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Endocrine System

Endocrine System

A gland in any organ that produces a secretion. Are organized groups of tissues which use materials from blood or lymph to make new compounds called hormones. Are also called ductless glands and glands of internal secretion. Hormones are secreted directly into bloodstream. Secretions are transported to all areas of the body where they have a special influence on cells, tissues and organs.

Function of the endocrine system

To secrete hormones or chemical messengers which coordinate and direct the activities of target cells and target organs.

Pituitary Gland

Tiny structure having a diameter about 10mm and weight approximately 0.5 g, about the size of a grape.Is known as the master gland because of its major influence on the bodys activities. It is even more amazing when you consider the size of this incredible gland.

Pituitary Hormones and Their Known FunctionsPITUITARY HORMONEKNOWN FUNCTIONAnterior LobeTSH - thyroid - stimulating hormone (thyrotropin)Stimulates the growth and the secretion of the thyroid glandACTH - adrenocorticotropicStimulates the growth and the secretion of the adrenal cortexFSH - follicle-stimulating hormonestimulates growth of new graafian (ovarian) follicle and secretion of estrogen by follicle cells in the female and the production of sperm in the maleLH - luteinizing hormone (female)Stimulates ovulation and formation of the corpus luteum. Corpus luteum secretes progesteroneICSH - Interstitial cell-stimulating hormone (male)Stimulates testosterone secretion by the interstitial of the testes.PRL - prolactinStimulates secretion of milk in females. Function in male is unknownGH - growth hormone (somatotropin, STH)Accelerates body growth and causes fat to be used for energy; this helps to maintain blood sugarPosterior Lobe - Hormones Produced by the HypothalamusVasopressin-antidiuretichormone (ADH)Maintains water balance by reducing urinary output. It acts on kidney tubules to reabsorb water into the blood more quickly. In large amounts, it causes contriction of arteriesOxytocinPromotes milk ejection and causes contraction of the smooth muscles of the uterusThyroid Gland

Is a butterfly-shaped mass of tissues located in the anterior part of the neck.It is about 2 inches long, with two lobes joined by strands of thyroid tissues called the isthmus.Thyroid gland has a rich blood supply. It fact, it has been estimated that about 4 to 5 liter (some 8.5 to 10.5 pints) of blood pass through the gland every hour.Thyroid gland secretes three hormones: thyroxine, triiodothyronine and calcitonin. The function of thyroxin (T4) and triiodothyronine (T3) are as follows:1. Controls the rate of metabolism in the body: how cell use glucose and oxygen to produce heat and energy.2. Stimulates protein synthesis and thus helps in tissue growth.3. Stimulates the breakdown of liver glycogenThyroid Gland

Calcitonin controls the calcium ion concentration in the body by maintaining a proper calcium level in the bloodstream.Approximately 99% of calcium stored in bones. Calcium is necessary for blood clotting, holding cell together and neuromuscular functions.Proper secretion of calcitonin into the bloodstream prevents hypercalcemia, a harmful rise in the blood calcium level.

Thymus Gland

Thymus gland is both an endocrine gland and lymphatic organ. Located under the sternum, anterior and superior to the heart.Fairly large childhood, it begins to disappear at puberty.The major hormone is thymosin which helps to stimulate the lymphoid cells that are responsible for the production of T cells, which fight certain diseases.

Adrenal Glands

The two adrenal glands are located on top of each kidneys one gland on each kidney. Each gland has two parts; the cortex and the medulla.Adrenocorticotrophic hormone (ACTH) from the pituitary gland stimulates the activity of the cortex of the adrenal gland.The hormones secretes by the adrenal cortex are known as corticoids. The corticoids are very effective as anti-inflammatory drugs.

The cortex secretes 3 groups of corticoids, each of which is of great importance :(a) Mineralocorticoids mainly aldosterone, affects the kidney tubules by speeding up the reabsorption of sodium into the blood circulation and increasing the excretion of potassium from the blood. They also speed up the reabsorption of water by the kidneys

(b) Glucocorticoids namely cortisone and cortisol, increase the amount of glucose in the blood. This is done by (1) the conversion of proteins and fats to glycogen in the liver, followed by (2) breakdown of the glycogen into glucose.(c) Sex hormones for both male and female androgens are male sex hormone which together with similar hormones from the gonads, bring about masculine characteristics. Some estrogens are also present.

Fungsi adrenalin dalam membantu kecemasan Ia membesarkan arteri-arteri koronari untuk menambahkan bekalan darah ke otot-otot jantung.Ia membesarkan bronkus supaya menambah kandungan udara yang masuk ketika tarikan nafas berlaku.Ia mencerutkan salur-salur darah di dalam kulit. Ini membantu meningkatkan tekanan darah.Ia menambahkan kadar pertukaran glikogen kepada glukosa untuk pengecutan otot-otot . Glukosa merupakan satu sumber tenaga bagi otot supaya ia boleh bertindak semasa kecemasan.

Fungsi adrenalin dalam membantu kecemasan Ia menyebabkan pengecutan otot regang untuk menegakkan rambut.Ia juga menambah aktiviti-aktiviti kelenjar peluh.Ia membesarkan saiz anak mata.Ia mengecutkan limpa dan ini menambahkan isipadu darah yang mengalir di dalam badan.Ia melambatkan peristalsis salur pencernaan dan kurang air liur dikeluarkan.Gonads

The gonads, or sex glands, include the ovaries and testes.The ovary us responsible for producing the ova or egg and the hormone estrogen and progesterone. The testes are responsible for producing sperm and the hormone testosterone.

Female Hormones Estrogen and ProgesteroneEstrogen is produced by the graafian follicle cells of the ovary. It stimulates the development of the reproductive organs, including breast, and secondary sex characteristic such as pubic and axillary hair.Progesterone is produced by the cells of the corpus luteum of the ovary. Progesterone work with estrogen to build up the lining of the uterus for the fertilized egg. If no fertilized occurs, menstruation takes place. The cycles depends on the secretion of the anterior pituitary gland.

Male Hormone Testosterone Testosterone is produced by the interstitial of the testes and is responsible for the development of the male reproductive organs and secondary sex characteristics.Testosterone influences the growth of a beard and other body hair, deepening of the voice, increase in musculature and the production of sperm.The secretion if the hormone depends on the pituitary gland.

PancreaseLocated behind the stomach. Involved in production of insulin by the B cells of the islets of Langerhans on the pancreas.B cells produce insulin, which(1) promotes the utilization of glucose in the cells, necessary for maintenance of normal levels of blood glucose(2) promotes fatty acid transport and fat deposition into cells(3) promotes amino acid transport into cells(4) facilitates protein synthesisLack of insulin secretion by the island (islet) cells causes diabetes mellitusThe A cells contains in the islets of Langerhans secrete the hormone glucagon.The action of glucagon may br antagonistic or opposite to that of insulin.Glucagons function is to increase the level of glucose in the bloodstream. This is done by stimulating the conversion of liver glycogen to glucose.The control of glucagons secretion is achieved by negative feedback.Low glucose levels in the bloodstream stimulate the A cells to secrete glucagon, which quickly increases the glucose level in the bloodstream.

Pineal Gland

Is a small pinecone-shaped organ attached by a slim stalk to the roof of the third ventricle in the brain.The hormone produced by the pineal gland is called melatonin.The pineal gland is stimulated by a group of nerve cells called the suprachiasmatic nucleus (SCN), which are located in the brain over the pathway of fibers of the optic nerve.The amount of light affects the amount of melatonin secreted. The darker it is, the more melatonin is produced; the lighter it is, the less melatonin is produced.There are no clear answer to the function of melatonin.However, melatonin causes body temperature to drop. For example, falling asleep is associated with lowered body temperature, whereas waking up is associated with rising body temperature,