Pituitary gland physiology and anatomy.pptx

Pituitary gland anatomy and physiology of the pituitary gland physiology of the pituitary gland physiology of the pituitary gland

1. Pituitary gland Hypophysis cerebri ) )

2. The pituitary gland has an average weight 0.5 gram ,the pituitary gland is slightly heavier in females than in males , especially those who had born children , because oestrogen increases the number of certain cells as those producing prolactin . It lies in the sellaturcica at the base of the skull. It is connected with the hypothalamus by the pituitary stalk

3. It is formed of tow lobes :

4. Anterior lobe ( Adenohypophysis ) Adeno = glandular physis = growth It is ectodermal in origin. It is divided into pars distalis , pars intermediaand pars tuberalis . In lower animals, the pars intermediaforms a third separate lobe (intermediate lobe).

5. Post.lobe ( neurohypophysis ) It is nervous in origin. It is a downward , prolongation of the floor of the third ventricle. It is divided into pars nervosa, infundibulum (neural stalk), and the median eminence.

6. Interaction b/w hypothalamus & pituitary gland

7. Vascular connection ( portal circulation ): i.e., the hypothalamico - hypophyseal portal circulation which transports the hypothalamic releasing and inhibiting hormones to the pars distalis to regulate the secretion of hormones of the ant. pituitary. Portal circulation is a part of superior hypophyseal artery which breaks into a network of capillaries which supplies the median eminence and pituitary stalk.

8. Nervous connection i.e., the hypothalamico-hypophyseal tract which transports ADH and oxytocin from hypothalamus to be stored in posterior pituitary.

9. Adenohypophysis

10. Hormones of adenohypophysis

11. 1. Trophic hormones They regulate the secretion of thyroid,adrenal cortex and gonads. They are secretedby basophils (15% of the cells). Adrenocorticotrphic hormone "ACTH"(polypeptide MW 4500). Thyroid stimulating hormone "TSH"(glycoprotein MW 28000). Gonadotrophic hormones "GTH"(glycoprotein MW 33000).

12. 2.Hormones which have direct metabolic effect of the tissues : They are protein hormone secretedby acidophilic cells 35% Growthhormone ( somatotrophic hormone MW 22000). Prolactin (MW 23000).

13. 3. Melanocyte -stimulating hormone "MSH" (polypeptide ) Secreted from the pars intermedia (intermediate lobe). It does not appear to have function in man.

14. Notes, In males, FSH helps sperm formation and is called gametocyte stimulating hormone. In males, LH stimulates testosterone formation and is called interstitial cell stimulating hormone. ACTH stimulates adrenal cortex, lipocytes and melanocytes

15. Type of anterior pituitary cells

16. Type of anterior pituitary cells Chromophobe or reserve cells : Their cytoplasm contains no granules. They probably have no secretory function. They form 50% of the total cells. Chromophil cells Their cytoplasm contains large granules.

17. According to staining properties,there are 2 types 1.Acidophilic Somatotrophes for GH 40-50 % Mammotrophes for prolactin 25% 2.Basophilic Corticotrophes for TSH 22 % Thyrotrophesfor TSH 3-5 % Gonadotrophes 20-30%

18. Regulation of adenohypophyseal function

19. 1 Feedback control mechanism

20. Type of feedback control : a)) Long –loop feedback: i.e., feedback control by the hormones of the endocrine glands. This feedback control by the target organ hormones may affect either: Hypothalamus e.g., steroid hormones. Pituitary e.g., thyroid hormones . This feedback control may be: Inhibitory i.e., negative feedback. Stimulatory i.e., positive feedback

21. e.g. , under stressful condition , the hypothalamus secrete CRF which stimulate the pituitary to release ACTH which ,in turn, stimulate the adrenal cortex to secrete cortisol . Cortisol will exert an inhibitory effect on the hypothalamus to stop the release of CRF( corticotrophin releasing factor). b)) short-loop feedback: i.e., feedback control by the pituitary trophic hormones themselves. This feedback control by the pituitary hormones (GTH,ACTH and GH)on hypothalamus is inhibitory (short-loop inhibitory feedback). The pituitary hormones reach the hypothalamus either by the systemic circulation or back diffusion from the pituitary to hypothalamus.

22. c)) Ultra short feedback: i.e . the hypothalamic releasing factors feedback to control their synthesis . The feedback control is important to: Maintain the normal level of the target hormones in blood. Prevent over stimulation of the target glands by the trophic hormones. Adjust the rate of the target hormones according to the body need.

23. 2 Hypothalamic control ( hypothalamic – Neurosecretory mechanism)

24. The hypothalamus DETERMINES (SETS) the level of hormones according to the body need. i.e., the hypothalamus determines the level needed and the feedback mechanism maintains this level. The hypothalamus secretes neuro -hormonal factors that reach the ant. Pit. through the hypothalamico-hypophyseal portal circulation. These factors may be stimulatory (releasing factors [R.F.] ) or inhibitory (inhibitory factors [I.F] ).

25. These factors now commonly called hormones are: Growth hormones releasing factor: GRF. Growth hormones inhibitory factors: GIF ( somatostatin ). Prolactin -inhibitory factor: PIF. FSH- releasing factor: FRF. LH – releasing factor: LRF. FRF & LRF appear to be a single substance called gonadotropin releasing factor. TSH- releasing factor: TRF. Corticotropin (ACTH) releasing factor: CRF.

26. The hypothalamic regulatory centers are present in the median eminence of the hypothalamus. They receive afferent fibers from the limbic system, globuspallidus and fore- brain. The chemicaltransmitters are acetylcholine, nor adrenaline, dopamine serotonin, substance P and histamine

27. The hypothalamic releasing hormones have the following characters: They are secreted in pulses They are small peptides They combine with plasma membrane receptors and act through Ca++, cAMP and membrane phospholipid prostaglandins. They stimulate the synthesis and release of target pituitary hormones. They modify biological activity of target pituitary hormones by post translation effects through modifying their content of sugar or silica acid. They modulate effects by regulation of own receptors. They are non-specific in their action .e.g. TRF stimulate the secretion of TSF, PRL and sometimes GH. Note: PIH inhibits the secretion of PRL, GH andTSH

28. Growth hormone

29. Chemistry of GH It is a single chain polypeptide with MW 22,000. - It contains 191 amino acids and 2 disulfide bridges. - Human GH is active in many animals, but only primate growth hormones are active in man.

30. Secretion of GH It is secreted by acidophil cells of the pituitary. It circulates in plasma unbound. It has no specific target organ. The basal GH level in blood is normally less than 3 ng \ml pituitary gland contains 5-15 mg. It is high in women and very high in newly born. A rise in the level of GH occurs after activity, during sleep, in the middle of the menstrual cycle and during oestrogen administration

31. Factors which affect growth : GH is essential for postnatal somatic growth. Gonadal steroids are essential for growth before puberty. Insulin. Thyroxin is essential for intrauterine growth and the first 2 years of life. Genes. Nutrition.

32. Action of GH:- 1.Insulin like action : growth and protein metabolism . 2.anti-insulin effects : CHO and lipid metabolism . 3.Lactogenic effect.

33. 1)) Effect of growth hormone on growth : Increase the linear growth . Does not affect growth in intrauterine life . GH causes widening of epiphyseal plate . GH : ++ DNA & RNA synthesis . ++ Ca uptake by Epiphyseal plate . ++ Sulphur uptake to form chondroitin sulphuric acid . ++ Protein uptake by collagen to increase synthesis of hydroxyproline .

34. // Somatomedin // Is a polypeptide released from liver . Is responsible for skeletal growth as it stimulates DNA & RNA synthesis and collagen formation . Unlike GH , it has insulin like action . It has longer life than GH ( 3-5 hours ) . The formation of somatomedin is decreased in protein malnutrition , insulin deficiency and with glucocorticoids .

35.   2)) On protein : GH is protein anabolic hormone : GH increase the transport of amino acids across the cell membrane . GH decreases and urea in blood and sodium excretion . GH produce positive nitrogen and phosphorus balance . GH stimulate erythropoiesis .

36. 3)) On CHO : Diabetogenic : The diabetogenic effect of growth hormone is due to : GH stimulates gluconeogenesis . GH inhibits glucose uptake by the muscles by inhibiting hexokinase enzyme and decrease the sensitivity to insulin . GH stimulates the alpha cells of pancreatic islets to release the glucagon ,glucagon stimulates the glycogenolysis

37. 4)) On fat : // Ketogenic //: GH mobilizes the fatty acids causing lipaemia . GH stimulates ketone body formation by the liver . GH prevents lipogenesis from glucose under the influence of insulin .

38. 5)) Lactogenic effect : GH is similar in structure and function to prolactin . GH simulates the breast to secrete milk , ( If increase → Galactorrhoea ).

39. Control of growth hormone secretion :

40. The hypothalamus affects the GH secretion by tow hormones : Growth hormone releasing hormone GHRH . Growth hormone inhibiting hormone GHIH ( somatostatin ) .

41. GH secretion is increased by : Amino acid infusion especially arginine . Decrease the minor substrates e.g. glucose & FFA Glucose + FFA long loop – ve feedback ++ GH . Fasting and sever malnutrition . Exercise . Neural stimuli e.g. emotional stress, operation , fear and onset of deep sleep . Neurotransmitters Encephaline , nonepinephrine and serotonin . Hormones : Estrogens : increase the number of somatotrops . Androgens : e.g. testosterone . Adrenalin : through alpha adrenergic effect .

42. GH secretion is decreased by : Continuous administration of glucose . Corticosteroid treatment .

43. Disorders of growth hormones secretion

44. PITUITARY DWARFISM:

45. Cause : deficiency of GH before puberty due to : Lesion in the hypothalamus leading to decreased GHRF. Organic lesion or surgical removal of pituitary. Inheritent growth hormone deficiency ( autosomal recessive gene) Secretion of inactive growth hormone. The liver is unable to secrete somatomedin . Lack of organ response to endogenous GH e.g., African pygmies or genetic dwarfism, this is the most important cause. It is due to lack of somatomedin receptors in the epiphysis, the blood level of HGH is normal and it rises normally in response to hypoglycemia and arginie infusion.

46. Characters 1. Symmetrical retardation of growth of bones: Ossification centers appear normally in life, but there is rapid union of epiphysis. Height is 100-120 cm in adult. Dentition is not delayed. 2. Symmetrical retardation of growth of soft tissues: However, birth weight is normal. 3. Mentality is normal, but drawf is emotionally unstable. Head is relatively large with tendency to obesity. i.e., the body proportions are of the child type.

47. PITUITARY INFANTALISM: Dwarfism accompanied by hypogonadism . It is due to deficiency of both GH and gonadotropins . Because of lack of gonadotropins , the secondary sexual organs remain infantile and the secondary sexual characters do not appear.

48. EXCESS SECRETION OF GH: It is caused by hyperplasia or adenoma of the acidophilic cell.

49. GIGANTISM: The condition results from over production of GH in the pre adult life i.e. before union of epiphysis .

50. Characteristic Features: Overgrowth of ALL BONES (2 meters or more) Gigantism is disproportionate; because the effect of GH is more on long bones of the limbs Overgrowth of SOFT TISSUES: a- Visceromegaly ( splanchnomegaly ) - Splenomegaly - Cardiomegaly b-Muscles in the early stage are strong. Later on, the muscles become weak; this because of the muscle growth does not go parallel to the skeletal growth.  

51. Characteristic Features : cont Hypogonadism: Gonads remain infantile. This is because the acidophilic cells cause pressure atrophy of basophilic cells, which secrete gonadotropin .  Hyperglycemia, glucosuria and insulin resistant diabetes. 4% of female patients develop lactation in absence of pregnancy. If overproduction of GH continues in the adult life, signs of acromegaly develop

52. Acromegaly : Acro = extremities Megaly = large The condition results from overproduction of GH in the adult life, i.e , after union of epiphysis.

53. Characteristic Features:

54. Characteristic Features: 1 .Overgrowth of terminal portions of the skeleton. Enlargement is especially marked in the small bones of the hands and feet and in the membranous bones. Skull: Supra orbital ridges: excess development Nose and ear pinna : double normal size Mandible broad: teeth separation Mandible thick: forward protrusion Hand and foot are thick an broad. i.e., spade lick hand and ape like face browing of the spine

55. Characteristic Features : cont 2 . Overgrowth of soft tissues of the nose , lips, forehead and scalp. The scalp is thrown into rinkles (Bulldog scalp). Overgrowth of body hair. Splanchnomegaly , i.e., hypertrophy of viscera. 3. Hyperglycemia and glucosuria and increased insulin resistance. The basal metabolic rate is raised by 70-90 %

56. Characteristic Features : cont 4 .In early cases . There is increased sexual function and may be lactation. but , In advanced cases , sexual functions are depressed.