ENDOCRINE SYSTEM GLANDS Endocrine system glands
Location and function
Hormones The adrenal cortex produces three hormones:
ADRENAL GLANDS
1. Mineralocorticoids: the most important of which is aldosterone. This hormone helps to maintain the body’s salt and water levels which, in turn, regulates blood pressure. Without aldosterone, the kidney loses excessive amounts of salt (sodium) and, consequently, water, leading to severe dehydration.
Alteration In rare cases, the adrenal glands can become either overactive or underactive. The two main disorders resulting from these are Cushing's syndrome and Addison's disease, respectively.
Cushing’s syndrome is due to 2. Glucocorticoids: predominantly cortisol. This hormone is overactive adrenal glands from involved in the stress response and also helps to excessive production of regulate body metabolism. Cortisol stimulates glucose cortisol. The clinical findings production by mobilising amino acids and free fatty include thinning and bruising acids. Cortisol also has significant anti-inflammatory of the skin, obesity, diabetes, effects. psychiatric disturbances, high blood pressure, muscle 3. Adrenal androgens: male sex hormones weakness, osteoporosis, mainly dehydroepiandrosterone (DHEA) excessive facial hair Located at the top of each kidney, the adrenal and testosterone. All have weak effects, but play a role and irregular periods in glands produce hormones that help the body control in early development of the male sex organs in women. It can result in growth blood sugar, burn protein and fat, react to stressors like a childhood, and in women during puberty. These are failure in children. Patients major illness or injury, and regulate blood pressure. Two involved in creating and maintaining the differences with cortisol excess also have of the most important adrenal hormones are cortisol and between men and women. impaired wound healing and aldosterone. The adrenal glands also produce adrenaline an increased susceptibility to and small amounts of sex hormones called androgens, Adrenocorticotropic hormone (ACTH) secreted by the anterior infection. among other hormones. pituitary primarily affects release of glucocorticoids and
The adrenal glands have two parts, each of which produces a set of hormones and has a different function:
adrenal androgens by the adrenal and to a lesser extent, also stimulates aldosterone release. The adrenal medulla produces catecholamines:
1. The outer part, the adrenal cortex, produces hormones called corticosteroids that influence or regulate salt and water balance in the body, the body's response to stress, metabolism, the immune system, and sexual development and function. 2. The inner part, the adrenal medulla, produces catecholamines, such as epinephrine. Also called adrenaline, epinephrine increases blood pressure and heart rate when the body experiences stress.
Catecholamines include adrenaline, noradrenaline and small amounts of dopamine - these hormones are responsible for all the physiological characteristics of the stress response, the so called ‘fight or flight’ response.
Adrenal insufficiency occurs when the adrenal glands don’t make enough cortisol, and sometimes, aldosterone. Symptoms include fatigue, muscle weakness, decreased appetite, and weight loss. Some people experience nausea, vomiting, and diarrhea. Adrenal insufficiency is treated with hormones that replace the hormones your body is lacking. Rarely, overproduction of aldosterone can occur, which causes a condition known as hyperaldosteronism. This causes high blood pressure, which is resistant to conventional blood pressure control tablets, and salt disturbances. High blood pressure may cause headaches and visual problems. Overproduction of androgens is also rare but may result in excessive hair growth and menstrual period disturbances.
Hormones secreted by the hypothalamus include: §
HYPOTHA LAMUS
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Any disorder that keeps the hypothalamus from An antidiuretic hormone, which increases how much water is properly working is known absorbed into the blood by the kidneys as a hypothalamic Corticotropin-releasing hormones that help regulate disease. Hypothalamic metabolism and immune response by working with the diseases are very hard to pituitary gland and adrenal gland to release certain steroids pinpoint because the Gonadotropin-releasing hormones that tell the pituitary hypothalamus has such a gland to release hormones that keep the sexual organs wide range of roles in the working endocrine system. Oxytocin is involved in many processes, including the release of a mother's breast milk, body temperature, and sleep cycles Prolactin-controlling hormones tell the pituitary gland to either start or stop breast milk production in lactating
The hypothalamus, a collection of specialized cells that is located in the lower central part of the brain, is the main § link between the endocrine and nervous systems. Nerve cells in the hypothalamus control the pituitary gland by mothers producing chemicals that either stimulate or suppress hormone secretions from the pituitary. § Thyrotropin-releasing hormone activates the thyroid; this The body's normal, balanced state of being is known as releases the hormones that regulate metabolism, energy homeostasis. The body is always trying to achieve this levels, and developmental growth. balance. The main job of the hypothalamus to keep the Growth hormones are also directly affected by the body in this state as much as possible. To do this, the hypothalamus acts as the connector between the endocrine and nervous systems. It plays a part in many essential functions of the body such as: §
Body temperature
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Thirst
hypothalamus. It tells the pituitary gland to either increase or decrease their number in the body. This is essential for both growing children and fully developed adults.
The hypothalamus also plays the important role of signaling the pituitary gland to release hormones to the rest of the endocrine system. As it is difficult for doctors to diagnose which gland isn't working properly, these disorders are often called hypothalamus-pituitary disorders. In these cases, there are some hormone tests that doctors may
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Appetite and weight control
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Emotions
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Sleep cycles
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Sex drive
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Childbirth
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Blood pressure and heart rate Production of digestive juices
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Balancing bodily fluids
prescribe to get to the root of the disorder.
As signals are sent to the brain from different areas of the body, they let the hypothalamus know if balance is not being achieved. The hypothalamus then responds by releasing the right hormones into the bloodstream to balance the body back out.
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PITUITAR Y GLAND
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Although it is no bigger than a pea, the pituitary gland, located at the base of the brain just beneath the hypothalamus, is
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The following hormones are made in the anterior (front part) of the pituitary gland: Prolactin - Prolactin stimulates breast milk production after childbirth. It also affects sex hormone levels from ovaries in women and from testes (testicles) in men, as well as fertility. Growth hormone (GH) - GH stimulates growth in childhood and is important for maintaining a healthy body composition and well-being in adults. In adults, GH is important for maintaining muscle mass and bone mass. It also affects fat distribution in the body. Read about growth hormone excess. Adrenocorticotropin (ACTH) - ACTH stimulates the production of cortisol by the adrenal glands—small
There are two types of tumors—secretory and non-secretory. Secretory tumors produce too much of a hormone normally made by the pituitary, and non-secretory tumors do not. Both types of tumors can cause problems if they are large and interfere with normal function of the pituitary gland and/or nearby structures in the brain.
considered the most important part of the endocrine system. It's often called the "master gland" because it makes hormones that control several other endocrine glands. The production and secretion of pituitary hormones can be influenced by factors such as emotions and changes in the seasons. To accomplish this, the hypothalamus provides information sensed by the brain (such as environmental temperature, light exposure patterns, and feelings) to the pituitary. The tiny pituitary is divided into two parts: the anterior lobe and the posterior lobe. The anterior lobe regulates the activity of the thyroid, adrenals, and reproductive glands.
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glands that sit on top of the kidneys. Cortisol, a "stress hormone," is vital to our survival. It helps maintain blood pressure and blood glucose (sugar) levels, and is produced in larger amounts when we’re under stress— 1. especially after illness or injury. Read about having too much ACTH. Thyroid-stimulating hormone (TSH) - TSH stimulates the thyroid gland to produce thyroid hormones, which 2. regulate the body's metabolism, energy balance, growth, and nervous system activity. Read about TSHsecreting tumors. Luteinizing hormone (LH) - LH stimulates testosterone production in men and egg release (ovulation) in women. Follicle-stimulating hormone (FSH) - FSH promotes sperm production in men and stimulates the ovaries to produce estrogen and develop eggs in women. LH and3. FSH work together to enable normal function of the ovaries and testes. The following hormones are stored in the posterior (back part) of the pituitary gland: Antidiuretic hormone (ADH) - ADH, also called vasopressin, regulates water balance in the body. It conserves body water by reducing the amount of water lost in urine. Oxytocin – Oxytocin causes milk to flow from the breasts in breastfeeding women, and may also help labor to progress.
The problems caused by pituitary tumors fall into three general categories: Hypersecretion: Too much of any hormone in the body is caused by a secretory pituitary tumor. Hyposecretion: Too little of any hormone in the body can be caused by a large pituitary tumor, which interferes with the pituitary gland’s ability to produce hormones. Hyposecretion can also result from surgery or radiation of a tumor. Tumor mass effects: As a pituitary tumor grows and presses against the pituitary gland or other areas in the brain, it may cause headaches, vision problems, or other health effects. Injuries, certain medications, bleeding inside or close to the pituitary, and other conditions can also affect
the pituitary gland. Loss of normal pituitary function also can occur after major head trauma.
Glucagon This pancreatic hormone helps to elevate your blood sugar levels. When levels of sugar in your blood declines, your pancreas produces glucagon, which stimulates the liver to produce more glucose. As a result, your blood glucose levels return to normal.
PANCREA S
The pancreas is an organ located in the abdomen. It plays an essential role in converting the food we eat into fuel for the body's cells.
Insulin Insulin helps to lower sugar levels in your blood. This important hormone aids in the transport of glucose into your different cells. Your pancreas in response to increasing blood glucose levels produces insulin. In addition, insulin helps in converting glucose into glycogen, which is stored in your liver for future use.
The pancreas carries out two important roles:
Somatostatin The hormone somatostatin helps stop the release of 1. It makes digestive juices, which consist of powerful enzymes. These are released into the either insulin and glucagon in your blood depending on your body needs. In addition, it slows down small bowel after meals to break down and absorption of nutrients in your small intestine. digest food. Pancreatic polypeptide
Pancreatitis is inflammation of the pancreas that occurs when pancreatic enzyme secretions build up and begin to digest the organ itself. It can occur as acute painful attacks lasting a matter of days, or it may be a chronic condition that progresses over a period of
years. When the cells that make insulin either stop working altogether, or become inefficient and don’t make enough insulin, this causes diabetes mellitus. Type 1 diabetes mellitus is caused when the body’s immune system attacks its own cells in the islets of Langerhans, meaning that
2. It makes hormones that control blood glucose levels. A healthy pancreas produces the correct chemicals in the proper quantities, at the right times, to digest the foods we eat. The pancreas contains exocrine glands that produce enzymes important to digestion. These enzymes include trypsin and chymotrypsin to digest proteins; amylase for the digestion of carbohydrates; and lipase to break down fats. The endocrine component of the pancreas consists of islet cells (islets of Langerhans) that create and release important hormones directly into the bloodstream. Two of the main pancreatic hormones are insulin, which acts to lower blood sugar, and glucagon, which acts to raise blood sugar. Maintaining proper blood sugar levels is crucial to the functioning of key organs including the brain, liver, and kidneys.
This pancreatic hormone prevents secretion of somatostatin by your pancreas. Also, pancreatic polypeptide inhibits contraction of your gallbladder wall and secretion of digestive enzymes by your pancreas.
these cells cannot produce insulin. Type 2 diabetes mellitus is a metabolic disorder where the body is no longer able to produce or respond to insulin. The most common form of pancreatic cancer is pancreatic adenocarcinoma, an exocrine tumor arising from the cells lining the pancreatic duct. The classic presentation of pancreatic cancer is referred to as painless jaundice, a yellowish skin discoloration with no other symptoms. The diagnosis is usually made using different radiographic imaging techniques.
The parathyroid glands produce a hormone called parathyroid hormone.
PARATH YROID
Parathyroid glands are small glands of the endocrine system which are located in the neck behind the thyroid. Parathyroid glands control the calcium in our bodies--how much calcium is in our bones, and how much calcium is in our blood.
The parathyroid glands are important in tightly controlling calcium levels in the bloodstream. Because of this, calcium levels are generally very stable. This is important to ensure the nervous system and the body’s muscles can work properly, and also that bones remain strong.
Sometimes the parathyroid glands can make too much Parathyroid hormone is secreted from the parathyroid hormone. In four parathyroid glands, which are small glands in the this case, patients neck, located behind the thyroid gland. Parathyroid develop a blood level of hormone regulates calcium levels in the blood, largely calcium that is too high by increasing the levels when they are too low. It (hypercalcaemia), which in does this through its actions on the kidneys, bones turn can make them feel and intestine: generally unwell. The commonest condition 1. Bones - Parathyroid hormone stimulates the which cause this is release of calcium from large calcium stores in called primary the bones into the bloodstream. This increases hyperparathyroidism. bone destruction and decreases the formation of new bone. If the high level of parathyroid hormone 2. Kidneys - Parathyroid hormone reduces loss of remains undetected for a calcium in urine. Parathyroid hormone also long time, it can cause stimulates the production of active vitamin D in calcium from the bones to the kidneys. be lost into blood and subsequently the 3. Intestine - Parathyroid hormone increases urine. This can eventually calcium absorption in the intestine from food via cause bones to become its effects on vitamin D metabolism. thin or spongy (osteoporosis). Too much calcium in the urine can
The main target organs where parathyroid hormone exerts its effects are the bones and the kidneys. When needed, parathyroid hormone is released by the parathyroid glands into the blood and causes the bones to release calcium and increase levels in the bloodstream. It also causes the kidneys to stop calcium being lost in urine as well as stimulating the kidneys to regulate vitamin D metabolism.
also cause calcium stones in the kidney. Occasionally, the parathyroid glands do not produce enough parathyroid hormone leading to low blood calcium levels (hypocalcaemia). This condition is called hypoparathyroidism .
PINEAL GLAND
Melatonin: The Pineal Gland Hormone The pineal gland secretes a single hormone— melatonin (not to be confused with the pigment melanin). This simple hormone is special because its secretion is dictated by light. Researchers have determined that melatonin has two primary functions in humans—to help control your circadian (or biological) rhythm and regulate certain reproductive hormones. Both melatonin and its precursor, serotonin, which are The pineal gland is one of the smallest and most derived chemically from the alkaloid substance important endocrine glands in the body. Located in the center of the brain close to the more well-known pituitary tryptamine, are synthesized in the pineal gland. Along gland, the pineal gland gets its name from its with other brain sites, the pineal gland may also characteristic pine cone shape. It is also known as the produce neurosteroids. Dimethyltryptamine (DMT), a pineal organ, the pineal body or the “third eye”. This hallucinogenic compound present in the Amazonian small gland controls your body’s sleep-wake pattern.
It is not unusual to see pineal cysts on magnetic resonance imaging (MRI) scans. These are benign and not harmful. However, on rare occasions, tumours of the pineal gland are found. There are some extremely rare reports of precocious puberty (early puberty) in individuals with pineal gland cysts or tumours. It is not clear whether these
The pineal gland has several critical functions including secretion of melatonin the hormone that causes sleepiness and regulation of certain endocrine functions. The gland also helps the body to convert signals from the nervous system to signals in the endocrine system. Physiologically, in conjunction with the hypothalamus gland, the pineal gland controls the sex drive, hunger, thirst and the biological clock which determines the body’s normal aging process. The primary function is that pineal gland secretes melatonin. This hormone is the primary one that controls your sleepiness and wakefulness. Natural light tends to turn this gland on. When the pineal gland is activated, your brain moves from sleeping to a state of wakefulness. This process is sometimes referred to as the awakening of the “Third Eye” – a common name for the pineal gland. It is the pineal gland that seems to be most affected during meditation and visualization yoga and all other forms of “out of the body travel”.
botanical drink ayahuasca, is chemically similar to melatonin and serotonin and is considered to be a trace substance in human blood and urine.
changes in puberty are caused by melatonin or some other hormone, such as human chorionic gonadotrophin, which is reported to be released by some pineal tumours. Otherwise, there are no known diseases associated with over or underactivity of the pineal gland.
OVARIES The ovaries have two main reproductive functions in the body. They produce oocytes (eggs) for fertilisation and they produce the reproductive hormones, oestrogen and progesterone. The function of the ovaries is controlled by gonadotrophin-releasing hormone released from nerve cells in the hypothalamus which send their messages to the pituitary gland to produce luteinising hormone and follicle stimulating hormone. These are carried in the bloodstream to control the menstrual cycle. The ovary is needed in reproduction since it is responsible for producing the female reproductive cells, or ova. During ovulation, a follicle (a small cavity in the ovary) expels an egg under the stimulation of gonadotropic hormones released by the pituitary gland, the luteinizing hormone and the follicle-
The major hormones secreted by the ovaries are oestrogen and progesterone, both important hormones in the menstrual cycle. Oestrogen production dominates in the first half of the menstrual cycle before ovulation, and progesterone production dominates during the second half of the menstrual cycle when the corpus luteum has formed. Both hormones are important in preparing the lining of the womb for pregnancy and the implantation of a fertilised egg, or embryo. If conception occurs during any one menstrual cycle, the corpus luteum does not lose its ability to function and continues to secrete oestrogen and progesterone, allowing the embryo to implant in the lining of the womb and form a placenta. At this point, development of the foetus begins.
The ovaries naturally stop functioning at the time of menopause. This occurs in most women around the age of 50. If this happens earlier, before the age of 40, it is called premature ovarian failure or premature ovarian insufficiency. The most common disorder of the ovaries is polycystic ovary syndrome which affects 5-10% of women of a reproductive age. In a polycystic ovary, the follicles mature to a certain stage, but then stop growing and fail to release an egg. These follicles appear as cysts in the ovaries on an ultrasound scan. Any abnormality which causes a loss of normal development of the ovaries, such as Turner syndrome, can result in the ovaries not functioning correctly and the loss of a woman’s fertility. The ovaries can be damaged by treatments for other conditions, particularly
stimulating hormone. The rest of the follicle, or the corpus luteum, secretes the sex hormones estrogen and progesterone, which regulate menstruation and control the development of the sex organs. The sex hormones and the gonadotropic hormones interact with each other to control the menstrual cycle. When an egg matures, it is released and passes into the fallopian tube toward the uterus. If the ovum is fertilized by the male reproductive cell, or sperm, conception happens and pregnancy begins.
TESTES
chemotherapy or radiotherapy for cancer treatment. If a woman stops having menstrual periods during her reproductive years, this condition is called amenorrhoea. It can be caused by a number of factors. These include anorexia (an eating disorder which causes severe loss of body weight) and very low levels of body fat in athletes who train at a very high level.
The main hormone secreted by the testes is testosterone, an androgenic hormone. Testosterone is secreted by cells that lie between the seminiferous tubules, known as the Leydig cells. The testes also produce inhibin B and anti-MĂźllerian hormone from Sertoli cells, and insulin-like factor 3 and oestradiol from the Leydig cells. Testosterone is important in the first stages of developing the male reproductive organs in a
a. Male infertility - due to absent or reduced sperm production or the production of sperm that do not function normally. There can be many causes including genetic and lifestyle factors. There are few treatments to correct male infertility and some form of assisted reproduction
The testes (plural) are the most essential organs of the male reproductive system. They are the glands where sperm and testosterone are produced.
foetus. It also causes the development of male characteristics such as growth of facial hair, deepening of the voice and the growth spurt that takes place during puberty. Testosterone is important in maintaining these secondary The testes have two functions - to produce male characteristics throughout a man’s life. sperm and to produce hormones, From puberty onwards, testosterone provides particularly testosterone. the main stimulus for sperm production.
may be required. b. Cryptorchidism - the failure of one or both testes to drop down into the scrotum before birth, so they remain in the abdominal space. This can harm normal development and function of the testes and lead to infertility. c. Epididymitis - an infection of the epididymis caused by a general infection or the sexually transmitted disease Chlamydia. Epididymitis can be treated with antibiotics.
d. Testicular cancer abnormal growth of cells within the testis. The growth can disrupt normal function of one or both testes. It is most common in young men. Urgent medical treatment is required. e. Klinefelter's syndrome - this is a genetic condition which stops the testes from developing normally. As a result, low levels of testosterone are produced and released.
Thymosin: The Hormone of the Thymus Thymosin stimulates the development of T cells. Throughout your childhood years, white blood cells called lymphocytes pass through the thymus, where they are transformed into T cells.
THYMUS
Once T cells have fully matured in the thymus, they migrate to the lymph nodes (groups of immune system cells) throughout the body, where they aid the immune system in fighting disease. However, some lymphocytes, regardless if they reside in the lymph nodes or thymus, can develop into cancers (known as Hodgkin disease and non-Hodgkin lymphomas). This gland secretes hormones that are commonly referred to as humoral factors and are important during puberty. The role of these hormones is to make sure a person develops a healthy immune system. The thymus gland, despite containing glandular tissue and producing several hormones, is much more closely associated with the immune system than with the endocrine system. The thymus serves a vital role in the training and development of T-lymphocytes or T cells, an extremely important type of white blood cell. T
Though the thymus gland is only active until puberty, its double-duty function as an endocrine and lymphatic gland plays a significant role in your longterm health.
Congenital Disorders
Several genetic defects cause thymus problems from birth. A rare condition called severe combined immunodeficiency, or SCID, develops when a person carries a mutation in a gene that regulates development of T cells. SCID disrupts the normal development of T cells in the thymus and other immune cells. This severely compromises a child's immune system, making him unable to fight off infections. In another rare disorder called DiGeorge syndrome, a piece of a chromosome is missing along with the genes it contains. This leads to poor development of the thymus and other organs in the immune system, causing weak immune responses and frequent illness. The severity of the disorder varies and can cause mild to severe symptoms.
cells defend the body from potentially deadly pathogens such as bacteria, viruses, and fungi.
Autoimmune Problems
The thymus is a soft, roughly triangular organ located in the mediastinum of the thoracic cavity anterior and superior to the heart and posterior to the sternum.
autoimmune diseases, the immune system attacks the body's own cells or substances made by cells, incorrectly perceiving them as foreign and harmful. One of these disorders, myasthenia gravis, is associated with a thymus gland that does not shrink but remains large after birth and functions abnormally. Although the disorder isn't fully understood, the thymus appears to be abnormally overactive, producing cells that attack a neurotransmitter called acetylcholine, which promotes normal muscle contraction in response to nerve impulses.
The function of the thymus is to receive immature T cells that are produced in the red bone marrow and train them into functional, mature T cells that attack only foreign cells. T cells first reside within the cortex of the thymus where they come in contact with epithelial cells presenting various antigens.
In disorders called
Thymus Cancer
Although rare, 2 types of cancer can develop it the thymus called thymomas and thymic carcinomas. Both
develop in populations of cells on the surface of the thymus, but they differ in other respects. Cells in thymomas grow relatively slowly. Thymic carcinoma cells divide rapidly and can quickly spread to other parts of the body. People with myasthenia gravis and other autoimmune disorders are at increased risk for thymomas.
The thyroid gland produces thyroxine (T4), which is a relatively inactive prohormone and lower amounts of the active hormone, triiodothyronine (T3). Collectively, T3 and T4 are referred to as the thyroid hormones. Twenty percent of the body’s triiodothyronine is made by the thyroid gland; the other 80% comes from thyroxine converted by organs such as the liver or kidneys.
THYROID
The thyroid gland produces hormones which regulate the body’s metabolic rate as well as heart and digestive function, muscle control, brain development and bone maintenance. Its correct functioning depends on having a good supply of iodine from the diet. The release of thyroid hormones from the thyroid gland is controlled by thyrotrophin-releasing hormone (TRH) from the hypothalamus in the brain and by thyroid stimulating hormone (TSH) produced by the pituitary gland. This forms part of a feedback loop called the hypothalamic-pituitary-thyroid axis.
The thyroid gland also produces calcitonin from cells called C-cells. Calcitonin is understood to play a role in regulating calcium levels in the body, but its exact function in humans remains unclear.
The thyroid gland can become overactive (hyperthyroidism) or underactive (hypothyroidism). This may, rarely, occur from birth, or develop later on in life. Hypothyroidism is often accompanied by an enlargement of the thyroid gland known as goitre. Thyrotoxicosis is the term given when there is too much thyroid hormone in the bloodstream. It may be a result of overactivity of the thyroid gland (hyperthyroidism) as in Graves’ disease, inflammation of the thyroid or a benign thyroid tumour. Sympto ms of thyrotoxicosis include intolerance to heat, weight loss, increased appetite, increased bowel movements, irregular menstrual cycle, rapid and irregular heartbeat, palpitations, tiredness, irritability, tremor, hair loss and retraction of the eyelids resulting in a ‘staring’ appearance. Hypothyroidism is the term given when low levels of thyroid hormones are produced by the thyroid gland. It may result from autoimmune diseases (when the
The thyroid gland is a butterfly-shaped organ located in the base of your neck. It releases hormones that control metabolism—the way your body uses energy. The thyroid's hormones regulate vital body functions, including: •
Breathing
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Heart rate
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Central and peripheral nervous systems
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Body weight
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Muscle strength
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Menstrual cycles
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Body temperature
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Cholesterol levels
person’s immune system starts to attack the body's own organs), poor iodine intake or be brought on by use of certain drugs.