientists.
The medical diary investigates a diverse range of areas in medicine, from human anatomy to pathology, drug chemistry to healthcare systems, hence giving a taste of everything.
This special edition focuses on the eleven body systems, and the roles which they play in the human body.
I hope you enjoy reading our articles.
Thank you,
Akila Wickramathilaka (Founder and editor)
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The Publishing Team Akila Wickramathilaka Founder and Editor An aspiring physician with great interest in the human genome, Kaposi Sarcoma, and the use of virtual high throughput screening (vHTS).
Shivam Wadhia Co-Editor An enthusiastic biologist interested in human anatomy, and the metabolic reactions that take place in the human body.
Kieran Graham Co-Editor An aspiring natural scientist with great interest in genetics and gene therapy.
Denis Efovi An aspiring physician with particular interest in the human genome and genetic engineering to treat diseases.
Ajay Krishna A prospective physician with a strong interest in neurology and neurosurgery.
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The Publishing Team Rama Jha An aspiring medic with a particular interest in mental health and its coexistence with physical health, and their impacts.
Mohammad Hakimi
A prospective medical student with particular interests in cancer research, and neuroscience.
Muse Berhe
An aspiring biologist with interest in botany and herbal medicine.
Sai Aakash Chanda An aspiring doctor with particular interest in cardiology, and neuroscience.
Sanka Wijayarathna An aspiring veterinarian with interest in animal and plant conservation.
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The Skeletal System Contrary to popular belief, bones are living tissues and there are two types of bone tissue; compact bones and spongy bones. Compact bones are the outer layer of bone and it’s hard and densely packed. However, spongy bones are found inside of bone as well as at the end of long bones; it’s the weaker part and contains the marrow (red and yellow marrow). By Sanka Wijayarathna
The Skeletal System: It’s ALIVE The skeletal system is composed of bones (206 in adults), and a network of tendons, ligaments and cartilage where more flexibility is required. Insects have exoskeletons; however humans have endo-skeletons which are more beneficial as it allows us to grow more by supporting more mass and gives us more freedom of movement. Even though men and women have the same number of bones, the female skeleton is lighter and smaller because a woman’s pelvis is broader and her shoulders are narrow. This article will focus on the endoskeleton.
Figure 2 structure of a bone
Bones and Cartilage The axial skeleton consists of bones of the head, neck and vertebral column and rib cage, which has 80 bones; it supports and protects organs in the dorsal (posterior) and ventral (anterior) body cavities as well as providing surface area for muscle attachment. The appendicular skeleton consists of the bones of the upper and lower limb, including the pectoral (shoulder) and pelvic girdles and it provides movement and has 126 bones. (interactive-biology). Figure 3 compact and spongy bone
Figure 1 axial and appendicular skeleton
The main function of the compact bone is to support the entire body and it’s also a store of calcium. Due to the porous nature of spongy or bone, spongy bone has a greater surface area compared to compact bone. This allows bone marrow to develop in the region of spongy bone. Red blood cells, platelets and most white blood cells form in red marrow; while some white blood cells develop in the yellow marrow (the yellow colour is caused due to the much higher number of fat cells present in this marrow).
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Compact bone vs Spongy Bone
COMPACT BONE
SPONGY BONE
Other name
Cortical Bone
Trebeculae Bone
Density
Compact
Porous
Location
Outer bone
Inner bone
Functional Unit
Osteon
Trebeculae
All the 206 bones in a human adult can be divided into 5 types; long bone, short bone, flat bone, irregular bone and sesamoid bone. Long bones are tubular and include the bones of the humerus, femur and tibia. Short bones are cube-shaped and are located only in the ankle and wrist. Flat bones serve protective functions and they are bones of the skull, ribs and scapulae. Irregular bones vary in shape and they can either be long, short or flat and are usually found in the bones of the face. Sesamoid bones are round and are formed from certain tendons and are located where the tendons of long bones cross and includes the knee cap or patella (these types of bones protects the tendon from excessive wear). (interactive-biology).
bones. The structure of cartilage varies according to its function, however all cartilage is composed of a matrix where there’s cells as well as fibres made up of collagen and elastin, another important aspect is that cartilage contains no blood vessels. (histology.leeds).
Figure 5 Types of synovial joints
Joints and Ligaments Joints are divided into two categories; synovial (mobile) and fibrous (fixed). Synovial joints are designed to allow for a wide range of movements and are lined with a coating called synovium. Bone ends are covered in a tough elastic material (articulating cartilage), and the entire joint is covered in a strong coating of tough gristle called the joint capsule (this holds the joint in place and prevents abnormal movement). Fibrous joints include the joints present in the skull, the sacrum and the pelvis. These joints have no synovium and are joined by fibrous tissue, permitting movement. However, the joints in the spine are a special exception since they’re flexible enough to allow some movement as well as maintaining their role of supporting the spinal column. (Clancy, 2011)
Figure 4 Structure of long bone
Cartilage (gristle) is a smooth, tough but flexible part of skeletal system. In adults, cartilage is found mostly in joints and also covers the ends of
Ligaments are a form of connective tissue, and can stretch a bit; hence it joins the two bones that form the joint and keeps them in place by restricting the amount of movement. The connective tissue in ligaments are made up mainly of collagen with some elastin, these tissues are arranged in bundles of fibres. These bundles of fibres are arranged in definite directions depending on the type of movement they resist. Ligaments are attached to the bones by fibres which penetrate the outer coating of the bone (the periosteum). 8
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(Clancy, 2011) Function of the Skeletal System The primary functions of the skeletal system are to provide support, protection and movement. The skeleton provides support to the body and keeps the internal organs in their proper place. The bones of the spine, pelvis and legs enable people to stand upright, supporting the weight of their entire body. Body cavities (hollow spaces framed by the skeleton) hold the internal organs. The muscular and skeletal systems work together (musculoskeletal system), as the tendons attach the muscles to the bones of the skeleton, which enables body movement and stability. The shape and the fit of bones allows for the different types of movement. The skeletal system also provides protection, the combination of strength and flexibility gives the skeleton the capacity to absorb the impact of blows to the body without breaking and thus protects the internal organs. The bones are a source of storage for calcium, phosphorus and fatty acids. (github) The bone matrix acts as a reservoir for a number of minerals important to the functioning of the body, especially calcium, and potassium. These minerals can be released back into the bloodstream to maintain levels needed to support physiological processes. Furthermore, the yellow marrow contains adipose tissue; the triglycerides stored in the adipocytes of the tissue can serve as a source of energy. (github) Another function of the skeletal system is that it’s the site of Haematopoiesis (the production of blood cells) takes place in the red marrow and the production of red blood cells, white blood cells, and platelets takes place. (histology.leeds)
histology.leeds. (n.d.). Cartilage, Bone & Ossification: Bone. Retrieved June 23, 2017, from http:// www.histology.leeds.ac.uk/bone/bone.php histology.leeds. (n.d.). Cartilage: The three types of cartilage. Retrieved June 23, 2017, from http:// www.histology.leeds.ac.uk/bone/ cartilage_types.php interactive-biology. (n.d.). AN INTRODUCTION TO THE SKELETAL SYSTEM: BONES AND CARTILAGES. Retrieved June 23, 2017, from http://www.interactivebiology.com/4381/an-introduction-to-the-skeletalsystem-bones-and-cartilage/
Summary The skeletal system is composed of bones, tendons, cartilage, ligaments and joints. There are two types of bone tissue; compact and spongy as well as another connective tissue (bone marrow). Cartilage is a form of connective tissue that can withstand a lot of pressure, tension and bending. Tendons connect muscles to bones and ligaments join two bones that form the joint. The main functions of the skeletal system are to provide support, movement and protection; in addition it’s the site of haematopoiesis, and acts as a mineral reservoir.
Bibliography Clancy, J. (2011). The Human Body Close-up. Quercus. github. (n.d.). Retrieved June 23, 2017, from http:// oerpub.github.io/epubjs-demo-book/content/ m46341.xhtml 9
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The Muscular System these myofibrils are arranged parallel to one another, thus giving rise to a striated appearance. (Wisegeek, 2009)
By Mohammad Hakimi
The main task of a muscle is to generate force, for movement to occur. Secondarily, they also serve to provide shape and form to organisms. In general, there are two basic types of muscle structure, smooth and striated, each of which have different anatomies and functions. These two basic types can be further sub-classed as skeletal muscle or cardiac muscle, however regardless of type, all muscles have the same common properties. These are: conductivity, irritability, contractibility, relaxation, elasticity and distensibility. (Gowitzke, 1998). This article will focus its attention specifically to contractibility, and how the contractions of two types of fibres aid in movement.
The primary differences within smooth and striated muscle is arrangement of sarcomeres. Smooth muscles are comprised of sarcomeres, these are the functional units of a cell. The sarcomeres are arranged at oblique angles to one another, and thus look relatively featureless under a light microscope. These sarcomeres can be defined as the sub-units of myofibrils, which in turn are strands of muscle fibres. In striated muscle,
Contractibility describes when a muscle can shorten, or produce tension between its ends. As seen in diagram 1, there are two different types of filaments within the sarcomeres of muscle fibres, actin and myosin. During contraction, these actin and myosin filaments create cross bridges, and slide past each-other. This results in the contraction of the muscle. This can be explained by the sliding Filament theory. In this theory, a stimulus must first be present. This is the impulse received by a motor neuron, which is the nerve that connects to muscle. This impulse then stimulates a few muscle fibres within the muscle itself, rather than the entire muscle. These stimulated muscles, along with the motor neuron itself, are known as the motor unit. The junction at which the muscle fibre is stimulated by the motor neurons axon is known as the neuromuscular junction. The process of contraction begins with the impulse reaching the muscle fibres via neuromuscular junctions, which then causes a reaction to occur in each sarcomere between the two filaments. In this reaction, the impulse causes the myosin filament to attach to the actin filament. The myosin filament then begins to pull the myosin filament towards itself, which shortens the sarcomere. This is the basic mechanism for the contraction of a muscle, however it should be noted that for the myosin and actin to bind during the reaction, sufficient levels of calcium should present within the muscle cell. The calcium binds with a complex of three proteins called troponin. Without calcium, troponin would attach to another protein called tropomyosin within the actin filaments. During relaxation, the tropomyosin blocks the attachment sites for the myosin cross bridges, thus preventing contraction since the myosin filament and actin filament cannot bind. During contraction however, calcium is released from the sarcoplasmic reticulum. The sarcoplasmic reticulum is essentially a calcium
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store for the muscle, and plays a role in the regulation of intracellular calcium concentrations (Jaurez, 2006). The calcium is released into the sarcoplasm, this is the fluid in the muscle cell. Some of this calcium attaches to troponin, which results in tropomyosin moving such that it can no longer block the attachment sites. This allows the cross bridges to form between actin and myosin filaments, leading to a contraction (ptdirect, 2010). The group of muscles involved in movement are known as skeletal muscles. Skeletal muscle fibres can be classed either as slow twitch oxidative (type 1), or fast glycolytic (type 2). Each fibre has different qualities to aid in movement. Type 1 fibres have a red appearance to them, due to large volumes of myoglobin and mitochondria. Myoglobin is a haemoprotein expressed solely in oxidative skeletal muscle fibres that can reversibly bind to oxygen in blood. It is what gives blood its red colour (Garry, 2004). Type 1 fibres are specialised for endurance activities which involve long-term repeated contractions, activities such as endurance running, or maintaining posture. Type 1 fibres have many mitochondria, to produce a constant supply of ATP from aerobic respiration. Through this, around thirty ATP molecules are produced per glucose molecule. Due to this slow, yet efficient transport of ATP, slow twitch fibres do not tire quickly. This can partially explain why long-distance runners, who have a higher proportion of type 1 to type 2 fibres do not fatigue as easily. The other group of skeletal muscle fibre is fast glycolytic which perform fast muscle contractions of short duration, this allows for rapid movements like jumping or sprinting. As previously mentioned, type 1 fibres rely on relatively high production of ATP molecules through aerobic respiration. This results in type 1 fibres being rate-limited since more strenuous work requires a higher production of ATP. Type 2 fibres however, are not rate limited as they rely on glycolysis alone (type 1 relies on glycolysis and Krebs cycle) to produce two molecules of ATP per glucose molecule. Although this less efficient, it allows for rapid bursts of movement to not be rate limited (Boundless, 2015) As stated in the opening paragraph, the main task of a muscle is to generate force. By understanding the mechanism for muscle contractions, one can link how force generated and the attachment of myosin and actin filaments are related. In paragraph three, the mechanism of contractibility is discussed. The force generated by the muscle is directly proportional to the amount of cross bridges formed by the myosin and actin filaments. Thus, when more muscle fibres contract through this mechanism, a greater force can be generated. In type 1 muscle
fibres, fewer cross bridges can be formed, and so they produce a weaker force. In type 2 fibres however, a greater number of cross bridges can be formed. This can explain why type 2 fibres are good at rapid burst of movement required a large force (Teachpe, 2017). In summation, although different groups of muscle are specific to individual purposes, they all perform the same key roles. Of these roles, contractibility can be regarded as the most important as it is directly responsible for the main task of a muscle: movement and the generation of force.
Bibliography Boundless, 2015. Slow-Twitch and Fast-Twitch Muscle Fibers. [Online] Available at: https://www.boundless.com/physiology/textbooks/ boundless-anatomy-and-physiology-textbook/muscular-system10/introduction-to-skeletal-muscle-96/slow-twitch-and-fast-twitch -muscle-fibers-538-5126/ [Accessed 25 June 2017]. Garry, O. &., 2004. Myoglobin: an essential hemoprotein in striated muscle. Journal of Experimental Biology . Gowitzke, B. A. M. M., 1998. Scientific bases of human movement. Rev. Ed ed. s.l.:Williams & Wilkins. Jaurez, R., 2006. Function and role of the sarcoplasmic reticulum. Archivos de cardiologa de Mexico. M, M., 1982. Ionic events responsible for the cardiac resting and action potential. American Journal of Cardiology. M, M., 1982. Ionic events responsible for the cardiac resting and action potential.. American Journal of Cardiology. Morad, 1982. Ionic events responsible for the cardiac resting and action potential.. American Journal of Cardiology. ptdirect, 2010. The Physiology of Skeletal Muscle Contraction. [Online] Available at: http://www.ptdirect.com/training-design/anatomyand-physiology/skeletal-muscle-the-physiology-of-contraction [Accessed 25 June 2017]. Teachpe, 2017. Muscle Fibre Types. [Online] Available at: http://www.teachpe.com/anatomy/fibre_types.php [Accessed 25 June 2017]. Wisegeek, 2009. What is a Sarcomere?. [Online] Available at: What is a Sarcomere? [Accessed 24 June 2017].
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The Endocrine System
By Kieran Graham
Endocrine System The Endocrine system, can also be referred to as the hormonal system since it consists of three primary elements: Glands which produce hormones, the hormones themselves which are released into the blood or tissue fluid around cells and the receptors present on tissues which receive the hormones and give a cellular response. Hormones are released from these glands in very low quantities, and only cells with the correct receptors will yield a cellular response. Generally, hormones are used for regulation, differentiation, growth and energy production but, they have been discovered to have other properties as well. The following essay will explore some of these hormones and their functions to provide a brief glimpse into the roles of these extraordinary globular proteins. 1
To start, we will discuss how the ‘Growth Hormone’ works; a hormone claimed to have ‘anti-aging’ properties by mass scientific media. This hormone is produced by the pituitary gland (found attached to the hypothalamus of the Brain) and when released, stimulates an increase in the production of protein (which assists in the growth and repair of muscle tissue), promotes the use of fat in the body (which can prove useful for weight loss), interferes with the action of insulin (which raises blood sugar levels and prevents glucose from being converted to glycogen in the liver and glucose from being taken in by adipose tissue) but also, in children and adolescents it stimulates the growth of bone and cartilage since these individuals still need to grow. In individuals with too much GH, Giantism can occur (growth beyond optimal levels) and in individuals with too little GH, Dwarfism can occur (growth stunted below optimal levels). The mechanism whereby growth hormone acts on adipose tissue is direct. GH binds to receptors on adipocytes (fat cells) and causes them to break down triglycerides but also reduces their affinity for circulating lipids. On the oth-
er hand, the method GH uses to stimulate the production of cartilage is indirect as the hormone first binds to the receptors on liver cells (among other tissue cells) to produce another hormone, IGF-1 which in turn causes the proliferation of chondrocytes (cartilage cells) and stimulates the proliferation and differentiation of myoblasts (muscle cells) which results in the growth and development of both muscles, cartilage and bones. 2, 3 Another hormone, Melatonin, is secreted by the pineal gland and regulates the circadian rhythm in the body (sleep/wake cycle). As a result, the hormone is produced in greater quantities when it is dark since that is usually the time when people go to sleep and it is suppressed when it is bright to keep people awake. Before the age of technology, this hormone would have functioned well since it was regulated by the light from the sun, however, now computer screens and artificial light (with a wavelength of blue light) can interfere with the production of melatonin at night causing conditions such as insomnia. Since melatonin is the hormone which regulates time cycles, it also controls the release of female reproductive hormones at certain times and so it affects a woman's menstrual cycle. To initiate this form of regulation, the hormone acts on the MT1 and MT2 receptors present on the Suprachiasmatic Nucleus (SCN) in the hypothalamus, which is why it has an effect on the activity of the Brain when it is produced. Furthermore, Melatonin has been discovered to have ‘powerful’ antioxidant properties which assists in the protection of the body from free radical damage (via free radical scavenging); it also stimulates antioxidative enzymes and augments the effect of other antioxidants. 4, 5, 6 Testosterone is often referred to as the ‘male sex hormone’; this is due to the hormone being produced in the highest quantities in the testes (the male sex organs) and its primary function is to develop male sexual characteristics such as: a deep voice, body hair, produce sperm and develop and increase the bone mass and muscle mass of a person as they mature. It is known that testosterone plays a role in spermatogenesis (maturation of male germ cells) however, the mechanism of action of the hormone for this process has not yet been discovered. Testosterone also has the ability to increase skeletal muscle
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mass and decrease fat mass and it does this through the use of a multitude of mechanisms, also affecting the pluripotent mesenchymal cells (which are stem cells found in an adult human responsible for producing bone cells, fat cells and cartilage cells) and resulting in an increase in muscular strength, however, as previously stated, the mechanisms have not yet been officially determined. 7, 8, 9
Oestrogen is known as the ‘female sex hormone’ due to its connection with the female reproductive system during pregnancy and it’s associating with female secondary sex characteristics. During pregnancy oestrogen levels rise and along with progesterone, regulate the structure of the Uterus as well as keep it functioning correctly. The hormones control the transcription of specific genes and are moderated by hormone receptors called ‘nuclear transcription factors’ to keep the process of regulation running correctly. Oestrogen also assists in the process of bone formation, combining with other hormones and vitamins and minerals (namely vitamin D and Calcium) to both break down and rebuild bones. The hormone also maintains the vaginal wall, assists in blood clotting and helps regulate mood, since low oestrogen levels result in a dampened mood in women. 10, 11
Hormones generally act slowly on the body (bar a few such as adrenaline) due to their secretion from glands in low quantities, however they have a large, long lasting effect on the body, especially since they are strongly linked to the development of an organism. Once secreted, they can be transported in blood and can also be found in tissue fluid until they reach their target cells, and bind to the specific receptor yielding a cellular response, as can be seen in the examples just given. 12
Bibliography
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US EPA. (2017). What is the Endocrine System? | US EPA. [online] Available at: https://www.epa.gov/endocrinedisruption/what-endocrine-system [Accessed 20 Jun. 2017].
conditions/growth-hormone-athletic-performance-andaging [Accessed 20 Jun. 2017].
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Bowen, R. (2017). Growth Hormone (Somatotropin). [online] Vivo.colostate.edu. Available at: http:// www.vivo.colostate.edu/hbooks/pathphys/endocrine/ hypopit/gh.html [Accessed 20 Jun. 2017].
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Ehrlich, S. (2017). Melatonin. [online] University of Maryland Medical Center. Available at: http:// www.umm.edu/health/medical/altmed/supplement/ melatonin [Accessed 21 Jun. 2017].
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Srinivasan V, e. (2017). Melatonin and melatonergic drugs on sleep: possible mechanisms of action. - PubMed NCBI. [online] Ncbi.nlm.nih.gov. Available at: https:// www.ncbi.nlm.nih.gov/pubmed/19326288 [Accessed 21 Jun. 2017].
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Reiter RJ, e. (2017). Melatonin as an antioxidant: biochemical mechanisms and pathophysiological implications in humans. - PubMed - NCBI. [online] Ncbi.nlm.nih.gov. Available at: https://www.ncbi.nlm.nih.gov/ pubmed/14740000 [Accessed 21 Jun. 2017].
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WH, W. (2017). Molecular mechanisms of testosterone action in spermatogenesis. - PubMed - NCBI. [online] Ncbi.nlm.nih.gov. Available at: https:// www.ncbi.nlm.nih.gov/pubmed/19095000 [Accessed 21 Jun. 2017].
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S, H. (2017). Testosterone action on skeletal muscle. PubMed - NCBI. [online] Ncbi.nlm.nih.gov. Available at: https://www.ncbi.nlm.nih.gov/pubmed/15075918 [Accessed 21 Jun. 2017].
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Publications, H. (2017). Growth hormone, athletic performance, and aging - Harvard Health. [online] Harvard Health. Available at: http://www.health.harvard.edu/diseases-and-
Wein, H. (2017). Understanding How Testosterone Affects Men. [online] National Institutes of Health (NIH). Available at: https://www.nih.gov/news-events/nihresearch-matters/understanding-how-testosterone-affects -men [Accessed 21 Jun. 2017]. 13
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DeMayo FJ, e. (2017). Mechanisms of action of estrogen and progesterone. - PubMed - NCBI. [online] Ncbi.nlm.nih.gov. Available at: https://www.ncbi.nlm.nih.gov/pubmed/11949965 [Accessed 21 Jun. 2017].
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Bradford, A. (2017). What Is Estrogen?. [online] Live Science. Available at: https://www.livescience.com/38324-what-isestrogen.html [Accessed 21 Jun. 2017].
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E.hormone.tulane.edu. (2017). e.hormone | Endocrine System : Types of Hormones. [online] Available at: http:// e.hormone.tulane.edu/learning/types-of-hormones.html [Accessed 21 Jun. 2017].
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The Cardiovascular System
By Akila Wickramathilaka
At its simplest, the cardiovascular system delivers oxygen and other nutrients to all body cells, and removes carbon dioxide and other wastes from them. It comprises the heart, blood vessels, and blood. The heart works as a pump, beating regularly to send oxygen-saturated blood into tough, elastic tubes called arteries, which carry blood around the body. The arteries divide into smaller arterioles, and then into capillaries, which have walls that are so thin that oxygen and other nutrients can pass through it easily to the surrounding cells and tissues. Waste products flow from the tissues and cells into the blood in the capillaries for disposal. The capillaries join together to form venules, which in turn enlarge to form large veins which carry deoxygenated blood back to the heart. Usually, vessels that carry oxygenated blood are arteries, with the exception of the pulmonary vein. Likewise, vessels that carry deoxygenated blood are usually veins, apart from the pulmonary artery. This intricate network of blood vessels is approximately 150,000 kilometres in length, roughly equivalent to four times the circumference of the earth. (Parker, 2009)
with roughly 50-55% of it being plasma- which itself is 90% water. There is a plethora of dissolved substances in the plasma, such as glucose, hormones, enzymes, and also waste products such as lactic acid and urea. It also contains proteins such as albumins, fibrinogen which serves a function in clotting, and globulins. Alpha and beta globulins help transport lipids, whereas gamma globulins fight disease- more commonly known as antibodies. The remaining 45-55% of blood comprises three specialised cell types: erythrocytes (red blood cells), leucocytes (white blood cells), and thrombocytes (platelets). In 1mm3 of blood, there are approximately 5 million erythrocytes, 10,000 leucocytes, and 300,000 thrombocytes. (Aviva PLC, 2017)
Arteries are blood vessels that carry blood away from the heart, towards the various organs and tissues that make up the human body. They have thick walls with muscular and elastic layers, which allows them to withstand the high pressures created as the heart pumps blood. Veins are more flexible, and have thinner walls than arteries. Veins contain valves that prevent backflow of blood, which might occur due to the prolonged path blood takes since it is under relatively lower pressure. Muscles around the veins also help carry out this job by contracting during movement. Capillaries are the smallest and most abundant of the blood vessels. They convey blood between arteries and veins. A typical capillary has a diameter of about 0.01mm, only slightly wider than a red blood cell, and has very thin walls that are only one cell thick. Due to their small size, many capillaries enter tissue to form a capillary bed, where oxygen and other nutrients are released, and where waste matter is exchanged into the blood. (IvyRose Holistic Health, 2017)
Blood consists of specialised cells suspended in a strawcoloured liquid called plasma. Flowing around the body, it carries oxygen and nutrients, collects waste, distributes hormones, and spreads heat. An adult has about 5 litres of blood,
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tween the left ventricle and the aorta. (Cleveland Clinic, 2017)
The heart itself is about the same size as a clenched fist. It is located in the thoracic cavity, behind the sternum, between the lungs (slightly to the left). The heart has a muscular wall (myocardium), which is constantly active, and hence needs a supply of glucose and oxygen from the blood. In order to achieve this, the heart muscle has its own blood vessels- the left and right coronary arteries (which branch from the aorta, just after it leaves the heart). Waste from the heart tissue is removed by the coronary sinus, which is a large vein at the back of the heart. In the upper heart, there are four rigid, cusp-shaped rings, called the cardiac skeleton. This provides points of attachment for the four heart valves, and for the heart muscle. (Parker, 2009)
The walls of the heart are made of a special type of muscle known as cardiac muscle, which is endemic to the heart. Unlike the various other types of muscle, the heart muscle can contract repeatedly without becoming tired, although it does require a constant blood supply, as mentioned previously. The heart adopts a double circulation system, consisting of two substituent parts which are interlinked; the pulmonary circulation, and the systemic circulation around the rest of the body. The right side of the heart pumps blood to the lungs to be oxygenated, and then back to the left side of the heart (pulmonary circulation). The left side of the heart pumps blood to all the body’s tissues and deoxygenated blood back to the right side of the heart (systemic circulation). The two lower chambers of the heart- the ventricles, have thick, muscular walls that contract to squeeze blood into the arteries. The upper chambers- the atria, have thinner walls and partly act as reservoirs for blood as it enters from the main veins.
The heart has four valves which control blood flow, each with the same basic structure. The two atrioventricular valves lie between the atria and the ventricles. They differ in that the mitral valve on the left side has two cusps, whereas the tricuspid valve on the right side has three cusps- as its name suggest. The mitral valve controls blood flow from the left atrium into the left ventricle, and the tricuspid valve from the right atrium to the right ventricle. There are also two semilunar valves located at the exits from the ventricles; with the pulmonary valve controlling blood flow between the right ventricle and the pulmonary artery, and the aortic valve be-
The cardiac cycle has two phases: diastole and systole. During diastole phase of the heartbeat sequence, the muscular walls of the heart relax. The atrial chambers balloon slightly as they fill with blood coming in under quite low pressure from the main veins- the vena cava and the pulmonary vein. Deoxygenated blood from the body enters the right atrium, whilst oxygenated blood from the lungs enters the left atrium. Some of the blood in the atria flows into the ventricles. At the end of this phase, the ventricles are filled to about 80% capacity. The sinoatrial node which acts as the heart’s natural pacemaker, is located in the upper part of the right 16
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atrium. During atrial systole, electrical impulses are fired by it, that are similar to those generated by nerves. This stimulates the contraction phase of the cardiac cycle. Some of these impulses spread through the atrial walls and cause the cardiac muscle to contract, which squeezes the blood inside the atria increasing the pressure inside it. When the atrial pressure exceeds the ventricular pressure, the atrioventricular valves open, allowing blood to flow into the ventricles, whose walls remain relaxed. During ventricular systole, the thick cardiac muscle in the ventricular walls contract, stimulated by electrical impulses relayed by the atrioventricular node. The ventricular pressure skyrockets, which opens the aortic and pulmonary valves at the exits of the ventricles. Blood is forced out into the main arteries, making the atrioventricular valves shut. The ventricular walls then begin to relax, causing the ventricular pressure to decrease. The pressure of the newly ejected blood in the arteries is now high, which causes both semi lunar valves to shut. This ensures that there is no backflow of blood from the arteries into the ventricles. This forms a continuous cycle, which causes blood to circulate endlessly. (Parker, 2009)
There are several disorders associated with the circulatory system. These may affect the heart itself, causing structural damage or disrupting its natural rhythm. They may also cause blockages in the blood vessels which can starve tissues of oxygen, leading to severe problems anywhere in the body. By far the most common disorder is myocardial infarction (heart attack). This is a result of coronary heart disease due to atherosclerosis (covered later), leading to the formation of a thrombus (blood clot) in the coronary arteries. Following its formation, the thrombus can completely block the blood flow to the heart muscle, depriving it of oxygen and causing the production of poisonous waste products, eventually causing tissue death. When treating a heart attack, the blood flow to the heart muscle must be replenished as quickly as possible. Since heart attacks occur suddenly, and without warning, it is
essential that any treatment is rapid. The chest pain caused is usually excruciating, and does not cease even when resting. Sweating, shortness of breath, nausea and loss of consciousness may also result from a heart attack. (Wikipedia, 2017) Atherosclerosis begins with abnormally high levels of excess fats and cholesterol in the blood. These substances infiltrate the lining of the arteries, forming deposits known as an atheroma. These deposits can form in any artery, including the ones supplying the brain with blood- leading to a stroke. These atheromatous deposits gradually form raised patches called plaques, which consist of fatty cores within the arterial wall, covered by fibrous caps. The plaques decrease the diameter of the arteries, narrowing the lumen so that there is decreased blood flow to the tissue beyond the site. They also result in turbulence that disrupts the flow of blood, and the eddies over the plaque surface make the blood more likely to clot. Major risk factors for atherosclerosis include smoking, a diet that is high in saturated fats, lack of exercise, and excess weight. (British Heart Foundation, 2017)
There are two different types of heart valve disorder; stenosis and incompetence. In stenosis, the valve outlet is too narrow and so restricts blood flow. The condition may be congenital (present at birth), due to an infection such as rheumatic fever, or part of the ageing process. In incompetence, the heart valve does not close fully, allowing backflow of blood. This problem results from a heart attack or an infection of the valve. An arrhythmia is a heart rate that is unusually slow or fast, or erratic. A normal heartbeat is initiated by specialised cells in the sinoatrial node, at the top of the right atrium. Electrical 17
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impulses are sent through the atrial muscle tissue, stimulating it to contract. These signals are relayed by the atrioventricular node along nerve-like fibres through the septum, and into the thick muscle tissue of the ventricle walls. A fault in this electrical pathway can cause various arrhythmias; sinus tachycardia, atrial fibrillation, ventricular tachycardia. (Parker, 2009) In hypertension, the blood is constantly under pressure greater than the normal limits. There are no initial symptoms of hypertension, but despite this, over time it increases the risk of many serious disorders such as stroke. No obvious causes of hypertension are known of, although lifestyle and genetic factors are thought to contribute to the condition, as well as other factors such as obesity, smoking, the consumption of large amounts of alcohol, and having a high-salt diet. Hypertension is most common in middle-aged and elderly people, as the amount of stress in one’s life increases with age, and this may aggravate the condition. (NHS UK, 2017)
Available at: http://www.nhs.uk/conditions/Blood-pressure(high)/Pages/Introduction.aspx [Accessed 24 June 2017]. Parker, S., 2009. Cardiovascular System. In: P. M. M. P. Ann Baggaley, ed. The Concise Human Body Book. s.l.:DK, pp. 144156. Wikipedia, 2017. Myocardial Infarction. [Online] Available at: https://en.wikipedia.org/wiki/ Myocardial_infarction [Accessed 24 June 2017].
To sum up, the cardiovascular system plays arguably the most important role in the functioning of a normal human body, although it is susceptible to various disorders as with any other body system.
References Aviva PLC, 2017. Structure: Compontents of Blood. [Online] Available at: https://www.aviva.co.uk/health-insurance/ home-of-health/medical-centre/medical-encyclopedia/entry/ structure-components-of-blood/ [Accessed 24 June 2017]. British Heart Foundation, 2017. Atherosclerosis. [Online] Available at: https://www.bhf.org.uk/heart-health/ conditions/atherosclerosis [Accessed 24 June 2017]. Cleveland Clinic, 2017. Heart & Blood Vessels: How Valves Work. [Online] Available at: https://my.clevelandclinic.org/health/articles/ heart-blood-vessels-valves/how-valves-work [Accessed 24 June 2017]. IvyRose Holistic Health, 2017. Blood Vessels. [Online] Available at: http://www.ivyroses.com/HumanBody/Blood/ Blood_Vessels.php [Accessed 24 June 2017]. NHS UK, 2017. High blood pressure (hypertenstion). [Online] 18
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The Respiratory System
By Denis Efovi
The respiratory system is a combination of organs which take in oxygen and expel carbon dioxide to allow respiration to take place in cells. The main organ responsible for this process consists of the lungs. Paired with blood capillaries, the lungs absorb air and oxygen is absorbed by red blood cells, while carbon dioxide is liberated. Air is enters through the nose where the convoluted shape forces air to make contact with the mucous membranes present where it is humidified and warmed by the blood vessels. This process is necessary so that the air does not stick to the lung’s interior and prevents a high temperature difference damaging the fragile organs. The oral cavity and nasal cavity are connected by the pharynx, a muscular tube lined with mucous membranes, which transports both food and air in different sections. The larynx is essential in its role of preventing food from entering the trachea. It is also referred to as the body’s voice box, due to its role in phonation. Sound is produced when air is expelled through the opening between vocal folds, creating a pressure drop within the larynx. When the threshold phonation pressure is reached, the vocal cords start to oscillate. The most important role of the larynx is to prevent pulmonary aspiration, which is prevented by coughing. The membranes of the larynx are very sensitive and will initiate a cough reflex upon contact with anything else than air. It is started by deep inhalation followed by tight adduction of the vocal folds and elevation of the larynx. After forced expiration, the vocal cords are forced apart and the irritating object is expelled out of the throat due to high pressure..
The trachea is a tough yet flexible tube with a diameter of approximately 2.6cm. Its structure is sustained by 16-20 Cshaped cartilage rings stacked on top of each other. These are required to allow space for the oesophagus when food is being
ingested. The innermost layer of the trachea consists of the mucosa; a ciliated columnar epithelium with many goblet cells which produce sticky mucus to intercept debris, while also warming the air. The submucosa is the successive layer made up of areolar connective tissue which contains blood vessels and nervous tissue and its purpose is to humidify the air. The trachea then bifurcates into the left and right bronchi by the carina. The bronchi become narrower as distance increases and eventually branch out into bronchioles which are made up of non-ciliated bronchiolar secretory cells (Clara cells) with the purpose of limiting the possibility of lung collapse by secretion of enzymes. The lungs are located in the thoracic cavity and part of the lower respiratory tract. They are enclosed by the ribcage, a protective arrangement of bones. The left lung is slightly smaller than the right lung due to the presence of the cardiac notch where the heart resides. The lungs are enclosed in a pleural sac, a double layered serous membrane attached to the thoracic cavity. The inner layer is called the visceral pleura and covers the surface of the lungs, while the uppermost layer is the parietal pleura, which forms the outer layer of the membrane. The gap in -between the pleura is the pleural cavity, where serous fluid is secreted to maximise the expansion size of the alveoli, reduce irritation of the lungs and to reduce friction against neighbouring walls. The right lung is made up of three lobes, the superior, middle and inferior, while the smaller left lung is only composed of two, the superior and inferior, with each lobe being separated by connective tissue. The two lungs are divided into a multitude of alveoli: small air sacs which contribute to a larger surface area to increase rate of gas exchange; together, they contain 300-500 million alveoli, with a surface area of approximately 70m2. 90-95% of the alveoli is made up of type I alveolar cells, which are squamous cells as thin as 25nm, their main purpose being the larger surface area to volume ratio and short diffusion distance which increases diffusion rate. Type II alveolar cells constitute a very small fraction of the total alveolar surface area and they are required to secrete pulmonary surfactant, a lipoprotein complex which decreases the surface tension within the alveoli.
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"Lungs." InnerBody. Web. 21 June 2017. The base of the lungs is concave to house the diaphragm, an upward domed sheet of muscle which separates the thoracic cavity from the abdominal cavity. It is the main muscle involved in quiet breathing (inhalation and exhalation). When air is drawn into the lungs, the diaphragm contracts, causing the volume in the thoracic cavity to increase, therefore causing a pressure difference between the lungs and the atmosphere, which draws air in, . As the diaphragm flattens, it also pushes the abdominal organs downwards. Simultaneously, the external intercostal muscles contract, causing the ribcage to expand upwards and outwards. During exhalation the diaphragm and external intercostal muscles relax, while the internal intercostal muscles contract, causing the ribcage to be flattened downwards and inwards, reducing gas volume and therefore increasing pressure, which forces air out of the lungs. This returns the chest to a position determined by their anatomical elasticity. The pulmonary artery carries deoxygenated blood from the heart. It branches out in the lungs to form thin, narrow pulmonary capillaries in order to increase surface area and to reduce diffusion distance. This is required as oxygen has a relatively low partial pressure. Oxygen diffuses into the capillaries and dissolves into the blood, while carbon dioxide diffuses into the alveoli, where it is later expelled. As described by Henry’s law, different gases display different behaviours when they come into contact with a liquid, such as blood. The concentration of a gas in a liquid is dependent on the solubility of the gas. Nitrogen, for example, is abundant in air, but only a small portion of it dissolves into blood due to its low solubility. Oxygen is able to rapidly diffuse across the alveoli due to the drastic difference in partial pressure between the alveoli and the capillaries (~64 mmHg), which counteracts the low solubility of oxygen and allows efficiency diffusion.
OpenStax. "Anatomy and Physiology." 22.4 Gas Exchange | Anatomy and Physiology. OpenStax, 06 Mar. 2013. Web. 21 June 2017. Tortora, Gerard J., and Nicholas Peter Anagnostakos. Principles of Anatomy and Physiology. New York: Harper & Row, 1987. Print. Widdicombe, J. G., and R. J. Pack. "The Clara Cell." European Journal of Respiratory Diseases. U.S. National Library
of Medicine, May 1982. Web. 21 June 2017. "The Minimum Lung Pressure to Sustain Vocal Fold Oscillation: The Journal of the Acoustical Society of America: Vol 98, No 2." The Journal of the Acoustical Society of America. Web. 21 June 2017.
Works Cited Jarrard, J. A., R. I. Linnoila, H. Lee, S. M. Steinberg, H. Witschi, and E. Szabo. "MUC1 Is a Novel Marker for the Type II Pneumocyte Lineage during Lung Carcinogenesis." Cancer Research. U.S. National Library of Medicine, 01 Dec. 1998. Web. 21 June 2017.
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The Integumentary System The Epidermis
By Shivam Wadhia
The skin, along with hair, nails and exocrine glands, is a part of the integumentary system. Similarly to more ‘well known’ organ systems, the integumentary system has a variety of different functions. Although it may seem bland, the integumentary system is truly quite amazing; a self-healing one-way wall against pathogens that also acts as our first contact to the environment around us, whilst also taking part in vital bodily functions should not be taken for granted. The skin is the main organ in the integumentary system. It covers almost the entire surface of the human body, making it our largest organ. The surface area of the skin, on average, is around 2 sq m and is dependent on the relative size of the individual. The skin varies in thickness, being thickest in areas which are in constant contact with the environment, e.g. the soles of our feet (4mm), and being thinnest in delicate areas, such as eye lids (0.5mm). In the past there have been debates as to the true classification of skin. Before all the functions of the skin were known, it was once thought that the skin was a tissue as opposed to an organ. The skin is now considered an organ as it fits the definition for one, which is a group of related cells which combine together to perform one or more specific functions in the body. The skin is made up of three layers, each with their own functions: the epidermis, dermis and the hypodermis:
The epidermis is the thin, yet tough, outer layer of skin. The epidermis is avascular (does not have any blood vessels within). The epidermis consists of five layers of epithelial cells beginning with the innermost layer called the stratum basale, followed by the stratum spinosum, stratum granulosum, stratum lucidum (not always present), and ending with the outermost layer, the stratum corneum. Skin containing all five layers of epidermis is called “thick skin” and is found is only on the palms of the hands and the soles of the feet. “Thin skin” is skin containing only four layers of the epidermis and is found everywhere else. Keratinocytes are the most common cell type in the epidermis, accounting for 90-95% of the total number of cells. They are found in all five layers apart from the stratum basale. A keratinocyte is a type of cell which creates and stores the fibrous protein keratin. The keratin found in the skin is referred to as ‘soft keratin’. The keratin found in the appendages of the skin, such as the hair and nails, is referred to as ‘hard keratin’. The difference between the two is the amount of cysteine present. Cysteine is an amino acid, found in keratin, which contributes to the strength and flexibility of the protein. Cysteine can form disulphide crosslink’s (S-S). An increase cysteine content of the keratin causes the formation of more disulphide crosslink’s, hence increasing the strength yet decreasing the flexibility of the protein. The epidermal layer of the skin is a tissue which is directly exposed to the outside world; therefore is most vulnerable to its damaging effects. To counter this, new cells are continuously being made and older ones are replaced. The process of cell division (mitosis) occurs in the very bottom layer of the epidermis, called the stratum basale. Basal cells are the cells which make up this one cell thick layer of cells closest to the dermis. A basal cell is a type of multipotent stem cell and the parent cell of a keratinocyte. Three other types of cells are also found in the stratum basale: the first is a Merkel cell, which act like a receptor which is responsible for stimulating sensory nerves that the brain perceives as touch. These cells are especially common on the surfaces of the hands and feet. The second cell is a melanocyte, a cell that synthesis the pigment melanin, giving skin its colour and protection
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against UV radiation. The third type of cell found in the epidermis is a Langerhans cell. These cells make up the skin’s immune system by helping to detect foreign substances within the skin. As new cells are formed, existing cells are pushed upwards and away from the stratum basale. These cells are eventually shed at the very top layer called the stratum corneum. As cells move up the layers of the epidermis, their structures change and a process known as keratinisation (cornification) takes place. Keratinisation occurs in the upper layers of the epidermis and leads to the formation of the outermost skin barrier. Keratinisation is a unique form of cell differentiation in which the cytoplasm’s of outer keratinocyte’s is replaced by keratin, essentially killing the cell. Keratin is insoluble in water and a fibrous protein; therefore an increase in keratin strengthens cells and makes them almost water proof. Other proteins, such as collagen and elastin, also contribute to the strength of the skin. The Dermis The dermis is the mid layer of skin; it is found beneath the epidermis (epi meaning over) and above the hypodermis (hypo meaning below). The epidermis and dermis are bonded together via intertwining collagen fibres called the basement membrane. The dermis is mainly made up of fibrous tissue, mostly made from collagen, with an addition of elastic tissue, made from elastin. The combination of the two, known as areolar connective tissue (connective tissue which is strong, yet flexible, with fibres far enough apart to allow ample space for interstitial fluid in-between) gives skin its strength as well as flexibility. The dermis is considered the main “core” of the skin and is composed of two layers: the papillary layer and the reticular layer:
hence making support one of its main functions. It contains more blood vessels and sympathetic nerves than the papillary layer. The reticular layer also contains hair follicles, sweat glands and sebaceous glands. Sweat glands can be one of two types: either an apocrine gland, such as those found in the groin and the armpits, or eccrine glands, which are found all over the body. The sebaceous glands secrete a substance called sebum that helps to lubricate and protect our skin from drying out. The Hypodermis The hypodermis, also known as the subcutaneous layer or the superficial fascia, is the bottom-most layer of the skin. Its main function is to connect the skin to the underlying bones and skeletal muscles. It is well vascularised, similarly to the dermis, making distinction between the two layers hard. The hypodermis, however, tends to contain more adipose tissue and areolar connective tissue. This increase in connective tissue allows the hypodermis to connect the skin, above it, to the underlying fibrous tissue of the bones and skeletal muscles. Adipose tissue, consisting of cells called adipocytes, acts as a store of fat which can be used as a source of energy as well as insulation and cushioning underlying structures from trauma. Hair Apart from a few exceptions, such as the lips, soles of the feet, palms of the hands and scar tissue, hairs covers almost the entirety of the human body. Hairs are extremities that originate from the dermal layer in the skin. Hairs have a variety of different functions, from gender identity, to being a barrier to foreign particles. Hair is made up of two separate structures: the hair follicle and the hair shaft.
The main function of the papillary layer is to provide the layer above it, the epidermis, with nutrients to allow the constant production of keratinocytes. Unlike the epidermis, the dermis is vascular with an abundance of small blood vessels. This also allows waste substances to be removed readily as well as helping temperature regulation. The papillary layer also contains fibroblasts; the cells that synthesise collagen, as well as phagocytes; cells that engulf (phagocytose) foreign particles or cells. Nerve fibres and touch receptors are found in the upper layers of the dermis, similar to the epidermis. The reticular layer is much thicker than the papillary layer. It is the layer where most of the elastic and fibrous tissue is found;
The hair follicle, also known as the hair root, is the living
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part of the hair found under the outer layer of skin. The hair follicle contains some of the main structures of the hair, including the bulb, papilla and the germinal matrix. The hair bulb is the base of the hair follicle and has a bulbshaped structure, hence the name. The hair bulb houses the papilla and the germinal matrix. The papilla is a well vascularised region found at the bottom of the hair bulb. It consists of many blood vessels which serve the purpose of supplying the growing hair with nutrients. The germinal matrix is made up of stem cells that rapidly undergo mitosis when the existing hair has been shed, in order to produce a new strand of hair. The process is similar to the cell differentiation that occurs in the stratum basale. Hair erector muscles also make up the hair follicle. They are smooth muscles; they are unconscious as opposed to conscious, unlike skeletal muscles. The erector pili muscle, associated with a hair follicle, extends from its side. When the muscle is at rest, the hair shaft appears above the skin at a shallow angle. When the body is subjected to pressures, such as low temperatures and fears, the erector pili muscles contract, causing the hair shaft to appear out of the skin almost perpendicular to it. This causes the phenomena known as ‘goosebumps’. The hair shaft is the visible part of the hair that we can see. Similarly to the cells of the epidermis, the cells of the hair shaft are dead keratinised cells (keratinocytes). The hair shaft is composed of three layers: the medulla, the innermost layer (not always present), the cortex and the cuticle. The medulla is the innermost layer. It is only present in thick hairs, e.g. pubic hairs and the ones on your scalp. The cortex is the middle layer of the hair shaft. Large numbers of melanocytes are found in the cortex, making it the layer that determines the colour of the hairs. The cuticle is the outermost layer of the hair. It is made up of dead cells, overlapping in layers to form a scale-like structure. Its main function is to protect the inner cuticle.
As mentioned before, the nails are composed of ‘hard’ keratin. Similarly to the skin and hair, the nails are made from dead keratinocytes. The structure of the nail is divided into six different parts: the root, nail bed, nail plate, eponychium, paronychium, and the hyponychium. Each component has a specific function. The root of the nail is called the germinal matrix and serves the same function as the germinal matrix in the hair follicle. The nail root lies below the epidermal layer of skin and extends several millimetres into the skin. Stem cells make up the very base of the nail root. They rapidly multiply and produce keratinocytes, causing the nail to continuously grow. The nail bed extends from the nail root. The nail bed contains blood vessels which provide the growing nail with nutrients. It also contains nerves and melanocytes. As the root grows the nail, the nail streams down along the nail bed and adds material to the underside of the nail to make it thicker. The nail plate is the portion of the nail that is visible to us. It’s made out of translucent keratin. The pinkish colouration is due to the underlying blood vessels. The underside of the nail plate anchors it to the nail bed.
The melanin, synthesised by our melanocytes, which makes its way into the keratinocytes, protects structures such as the nucleus from cellular damage caused by the UV light produced by the sun. Eyebrows and eyelashes protect our eyes from small particles. The hair in our nostrils filters out small particles found in the air we breathe.
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Bibliography Author
Kathleen Esposito
Article title:
Structure of the Nail
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LoveToKnow
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http://skincare.lovetoknow.com/Structure_of_the_Nail
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Skin
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En.wikipedia.org
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5.1 Layers of the Skin | Anatomy and Physiology
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The Lymph and Immune System
By Ajay Krishna
The immune and lymphatic systems are two closely related organ systems that work together to help our body fight infection. The immune system is our body's defence system and contains many biological structures and processes to protect against diseases. To function properly, it must detect a wide variety of pathogens, such as viruses, bacteria and fungi as well as parasitic animals and protists, and distinguish them from our healthy tissue. They also need to keep these harmful agents out of the body and attack those that manage to enter (Immune system, 2017). The lymphatic system is a part of the circulatory system and a vital part of our immune system. It comprises of capillaries, vessels, nodes and other organs that transport a clear fluid called lymph from the tissues as it returns to the bloodstream (Lymphatic system, 2017). The lymphatic tissue of these organs helps to filter the lymph of any debris, abnormal cells or pathogens. The fatty acids produced in the intestines are transported to the circulatory system via the lymphatic system (Taylor, n.d.). Red Bone Marrow (RBM) and Leukocytes: RBM is a highly vascular tissue found mostly in the spaces between trabeculae of spongy bone and near the points of attachment of the long bones and the flat bones of the body. RBM is a hematopoietic tissue containing many stem cells that produce blood cells; RBM also helps in the filtration of aged cells from the circulation. All of the leukocytes of the immune system are produced by the RBM. Leukocytes can be further separated into 2 groups according to the stem cells that produce them: myeloid stem cells and lymphoid stem cells (Taylor, n.d.). Myeloid stem cells produce monocytes and granulocytes. Monocytes once made travels through the blood to the tissues in the body, where it becomes a macrophage or a dendritic
cell (Monocytes, n.d.). Granulocytes are a part of the innate immune system and have non-specific and broadbased activity (Granular leukocyte, 2016). There are 3 types of granulocytes - Eosinophils (reduces allergic inflammation and help body fight off parasites), Basophils (triggers inflammation by releasing chemicals heparin and histamine) and Neutrophils (uses chemotaxis to detects chemicals produced infectious agents and quickly move to the site of infection then ingest the pathogen via phagocytosis and release chemicals to trap and kill the pathogens) (Taylor, n.d.). Lymphoid stem cells produce T lymphocytes (T-cells) and B lymphocytes (B-cells). T-cells detect certain antigens present on the cell surface and then clone itself to produce memory cells or T-helper cells (Th-cells). The Thcells produce cytokines which activate other T-cells such as the cytotoxic T-cells, which then directly attacks and destroys the pathogen (T cells, n.d.). B-cells are also involved in detecting and fighting specific pathogens. Once a B-cell has been activated, it clones itself to produce memory cells or plasma cells. The plasma cells produce antibodies against the pathogen, which neutralises the pathogen until other immune cells can destroy them. Natural Killer cells (NK cells) are also lymphocytes and are able to respond to a wide range of pathogens. NK cells travel with the blood and are found along the lymphatic system and RBM where they fight most infections (Taylor, n.d.). Lymph capillaries: They are thin walled vessels and facilitate diffusion of nutrients gases and wastes. The structure of a lymphatic capillary is similar to that of a blood capillary, but its function is different. The lymph capillaries pick up the fluid that has leaked into the tissues and help return it to the circulatory system (Lymphatic Capillaries, n.d.). Lymph: The interstitial fluid picked up by the capillaries is known as lymph and it resembles the blood plasma. It contains lymphocytes and other white blood cells (WBCs). It also contains waste products and cellular debris together with bacterial cells picked up from diseased tissue and WBCs that fight these pathogens and proteins (Lymphatic sys25
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tem, 2017). Lymphatic Vessels: Lymph capillaries merge together to form lymphatic vessels. These have a similar structure to veins and also they carry the lymph to the circulatory system via one of the subclavian veins. Like veins, the muscle contractions help the lymphatic vessels to transport the lymph (Lymphatic system, 2017). Lymph nodes: They are small, capsule-like organs of the lymphatic system and there are several hundreds of lymph nodes. Most of the lymph nodes are found throughout the abdomen and thorax of the body with the highest concentrations in the axillary and inguinal regions. The lymph node is filled with reticular tissue which contains many lymphocytes and macrophages; this allows the lymph node to act as a filter. The nodes filter the lymph that enters from several different lymph vessels by acting as a net to catch any debris or cells present in the lymph. The macrophages and lymphocytes will then attack and kill any microbes caught in the reticular fibres (Taylor, n.d.). Lymphatic Ducts: All of the lymphatic vessels carry the filtered lymph to one of the 2 lymphatic ducts: thoracic duct and right lymphatic duct (RLD). The thoracic duct connects the lymphatic vessels of the legs, abdomen, left arm and the side of the head, neck and thorax to the left brachiocephalic vein. The RLD connects the lymphatic vessels of the right arm and the right side of the head, neck and the thorax to the right brachiocephalic vein (Taylor, n.d.). Lymphatic Nodules: They are small localised collection of lymphoid tissue and are usually located in the connective tissue beneath the epithelial membranes. The nodules are associated with the mucous membranes of the body, where they work to protect the body from pathogens entering the body through open body cavities. These are usually found in the epithelial membranes of the digestive system, respiratory system and urinary bladder and some of them are tonsils, peyer's patches, spleen and thymus (lymph nodule, n.d.).
Our body has many different ways to protect ourselves from infections caused by pathogens. The defences can be external to stop the pathogen from getting into the body but it can also
be internal to destroy pathogens that enter the body. Among the internal defences, some are specific to only one pathogen or may be innate and defend against many pathogens (Taylor, n.d.). Innate immunity:
This immunity contains non-specific defence mechanisms, which enables it to fight against a broad spectrum of pathogens. These mechanisms include physical barriers (external defence) and internal defence. The innate immune response is activated by the chemical properties of the antigen (Innate vs. Adaptive Immunity, n.d.). External defences examples: (The Body's Defense System, n.d.) The skin provides a physical block to stop pathogens entering directly into the bloodstream. Tears in the eyes and mucus in nose and throat Saliva contains enzymes that break down the cell walls of many bacteria Stomach acid is highly corrosive and kills much of what remains Internal defences examples: (Taylor, n.d.) Fever increases the body’s internal temperature. It also helps to speed up the response to an infection while at the same time slowing down the reproduction of pathogens. Inflammation stops the spread of the disease. It is the result of localised vasodilation which allows extra blood flow to that region and thus bringing more leukocytes to fight the infection. NK cells recognise and kill virus-infected cells and tumour cells. Phagocytes engulf pathogen. Cell-mediated specific immunity uses T-cells and B-cells to kill the pathogen. Bibliography Granular leukocyte. (2016, 13 5). Retrieved 06 20, 2017, from MedicineNet: http://www.medicinenet.com/ script/main/art.asp?articlekey=8819 Immune system. (2017, 05 17). Retrieved 06 20, 2017, from Wikipedia: https://en.wikipedia.org/wiki/ Immune_system Innate vs. Adaptive Immunity. (n.d.). Retrieved from The Biol-
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ogy Project: http://www.biology.arizona.edu/ immunology/tutorials/immunology/page3.html lymph nodule. (n.d.). Retrieved 06 20, 2017, from EncyclopĂŚdia Britannica: https://www.britannica.com/science/ lymph-nodule
Lymphatic Capillaries. (n.d.). Retrieved 06 20, 2017, from Study.com: http://study.com/academy/lesson/ lymphatic-capillaries-function-lesson-quiz.html Lymphatic system. (2017, 05 20). Retrieved 06 20, 2017, from Wikipedia: https://en.wikipedia.org/wiki/ Lymphatic_system Monocytes. (n.d.). Retrieved 06 20, 2017, from PubMed Health: https://www.ncbi.nlm.nih.gov/pubmedhealth/ PMHT0022057/ T cells. (n.d.). Retrieved 06 20, 2017, from National ms society: http://www.nationalmssociety.org/What-is-MS/ Definition-of-MS/T-cells Taylor, T. (n.d.). Immune and lymphatic systems. Retrieved 06 20, 2017, from inner body: http:// www.innerbody.com/image/lympov.html#fulldescription
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The Digestive System
By Kieran Graham
The Digestive system is the region in the body whereby macromolecules, vitamins and minerals are extracted from food and absorbed into the body for various physiological processes. It consists primarily of the ‘gastrointestinal (GI) tract’ (which encompasses the mouth, oesophagus, stomach, small intestine, large intestine and anus), the liver, the pancreas and the gall bladder. Digestion begins in the mouth where food is mechanically broken down by the movement of teeth so the food is small enough to pass through the oesophagus without causing choking. Salivary amylase is also secreted by salivary glands in the mouth and this helps to break down starch. Following this, food passes through the oesophagus until it reaches the stomach. 1
Once food has entered the stomach, it is mixed with more digestive fluids and here proteins are digested. To do this, the stomach has several layers and sections, each with its own unique function. For instance, the walls of the stomach consist of the mucosa, the submucosa, muscular layers and the serosa (with the mucosa on the inside and the serosa on the outside). Parietal cells, which are present in the glands in the mucosa, secrete hydrochloric acid which is used to activate pepsinogens, the enzymes which break down proteins into amino acids, (it also functions as one of the chemical barriers of the immune system, destroying pathogens which have entered the body through the mouth) whilst other specialised cells (also found in the mucosa) secrete pepsinogens (enzymes which digest proteins). The muscular layers are responsible for contracting and emptying the stomach which is important for mixing food with the digestive fluids and moving it through the system. Mucus is also secreted to protect the stomach from the corrosive effects of hydrochloric acid. 2
When the stomach needs to be purged (which can be for a number of different reasons), vomiting occurs, which is the expulsion of the contents of the stomach back up the GI tract and out of the mouth. When the glottis is closed, spasmodic respiratory movements occur along with contractions of the antrum (in the stomach) whilst the fundus and cardia regions of the stomach relax. After this, a deep breath is taken in (with the glottis still closed, and the larynx raised), the diaphragm is contracted downward in a rapid motion, the muscles of the abdomen contract vigorously, applying pressure to the stomach and since the pylorus (lower region of the stomach) is closed, food travels up the oesophagus and out of the mouth. 2, 3
Continuing with digestion, from the stomach, food passes through the pylorus and enters the small intestine which is divided into three regions: the duodenum, the jejunum and the ileum. The duodenum contains ‘Brunner’s glands’ which secrete an alkali solution which neutralises the acidity produced by the stomach, so the lining of the intestines aren’t damaged. The jejunum does not contain specialised regions (such as the ‘Brunner’s glands’ in the duodenum or the Peyer’s patches in the Ileum) in relation to the rest of the small intestines however, most of the absorption of nutrients occurs here. The Ileum contains ‘Peyer’s patches’ which are clusters of lymph nodules that are not important for digestion but, are instead present to monitor the presence of pathogens in the small intestine and supply an immune response if any are present. 4, 5
To move food through the small intestine, rhythmic muscular contractions occur in the process known as ‘Peristalsis’. This also allows digestive fluids that have been produced by the pancreas, to mix with food (like in the stomach). These digestive fluids travel along the pancreatic duct, which then combines with the bile duct, to form the ampulla of Vater before finally entering the duodenum. Pancreatic protease breaks down proteins into amino acids (following digestion in the stomach), pancreatic amylase breaks down carbohydrates into glucose (following digestion from salivary amylase in the mouth)
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and pancreatic lipase breaks down lipids into fatty acids and glycerol however, the lipids must first be emulsified by bile to be fully digested which is why the Gallbladder is important. It is important to note that while the Gallbladder concentrates and stores bile, it is the Liver that actually produces bile. The walls of the small intestine are similar to that of the stomach (composed of mucosa, submucosa, smooth muscular layers (used in peristalsis) and serosa) however, the small intestine also contains villi (which contain microvilli). Villi are tube-like structures which line the small intestine, increasing the surface area. They have a great surface area as they are involved in the absorption of nutrients and minerals from digested foods. Inside each villus is a capillary network which ensures that the nutrients enter the bloodstream after they have diffused through the villi wall. 5, 6, 7
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'Stomach And Duodenum | Organs | MUSC Digestive Disease Center' (Ddc.musc.edu, 2017) <http:// ddc.musc.edu/public/organs/stomach-duodenum.html#> accessed 24 June 2017
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Bowen R, 'Physiology Of Vomiting' (Vivo.colostate.edu, 2017) <http://www.vivo.colostate.edu/hbooks/pathphys/ digestion/stomach/vomiting.html> accessed 24 June 2017
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King D, 'SIU SOM Histology GI' (Siumed.edu, 2017) <http:// www.siumed.edu/~dking2/erg/smallint.htm#duodenum> accessed 24 June 2017
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After the food has passed through the small intestine and been chemically digested, it enters the large intestine. As with the rest of the GI tract, the walls of the large intestine consist of mucosa, submucosa, a muscular layer and serosa however, unlike the small intestine, the large intestine does not have any villi and instead has an abundance of Goblet cells. The muscular layer is also different to the small intestine since it is incomplete and formed by three bands called â&#x20AC;&#x2DC;Teniae Coliâ&#x20AC;&#x2122; and when these contract, food is able to move along the colon. No more digestion of food occurs in this region although, water, along with electrolytes are absorbed and faeces is forced towards the rectum and out of the anus. There are muscles present in the anus called sphincter muscles. The internal sphincter is composed of smooth muscle tissue and is an involuntary system whereas the external sphincter is composed of skeletal muscle and is voluntary (in use when preventing defecation in an unfavourable situation). 5
'SEER Training:Small & Large Intestine' (Training.seer.cancer.gov, 2017) <https:// training.seer.cancer.gov/anatomy/digestive/regions/ intestine.html> accessed 24 June 2017
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'Pancreas Function' (Pathology.jhu.edu, 2017) <http:// pathology.jhu.edu/pancreas/basicoverview3.php?area=ba> accessed 24 June 2017
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'Exocrine Secretions Of The Pancreas' (Vivo.colostate.edu, 2017) <http://www.vivo.colostate.edu/hbooks/pathphys/ digestion/pancreas/exocrine.html> accessed 24 June 2017
Bibliography:
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Information, H., Diseases, D., Works, T., Works, T., Center, T. and Health, N. (2017). The Digestive System & How it Works | NIDDK. [online] National Institute of Diabetes and Digestive and Kidney Diseases. Available at: https://www.niddk.nih.gov/ health-information/digestive-diseases/digestive-system-how-it -works [Accessed 23 Jun. 2017].
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The Urinary System properly’ (Kidney Health Australia, 2004). This specifically involves chemicals, salts and acids in the blood.
By Muse Berhe
The urinary system, sometimes referred to as the renal system, consists of several organs that work in conjunction with one another to carry out a function. The urinary system ‘produces, stores and eliminates urine’ (LIVESCIENCE, 2016), the fluid waste that is produced by the primary organ in the urinary system, the kidneys. Urine is stored in the bladders and is excreted out of the urethra. A brief overview of the urinary system is that urine is produced in the kidneys, is transported to the bladder via the ureter and then released out of the bladder via the urethra. (Stanford’s Children of Health, 2017)
To gain a thorough understanding of the kidneys, we need to fully appreciate how the kidneys work. The main function of the kidneys is blood filtration. Not everything in our blood is beneficial to our body, so the kidneys work to filter our blood to remove these substances. There are five main parts of the kidneys being the nephrons, ureter, renal pelvis, renal cortex and renal medulla. An interesting fact about the kidneys is that each kidney contains approximately one millions nephrons, the functional unit of the kidneys. The kidneys have a range of other functions such as balancing fluid content in the body and adjusting ‘levels of minerals and other chemicals to keep the body working
An understanding of the blood flow in the kidneys will help us to understand how they perform their function. The nephrons are the structures where filtration takes place, but before the blood gets to the nephrons it first has to enter the kidney via the renal artery. The renal artery branches into many smaller arterioles, which are essentially smaller arteries albeit being narrower and having less muscular and elastic walls. The blood in the arterioles is at a very high pressure and flows through them until they reach a ‘tiny knot of vessels’ called the glomerulus. (The University of Nottingham, 2004, Page 3). The arterioles that supply the glomerulus are referred to as the ‘afferent arterioles’. Within the glomerulus, the blood pressure drops and blood flows into arterioles which coil around the nephrons. These arterioles, which are referred to as ‘efferent arterioles’ connect to venules which will eventually congregate to form the renal vein. Each nephron contains a globule, which acts as a filter. They also contain a tubule, a relatively small tube. When blood enters the glomerulus, fluid and waste products pass through its selectively permeable membrane, however larger products are not able to pass through this membrane, due to the fact that they are too large to enter through the pores. This is incredibly useful, as it allows the products that need to remain in the blood, like proteins, from being filtered out. ‘The glomerulus is a series of specialised capillary loops.’ (Kidney Health Australia, 2004). Each glomerulus is surround by what is referred to as a ‘bowman’s capsule’. There are specialised cells that make up the Bowman’s capsule called ‘podocytes’, which wrap around the capillaries of the glomerulus. The space within the bowman’s capsule is referred to as the ‘bowman’s space’, which is where the filtrate initially resides. It’s important to acknowledge that the filtrate isn’t referred to as urine just yet. The filtrate now travels through the proximal tubule, sometimes referred to as the ‘convoluted proximal tubule’. The function of the proximal tubule is to allow some wanted products within the filtrate, such as glucose, to be reabsorbed via active transport. The next part of the system is called the ‘loop of Henle’. The function of the
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loop of Henle is to make the renal medulla, through which it passes, become salty. This is done in the ascending part of the loop of Henle and is carried out by actively transporting ions such as Na(+), Cl(-) and K(+). This part of the loop of Henle is not permeable to water, whereas the descending limb is only permeable to water. And as the medulla in close proximity to the descending limb of the loop of Henle is hypertonic, water is able to move into the medulla via osmosis. The loop of Henle is relatively long, allowing adequate time for both the ions and the water to enter the medulla.
there lies the internal urethral sphincter. A common misconception is that we have conscious control over this sphincter when in reality we don’t.
(KhanAcademy, 2014) Continuing on from the entrance of the loop of Henle into the cortex, we have another tubule referred to as the ‘distal convoluted tubule’. This is another site of reabsorption of wanted products. The remaining filtrate is then held in collecting ducts, which enter the medulla yet again. Hormones present in the collecting ducts, referred to as ‘antidiuretic hormones’, determine how porous the collecting tubes are. The more porous the collecting tubes, the more water is reabsorbed into the medulla. The function of the kidneys is the predominant part of the urinary system. Once urine is produced, it is stored in the collecting ducts. The renal calyx, which is located by the inner part of the medulla, collects the urine from the collecting ducts. And several of these renal calyces congregate to form the renal pelvis. It is to the renal pelvis that the ureters are attached. These transport urine to the bladder and are attached to the back of the bladder. The ureters contain valves which prevent the backflow of urine back towards the kidneys. The bladder itself is lined with transitional epithelium, which allows the bladder to expand. At the entrance to the urethra,
Thus far, the function of the kidneys has been discussed, but many details are absent in the overview above. The kidneys are located on either side of our spine and are both behind the liver. When the kidneys are fully developed, they are approximately the size of a human fist. The kidneys also help the body to produce vitamin D. If a person’s urinary system is compromised, they would have to rely on a dialysis machine to filter their blood. This would involve said person having to go to a hospital approximately three days a week, which is very time consuming, thus highlighting the importance of the urinary system.
Bibliography LiveScience, 2016, Urinary System: Facts, Functions & Diseases, https://www.livescience.com/27012-urinarysystem.html Date Accessed: 21/06/2017
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The University of Nottingham, 2013, The Anatomy of the Kidneys, http://www.nottingham.ac.uk/nmp/sonet/rlos/bioproc/ kidneyanatomy/3.html, Date Accessed: 22/06/2017 Kidney Health Australia, 2004, What your kidneys do, http:// kidney.org.au/your-kidneys/prevent/what-your-kidneys-do, Date Accessed: 22/06/2017 Stanford Childrenâ&#x20AC;&#x2122;s Health, 2017, Anatomy of the Urinary System, http://www.stanfordchildrens.org/en/topic/default% 3Fid%3Danatomy-of-the-urinary-system-85-P01468&, Date Accessed: 22/06/2017 KhanAcademy, 2014, Glomerular filtration in the nephron, https://www.khanacademy.org/science/health-and-medicine/ human-anatomy-and-physiology/introduction-to-the-kidneys/ v/glomerular-filtration-in-the-nephron, Date Accessed: 23/06/2017
Sal Khan, Khan Academy 11:14 the kidney and nephron
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The Reproductive System ova before entering menopause (Harrison, 2017). The uterus is a hollow, muscular organ which has a glandular lining called the endometrium. The lower end is the cervix made up of fibrous connective tissue, which projects into the vagina and uterus is attached to the ovaries via the fallopian tubes. The external organs By Rama Jha
7 billion and counting â&#x20AC;&#x201C; the population seems to be evergrowing with no indication of stopping in the near future but the question is how is this possible? Simple! The Reproductive System - a collection of internal and external organs (within both males and females) working together for the purpose of procreation (Zimmermann, 2016). Along with the various other bodily systems, this is among one of the most important as it is vital for each species survival, linking with offspring and adaptations. In this short article you will learn more about the differences in the reproductive system of both males and females which is unique to this system and the functions of each. The Female Reproductive System
The vulva consists of the external female sex organs. The mons pubis is made by fatty tissue which consists of the hairy region. There is then clitoris which is a small, sensitive organ located at the top of the vulva with the function of providing pleasure to females. It is structurally and functionally homologous to the penis but unlike the latter, plays no role in urination (InnerBody, 2017). There are also the Bartholdiâ&#x20AC;&#x2122;s glands which are located to the left and right of the opening of the vagina. They secrete mucus to lubricate the vagina for comfort (Perry, 2015). The labia majora has the function of enclosing and protecting the other external organs due to its fleshy folds of tissue. All of these external genital organs have three main functions (Knudtson) consisting of primarily, enabling the sperm to enter the body. This is required for fertilization to occur and makes up the succinct system that we have with us today. Another function is to protect the internal genital organs which are vital for its functioning as if infected from micro-organisms, it can cause great damage preventing reproduction but even further illnesses. Lastly, another function of the external genital organs is sexual pleasure. The Male Reproductive System
The internal organs The major internal organs consist of the vagina and uterus (act as the receptacle for semen) and the ovaries which produce the ova. Unlike males, the female reproductive system is cyclical in the sense that they produce and release a set number of
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The male reproductive system is unique in the sense that the penis and urethra belong to both the urinary and reproductive system (Zimmermann, 2016). It consists of the epididymis which is the sperm storage area, wrapping around the superior and posterior edge of the testes. It is made up of several long, thin tubules, tightly coiled into a small mass (InnerBody). Sperm move into the epididymis from the testes to mature before being passed on. They also have the vas deferens which are a muscular tube that carries sperm from the epididymis to the ejaculatory duct. Another vital organ is the various glands one such being the bulbourethral glands â&#x20AC;&#x201C; these lubricate the urethra and neutralizes acid from the urine which enters the urethra during sexual arousal. The external organs Unlike the female reproductive system, much of the male reproductive system is located outside of the body. These include the penis, scrotum and testicles. The penis is what is used in sexual intercourse and has three parts; the root which attaches to the wall of the abdomen, the body and the glans which is covered with foreskin (MRS, 2017). The penis contains the urethra hence controls the transportation of both semen and urine. The scrotum on the other hand is a sac-like organ which houses the testes, made up of skin and muscles. It has two side-by-side pouches (InnerBody). There are also two testes (testicles) which are responsible for the production of sperm and testosterone. It is connected to the abdomen via a spermatic cord. The function of the organs of this system is to perform the various functions (MRS, 2017) one of which is to produce, maintain and transport sperm and semen. This is a necessity as it allows the process of reproduction due to the haploid nucleus of the sperm and allow the birth of offspring. This all achieved via the organs discharging the sperm within the female reproductive tract during sex which is the second function. Lastly, it produces and secretes male sex hormones which is responsible for maintaining the male system â&#x20AC;&#x201C; it allows smooth running and this validates the male system, fit to be used within its functionalities.
tive system is unique in the sense that it is different for both male and female but when it works together, it creates life and does so seamlessly hence I hope that you have been informed about the biological side of our system and this will inspire you to read further and enrich yourself!
Works Cited Harrison, R. J. (2017). Human reproductive system. Retrieved from Britannica: https://www.britannica.com/ science/human-reproductive-system InnerBody. (2017). Clitoris. Retrieved from InnerBody: http://www.innerbody.com/image_dige04/repo18.html InnerBody. (n.d.). Male Reproductive System. Retrieved from InnerBody: http://www.innerbody.com/image/ repmov.html Knudtson, J. (n.d.). Female External Genital Organs. Retrieved from MSD Manual: http://www.msdmanuals.com/en -gb/home/women-s-health-issues/biology-of-the-femalereproductive-system/female-external-genital-organs MRS. (2017). The Male Reproductive System. Retrieved from Webmd: http://www.webmd.com/sex-relationships/guide/ male-reproductive-system#1 Perry, T. F. (2015, November 18). Bartholin Gland Marsupialization. Retrieved June 18, 2017, from Emedicine: http:// emedicine.medscape.com/article/1894499-overview Zimmermann, K. A. (2016, March 11). Reproductive System: Facts, Functions & Diseases. Retrieved June 18, 2017, from LIVESCIENCE: https://www.livescience.com/26741reproductive-system.html
As you can see, the human reproductive system is vast and inscapes many important organs and functions within itself. Without this amazing system, none of us would be alive and sitting where we are today, hence this not only marked our existence, but the existence of man-kind itself. The reproduc34
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The Nervous System sleep.
By Sai Aakash Chanda
The human nervous system is what’s responsible for the coordination of all of the body’s activities, and its responses to internal and external stimuli. It consists of 2 parts: the central nervous system consisting of the brain and the spinal cord (CNS), and the peripheral system which connects the CNS to the rest of the body. (Thoughtco. Website) The CNS is protected by bone, and cushioned by cerebrospinal fluid (CSF). The brain is made up of soft nerve tissue and is found within the skull. The grey matter in the brain is mainly made up of nerve cell bodies, and white matter which are cell processes. The brain is further divided into 4 parts: the cerebrum, cerebral cortex, cerebellum and the medulla. The cerebrum is the largest part of the brain, being responsible for the thoughts and intelligence. The right half controls movement and activities on the left side of the body and vice versa. There are designated parts of the cerebrum which are responsible for the speech, hearing, smell, sight, memory learning and motor and sensory areas accordingly. The cerebral cortex is fond on the outside of the cerebrum, and it’s responsible for learning, reasoning, language and memory. It is generally 2 to 6 mm thick. The left and right sides of the cortex, are connected by a thick set of fibres called the “Corpus Callosum”. The corpus has several gyri (bumps) and sulci (grooves), primarily to increase its surface area. Each hemisphere can be viewed to have 4 lobes, the frontal, parietal, occipital and the temporal. A small part of the cortex is responsible for specific motor or sensory functions, in the cortex. The cerebellum lies underneath the cerebrum, at the very back of the skull. It functions to control voluntary muscles, balance and muscle tone. This too has a cortex which covers its 2 hemispheres. The cerebrum is important for coordinated movements, and for the integration of distinct sensory information mainly for controlling movement, from simple things like picking up a glass, to typing essays. A structure found at the bottom of the brain is the reticular activating system. The reason that the RAS is located at the very base of the brain, is to allow it to send out impulses to other structures in the brain, making it important as it can affect the entire brain. It’s responsible for attention, wakefulness and sleepiness. Stimulating the RAS wakes the animal up, and a lesion makes it go to
The Medulla on the other hand, controls heart rate, breathing, swallowing, coughing, vomiting. It coordinates with the pons and midbrain, to form the brain stem which connects the cerebrum and the spinal cord. Within the brain stem, the medulla, pons, tectum, reticular formation and the tegmentum are found. The medulla is vital for basic survival in this regard, and is the least important for complex processing. The brainstem along with the hindbrain form the brainstem. The midbrain connects the forebrain and the hind. (Thoughtco website) The hindbrain consists of structures like the earlier mentioned pons, and the cerebellum. The medulla oblongata is also part of the hindbrain. The other part of the CNS is the spinal cord, known by many to be responsible for reflex actions. The spina cord, is a bundle of nerve tissue and fibres which are connected directly to the brain. The spinal cord is found to run from the neck to the lower back (lumbar region). The cord is well protected by the spinal column which is made up of disc shaped bones. “The spinal cord nerves transmit information from body organs and external stimuli to the brain and send information from the brain to other areas of the body” (Thoughtco website). Essentially, it’s like a mediator between the brain and the rest of the body, and external stimuli. There are 2 pathways in the spinal cord: ascending nerve tracts, and descending nerve tracts. They carry sensory information from the body to the brain, and from the brain to the rest of the body respectively. Another essential part of the CNS, are the neurons, which have “nerve processes which are “finger-like” projections that extend from the nerve cell body” (Thoughtco website). These nerves have axons and dendrites which can carry electrical impulses. Axons and dendrites together form the nerves that we’re all familiar with. There are 3 types of neurons: motor, sensory and relay. Sensory neurons send information to the relay neurons about some stimulus/stimuli. The relay neurons send the impulses to CNS, and “relay” that information back to motor neurons which cause an effector to move, and respond to the stimulus or stimuli. One of the diseases in humans that effect the nervous system in particular, is Motor neurone disease. This is a progressive (makes the muscles wear away) neurodegenerative disease. However the degree to which the patients are affected, is varied. One of the most famous people who has had this disease is the world renowned Professor Stephen Hawking. Unfortunately, there is no cure for the disease as of yet. When some specialist nerve cells cease to function correctly, the muscles wear away. As the name suggests, the disease mainly effects the aforementioned motor neurones which are found
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throughout the CNS. Since this means that muscles can’t be used, they wear away. It is not yet known why the motor neurones fail to work normally. Theories by scientists suggest that the trigger for the disease could be genetic, or environmental or both.
With regards to the respiratory care, a mask ventilator system (quite small and portable) is given to the patient to wear overnight to prevent sleep apnea to an extent. This not only extends the lifespan, but improves the patient’s quality of life.
There are several serious symptoms of MND. Each one affecting a major aspect of your life, such as the ability to walk, talk eat, drink and breathe (Webmd.boots), and as it’s a progressive disease, each symptom gets worse over time. Also, the initial symptoms vary based on the type of ALS that the patient has. However, these can be quite misleading and can make doctors diagnose it as a different disease altogether.
Furthermore, in order to help with the difficulty in feeding and swallowing, thickened fluid is fed into the patient, and sitting upright while consuming the fluid is also helpful. Loss of weight due to feeding difficulties is aided by insertion of a gastronomy, a feeding tube inserted into the stomach. (patient.info)
Limb-onset MND will cause a fatigue and weakness in the limbs, along with frequent cramps and twitching. Bulbar-onset MND on the other hand will cause the speech to be slurred because the tongue becomes smaller. Swallowing will become difficult. Finally, respiratory-onset MND will cause breathing difficulties along with severe headaches in the mornings and sleep apnea. MND is hard to diagnose due to the variations in the initial symptoms and the severities. Sometimes a blood test can indicate muscle breakdown (certain chemicals are detected in blood test when this happens). An important test for MND is Electromyography (EMG), where fine needles are used to measure nerve impulses. This indicates if muscles have lost nerve supply. An abnormality in this test is a good indicator that MND is taking place. Similarly, nerve conduction tests can be conducted to measure the speed of the electric impulses that nerves carry. Along with tests, sometimes the visible symptoms will tell a lot: excess production of saliva which can be observed through drooling, stiff muscles causing pains, speaking and swallowing difficulties, excessive yawning, episodes of spontaneous crying and rarely laughing, changes in concentration levels, use of language etc. As mentioned previously, MND has no cure at the moment and so all treatment is focussed primarily on symptom control using medication, clinical equipment or a combination of both, but depends on how severely the symptoms are manifested. Usually, a multi-disciplinary approach is taken to support the individual in each of their problems caused by the MND. Occasionally, those in the later stages of the disease are referred to palliative care or a hospice to recue psychological discomfort to the patient in their last days. (Webmd. Boots)
Usually, in the end-stage of the disease, patients will be paralysed, and have shortness of breath. The patient will feel drowsy and most often fall into a deep sleep in which they die peacefully. Statistics show that about 70% of people with ALS-MND die within 3-5 years of the onset of symptoms, 20% survive 5 years, and 10% survive 10 years. (patient.info) References:
https://en.wikipedia.org/wiki/Nervous_system#Worms http://www.healthline.com/human-body-maps/nervous -system https://www.lecturio.com/magazine/nervous-system/ https://cnx.org/contents/yEs2p8R_@6/Basic-Structureand-Function-o https://www.britannica.com/science/human-nervoussystem/Functions-of-the-human-nervous-system https://www.thoughtco.com/central-nervous-system373578 http://web.mst.edu/~rhall/ neuroscience/02_structure_and_pharmacology/ structure.pdf http://www.news-medical.net/health/Function-of-theNervous-System.aspx http://lrrpublic.cli.det.nsw.edu.au/lrrSecure/Sites/ LRRView/7700/ documents/5657/5657/5657_05.htm http://www.webmd.boots.com/a-to-z-guides/motorneurone-disease?page=2 https://patient.info/in/health/motor-neurone-diseaseleaflet
One of the drugs used to treat MND, is Riluzole. It slows the progress of the disease, and extends the lifespan of the patient by a few months. This is demonstrated by improvement in the symptoms in clinical trials of the drug. The drug works by inhibiting the amount of glutamate released in nerve impulse transmissions. Glutamate is the chemical that relays signals between a nerve and another cell in the CNS. Excess release of the chemical is shown to damage the CNS, by damaging the brain and the spinal cord, along with a protective layer on the nerves. It is a theory that antioxidants help with the disease although the lack of evidence in favour of this theory makes it unreliable information. (patient.info) 36
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A Closing Message The medical diary was established by a couple of us, inspired, scientific minds, wishing to publish our own material with the intent of developing the interest of other students and scientists alike. We started off as a team of five, which naturally increased to ten following the publication of our first magazine in March 2017, as more students showed interest in writing for us. Issue I was largely successful amongst the scientific and student community, having over 150 reads, and 900 impressions. In this special gold edition of the Medical Diary, we aim to do even better than that. I hope you have enjoyed reading through our publication, and have taken away something new from the articles. A lot of hard work has gone into the making of this magazine, and so I would like to thank all the diligent writers, who have written with such great passion. If you have any queries, comments or suggested improvements, please feel free to contact us via the email stated on the back cover.
Thank you,
Akila Wickramathilaka (Editor)
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To provide feedback: Please contact us at 5284@tiffin.kingston.sch.uk Cover image provided courtesy of Wikipedia 38