Anatomy - pituitary gland and hypothalamus

Anatomy - pituitary gland and hypothalamus

1. Anatomy -PITUITARY GLAND AND HYPOTHALAMUS

2. The pituitary gland ( hypophysis ) and the hypothalamus act as a unit , regulating the activity of most of the other endocrine glands.

3. The pituitary gland lies (positioning) in the hypophyseal fossa of the sphenoid bone below the hypothalamus, to which it is attached by a stalk.

4. It is the size of a pea (round shape), weighs about 500 mg and It consists of three distinct parts that originate from different types of cells.

5. ANTERIOR PITUITARY The anterior pituitary ( adeno hypophysis ) is an up growth of glandular epithelium from the pharynx .

6. Posterior pituitary The posterior pituitary ( neuro hypophysis ) is a down growth of nervous tissue from the brain.

7. There is a network of nerve fibres between the hypothalamus and the posterior pituitary.

8. Between these lobes there is a thin strip of tissue called the intermediate lobe and its function in humans is not known.

9. BLOOD SUPPLY Arterial blood. This is supplied by branches from the internal carotid artery.

10. The anterior lobe is supplied indirectly by blood that has already passed through a capillary bed in the hypothalamus but the posterior lobe is supplied directly.

11. VENOUS BLOOD. This comes from both lobes, containing hormones, and leaves the gland in short veins that enter the venous sinuses between the layers of dura mater.

12. THE INFLUENCE OF THE HYPOTHALAMUS ON THE PITUITARY GLAND The influence of the hypothalamus on the release of hormones is different in the anterior and posterior lobes of the pituitary gland.

13. ANTERIOR PITUITARY Some of the hormones secreted by the anterior lobe ( adeno hypophysis ) stimulate or inhibit (stoppage) secretion by other endocrine glands (target glands) while others have a direct effect on target tissues.

14. The release of an anterior pituitary hormone follows stimulation of the gland by a specific releasing hormone produced by the hypothalamus and conveyed to the gland through the pituitary portal system of blood vessels.

15. The whole system is controlled by a negative feedback mechanism.

16. when there is a low level of a hormone in the blood supplying the hypothalamus it produces the appropriate releasing hormone which stimulates release of a trophic hormone by the anterior pituitary.

17. This in turn stimulates the target gland to produce and release its hormone.

18. As a result the blood level of that hormone rises and inhibits the secretion of releasing factor by the hypothalamus.

19. HORMONES SECRETED BY ANTERIOR PITUITARY GLAND

20. HORMONES SECRETED BY ANTERIOR PITUITARY GLAND Growth hormone (GH) Thyroid stimulating hormone (TSH) A drenocorticotrophic hormone (ACTH) Prolactin (PRL) Follicle stimulating hormone (FSH) Luteinising hormone (LH

21. GROWTH HORMONE (GH) Function : Regulates metabolism, promotes tissue growth especially of bones and muscles

22. This is the most abundant (excess) hormone synthesized (producing/developing) by the anterior pituitary.

23. It stimulates growth and division of most body cells but especially those in the bones and skeletal muscles.

24. It also regulates aspects of metabolism in many organs,

25. e.g. liver, intestines and pancreas; stimulates protein synthesis; promotes breakdown of fats; Increases blood glucose levels.

26. Its release is stimulated by growth hormone releasing hormone (GHRH) .

27. Its suppressed by growth hormone release inhibiting hormone (GHRIH) both of which are secreted by the hypothalamus.

28. Secretion of GH is greater at night during sleep hypoglycaemia , exercise and anxiety also stimulate release.

29. The daily amount secreted peaks (high) in adolescence and then declines with age.

30. Inhibition of GH secretion occurs by a negative feedback mechanism when the blood level rises and also

31. when GHRIH (Growth hormone release inhibiting hormone (GHRIH) ( somatostatin ) is released by the hypothalamus.

32. GHRIH also suppresses secretion of TSH and gastrointestinal secretions, e.g . gastric juice, gastrin and Cholecystokinin.

33. Cholecystokinin Cholecystokinin ( a hormone secreted by duodenum and stimulate the release of bile into the intestine).

34. THYROID STIMULATING HORMONE (TSH) FUNCTION: Stimulates growth and activity of thyroid gland and secretion of T3 and T4.

35. This hormone is synthesised by the anterior pituitary and its release is stimulated by TRH (TRH- Thyrotropin releasing hormone) from the hypothalamus.

36. It stimulates growth and activity of the thyroid gland, which secretes the hormones Thyroxine (T4) and Triiodothyronine ( T3).

37. Release is lowest in the early evening and highest during the night. Secretion is regulated by a negative feedback mechanism.

38. When the blood level of thyroid hormones is high, secretion of TSH is reduced, and vice versa.

39. ADRENOCORTICOTROPHIC HORMONE (CORTICOTROPHIN, ACTH) FUNCTION: Stimulates the adrenal cortex to secrete glucocorticoids .

40. ADRENOCORTICOTROPHIC HORMONE (CORTICOTROPHIN, ACTH) Corticotrophin releasing hormone (CRH) from the hypothalamus promotes the synthesis and release of ACTH by the anterior pituitary.

41. This increases the concentration of cholesterol and steroids (decreases inflammation) within the adrenal context and the output of steroid hormones, especially cortisol.

42. ACTH levels are highest at about 8 a.m. and fall to their lowest about midnight, although high levels sometimes occur at midday and 6 p.m.

43. This circadian rhythm is maintained throughout life. Circadian rhythm are physical, mental and behavioral changes followed a daily cycle.

44. It is associated with the sleep pattern and adjustment to changes takes several days, following, e.g ., shift work changes, travel to a different time zone (jet lag).

45. Secretion is also regulated by a negative feedback mechanism, being suppressed when the blood level of ACTH rises.

46. Other factors that stimulate secretion include hypoglycaemia , exercise and other stressors, e.g . emotional states and fever.

47. PROLACTIN FUNCTION: Stimulates milk production in the breasts.

48. PROLACTIN This hormone stimulates lactation (milk production) and has a direct effect on the breasts immediately after parturition (childbirth).

49. The blood level of prolactin is stimulated by prolactin releasing hormone (PRH) released from the hypothalamus

50. and it is lowered by prolactin inhibiting hormone (PIH, dopamine) and by an increased blood level of prolactin.

51. After birth, suckling stimulates Prolactin secretion and lactation.

52. The resultant high blood level is a factor in reducing the incidence of conception during lactation.

53. Prolactin together with oestrogens , corticosteroids , insulin and thyroxine is involved in initiating and maintaining lactation.

54. Prolactin secretion is related to sleep, i.e . it is raised during any period of sleep, night or day. Emotional stress increases production.

55. GONADOTROPHINS

56. After puberty two gonadotrophins (sex hormones) are secreted by the anterior pituitary in response to luteinising hormone releasing hormone (LHRH), also known as gonadotrophin releasing hormone ( GnRH ).

57. In both males and females these are: • Follicle stimulating hormone (FSH) • Luteinising hormone (LH).

58. In both sexes. FSH stimulates production of gametes (ova or spermatozoa).

59. Follicle stimulating hormone (FSH) Stimulates production of sperm in the testes, stimulates secretion of oestrogen by the ovaries, maturation of ovarian follicles, ovulation .

60. IN FEMALES. LH and FSH are involved in secretion of the hormones oestrogen and progesterone during the menstrual cycle.

61. As the levels of oestrogen and progesterone rise secretion of LH and FSH is suppressed.

62. IN MALES. LH, also called interstitial cell stimulating hormone (ICSH) stimulates the interstitial cells of the testes to secrete the hormone testosterone.

63. Luteinising hormone (LH) Stimulates secretion of testosterone by the testes, stimulates secretion of progesterone by the corpus luteum .

64. Oxytocin and antidiuretic hormone (ADH or vasopressin) are the hormones synthesised in the hypothalamus and then released from the axon terminals within the posterior pituitary gland.

65. These hormones act directly on non-endocrine tissue and their release by exocytosis is stimulated by nerve impulses from the hypothalamus.

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