Endocrine gland

endocrine glands: name, location, hormones and functions.

1. ENDOCRINE GLAND BY SONI KUMARI SHAH

2. Glands Glands are group of epithelial cells which produce specialized secretion. All glands have rich blood supply. Glands secrete the necessary materials from blood stream. These materials are utilized for making the secretion. Types Of Glands: Exocrine gland Endocrine gland

3. Endocrine Gland Endocrine glands are groups of secretory cells surrounded by an extensive network of capillaries that facilitates diffusion of hormones (chemical messengers) from the s ecretory cells into the bloodstream. They are also referred to as ductless glands because hormones diffuse directly into the bloodstream. Hormones are then carried in the bloodstream to target tissues and organs that may be quite distant, where they influence cell growth and metabolism.

4. Differences Between Endocrine And Exocrine Gland S. No. Exocrine gland Endocrine gland 1. Glands with duct Ductless gland 2. Discharge their secretion into the ducts Discharge their secretion directly into the blood 3. Glands are present near the site of action Glands may be present at a far away site than action 4. Secretions are called enzymes Secretions are called hormones 5. Eg. Salivary gland, gastric gland, etc. Eg. Pituitary gland, thyroid gland, parathyroid gland, etc.

5. Hormone Hormones are the chemical messengers produced by the endocrine glands, organs or parts of the body, which is carried through the blood to another part of the body, stimulating by chemical action to increase its activity or to increase secretion of another hormone. The hormones are derived from Greek word it means “to set in motion”. The first hormone discovered was secretin by British physiologist William Bylish and Ernest Starling in1902.

6. How Hormones Work A hormone is formed in one organ or gland and carried in the blood to another organ(target organ or tissue), probably quite distant, where it influences cellular activity, especially growth and metabolism. When all cells are exposed to hormones circulating in the bloodstream, not all cells react. Only a hormones “target” cells, which have receptors for that hormone, will respond to its signal. When the hormone binds to its receptor, it causes a biological response within the cell.

7. Functions Of Hormone It stimulates growth in all organs or tissues. Eg. Growth hormone It helps in metabolism. Eg. Insulin It helps in reproduction. Eg. Sex hormone Maintenance of homeostasis. Eg. Hormones of hypothalamus Regulation of watr and electrolyte balance within the body. Eg. ADH, aldosterone It helps in anti-stress action. Eg. adrenalin

8. Differences Between Hormone And Enzyme S. No. Hormones Enzymes 1. They are produced at one site and are passed by blood to another site for action. They may act at site where they are produced or carried to another site for action. 2. They may act slowly or quickly They act slowly. 3. They are used up in their action. They are not used up in their action. 4. They have lower molecular weight. They have very high molecular weight 5. It may be steroids, peptides, proteins or amino acid derivatives. They are simple proteins. 6. The chemical controlled reactions are not reversible. The chemical controlled action are reversible. 7. Excess or deficiency of hormones may cause disorders. Excess or deficiency of enzymes which catalyzed the chemical reactions.

9. Endocrine Glands Present In Human Body Hypothalamus Pituitary gland Thyroid gland Parathyroid gland Adrenal gland Thymus gland Ovary in female Testes in male Pineal gland Pancreas

10. Position Of Endocrine Glands

11. Hypothalamus The hypothalamus is a structure of the diencephalon of the brain located anterior and inferior to the thalamus. It has both neural and endocrine functions, producing and secreting many hormones. In addition, the hypothalamus is anatomically and functionally related to the pituitary gland (or hypophysis),

12. Hormones Secreted By Hypothalamus Adrenocorticotrophic Releasing Hormone(ARH): it stimulates the anterior pituitary gland to secrete its Adrenocorticotropic hormone(ACTH). Somatotrophin Releasing Hormone(SRH): it stimulates the anterior pituitary gland to release growth hormone(GH) or somatotrophin. Thyrotrophin Releasing Hormone(TRH): it stimulates the anterior pituitary gland to its thyroid stimulating hormone(TSH). Growth Inhibiting Hormone(GIH): this hormone is also called somatostatin.it inhibits the secretion of growth hormone from anterior lobe of pituitary gland. Prolactin Releasing Hormone(PRH): it stimulates the anterior pituitary gland to secrete prolactin.

13. Hormones Secreted By Hypothalamus Prolactin inhibiting hormone(PIH): it inhibits the secretion of prolactin from the anterior lobe pituitary gland. Gonadotrophin releasing hormone(GRH): it stimulates the anterior pituitary to secrete follicle stimulating hormone (FSH) and luteinizing hormone(LH) in ovaries and to secrete interstitial cells stimulating hormone (ICSH) in testes. Melanocytes inhibiting hormone(MIH): it inhibits the secretion of melanocytes stimulating hormone from the intermediate lobe of pituitary gland. Melanocytes releasing hormone(MRH): it stimulates the intermediate lobe of pituitary gland to secrete its melanocyte stimulating hormone(MSH).

14. Pituitary Gland P ituitary gland (or hypophysis), a bean-sized organ suspended from it by a stem called the infundibulum (or pituitary stalk). The pituitary gland is cradled within the sella turcica of the sphenoid bone of the skull. It consists of two lobes that arise from distinct parts of embryonic tissue: the posterior pituitary (neurohypophysis) is neural tissue, whereas the anterior pituitary (also known as the adenohypophysis) is glandular tissue that develops from the primitive digestive tract.

15. Structure Of Pituitary Gland Posterior Pituitary The posterior pituitary is actually an extension of the neurons of the paraventricular and supraoptic nuclei of the hypothalamus. The posterior pituitary gland does not produce hormones, but rather stores and secretes hormones produced by the Hypothalamus . .

16. Anterior Pituitary T he anterior pituitary does manufacture hormones. However, the secretion of hormones from the anterior pituitary is regulated by two classes of hormones. These hormones secreted by the hypothalamus are the releasing hormones that stimulate the secretion of hormones from the anterior pituitary and the inhibiting hormones that inhibit secretion

17. Hormones Of Pituitary Gland Anterior Pituitary Growth Hormone(GH) : it is necessary for the normal growth and development of the body. Thyroid Stimulating Hormone(TSH) : it regulates the synthesis of thyroid hormone in the thyroid gland. Adrenocorticotrophic Hormone(ACTH): it stimulates the adrenal cortex to synthesize glucocorticoid hormones. Prolactin : it stimulates milk production in breast.

18. Hormones Of Pituitary Gland Anterior Pituitary Follicle Stimulating Hormone(FSH): it stimulates ovarian follicles of ovary in female to synthesize estrogen and stimulates seminiferous tubules in testes to secrete spermatozoa. Luteinizing Hormone(LH): it stimulates corpus luteum of ovary in female to produce progesterone and interstitial cells of testes in males to produce testosterone.

19. Posterior Pituitary Oxytocin Functions: contraction of uterus during delivery and to bring about parturition. ejection of milk from breast. Vasopressin Function : decreasing urine output by increasing tubular reabsorption in the kidney. Increasing blood pressure by contracting capillaries and arterioles.

20. Negative Feedback Regulation Of Secretion Of Hormones By The Anterior Lobe Of The Pituitary Gland.

21. Hormonal Regulation Of Growth

22. Regulation Of Secretion Of Oxytocin Through A Positive Feedback Mechanism

23. Negative Feedback Regulation Of Secretion Of Antidiuretic Hormone (ADH).

24. Thyroid Gland The thyroid gland is situated in the neck in front of the larynx and trachea at the level of the 5th, 6th and 7 th cervical and 1st thoracic vertebrae. It is a highly vascular gland that weighs about 25 g and is surrounded by a f ibrous capsule. It resembles a butterfly in shape, consisting of two lobes, one on either side of the thyroid cartilage and upper cartilaginous rings of the trachea. The lobes are joined by a narrow isthmus , lying in front of the trachea. The lobes are roughly cone shaped, about 5 cm long and 3 cm wide .

25. Thyroid Gland The arterial blood supply to the gland is through the superior and inferior thyroid arteries . The superior thyroid artery is a branch of the external carotid artery and the inferior thyroid artery is a branch of the subclavian artery. The venous return is by the thyroid veins, which drain into the internal jugular veins.

26. Thyroid Gland The gland is composed of largely spherical follicles formed from cuboidal epithelium. These secrete and store colloid , a thick sticky protein material. Between the follicles are other cells found singly or in small groups: parafollicular cells , also called C-cells , which secrete the hormone calcitonin .

27. Functions Of Thyroid Hormone T3 and T4 Increase in basal metabolic rate Increase in oxygen consumption and heat production. Increases the absorption and utilization of glucose. Myelination of CNS Increase in rate of cholesterol synthesis in liver. Storage of iodine. Synthesis of protein in cells. Calcitonin Deposition of calcium in bone. Increase the excretion of calcium through urine. It prevents the absorption of calcium from intestine into the blood.

28. Negative Feedback Regulation Of The Secretion Of Thyroxine (T4) And Tri-iodothyronine (T3).

29. A Classic Negative Feedback Loop Controls The Regulation Of Thyroid Hormone Levels .

30. Calcitonin The thyroid gland also secretes a hormone called calcitonin that is produced by the parafollicular cells (also called C cells) that stud the tissue between distinct follicles. Calcitonin is released in response to a rise in blood calcium levels . It appears to have a function in decreasing blood calcium concentrations by: Inhibiting the activity of osteoclasts, bone cells that release calcium into the circulation by degrading bone matrix Increasing osteoblastic activity Decreasing calcium absorption in the intestines Increasing calcium loss in the urine

31. Parathyroid Gland There are four small parathyroid glands, each weighing around 50 mg, two embedded in the posterior surface of each lobe of the thyroid gland. They are surrounded by fine connective tissue capsules that contain spherical cells arranged in columns with sinusoids containing blood in between them.

32. Parathyroid Gland The main function of PTH is to increase blood calcium levels. This is achieved by increasing the calcium absorption from the small intestine and reabsorption from the renal tubules. If these sources provide inadequate supplies then PTH stimulates osteoclasts (bone-destroying cells) and calcium is released from bones into the blood.

33. Parathyroid Gland Parathormone and calcitonin from the thyroid gland act in a complementary manner to maintain blood calcium levels within the normal range. This is needed for: • muscle contraction • transmission of nerve impulses • blood clotting • normal action of many enzymes.

34. Functions Of Parathormone Increased absorption of calcium from gastrointestinal tract Increases the absorption of calcium from bones into blood. Decreases the calcium absorption from kidney. Increases reabsorption of calcium from renal tubule.

35. Parathyroid Hormone In Maintaining Blood Calcium Homeostasis

36. Parathyroid Hormone In Maintaining Blood Calcium Homeostasis

37. Adrenal Gland The two adrenal (suprarenal) glands are situated on the upper pole of each kidney enclosed within the renal fascia. They are about 4 cm long and 3 cm thick. The arterial blood supply is by branches from the abdominal aorta and renal arteries . The venous return is by suprarenal veins. The right gland drains into the inferior vena cava and the left into the left renal vein.

38. Adrenal Gland The glands are composed of two parts which have different structures and functions. The outer part is the cortex and the inner part the medulla . The adrenal cortex is essential to life but the medulla is not.

39. Adrenal Cortex The adrenal cortex produces three groups of steroid hormones from cholesterol. They are collectively called adrenocorticoids (corticosteroids). The groups are: glucocorticoids mineralocorticoids sex hormones (androgens). The hormones in each group have different characteristic actions but as they are structurally similar their actions may overlap.

40. Glucocorticoids Cortisol (hydrocortisone ) is the main glucocorticoid but small amounts of corticosterone and cortisone are also produced. Commonly these are collectively known as ‘steroids’; they are essential for life, regulating metabolism and responses to stress.

41. Glucocorticoids Glucocorticoids have widespread metabolic effects generally concerned with catabolism (breakdown) of protein and fat that makes glucose and other substances available for use. These include: hyperglycemia (raised blood glucose levels) caused by breakdown of glycogen and gluconeogenesis (formation of new sugar from, for example, protein) lipolysis (breakdown of triglycerides into fatty acids and glycerol for energy production) raising circulating levels of free fatty acids stimulating breakdown of protein, releasing amino acids, and increasing blood levels. Amino acids are then used for synthesis of other proteins, e.g. enzymes, or for energy production. promoting absorption of sodium and water from renal tubules (a weak mineralocorticoid effect).

42. Functions Of Glucocorticoids It increases blood glucose level. It increases breakdown of protein. It helps in breakdown of fat into fatty acid and glycerol It blocks the inflammatory response to allergic reaction. It decreases body immunity.

43. Negative Feedback Regulation Of Glucocorticoid Secretion.

44. Mineralocorticoids (Aldosterone) Aldosterone is the main mineralocorticoid. It is involved in maintaining water and electrolyte balance. Through a negative feedback system it stimulates the reabsorption of sodium (Na + ) by the renal tubules and excretion of potassium (K + ) in the urine. Sodium reabsorption is also accompanied by retention of water and therefore aldosterone is involved in the regulation of blood volume and blood pressure too.

45. Functions Of Mineralocorticoids Increase the reabsorption of sodium ions from distal convoluted tubules and collecting duct. Aldosterone increases the potassium excretion through the renal tubule.

46. Renin–Angiotensin–Aldosterone System When renal blood flow is reduced or blood sodium levels fall, the enzyme renin is secreted by kidney cells. Renin converts the plasma protein angiotensinogen , produced by the liver, to angiotensin 1 . Angiotensin converting enzyme (ACE), formed in small quantities in the lungs, proximal kidney tubules and other tissues, converts angiotensin 1 to angiotensin 2 , which stimulates secretion of aldosterone. Angiotensin 2 causes vasoconstriction and increases blood pressure closing the negative feedback loop.

47. Negative Feedback Regulation Of Aldosterone Secretion.

48. Sex Hormones Sex hormones secreted by the adrenal cortex are mainly androgens (male sex hormones) although the amounts produced are insignificant compared with those secreted by the testes and ovaries in late puberty and adulthood.

49. Functions Of Androgens It helps in maintenance of growth and development of reproductive organs. It helps to develop secondary sexual characteristics. It helps in process of spermatogenesis. It helps in male pattern of aggressive behavior. It promotes RNA synthesis and protein synthesis. It increases glycolysis and also increase fatty acid synthesis and citric cycle. They are responsible for bone maturation.

50. Adrenal Medulla The medulla is completely surrounded by the adrenal cortex. When stimulated by extensive sympathetic nerve supply, the glands release the hormones adrenaline (epinephrine, 80%) and noradrenaline (norepinephrine, 20%).

51. Adrenaline (Epinephrine) And Noradrenaline (Norepinephrine) Noradrenaline is the postganglionic neurotransmitter of the sympathetic division of the autonomic nervous system. Adrenaline and some noradrenaline are released into the blood from the adrenal medulla during stimulation of the sympathetic nervous system.

52. Adrenaline (Epinephrine) And Noradrenaline (Norepinephrine) T hey potentiate the fight or flight response by: increasing heart rate increasing blood pressure diverting blood to essential organs, including the heart, brain and skeletal muscles, by dilating their blood vessels and constricting those of less essential organs, such as the skin increasing metabolic rate dilating the pupils. Adrenaline has a greater effect on the heart and metabolic processes whereas noradrenaline has more influence on blood vessel diameter.

53. Functions Of Adrenaline And Noradrenaline Vasoconstriction and increase in blood pressure. Dilatation of pupil. Relaxation of intestine.

54. Response To Stress When the body is under stress homeostasis is disturbed. To restore it and, in some cases, to maintain life there are immediate and, if necessary, longer-term responses. Stressors include exercise, fasting, fright, temperature changes, infection, disease and emotional situations. The immediate response is sometimes described as preparing for ‘fight or flight’. This is mediated by the sympathetic nervous system. In the longer term , ACTH from the anterior pituitary stimulates the release of glucocorticoids and mineralocorticoids from the adrenal cortex providing a more prolonged response to stress.

55. Responses To Stressors That Threaten Homeostasis

56. Differences Between Physical And Psychological Stress

57. Differences Between Physical And Psychological Stress

58. Pineal Gland The pineal gland is a small body attached to the roof of the third ventricle and is connected to it by a short stalk containing nerves, many of which terminate in the hypothalamus. The pineal gland is about 10 mm long, reddish brown in colour and surrounded by a capsule. The gland tends to atrophy after puberty and may become calcified in later life.

59. Pineal Gland The pinealocyte cells that make up the pineal gland are known to produce and secrete the amine hormone melatonin , which is derived from serotonin. The secretion of melatonin varies according to the level of light received from the environment.

60. Melatonin This is the main hormone secreted by the pineal gland. Secretion is controlled by daylight and darkness; levels fluctuate during each 24-hour period, the being highest at night and the lowest around midday. Secretion is also influenced by the number of daylight hours, i.e. there may be seasonal variations.

61. Melatonin The secretion of melatonin may influence the body’s circadian rhythms, the dark-light fluctuations that affect not only sleepiness and wakefulness, but also appetite and body temperature. Interestingly, children have higher melatonin levels than adults, which may prevent the release of gonadotropins from the anterior pituitary, thereby inhibiting the onset of puberty. Finally, an antioxidant role of melatonin is the subject of current research.

62. Functions Of Melatonin Coordination of circadian rhythms Inhibition of growth and development of the sex organs before puberty, possibly by preventing synthesis of gonadotropins.

63. Gonads Testes The testes (or testicles) are a pair of sperm-producing organs that maintain the health of the male reproductive system. The testes are twin oval-shaped organs about the size of a large grape. They are located within the scrotum. Within the testes are coiled masses of tubes called seminiferous tubules. These tubules are responsible for producing the sperm cells through a process called spermatogenesis.   In addition to their role in the male reproductive system, the testes also have the distinction of being an endocrine gland because they secrete testosterone—a hormone that is vital to the normal development of male physical characteristics.

64. Ovary The ovaries are a pair of ova-producing organs (that is, they produce egg cells) that maintain the health of the female reproductive system. The ovaries are oval shaped and about the size of a large grape. They are located on opposite ends of the pelvic wall, on either side of the uterus. The ovaries are each attached to the fimbria (tissue that connects the ovaries to the fallopian tube). In addition to their role in producing ova, the ovaries also have the distinction of being an endocrine gland because they secrete hormones—primarily estrogen and progesterone—that are vital to normal reproductive development and fertility.

65. Gonadal Hormones The male and female reproductive system is regulated by follicle-stimulating hormone (FSH) and luteinizing hormone (LH) produced by the anterior lobe of the pituitary gland in response to gonadotropin-releasing hormone (GnRH) from the hypothalamus.

66. Hormones Of Male Gonad (Testes) The primary hormone produced by the male testes is testosterone , a steroid hormone important in the development of the male reproductive system, the maturation of sperm cells, and the development of male secondary sex characteristics such as a deepened voice, body hair, and increased muscle mass. Interestingly, testosterone is also produced in the female ovaries, but at a much reduced level. In addition, the testes produce the peptide hormone inhibin , which inhibits the secretion of FSH from the anterior pituitary gland. FSH stimulates spermatogenesis.

67. Functions Of Testosterone Increase in size of penis, scrotum and testes. Development of muscular growth. Increase in bone growth. Increase in thickness and color of skin. Hair distribution growth increase. Change in voice.

68. Hormones Of Female Gonad (Ovary) The primary hormones produced by the ovaries are estrogens , which include estradiol, estriol, and estrone. Estrogens play an important role in a larger number of physiological processes, including the development of the female reproductive system, regulation of the menstrual cycle, the development of female secondary sex characteristics such as increased adipose tissue and the development of breast tissue, and the maintenance of pregnancy. Another significant ovarian hormone is progesterone , which contributes to regulation of the menstrual cycle and is important in preparing the body for pregnancy as well as maintaining pregnancy

69. Functions Of Estrogen Enlargement of uterus about double of its childhood size. Increase in blood supply to endometrium. It increases size of uterine tube. It reduces the pH of vagina. It increases the shape and size of vagina. It develops the mammary gland(breast). It develops hair in the pubic region and axilla. It brings softness and smoothness to skin. It increases bone growth(osteoblast activity. Voice: the larynx remains in pre pubertal stage which produces high pitch voice.

70. Functions Of Progesterone It increases the thickness of endometrium. It increases the size of uterine gland. It increases the secretory activities of glandular cells. It increases the deposition of lipid and glycogen in the stromal wall. It promotes secretory changes in the mucosal lining of the fallopian tube.

71. Thymus Gland The  thymus gland  is a small organ behind the breastbone that plays an important function both in the immune system and endocrine system. Though the  thymus  begins to atrophy (decay) during puberty, its effect in "training" T lymphocytes to fight infections and even cancer lasts for a lifetime.

72. Hormones of Thymus Gland It secretes Thymosin hormone which promotes immune competence in young T-lymphocytes. It secretes Thymine hormone which inhibits acetylcholine release at motor nerve endings.

73. Pancreas The pancreas is a long, slender organ, most of which is located posterior to the bottom half of the stomach. It is made up of soft lobulated glandular tissue. It has four parts: head neck Body Tail Although it is primarily an exocrine gland, secreting a variety of digestive enzymes, the pancreas has an endocrine function.

74. Pancreas The endocrine pancreas consists of clusters of cells, known as the pancreatic islets (islets of Langerhans), scattered throughout the gland. Pancreatic hormones are secreted directly into the bloodstream and circulate throughout the body. This is in contrast to the exocrine pancreas and its associated ducts. There are three main types of cells in the pancreatic islets: • α (alpha) cells, which secrete glucagon • β (beta) cells, which are the most numerous, secrete insulin • δ (delta) cells, which secrete somatostatin (GHRIH,.

75. Pancreas The normal blood glucose level is between 3.5 and 8 mmol/ litre (63 to 144 mg/100 mL). Blood glucose levels are controlled mainly by the opposing actions of insulin and glucagon: • glucagon increases blood glucose levels • insulin reduces blood glucose levels.

76. Cells and Secretions of the Pancreatic Islets The pancreatic islets each contain four varieties of cells: The alpha cell produces the hormone glucagon and makes up approximately 20 percent of each islet. Glucagon plays an important role in blood glucose regulation; low blood glucose levels stimulate its release. The beta cell produces the hormone insulin and makes up approximately 75 percent of each islet. Elevated blood glucose levels stimulate the release of insulin. Insulin converts excess of glucose into glycogen in the liver and muscles. Deficiency of insulin causes diabetes mellitus.

77. Cells and Secretions of the Pancreatic Islets The delta cell accounts for four percent of the islet cells and secretes the peptide hormone somatostatin. The somatostatin hormone decreases the rate of nutrient absorption into the blood from GI tract. It also inhibits the secretion of growth from anterior lobe of pituitary gland. The PP cell accounts for about one percent of islet cells and secretes the pancreatic polypeptide hormone. It inhibits the release of pancreatic juice. It is thought to play a role in appetite, as well as in the regulation of pancreatic exocrine and endocrine secretions. Pancreatic polypeptide released following a meal may reduce further food consumption; however, it is also released in response to fasting.

78. Functions Of Insulin It converts excess glucose into glycogen in the liver and muscles. It decreases the breakdown of glycogen (glycogenolysis). It prevents formation of new glucose from protein and fat (gluconeogenesis).

79. Functions Of Glucagon It increases glycogenolysis(breakdown of glycogen into glucose) in the liver. It increases gluconeogenesis(formation of glucose from protein) in the liver. It increases the secretion of bile. It inhibits the secretion of gastric juice.

80. Regulation of Blood Glucose Levels by Insulin and Glucagon Glucose is required for cellular respiration and is the preferred fuel for all body cells. The body derives glucose from the breakdown of the carbohydrate-containing foods and drinks we consume. Glucose not immediately taken up by cells for fuel can be stored by the liver and muscles as glycogen, or converted to triglycerides and stored in the adipose tissue. Hormones regulate both the storage and the utilization of glucose as required. Receptors located in the pancreas sense blood glucose levels, and subsequently the pancreatic cells secrete glucagon or insulin to maintain normal levels.

81. Homeostatic Regulation of Blood Glucose Levels