The endocrine system The endocrine system - PowerPoint Presentation

1. The endocrine system

2. The endocrine system

3. The endocrine system is one of the body's two major communication system the nervous system being the other. The endocrine system consist s of all those glands termed endocrine glands or gland of internal secretion . The endocrine glands are glands without excretory ducts that secrete hormones.Hormones are chemical messengers that are carried by the blood from endocrine glands to the cells upon which they act . the cells influenced by a particular hormone are the target cells for that hormone. The endocrine system differs form most of the other organ systems of the body in that the various glands are not anatomically continuous however they do form a system in the functional sense.

4. Classification of hormones Hormones fall into three chemical classes :1-amine hormones amine hormones are derivatives of the amino acid tyrosine they include the thyroid hormones .epinephrine and nor epinephrine (produced by the adrenal medulla) and dopamine(produced by the hypothalamus ).

5.   2-peptide hormones The great majority of hormones are either peptides or proteins . they range in size from small peptides having only three amino acids to small proteins (some of which are glycoproteins.) in many cases the initially synthesized on the ribosomes of the endocrine cells . many peptides serve as both neurotransmitters and as hormones . for example most of the hormone secreted by the endocrine glands in the gastrointestinal tract (for example cholecystokinin) are also produced by neurons in the brain where they function as neurotransmitters

6.  3- steroid hormones steroid hormones are produced by the adrenal cortex and the gonads (tests and ovaries ).as well as by the placenta during pregnancy .in addition 1.25-dihydroxyvitamin D3.the active from of vitamin D. is a steroid derivative .cholesterol is the precursor of all steroid hormones. Hormone transport in the blood Peptide and catecholamine hormones are water –soluble .therefore with the exception of a few peptides these hormones are transported simply dissolved in plasma .in contrast the steroid hormones and the thyroid hormones circulate in the blood largely bound to plasma proteins .

7. Effects of peptide hormones and catecholamines  The receptors for peptide hormones and the catecholamine hormones are located on the outer surface of the target cells plasma membrane .when activated by hormones binding the receptors trigger one or more of the signal transduction pathways .that is the activated receptors directly influence :1-ion channels that are part of the receptors .2-Enzymne activity that is part of the receptors.3-G proteins coupled in the plasma membrane to effector proteins –ion channels and enzymes .The changes in enzyme activity produce changes in the conformation and hence the activity of various cellular proteins .in some cases the signal transduction pathways also lead to stimulation or inhibition of the synthesis of new proteins by the cell .

8. Effects of steroid hormones  The steroid hormones are lipid –soluble messengers .their receptors are intracellular and are inactive when no messenger is bound to them for certain lipid –soluble messengers the inactive receptors are in the cytosol.The messenger diffuses across the cells plasma membrane and enters the cytosol .where the receptor is in the cytosol the messenger combines with it there and hormones \receptor complex then moves into the nucleus .with intra nuclear receptors the hormones diffuses by itself into the nucleus and binds to the receptor there .the receptor activated by the the binding of hormone to it then functions in the nucleus as any regulatory protein that directly influences gene transcription .the result is an increase in the cellular concentration of the protein or its rate of secretion .

9. Inputs that control hormone secretion Hormone secretion controlled mainly by three types of inputs to endocrine cells :1-changes in the plasma concentration of mineral ions or organic nutrients .there are at least 5 hormones whose secretion is directly controlled by the plasma concentrations of specific mineral ions or organic nutrients .in each case a major function of the hormone is to regulate in a negative –feedback manner the plasma concentration of the ion or nutrient controlling its secretion .for example insulin secretion is stimulated by an elevated plasma glucose concentration and the additional insulin then causes by several actions the plasma glucose concentration to decrease .

10. 2-neurotransmitters released from neurons impinging on the endocrine cell .the autonomic nervous system is the neural input controlling many hormones (the adrenal medulla is stimulated by sympathetic preganglionic fibers the secretion of insulin and gastrointestinal hormones are stimulated and inhibited by both sympathetic and parasympathetic inputs ) the controlled by neurons in the brain-

11. 3-another hormone acting on the endocrine cell .In many cases the secretion of a particular hormone is directly controlled by the blood concentration of another hormone .a hormone that stimulates the secretion of another hormone is often referred to as a topic hormone .the topic hormones usually stimulate not only secretion but the growth of the stimulated gland as well.4-Chemical and physical factors in the lumen of the gastrointestinal tract .this applies only to the hormones secreted by the gastrointestinal tract

12. Control system involving the hypothalamus and pituitary pituitary gland comprising the anterior pituitary and posterior pituitary is connected to the hypothalamus by a stalk containing nerve axons and blood vesselsThe axons whose cell bodies are in the hypothalamus terminate in the posterior pituitary and release oxytocin or vasopressin.The anterior pituitary secretes growth hormone (GH) , thyroid-stimulating hormone (TSH) , adrenocorticotropic hormone (ACTH) , prolactin ,and two gonado- tropic hormones- follicle- stimulating hormone (LH).

13. Secretion of the anterior pituitary hormones is controlled mainly by hypophysiotropic hormones secreted into capillaries in the median eminence of the hypothalamus and reaching the anterior pituitary via the portal vessels connecting the hypothalamus and anterior pituitary.

14. Each hypophysiotropic hormone is named for the anterior pituitary hormone whose secretion it controls . 1-Corticotrophin releasing hormone (CRH) stimulates secretion of ACTH(cortico- tropin) .2-Growth hormone releasing hormone (GHRH) stimulates secretion of growth hormone (GH).3-Thyrotropin releasing hormone (TRH) stimulates secretion of thyroid –stimulating hormone (thyrotropin) .4-Gonadotropin releasing hormone (GnRH) stimulate secretion of both luteinizing hormone and follicle – stimulating hormone (the gonadotropins) .5-Somatostatin (SS) inhibits secretion of growth hormone . 6-Prolactin- inhibiting hormone (PIH) inhibits secretion of prolactin 7-Prolactin releasing hormone (PRH) stimulates secretion of prolactin

15. Neural control of Hypophysiotropic hormones  Neurons of the hypothalamus receive synaptic input, both stimulatory and inhibitory , from virtually all areas of the central nervous system , and specific neural path ways influence secretion of the individual hypophysiotropic hormones . A large number ofneurotransmitters ,including the catecholam –ines and acetylcholine , are found at the synapses on the hormone – secreting hypothalamic neurons , and this explain why the secretion of the hypophysiotropic hormones can be altered by drugs that influence these neurotransmitters.

16.  For example , awide variety of stresses , both physical and emotional , act via neural pathways to the hypothalamus to increase CRH secretion and , hence , ACTH and cortisol secretion , markediy above basal values . Thus , stress is the common denominator of reflexes leading to increased cortisol secretion . cortisol then functions to facilitate an individuals response to stress. 

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18.  CRH- ACTH – cortisol sequence . The stress input to the hypothalamus is via neural pathways ,cortisol exerts a negative – feedback control . over the system by acting on (1) the hypothalamus to inhibit CRH secretion and (2) the anterior pituitary to reduce responsiveness to CRH Hormonal feedback control of the hypothalamus and anterior pituitary .

19. A prominent feature of each of the hormonal sequences initiated by a hypophysiotropic hormone is negative feedback exerted upon the hypothalamo-pituitary system by one or more of the hormones in its sequence . for example , in the CRH – ACTH – cortisol sequence , the final hormone , cortisol , acts upon the hypothalamus to reduce secretion of CRH by causing a decrease in the frequency of action potentials in the neurons secreting CRH . In addition , cortisol acts directly on the anterior pituitary to reduce the response of the ACTH- secreting cells to CRH . Thus , by a double barreled action , cortisol exerts a negative – feedback control over its own secretion. Such a system is effective in damping hormonal response, that is , in limiting the extremes of hormone secretory rates.

20. Another adaptive function of these negative – feedback mechanisms is that they maintain the plasma concentration of the final hormone in a sequence relatively constant whenever a disease- induced primary change occurs in the secretion or metabolism of that hormone.Hormones not in a particular sequence can also influence secretion of the hypothalamic and anterior pituitary hormones in that sequence. For example, estrogen markedly enhances the secretion of prolactin by the anterior pituitary , even though estrogen secretion is not controlled by prolactin.

21. Hypothalamus -1

22. Hypothalamus -1The hypothalamus lies below the thalamus , it contains different cell groups and pathways that form the master command center for neural and endocrine coordination . the pituitary gland is connected to the hypothalamus by a stalk containing nerve axons and blood vessels.The axons, whose cell bodies are in the hypothalamus terminate in the posterior pituitary and release oxytocin or vasopressin. Between the hypothalamus and anterior pituitary gland there is an unusual blood flow directly from the hypothalamus to the anterior pituitary.

23. Hypothalamus secretes hormones , which are collectively termed hypophysiotropic hormones (hypothalamic releasing hormones). The major function of these hormones is control of secretion of hormones is control of secretion of hormones by the anterior pituitary.

24. The hypophysiotropic hormones are :.1 Corticotropic releasing hormone (CRH) , which controls the secretion of ACTH (STIMULATION).2. Thyrotropin releasing hormone (TRH) , Which controls the secretion of TSH (STIMULATION) .3. Growth hormone releasing hormone (GHRH) , Which controls the secretion of GH (inhibition) .4. Somatostatin (SS) , which controls the secretion of GH (inhibition) .5. Gonadotropin releasing hormone (GnRH) ,which controls secretion of LH and Fsh (stimulation) 6. Dopamine (DA,also called prolactin – inhibiting hormone , PIH), which controls secretion of prolactin (inhibition).

25. II-PITUITARY GLAND (Hypophysis)

26. II-PITUITARY GLAND (Hypophysis) The pituitary gland lies in a pocket (the sella turcica) of the sphenoid bone at the base of the brain , just below hypothalamus . The pituitary gland is composed of two adjacent lobes:the anterior pituitary (adenohypophysis) which has blood vessel connection with hypothalamus , and the posterior pituitary (neurohypophysis),which has neural connection with hypothalamus.

27. 1-Posterior pituitary hormonesThe hormones are not synthesized in the posterior pituitary itself but in the hypothalamus , and by the axons , which terminate in posterior pituitary release them . the hormones are :a-Oxytocin , which controls of milk let –down , and uterine motility .b-vasopressin (antidiuretic hormone , ADH), Which control of water excretion by the kidneys,and blood pressure.

28.  2-Anterior pituitary hormones a-Growth hormone (GH, Somatotropin ) is the major stimulus of postnatal growth : induces precursor cells to differentiate and secrete insulin –like growth factor I(IGF-I) , WHICH Stimulates cell division .GH stimulates protein synthesis.b-Thyroid-stimulating hormone (TSH.thyrotoropin) .which stimulates secretion of T3; T4(thyroid gland) .c-adrenocorticotropic hormone (ACTH. Corticotrophin) which stimulates secretion of adrenal cortex. d- Prolaction ,which stimulates breast growth and milk production . Prolaction many be permissive for certain reproductive functions in male .

29. e-Gonadotropic hormones :Follicle-stimulating hormone(FSH),and Luteinzing hormone(LH), which controls of gonads (gamete production and sex hormone secretion)f-Beta lipotropin ,which has unknown function.g-Beta endorphin,which has unknown function.

30. III-The pineal gland

31.  III-The pineal glandThe pineal gland is an outgrowth from the roof of the diencephalons of the brain. It is a rudimentary organ. Pineal gland secretes the melatonin (candidate hormone). The exact functions of melatonin in hormons are unknown, but this hormone probably plays an important role in the setting of the bodys circadian rhythms.

32. IV-The thyroid gland

33.  IV-The thyroid gland The thyroid gland is located in the lower pasrt of the neck wrapped around the front of the trachea.It composed of many spherical structures called follicles, each consisting of a single layer of epithelial cell surrounding an extracellular central space filled with a glycoprotein colloid called amine hormones- thyroxine (T4) and triiododothyronine (T3), parafollicular cells, which are located between follicles, secrete a third hormone- a peptide called calcitonin, this hormone does not contain iodine and not included in the term (thyroid hormone). Iodine is an essential element that functions as a component of T4 and T3. T4 is secreted in much larger ammounts than is T3. However, a variety of tissues, particularly the liver and kidneys, convert most of this T4 into T3. This is an important point because T3 is a much more active hormone than T4. Indeed, it is likely that T4 has little or no action unless it is converted into T3.

34. Major function of thyroid hormones:Virtually every tissue in the body is afficted by the thyroid hormone. This effect include :1-Regulation of netabolic rate . The Thare the single most important determinat of basal metabolic rate. TH increase the oxygen consumption and heat production of most body tissues ,anotable exception being the brain . This ability to increase BMR is termed a calorigenic effect.2-Control of growth .TH are essential for normal growth because they are required for both the synthesis of growth hormone and the growth-promoting effects of the hormone. Accordingly , infants and children with hypothyroidism (deficient thyroid function) manifest retarded growth due to slowed bone growth .

35. 3- Control of brain development and function .TH is permissive for normal development of the central nervous system during fetal life .Inadequate production of maternal and fetal TH due to severe iodine deficiency during pregnancy is one of the world's most common preventable causes of mental retardation termed endemic cretinism.

36.  This effect on brain development must be distinguished from other stimulatory effects TH exerts on the nervous system throughout life not just during infancy . Ahypothyroid person exhibits sluggishness and poor mental function and these effects are completely reversible at any time with administration of TH .conversely a person with hyperthyroidism (excessive secretion of TH) is jittery and hyperactive.

37. Major functions of calcitonin:1-Control of plasma calcium .It has long been thought that calcitonin helps to regulate plasma calcium but present evidence indicates that it plays a minor role in this regard.

38. V-Parathyroid glands

39. V-Parathyroid glands The Parathyroid glands are located on the posterior surface of the thyroid gland. There are four Parathyroid glands .They secrete a hormone called parathyroid hormone .Parathyroid hormone production is controlled by the extracellular calcium concentration acting directly on the secretory cells ( via a plasma –membrane calcium receptor ). Decreased plasma calcium concentration stimulates parathyroid hormone secretion and an increased plasma calcium concentration does just the opposite.

40. Parathyroid hormone exerts multiple action that increase extracellular calcium concentration:1-It directly increases the resorption of bond by osteoclasts which results in the movement of calcium ( and phosphate ) from bone into extracellular fluid.2-It directly stimulates the activation of vitamin D and this latter hormone then increases intestinal absorption of calcium .Thus the effect of parathyroid hormone on the intestinal tract is an indirect one. 3- It directly increases renal tubular calcium reabsorption thus decreasing urinary calcium excretion .

41. In addition parathyroid hormone directly reduces the tubluar reabsorption of phosphate thus raising its uninary excretion .This keeps plasma phosphate from increasing at a time when parathyroid hormone is stimultaneously causing increased release of both calcium and phosphate from bone .

42. VI-THE ADRENAL (SUPRARENAL ) GLANDS

43. VI-THE ADRENAL (SUPRARENAL ) GLANDS There are two adrenal glands one on the top of of each kidney .Each adrenal gland constitutes two distinct endocrine glands an inner adrenal medulla which secretes amine hormones and a surrounding adrenal cortex which secretes steroid hormones .A drenal medulla is really a modified sumpathetic ganglion whose cell bodies do not have axons but instead release their secretions into the blood thereby fulfilling a criterion for an endocrine gland . The adrenal medulla secretes mainly two amine hormones epinephrine (E) and norepinephrine (NE) .In humans the adrenal medulla secretes approximately four times more epinephrine than norepinephrine .

44. epinephrine and norepinephrine exert actions similar to those the sympathetic nerves .These effects are :1-Increased hepatic and muscle glycogenolysis ( provides a quick source of glucose).2-Increased breakdown of adipose tissue triacylglycerol (provides a supply of glycerol for gluconeogenesis and of fatty acids for oxidation).3-Decreased fatigue of skeletal muscle.4-Increased cardiac output secondary to increased cardiac contractility and heart rate.5-Shunting of blood from viscera to skeletal muscles by means of vasoconstriction in the former beds and vasodilation in the latter.6-Increased ventilation .7-Increased coagulability of blood.The adrenal medulla also secretes small amounts of dopamine and several substances.

45. Hormones of the adrenal cortex The five hormones normally secreted in physiologically significant amounts by the adrenal cortex are :1-ALDOSTERONE (secreted by zona glomerulosa ) is known as a mineralocoticoid because its effects are on salt (mineral ) balance mainly on the kidneys handlind of sodium potassium and hydrogen ions.2-CRTISOL and CORTYCOSTERONE (secreted by zona fasiculata and zona reticulais) are called glucocorticoids because they have important effects on the metabolism of glucose and other organic nutrients .Cortisol is by far the more important of two glucocorticoids in human

46. The main functions of the cortisol are : 1-Effect on organic metabolism :increased plasma concentrations of amin acids glucose and free fattu acids.2-Antigrowth effects : inhibits bond growth stimulates protein catabolism responsible for the retarded growth that occuas with illness .3-Effects during stress:a-Effect on organic metabolism :stimulation of protein catabolism stimulation of liver uptake of amino acids and their conversion to glucose (gluconeogenesis) inhibition of glucose uptake and oxidation by many body cells (insulin antagonism ) but not by the brain and stimulation of triacylglycerol catabolism in adipose tissue with release of glycerol and fatty acids into the blood .b-Enhanced vascular reactivity that is increased ability to maintain vasoconstriction in response to norepinephrine and other stimuli .

47. c-Unidentified protective effects against the damaging influences of stress . d-Inhibitione of inflammation and specific immune response.4-Regulation of the immune system .3- ANDROGENS ( secreted by zona fasiculata and zona reticularis) consist of dehydroepiandrosterone and androstenedione. Androgens also includes the male sex hormone testosterone produced bu the testes . All androgens have actions similar to those of testosterone .Because the adrenal androgens are much less potent than testosterone they are of little physiological significance in the male they do however play roles in the female .

48. Effect of testosterone (androgens ) in the male :1-Required for initation and maintenance of spermatogenesis.2-Decreases GNRH secretion via an action on the hypothalamus.3-Inhibits LH secretion via an action on the anterior pituitary.4-Induces differentiation of male accessory reproductive organs and maintains their function .5- Induces male secondary sex characteristic opposes action of estrogen on breast growth .6-Stimulates protein anabolism bone growth and cessation of bone growth.7-Required for sex drive and may enhance aggressive behavior. 

49. Androgens in women: Testosterone is found in low concentration in blood of normal women. Other androgens are also found in significant concentrations in the blood of women. All these androgens play several important roles in the female, including stimulation of the growth of pubic hair , axillary hair , and possibly skeletal muscle. In several diseases states, the female adrenals may secrete abnormally large quantities of androgens , which produce virilism.

50. VII-Thymus:

51. VII-Thymus: This gland is situated in the anterior mediastinum of the thorax. It is relatively large at birth and continues to increase in size until puberty, when it gradually diminishes. Thymus is primary lymphoid organ. It secretes Thymopoietin hormone, which control T-lymphocyte function.

52. VIII- The pancreas:

53.  VIII- The pancreas: The pancreas is an elongated gland located behind the stomach , has both endocrine and exocrine functions. Hormones are secreted by the islets of Langerhans , clusters of endocrine cells in the pancreas . There are several distinct types of islet cells, each of which secretesa different hormone. These hormones are: 1 – Insulin, which secreted by beta cells , Insulin's many actions are often divided into two broad categories : (A) – metabolic effects on carbohydrate, lipid, and protein synthesis, and (B) – growth-promoting effects on DNA synthesis, cell division , and cell differentiation. The major controlling factor for insulin secretion is the plasma glucose concentration , which affects the beta cells directly.

54. 2- Glucagon, is the peptide hormone produced by the alpha cells of the pancreatic islets . The major physiological effects of glucagons are all in the liver and are opposed to those of insulin : (a) increased glycogen breakdown , (b) increased gluconeogenesis , and ( c) synthesis of ketones. 3- Somatostatin , secreted by delta cells has unknown function. 4- Pancreatic polypeptide has unknown function.

55. IX- Ovaries:

56. IX- Ovaries: The ovaries are almond-sized organs in the upper pelvic cavity , one on each side of the uterus .The ovary serves a dual purpose: (1) oogenenesis , the production of the gametes-the ova, and (2) secretion of the female steroid hormones. The hormones secreted by ovaries are: 1 – Estrogen is secreted during the follicular phase mainly by the granulose cells , Following ovulation , it is secreted by the corpus luteum . Effects of estrogen are: a – Stimulates growth of ovary and follicles.

57. b- Stimulates growth of smooth muscle and proliferation of epithelial linings of reproductive tact . In addition: -Uterine tubes: increases contractions and ciliary activity. -Uterus: increases myometrial contractions and responsiveness to oxytocin. -Vagina: increases layering of epithelial cells. -Stimulates external genitalia growth . - Stimulates breast growth , particularly ducts and fat deposition. - Stimulates female body configuration development; narrow shoulders , broad hips , female fat distribution ( deposition on hips , abdomen, and breast). -Stimulates a more-fluid sebaceous gland secretion( this antiance effect opposes the acne-producing effects of androgens) -Stimulates development of femalepubic hair pattern ( growth , as opposed to pattern, of pubic and axillary hair is androgen

58. -Stimulates bone growth and ultimate cessation of bone growth ( closure of ebibhyseal osplates );protects against osteoporosis; does not have an anabolic effects on skeletal muscle . -Vascular effects( deficiency products '' hot flashes''). -Has feedback effects on hypothalamus and anterior pituitary. -Stimulates fluid retention. -Stimulates prolactin secretion but inhibits prolactin's milk-inducting action on the breast. -Protects against atherosclerosis, at least in part by effect on plasma cholesterol.

59. 2- Progesterone is secreted in very small amounts by the granulose and theca cells before ovulation, but its major source is the corpus luteum . Effecte of progesterone are: a – Converts the estrogen-primed endometeium to an actively secreting tissue suitable for implantation of an embryo. b- Induces thick, sticky cervical mucus. c-Decreases contraction of uterine tubes and myometrium. d-Decreases proliferation of vaginal epithelial cells. e- Stimulates breast growth , particularly glandular tissue. f-Inhibits milk-inducting effects on prolactin. g-Has feedback effects on hypothalamus and anterior pituritary. h- Probably increases body temperature.

60. 3- Inhibin, a peptide hormone , is secreted by both the granuloses cells and corpus luteum. 4- Relaxin and Activin , which have not clear function.

61. X- Placenta:

62. X- Placenta: Is a combination of interlocking fetal and maternal tissues that serves as the organ of exghange between mother and fetus for the remainder of pregnancy. Throughout pregnancy, plasma concentration of estrogen and progesterone remain high The placenta converts the androgens mainly into estriol, the major estrogen of pregnancy The trophoblast cells of the placenta produce inhibin , and placental loctogen. Gastrointestinal tract:

63. The hormones that control the gastrointestinal system are secreted mainly by endocrine cells scattered throughout the epithelium of the stomach and small intestine .One surface of each endocrine cell is exposed to the lumen of the GIT. At this surface , various chemical substances in the chime stimulates the cell to release its hormones from the opposite, blood side of the cell .The gastrointestinal hormones are: secretin ,cholecystokinin (CCK), gastrin, and glucose-dependent insulinotropic peptide (GIP).

64.  The major effects of each are: 1 – Secretin is released from the small intestine in response to increased luminal acidity. 2- Chlecystokinin is released from the small intestine in response to the products of fat and protein digestion, and stimulates pancreatic enzyme secretion. 3- Gastrin is released from the antrum of stomach in response to increased amount of amino acids and peptides in stomach, and to parasympathetic nerves. 4- Glucose-dependent insulinotropic peptide is released from small intestine in response to glucose and fat in small intestine . GIP stimulates insulin secretion.

65. XII-Testes:

66. XII-Testes: The testes are the primary reproductive organs in the male. The testes serve dual functions : ( 1) gametogenesis, and (2) secretion of steroid hormones (sex male hormones). The Leydig cells ( interstitial cells), which lie in small connective tissue spaces between the tubules , are the cells that secrete testosterone .

67. The following hormones are released from test: 1 – Testosterone belongs to a group of steroid hormones that have similar masculinizing actions and are collectively called androgens. In the male, only the testes secrete significant amounts of testosterone. 2- Inhibin is a protein hormone, released from sertoli cells. 3- Mullerian –inhibiting hormone is released from sertoli cells during embryonic life. It causes the primordial female duct system to regress