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The endocrine system is a collection of glands that secrete chemical messages we call hormones. These signals are passed through the blood to arrive at a target organ, which has cells possessing the appropriate receptor. Exocrine glands (not part of the endocrine system) secrete products that are passed outside the body. Sweat glands, salivary glands, and digestive glands are examples of exocrine glands.
Hormones are grouped into three classes based on their structure: steroids peptides amines
STEROIDS Steroids are lipids derived from cholesterol. Testosterone is the male sex hormone. Estradiol, similar in structure to testosterone, is responsible for many female sex characteristics. Steroid hormones are secreted by the gonads, adrenal cortex, and placenta.
PEPTIDES AND AMINES Peptides are short chains of amino acids; most hormones are peptides. They are secreted by the pituitary, parathyroid, heart, stomach, liver, a nd kidneys. Amines are derived from the amino acid tyrosine and are secreted from the thyroid and the adrenal medulla. Solubility of the various hormone classes varies.
SYNTHESIS, STORAGE, AND SECRETION Steroid hormones are derived from cholesterol by a biochemical reaction series. Defects along this series often lead to hormonal imbalances with serious consequences. Once synthesized, steroid hormones pass into the bloodstream; they are not stored by cells, and the rate of synthesis controls them. Peptide hormones are synthesized as precursor molecules and processed by the endoplasmic reticulum and Golgi where they are stored in secretory granules. When needed, the granules are dumped into the bloodstream. Different hormones can often be made from the same precursor molecule by cleaving it with a different enzyme. Amine hormones (notably epinephrine) are stored as granules in the cytoplasm until needed.
The hypothalamus contains neurons that control releases from the anterior pituitary. Seven hypothalamic hormones are released into a portal system connecting the hypothalamus and pituitary, and cause targets in the pituitary to release eight hormones.
THE ADRENAL GLANDS Each kidney has an adrenal gland located above it. The adrenal gland is divided into an inner medulla and an outer cortex. The medulla synthesizes amine hormones, the cortex secretes steroid hormones. The adrenal medulla consists of modified neurons that secrete two hormones: epinephrine and norepinephrine. Stimulation of the cortex by the sympathetic nervous system causes release of hormones into the blood to initiate the "fight or flight" response. The adrenal cortex produces several steroid hormones in three classes: mineralocorticoids, glucocorticoids, and sex hormones. Mineralocorticoids maintain electrolyte balance. Glucocorticoids produce a long-term, slow response to stress by raising blood glucose levels through the breakdown of fats and proteins; they also suppress the immune response and inhibit the inflammatory response.
THE PANCREAS The pancreas contains exocrine cells that secrete digestive enzymes into the small intestine and clusters of endocrine cells (the pancreatic islets). The islets secrete the hormones insulin and glucagon, which regulate blood glucose levels. After a meal, blood glucose levels rise, prompting the release of insulin, which causes cells to take up glucose, and liver and skeletal muscle cells to form the carbohydrate glycogen. As glucose levels in the blood fall, further insulin production is inhibited. Glucagon causes the breakdown of glycogen into glucose, which in turn is released into the blood to maintain glucose levels within a homeostatic range. Glucagon production is stimulated when blood glucose levels fall, and inhibited when they rise. Diabetes results from inadequate levels of insulin. Type I diabetes is characterized by inadequate levels of insulin secretion, often due to a genetic cause. Type II usually develops in adults from both genetic and environmental causes. Loss of response of targets to insulin rather than lack of insulin causes this type of diabetes. Diabetes causes impairment in the functioning of the eyes, circulatory system, nervous system, and failure of the kidneys. Diabetes is the second leading cause of blindness in the US. Treatments involve daily injections of insulin, monitoring of blood glucose levels and a controlled diet.
OVARIES The ovaries are a pair of oval or almond-shaped glands which lie on either side of the uterus and just below the opening to the fallopian tubes. In addition to producing eggs or "ova," the ovaries produce female sex hormones called estrogen and progesterone. The ovaries produce a female hormone, called estrogen, and store female sex cells or "ova." The female, unlike the male, does not manufacture the sex cells. A girl baby is born with about 60,000 of these cells, which are contained in sac-like depressions in the ovaries. Each of these cells may have the potential to mature for fertilization, but in actuality, only about 400 ripen during the womans lifetime. Pregnant and prenatal both come from the same Latin roots. "Prae" means "before" and "nascor" means "to be born". Nascor is also the derivative of nature, innate and native. Only a few years ago, the word, "pregnant" was seldom used in mixed company. Polite society referred to a pregnant woman as "expecting" or "being in the family way."
PITUITARY GLAND he pituitary gland, which is located in the center of the skull, just behind the bridge of the nose, is about the size of a pea. It is an important link between the nervous system and the endocrine system and releases many hormones which affect growth, sexual development, metabolism and the system of reproduction. The "hypothalamus" is a tiny cluster of brain cells just above the pituitary gland, which transmits messages from the body to the brain. The pituitary gland has two distinct parts, the anterior and the posterior lobes, each of which releases different hormones which affect bone growth and regulate activity in other glands. This gland was once believed to be the main controlling gland of the body, but we now know that, important as it is, it is subservient to a master gland called the hypothalamus, which is the needed link between the pituitary gland and the brain. This "master gland" is really a way station between the body and the brain and sorts out messages going to and from the brain. It responds to the body through the pituitary gland, which is suspended just below it. It sometimes replies by nerve impulses and sometimes with needed hormones. The pituitary gland then makes hormones of its own in answer to the bodys needs. These are then circulated in the blood to a variety of the bodys tissues, including other endocrines, such as the adrenal gland.
TESTICLES The scrotum is a sac that hangs under the penis and holds the testes. It is divided internally into two halves by a membrane; each half containing a testis. It has an outer layer of thin, wrinkled skin over a layer of tissue which contains muscle. The testicle lies inside the scrotum and produces as many as 12 trillion sperm in a males lifetime, about 400 million of which are ejaculated in one average intercourse. Each sperm takes about seventy-two days to mature and its maturity is overseen by a complex interaction of hormones. The scrotum has a built-in thermostat, which keeps the sperm at the correct temperature. It may be surprising that the testicles should lie in such a vulnerable place, outside the body, but it is too hot inside. The sperm production needs a temperature which is three to five degrees below body temperature. If it becomes too cool on the outside, the scrotum will contract to bring the testes closer the body for warmth.
THYMUS The thymus is a gland that forms part of the immune system. It is situated in the upper part of the chest, behind the breastbone, and is made up of two lobes that join in front of the trachea. Each lobe is made of lymphoid tissue, consisting of tightly packed white blood cells and fat. The thymus enlarges from about the 12th week of gestation until puberty, when it begins to shrink. Its function is to transform lymphocytes (white blood cells developed in the bone marrow) into T-cells (cells developed in the thymus). These cells are then transported to various lymph glands, where they play an important part in fighting infections and disease. Swelling of lymph glands and fever are a signal that immune cells are multiplying to fight off invaders of the body: bacteria, fungi, viruses or parasites. Edward Jenner showed his faith in vaccination by injecting his own son with cowpox, therefore immunizing the child against smallpox, a deadly disease at that time in history
THYROID AND PARATHYROID GLANDS The thyroid gland is shaped like a butterfly and usually weighs less than one ounce. The thyroid cartilage covers the larynx and produces the prominence on the neck known as the "Adams Apple". The thyroid gland controls the rate at which the body produces energy from nutrients. If the body does not get enough iodine, the thyroid gland cannot produce a proper amount of hormones for this conversion process. The result can be a goiter, an enlargement of the thyroid gland. In some parts of the world, iodine is so scarce that most of the population have goiters. The parathyroid glands are four small oval bodies located on either side of and on the dorsal aspect of the thyroid gland. These glands control the level of calcium in the blood. The thyroid gland secretes hormones which regulate energy, and emotional balance may rely upon its normal functioning. When the rate of production is excessive, the results can be weight loss, nervousness, or even emotional disturbances. If the rate of production is excessively low, a slowing of bodily functions may result. The parathyroid glands, located behind the thyroid, control the blood-calcium level. Calcium is important, not only for bones and teeth, but also for nerve functioning, muscle contractions, blood clotting and glandular secretion. If we dont have enough calcium for these functions, the body will take it from the bones, causing them to easily fracture. It may also cause twitching, spasms, convulsions and even death. Too much calcium may cause a weakening of muscle tone and kidney stones.
Term Cause Effect (Symptoms)Addisons Syndrome Inadequate secretion of Symptoms: include weakness, loss coricosteroid hormones by the of energy, low blood pressure, and adrenal glands, sometimes as a dark pigmentation of the skin. result of tuberculous infection. Treatment: Formerly fatal, this disease is now treatable by replacement hormone therapy.Amenorrhoea Primary amenorrhoea (menstrual The absence or stopping of the periods fail to appear at puberty) menstrual periods. (It is normal for may be caused by absence of the the periods to be absent before uterus or ovaries (e.g. Turner’s puberty, during pregnancy and milk syndrome) or a hormonal secretion, and after the end of the imbalance. reproductive period.) Secondary amenorrhoea (menstrual periods stop after establishment of puberty) may be caused by disorders of the hypothalamus, deficiency of ovarian, pituitary, or thyroid hormones, mental disturbance, depression, anorexia nervosa, or a major change of sur
Term Cause Effect ( Symptoms)Cushings Syndrome Excess amounts of cortico- Symptoms include: weight steroid hormones in the gain; reddening of the face body. and neck; excess growth of body and facial hair; raised blood pressure; loss of mineral from the bones (osteoporosis); raised blood glucose levels; and sometimes mental disturbances.Menopause Cessation of viable egg Leads to hormonal imbalance; lack of negative feedback to the production in the female. hypothalamus/activity; continued release of FSH. Symptoms: hot flushes; night sweats; mood swings; increased risk of heart attack; osteoporosis speeds up. Treatment: Hormone Replacement Therapy (HRT), with associated increased risk of breast cancer.
Term Cause Effect ( Symptoms)Pre-menstrual Syndrome Associated with the Nervousness; irritability; accumulation of salt and emotional disturbance; water in tissues.The headache; and/or hormone progesterone is depression – said to affect thought to be a causative some women for up to element and a deficirncy of about 10 days prior to fatty acids has also been menstruation. observed.Polycystic Ovarian A hormonal disorder Further hormoneSyndrome characterized by imbalance results in incomplete development of obesity, hirsutism and acne Graafian follicles in the and the woman is infertile ovary due to inadequate due to the lack of secretion of luteinizing ovulation.The treatment is hormone; the follicles fail administration of the to ovulate and remain as appropriate hormones. multiple cysts distending the ovary.
HOW TO KEEP THE ENDOCRINE SYSTEMHEALTHY Keep minor endocrine diseases under control. Some people let minor or controllable diseases of the endocrine system go untreated. These diseases can develop into something much bigger if untreated or unnoticed. Diabetes should be given attention on a daily basis. It is recommended that you take special note and precaution to endocrine disorders. Know your family history. Knowledge of your family history is a powerful tool to have. It is especially useful when you get into your twenties. Many endocrine disorders develop in people over twenty except type I diabetes. Knowing your family history can help you learn the precautions, and you can often prevent an endocrine disorder through lifestyle changes. Eat a healthy diet. It is always very important to eat a healthy and well balanced diet every single day. Not eating healthy can lead to type II diabetes (an endocrine disorder), and type II diabetes can later lead to blindness and kidney failure (a serious endocrine disorder). It is recommended that you talk to your doctor if you need help developing and staying on a healthy diet.
Minimize stress in your life. Having a lot of stress in your life can cause the overproduction of hormones. This can lead to the failure or malfunction of many endocrine organs. It is recommended that you get plenty of exercise. Allow six to eight hours of sleep per night in order to reduce stress and keep hormones balanced. Stay in touch with your doctor. You should especially stay in close contact with an endocrinologist if you consider yourself to be a high risk for diabetes and other diseases. Your endocrinologist can run tests, help you assess the disorders you are more at risk for and help you keep your chances of getting these disorders low. Ask your medical doctor about a referral to an endocrine specialist if you feel you are in need of one.
TIPS AND WARNINGS Pay attention to your overall health, and a healthy endocrine system will probably happen as well! If you dont keep your endocrine system healthy, developing an endocrine disorder can bring about a totally different order to your life as you know it.
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