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Body systems Cardiovascular system The cardiovascular system contains the Heart, Blood vessels and blood. There is approximately 5 liters of blood that courses through these blood vessels as it’s pumped by the Heart. The cardiovascular system transports nutrients, oxygen, cellular waste products and hormones to the rest of the body. The heart pumps blood throughout the body every minute.

The Heart The heart is a fist sized organ located in the thoracic region. The great blood vessels (aorta, pulmonary trunk, vena cava and pulmonary veins) are connected at the top of the heart.

There are two circulatory loops, the systemic circulatory loop and the pulmonary circulatory loop.

The systemic loop carries oxygenated blood from the left side of the heart to the body tissues and organs (except to the heart and lungs) and returns deoxygenated blood to the right side of the heart. The systemic circulatory loop also gets rid of waste from body tissues.

The pulmonary circulation loop carries deoxygenated oxygen from the right side of the heart to the lungs where it picks up oxygen and returns it to the left side of the heart.

The heart contains four chambers: right atrium, right ventricle, left atrium, left ventricle.

Blood vessels

Blood vessels are the blood ‘highways’ of our body. The size of the vessel corresponds to the quantity of blood that goes through (arteries are thick and capillaries thin). The hollow portion of the blood vessel through which blood passes is called the lumen. Blood vessels are lined with a thin layer of epithelium known as endothelium. the endothelium prevents blood clots and protects blood cells.

There are three types of blood vessels: arteries, veins and capillaries.

Blood vessels are usually named according to the region they carry blood or nearby body structures.

Arteries- They carry blood away from the heart. All arteries except the pulmonary trunk and arteries of the pulmonary circulation loop carry highly oxygenated blood to tall parts of the body. Due to the pressure of blood going through arteries they are usually thick walled, muscular and elastic.

Arterioles are small arteries that branch off from the main arteries and carry blood to capillaries.

Capillaries- They are the smallest, thinnest and most common vessels in the body. Capillaries connect to arterioles on one end and to venules on the other. Capillaries help in the exchange of gases, nutrients and waste products. The endothelium of the capillaries is very thin , it acts as a filter to allow for gases, liquids and nutrients to go through while keeping the blood cells inside the capillaries.

Veins- they carry deoxygenated blood to the heart. They usually undergo low blood pressure and their walls are therefore thin, less elastic and less muscular. Since veins do not rely on the heart to pump blood back, they rely on gravity, inertia and skeletal muscle contractions to help in blood flow. Vein contain one-way valves to prevent the blood from flowing away from the heart.

Venules are like arterioles but connect to veins.

Coronary Circulation The heart has blood vessels that provide the myocardium with oxygen and nutrients. The left and right coronary arteries provide blood to the left and right sides of the heart. The coronary sinus is a vein that returns deoxygenated blood from the myocardium to the vena cava

Hepatic Portal Circulation The hepatic portal vein carries blood from the stomach and small intestines to the liver. The liver removes toxins, stores sugars and processes the products of digestion before they reach other body tissues. Blood from the liver then returns to the heart through the Vena Cava.

Blood The body carries about 5 liters of blood. Blood carries nutrients, wast and gases throughout the body. Blood is made up of red blood cells,

white blood cells, platelets,

and liquid plasma.

Red blood cells- They make up 45% of blood volume. Red blood cells are produced in the red bone marrow. About 2 million are produced every second! Red blood cells look like a concave disk. This shape gives them a high surface are and helps them squeeze through the capillaries. The high surface area to volume ratio allows oxygen to be easily transferred into and out of the cells. Red bloods cells contain no DNA and are unable to repair themselves.

Red blood cells transport oxygen throughout the body through the red pigment hemoglobin. Hemoglobin contains iron and proteins.

White blood cells- white blood cells make a small percentage of blood.

They help with immunity. There are two classes of white blood cells: granular leukocytes and agranular leukocytes.

Granular leukocytes- There are three types: neutrophils, eosinophils, and basophils. Neutrophils contain digestive enzymes that neutralize bacteria. Eosinophils contain digestive enzymes for digesting viruses that have been bound to by antibodies in the blood. Basophils release histamine to intensify allergic reactions and help protect the body from parasites.

2. Agranular Leukocytes- There are two types: lymphocytes and monocytes. Lymphocytes include T cells and natural killer cells that fight off viral infections and B cells that produce antibodies against infections by pathogens. Monocytes develop into cells called macrophages . They ingest pathogens and the dead cells from wounds or infections.

Platelets- They are responsible for clotting. Platelets form in the red bone marrow. They have a short lifespan, usually about a week.

Plasma- This is the liquid part of the blood. It contains water, proteins and dissolved substances. Plasma makes about 55% of the blood volume. The proteins in the plasma include antibodies and albumin. O dissolved in the plasma, including her substances dissolved in plasma include: oxygen, carbon dioxide, electrolytes, nutrients, and cellular waste products. The plasma functions as a transportation medium for these substances.

Functions of the cardiovascular System The cardiovascular system has three functions: regulation and protection.

transportation,

Transportation- It transports blood throughout the body. The blood transports nutrients, hormones and oxygen and removes waste materials and carbon dioxide to be processed or removed from the body.

Protection- The cardiovascular system protects the body through its white blood cells. The platelets and red blood cells create protection against outside infection by creating scabs. Blood lso carries antibodies that provide immunity.

Regulation- Blood vessels help maintain a stable body temperature by controlling the blood flow to the surface of the skin. Blood also helps maintain the body’s pH. The albumins in the blood help balance the osmotic concentration of the body’s cells.

Cardiovascular conditions/Diseases Coronary artery disease ( also known as coronary heart disease and ischaemic heart disease)- Coronary artery disease (CAD) is the most common type of heart disease and cause of heart attacks.

CAD is caused by plaque building up along the inner walls of the arteries of the heart, which narrows the arteries and reduces blood flow to the heart.

Signs and symptoms: Chest pain Decreased exercise tolerance Heartburn Difficulty in breathing Swelling of the extremities Risks: Smoking Lack of exercise

Hypertension Hyperglycemia Genetics Alcohol consumption Stress Age (men over 60, women over 65) Obesity Diet rich in saturated fats, low in antioxidants Low hemoglobin Diagnosis: EKG Stress test Coronary angiography Intravascular ultrasound MRI

Treatment: Medical treatment - drugs (e.g. cholesterol lowering medications, beta-blockers, nitroglycerin, calcium antagonists, etc.); Coronary interventions- angioplasty and coronary stent-implantation; Coronary artery bypass grafting (CABG - coronary artery bypass surgery).

Stem cell therapy Angiogenesis Cardiomyopathy - is the deterioration of the function of the myocardium (the heart muscle), usually leading to heart failure Signs and Symptoms: Breathlessness Swelling of the legs Irregular heartbeat Chest pain Treatment: Medications

Pacemaker Defibrillators Ventricular assist devices Hypertensive heart disease - diseases of the heart secondary to high blood pressure Signs and symptoms: Fatigue Irregular pulse or palpitations Swelling of feet and ankles Weight gain Nausea Shortness of breath Difficulty sleeping flat in bed (orthopnea) Bloating and abdominal pain Greater need to urinate at night An enlarged heart (cardiomegaly) Heart failure Cor pulmonale - a failure at the right side of the heart with respiratory system involvement Cardiac dysrhythmias - abnormalities of heart rhythm Inflammatory heart disease Endocarditis – inflammation of the inner layer of the heart, the endocardium. The structures most commonly involved are the heart valves.

Inflammatory cardiomegaly Myocarditis – inflammation of the myocardium, the muscular part of the heart.

Valvular heart disease Cerebrovascular disease - disease of blood vessels that supplies to the brain such as stroke Peripheral arterial disease - disease of blood vessels that supplies to the arms and legs Congenital heart disease - heart structure malformations existing at birth Rheumatic heart disease - heart muscles and valves damage due to rheumatic fever caused by streptococcal bacteria infections

Digestive System The digestive system converts food into energy and other nutrients that fuel the body. The digestive system is made up of the following: mouth, Pharynx, Esophagus, Small intestines, Liver and gall bladder, Pancreas, and large Intestines.

Mouth- Food embarks on its journey in the mouth. There are several organs that help in this early part: salivary glands, teeth, and tongue Teeth- Their main function is to chop down food into smaller pieces.

Teeth are made of a bony structure called dentine and covered by enamel. Teeth contain nerves and blood vessels underneath the dentine.

Tongue- The tongue is made up of several pairs of muscles. The tongue helps in gripping food as it’s moved. The tongue helps to push food further down to help in swallowing. The tongue also contains taste buds that help send information to the brain.

Salivary gland- There are three sets of salivary glands. Saliva helps to moisten food and begin digestion of carbohydrates.

Pharynx- The Pharynx (throat) is responsible for passing chewed food from the mouth to the esophagus. The throat also serves another purpose, it’s the path through which air passes on its way to the lungs.

The pharynx contains a flap that acts as a switch to route food to the esophagus and air to the larynx.

Esophagus- This is a muscular tube connecting the pharynx to the stomach. It has a ring called cardiac sphincter that closes to keep the food in the stomach.

Stomach- this is a muscular fist-sized sac found in the left side of the abdominal cavity.

The stomach contains: hydrochloric acid mucus digestive enzymes Functions: Storage of food Digestion Sanitizes food while it’s stored Storage- The average stomach retain 1-2 liters of food and liquid. It can hold up to 3-4 liters if stretched but this can make digestion difficult, cause discomfort and nausea. The stomach stores food for 1-2 hours as it digests it. The pyloric sphincter keeps food and stomach secretions in the stomach until they are ready to leave the stomach. During this period the pyloric sphincter opens intermittently to allow small amounts of digested food (chyme) to pass into the duodenum. This slow process of gastric emptying maximizes absorption of nutrients.

Secretion- The systemic produces and secretes products to help in digestion. These include:

Gastric juice- A mixture of mucus, hydrochloric acid and digestive enzymes. Helps promote digestion.

Exocrine cells- They secrete mucus which coat the lining of the stomach with a thick barrier. Mucus also neutralizes the pH of the stomach acid.

Parietal cells- Produce intrinsic factor and hydrochloric acid.

Intrinsic factor - This is a glycoprotein that binds vitamin B12 in the stomach and allows absorption of nutrients in the small intestine.

Hydrochloric acid- Kills bacteria found in food and aids in the digestion of proteins.

Chief Cellslipase

They produce digestive enzymes pepsinogen and gastric

pepsinogen- this is the inactive form of pepsin. When pepsinogen reaches the acidic pH in the stomach it becomes pepsin which breaks down proteins.

Gastric lipase- it digests fats.

G-cells- They release gastrin Gastrin- Stimulates glands and muscles of the stomach. The stimulation leads to increased secretion of gastric juice to increase digestion.

-Stimulates opening of the pyloric sphincter to move food to duodenium.

-binds receptor cells in the pancreas and gallbladder.

Digestion- There are two types of digestion Mechanical digestion Chemical digestion Mechanical digestion- the muscles of the stomach produce contractions (mixing waves) that mix food with gastric juices. This mixing produces a thick liquid called chyme Chemical digestion- enzymes in the gastric juice chemically digest

large molecules into smaller subunits. Gastric lipase breaks down fats into fatty acids and diglycerides. Pepsin breaks down proteins into smaller amino acids.

The stomach stores food so we don’t have to constantly eat. It also prepares fats and proteins for further digestion in the intestines.

Hormonal Control- The activity in the stomach is under the control of several hormones.

Gastrin- produced by the G-cells, it stimulates increased production of gastric juices, muscle contractions and gastric emptying Cholecystokinin- This is produced by the mucosa of the duodenum. It slows down gastric emptying by contracting the pyloric sphincter.

Cholecystokinin is usually produced in the presence of fats and proteins which are more difficult to digest. By slowing down gastric emptying it promotes more digestion by the stomach.

Secretin- This is produced by the duodenum’s mucosa. It usually responds to the acidity of chyme. Secretin slows the production of gastric juice, promotes the production of pancreatic juice and bile (contains acid-neutralizing ions). This protects the intestines from the damaging effects of acidic chyme.

Small intestines- The small intestine is a long, thin tube about 1 inch in diameter and some 18-23 feet long. This forms part of the lower gastrointestinal tract. The small intestines takes most of the abdominal cavity. The small intestine is divided into three parts: Duodenium Jejunum Ileum

Duodenium- receiving area for chemicals and partially digested food from the stomach Jejunum- this is where most of the nutrients are absorbed into the blood.

Ileum- This is where the remaining nutrients are absorbed before they move to the large intestines.

The small intestine is coiled, with the inside made up of folds to maximize the area of absorption.

Functions: Digestion of food Absorption of nutrients Around 90% of nutrients gets absorbed in the small intestine.

Liver and gallbladder- The liver is a triangular organ located on the left side of the stomach. The liver is the second largest organ in the body weighing in at about 3 pounds.

Function: production of bile which is secreted into the small intestine to aid in digestion Gallbladder- The gallbladder is a pear-shaped organ.

Functions: Used to store bile Recycles excess bile from the small intestine.

Pancreas- This is a six inches long organ shaped like a short, lumpy snake.

Functions:

Secretes digestive enzymes into the small intestine to complete the chemical digestion of food.

Large Intestine- The large intestine is a long, thick tube about 5 feet long and 2.5 inches thick. It wraps around the border of the small intestines. The large intestine contains: Anal canal Rectum Colon cecum

Functions: Absorbs water Absorbs vitamins (vitamin K, B12, thiamine, riboflavin) Aids in breaking down waste to extract nutrients.

Compacts and stores feces in the rectum

The large intestine doesn’t break down any food . That process will have been completed by the small intestine. Feces in the large intestine exit the body through the anal canal.

Functions of the digestive system Ingestion Secretion Mixing and movement Digestion Absorption Excretion Ingestion- this is the intake of food. The mouth of the only point of entry for food.

Secretion- The digestive system secretes about 7 liters of fluids. The fluid include saliva, mucus, hydrochloric acid, enzymes, and bile.

Saliva- moistens food and begins digestion of carbohydrates.

Mucus- protective barrier and lubricant inside the G.I tract Hydrochloric acid- digests food chemically and kills bacteria in the food.

Enzymes- they break down proteins, carbohydrates, and lipids into smaller components.

Mixing and Movement- The digestive system uses three main processes to move and mix food.

Swallowing- This is the process of pushing food out of the mouth, through the pharynx to the esophagus Peristalsis- a muscular wave that travels the length of the G.I tract. It moves partially digested food down the G.I tract.

Segmentation- occurs in the small intestines. Short segments of the intestine contract, this increases the absorption of nutrients.

Digestion- The process of turning large pieces of food into its

component chemicals.

Absorption- This is the process in which the broken down food is absorbed into the body system. Absorption begins in the stomach.

Water and alcohol is directly absorbed into the bloodstream. Most of the absorption takes place in the small intestines. Large intestines absorb water, vitamin B and K before feces leave the body.

Excretion- This is the final stage. Waste is excreted in a process called defecation. Defecation removes indigestible substances from the body. The timing of defecation is voluntarily controlled by the brain.

Muscular System

The muscular system is responsible for the movement of the human body. There are about 700 muscles attached to the skeletal system.

Muscles are made up of: Skeletal muscle tissue blood vessels tendons, Nerves

Muscle tissue helps to move substances in the heart, digestive organs and blood vessels.

Muscle Types There are three types of muscle tissue: Visceral Cardiac skeletal.

Visceral Muscle (smooth)- These are the weakest of all muscles.

Visceral muscle is found inside of organs like the stomach, intestines, and blood vessels. The visceral muscles make organs contract in order to move substances through the organ. These muscles are usually controlled by the unconscious brain. One cannot voluntarily control them. .

Cardiac Muscle- This is a muscle found only in the heart. The cardiac muscle is responsible for pumping blood to to the heart. Cardiac muscles are also controlled by the unconscious part of the brain. The muscle gets signals from the brain and stimulates itself to contract.

Because of its self-stimulation, cardiac muscle is considered to be autorhythmic or intrinsically controlled. The branched structure of the cardiac muscles allows the muscle cells to resist blood pressures and strain.

Skeletal Muscle- This is the only muscle that is voluntary. One can control skeletal muscles voluntarily. The skeletal muscles are vital to every physical movement we perform. The muscles contract to move parts of the body closer to the bone that the muscle is attached to.

Skeletal muscles are made up of long, multinucleated fibers.

Muscles move by: shortening their length

pulling on tendons moving bones closer to each other Classification of

Muscles

Classification of skeletal muscles depends on factors such as: location, origin and insertion, number of origins, shape, size, direction, and function.

Location- Many muscles derive their names from their anatomical region. Some other muscles are named after the part of the bone they are attached to. Some are named after a combination of both.

Origin and Insertion- Some muscles are named based on their connection to a stationary bone (origin) and a moving bone (insertion). These muscles are usually identified by the bones they are attached to.

Number of Origins- Some muscles connect to more than one bone or to more than one place on a bone, and therefore have more than one origin. These muscles are based on how many types of origin. A muscle with two origins is called a biceps. A muscle with three origins is a triceps muscle. A muscle with four origins is a quadriceps muscle.

Shape, Size, and Direction- Other muscles are classified depending on their shape. Some muscles are serrated (serratus) , others have a diamons shape (rhomboid). The size of the muscle can be used to differentiate between muscles in the same region. Some muscles in a region are large (maximus), medium (medius), and small (minimus).

Other muscles are named after their direction. The muscles whose fibers run up and down are rectus, the ones that run left to right are transverse and the ones at an angle are obliques.

Function- Muscles are sometimes classified by the type of function that they perform. Similar muscles in the same region are usually named based on their functions. Muscles that flex are called flexor, ones that roll over are called supinator. Ones that pull together are called adductors.

Muscular System Physiology Function of Muscle Tissue Muscles have several functions: Movement- The muscles’ ability to contract helps the muscles move parts of the body.

Posture and body position- Muscles hold the body still or in a particular position rather than to cause movement. The muscles responsible for the body’s posture have the greatest endurance of all muscles in the body.

Transporting substances inside the body- The cardiac and visceral

muscles are responsible for transporting substances like blood or food from one part of the body to another.

Generation of body heat- The muscles generate body heat by their contraction action. As a result of the high metabolic rate of contracting muscle, our muscular system produces a great deal of waste heat. Many small muscle contractions within the body produce our natural body heat.

Muscles as Levers- Skeletal muscles work together with bones and joints to form lever systems. The muscle acts as the effort force; the joint acts as the fulcrum; the bone that the muscle moves acts as the lever; and the object being moved acts as the load.

Motor Units- Nerve cells called motor neurons control the skeletal muscles by receiving signals from the brain. When the motor neurons receive the signal they stimulate the motor unit to move. Muscles that require precise movements have few muscle fibers in each motor unit while muscles that need a lot of strength have a lot of muscle cells in each motor unit. The body can control the strength of each muscle by determining how many motor units to activate for a given function.

Types of Muscle Contraction- There are several types of muscle contractions: Twitch contraction- this is when a single nerve impulse of a motor neuron causes a motor unit to to contract briefly before relaxing.

Isometric contractions- These are light contractions that increase tension in the muscle without moving the a body part; an example is holding an object still and holding the posture.

Isotonic contraction- This is a contraction that produces movement.

Muscle Metabolism and Fatigue- Muscles get their energy from different sources depending on the situation that the muscle is working in.

Aerobic respiration- Muscles use aerobic respiration when we need them to produce a low to moderate level of force. Aerobic respiration requires oxygen. Aerobic respiration is very efficient, and can continue as long as a muscle receives adequate amounts of oxygen and glucose to keep contracting.

Anaerobic respiration- We create energy using anaerobic respiration when we need vast amounts of energy. Instead it uses lactic acid fermentation. Under anaerobic respiration muscle tire easily. This form of energy formation is inefficient and lasts only a short period To keep muscles working for a longer period of time, muscle fibers contain several important energy molecules. Myoglobin, a red pigment found in muscles, contains iron and stores oxygen in a manner similar to hemoglobin in the blood. The oxygen from myoglobin allows muscles to continue aerobic respiration in the absence of oxygen. This helps to keep muscles working longer. Creatine also helps keep the muscles working. Muscle fibers contain energy-storing glycogen, a large macromolecule made of many linked glucoses. Active muscles break glucoses off of glycogen molecules to provide an internal fuel supply.

Muscle fatigue is When muscles run out of energy during either aerobic or anaerobic respiration. Muscle fatigue causes the muscle to quickly tire and lose its ability to contract. Fatigued muscles contains very little oxygen , therefore the body must work harder to take in extra oxygen. The body must take in extra oxygen after exertion to replace the oxygen that was stored in myoglobin in the muscle fiber as well as to power the aerobic respiration that will rebuild the energy supplies inside of the cell.

Oxygen debt- this is the name for the extra oxygen that the body must take in to restore the muscle cells to their resting state. The oxygen debt makes you feel out of breath after a particularly strenuous activity as your body tries to restore the depleted oxygen and get back to normal state.

Skeletal System The skeletal system includes all of the bones and joints in the body.

The bones are made up of many cells, protein fibers, and minerals.

Functions: The skeleton provides support Provides protection for the soft tissues that make up the rest of the body.

The skeletal system also provides attachment points for muscles to allow movements at the joints.

New blood cells are produced by the red bone marrow inside of our bones.

Bones act as the body’s warehouse for: calcium, iron, and energy in the form of fat. provides a framework for the rest of the body to grow along with it.

Skeletal System Anatomy The skeletal system in an adult body is made up of 206 individual bones. These bones are arranged into two major divisions: the axial skeleton and the appendicular skeleton.

Axial skeleton- runs along the body’s midline axis and is made up of 80 bones in the following regions: Skull Hyoid Auditory ossicles Ribs Sternum Vertebral column

The appendicular skeleton- is made up of 126 bones in the folowing regions: Upper limbs Lower limbs Pelvic girdle Pectoral (shoulder) girdle

Skull

The skull is made up of 22 bones that are fused together except for the mandible. These 21 fused bones are separate in children to allow the skull and brain to grow, but fuse to give added strength and protection as an adult. The mandible is the only movable joint of the skull remains. It connects to the temporal bone.

The bones of the superior portion of the skull are known as the cranium and protect the brain from damage. The bones of the inferior and anterior portion of the skull are known as facial bones and support the eyes, nose, and mouth.

Hyoid bone The hyoid is a small, U-shaped bone found just inferior to the mandible. The hyoid is the only bone in the body that does not form a joint with any other bone—it is a floating bone. The hyoid’s function is to help hold the trachea open and to form a bony connection for the tongue muscles.

Auditory ossicles

The malleus, incus, and stapes form the auditory ossicles. These are the smallest bones in the body. They transmit and amplify sound from the eardrum to the inner ear.

Vertebrae The vertebral column is made up of Twenty-six vertebrae. They are named by region: Cervical (neck) - 7 vertebrae Thoracic (chest) - 12 vertebrae Lumbar (lower back) - 5 vertebrae Sacrum - 1 vertebra Coccyx (tailbone) - 1 vertebra

Ribs and Sternum The sternum, or breastbone, is a thin, knife-shaped bone located along the midline of the anterior side of the thoracic region of the skeleton.

The sternum connects to the ribs by thin bands of cartilage called the costal cartilage.

There are 12 pairs of ribs that together with the sternum form the ribcage of the thoracic region. The first seven ribs are known as “true ribs” because they connect the thoracic vertebrae directly to the sternum through their own band of costal cartilage. Ribs 8, 9, and 10 all connect to the sternum through cartilage that is connected to the cartilage of the seventh rib, so we consider these to be “false ribs.”

Ribs 11 and 12 are also false ribs, but are also considered to be “floating ribs” because they do not have any cartilage attachment to the sternum at all.

Pectoral Girdle and Upper Limb

The pectoral girdle connects the upper limb (arm) bones to the axial skeleton. The pectoral girdle consists of: left and right clavicles and left and right scapulae.

The humerus is the bone of the upper arm. It forms the ball and socket joint of the shoulder with the scapula and forms the elbow joint with the lower arm bones. The radius and ulna are the two bones of the forearm. The ulna is on the medial side of the forearm and forms a hinge joint with the humerus at the elbow. The radius allows the forearm and hand to turn over at the wrist joint.

The lower arm bones form the wrist joint with the carpals, a group of eight small bones that give added flexibility to the wrist. The carpals are connected to the five metacarpals that form the bones of the hand and connect to each of the fingers. Each finger has three bones known as phalanges, except for the thumb, which only has two phalanges.

Pelvic Girdle and Lower Limb The pelvic girdle connects the leg bones to the axial skeleton. It is formed by the left and right hip bones.

The femur is the largest bone in the body and the only bone of the thigh (femoral) region. The femur forms the ball and socket hip joint with the hip bone and forms the knee joint with the tibia and patella.

Commonly called the kneecap, the patella is special because it is one of the few bones that are not present at birth. The patella forms in early childhood to support the knee for walking and crawling.

The tibia and fibula are the bones of the lower leg. The tibia carries almost all the weight of the body. The fibula is used to maintain balance. The tibia and fibula form the ankle joint with the talus, one of the seven tarsal bones in the foot.

The tarsals are a group of seven small bones that form the posterior end of the foot and heel. The tarsals form joints with the five long metatarsals of the foot. Then each of the metatarsals forms a joint with one of the set of phalanges in the toes. Each toe has three phalanges, except for the big toe, which only has two phalanges.

Microscopic Structure of Bones The skeleton makes up about 30-40% of an adult’s body mass. The skeleton’s mass is made up of nonliving bone matrix and many tiny bone cells. Roughly half of the bone matrix’s mass is water, while the other half is collagen protein and solid crystals of calcium carbonate and calcium phosphate.

Living bone cells are found on the edges of bones and in small cavities inside of the bone matrix.

The bone cells allow bones to: Grow and develop Be repaired following an injury or daily wear Be broken down to release their stored minerals Types of Bones There are five types of bones: long short flat irregular sesamoid.

Long- Long bones are longer than they are wide and are the major bones of the limbs. Long bones grow more than the other classes of bone throughout childhood and so are responsible for the bulk of our height as adults. A hollow medullary cavity is found in the center of long bones and serves as a storage area for bone marrow. Long bones include the femur, tibia, fibula, metatarsals, and phalanges.

Short- Short bones are about as long as they are wide and are often cubed or round in shape. The carpal bones of the wrist and the tarsal bones of the foot are examples of short bones.

Flat- They vary greatly in size and shape, but have the common feature of being very thin in one direction. Because they are thin, flat bones do not have a medullary cavity like the long bones. The frontal, parietal, and occipital bones of the cranium—along with the ribs and hip bones—are all examples of flat bones.

Irregular- Irregular bones have a shape that does not fit the pattern of the long, short, or flat bones. The vertebrae, sacrum, and coccyx of the spine—as well as the sphenoid, ethmoid, and zygomatic bones of the skull—are all irregular bones.

Sesamoid- The sesamoid bones are formed after birth inside of tendons that run across joints. Sesamoid bones grow to protect the tendon from stresses and strains at the joint and can help to give a mechanical advantage to muscles pulling on the tendon. The patella and the pisiform bone of the carpals are the only sesamoid bones that are counted as part of the 206 bones of the body. Other sesamoid bones can form in the joints of the hands and feet, but are not present in all people.

Parts of Bones

The long bones of the body contain many distinct regions due to the way in which they develop. At birth, each long bone is made of three individual bones separated by hyaline cartilage. Each end bone is called an epiphysis (epi = on; physis = to grow) while the middle bone is called a diaphysis (dia = passing through). The epiphyses and diaphysis grow towards one another and eventually fuse into one bone. The region of growth and eventual fusion in between the epiphysis and diaphysis is called the metaphysis (meta = after). Once the long bone parts have fused together, the only hyaline cartilage left in the bone is found as articular cartilage on the ends of the bone that form joints with other bones. The articular cartilage acts as a shock absorber and gliding surface between the bones to facilitate movement at the joint.

The outside of a bone is covered in a thin layer of dense irregular connective tissue called the periosteum. The periosteum contains many strong collagen fibers that are used to firmly anchor tendons and muscles to the bone for movement. Stem cells and osteoblast cells in the periosteum are involved in the growth and repair of the outside of the bone due to stress and injury. Blood vessels present in the periosteum provide energy to the cells on the surface of the bone and penetrate into the bone itself to nourish the cells inside of the bone.

The periosteum also contains nervous tissue and many nerve endings to give bone its sensitivity to pain when injured.

Deep to the periosteum is the compact bone that makes up the hard,

mineralized portion of the bone. Compact bone is made of a matrix of hard mineral salts reinforced with tough collagen fibers. Many tiny cells called osteocytes live in small spaces in the matrix and help to maintain the strength and integrity of the compact bone.

Deep to the compact bone layer is a region of spongy bone where the bone tissue grows in thin columns called trabeculae with spaces for red bone marrow in between. The trabeculae grow in a specific pattern to resist outside stresses with the least amount of mass possible, keeping bones light but strong. Long bones have a spongy bone on their ends but have a hollow medullary cavity in the middle of the diaphysis. The medullary cavity contains red bone marrow during childhood, eventually turning into yellow bone marrow after puberty.

Skeletal System Physiology Support and Protection- The skeletal system’s primary function is to form a solid framework that supports and protects the body's organs and anchors the skeletal muscles. The bones of the axial skeleton act as a hard shell to protect the internal organs—such as the brain and the heart—from damage caused by external forces.

The bones of the appendicular skeleton provide support and flexibility at the joints and anchor the muscles that move the limbs.

Movement- The bones of the skeletal system act as attachment points for the skeletal muscles of the body. Almost every skeletal muscle works by pulling two or more bones either closer together or further apart. Joints act as pivot points for the movement of the bones. The regions of each bone where muscles attach to the bone grow larger and stronger to support the additional force of the muscle. In addition, the overall mass and thickness of a bone increase when it is under a lot of stress from lifting weights or supporting body weight.

Hematopoiesis- Red bone marrow produces red and white blood cells in a process known as hematopoiesis. Red bone marrow is found in the hollow space inside of bones known as the medullary cavity.

Children tend to have more red bone marrow compared to their body size than adults do, due to their body’s constant growth and development. The amount of red bone marrow drops off at the end of puberty, replaced by yellow bone marrow.

Storage- The skeletal system stores many different types of essential

substances to facilitate growth and repair of the body. The skeletal system’s cell matrix acts as our calcium bank by storing and releasing calcium ions into the blood as needed. Proper levels of calcium ions in the blood are essential to the proper function of the nervous and muscular systems. Bone cells also release osteocalcin, a hormone that helps regulate blood sugar and fat deposition. The yellow bone marrow inside of our hollow long bones is used to store energy in the form of lipids. Finally, red bone marrow stores some iron in the form of the molecule ferritin and uses this iron to form hemoglobin in red blood cells.

Growth and Development- The skeleton begins to form early in fetal development as a flexible skeleton made of hyaline cartilage and dense irregular fibrous connective tissue. These tissues act as a soft, growing framework and placeholder for the bony skeleton that will replace them. As development progresses, blood vessels begin to grow into the soft fetal skeleton, bringing stem cells and nutrients for bone growth. Osseous tissue slowly replaces the cartilage and fibrous tissue in a process called calcification. The calcified areas spread out from their blood vessels replacing the old tissues until they reach the border of another bony area. At birth, the skeleton of a newborn has more than 300 bones; as a person ages, these bones grow together and fuse into larger bones, leaving adults with only 206 bones.

Flat bones follow the process of intramembranous ossification where the young bones grow from a primary ossification center in fibrous membranes and leave a small region of fibrous tissue in between each other. In the skull these soft spots are known as fontanels, and give the skull flexibility and room for the bones to grow. Bone slowly replaces the fontanels until the individual bones of the skull fuse together to form a rigid adult skull.

Long bones follow the process of endochondral ossification where the diaphysis grows inside of cartilage from a primary ossification center until it forms most of the bone. The epiphyses then grow from secondary ossification centers on the ends of the bone. A small band of hyaline cartilage remains in between the bones as a growth plate.

As we grow through childhood, the growth plates grow under the influence of growth and sex hormones, slowly separating the bones. At the same time the bones grow larger by growing back into the growth plates. This process continues until the end of puberty, when the growth plate stops growing and the bones fuse permanently into a single bone. The vast difference in height and limb length between

birth and adulthood are mainly the result of endochondral ossification in the long bones.