1. Anterior Pituitary Gland

2. Lecture Objectives
Explain hypothalamus as the major integrative site for the neuroendocrine system.
Describe the general characteristics of hypothalamic releasing and inhibiting hormones and describe their route of transport from the hypothalamus to the anterior pituitary.
Identify appropriate hypothalamic hormones that control the secretion of each of the anterior pituitary hormones.
Diagram short-loop and long-loop negative feedback control of anterior pituitary hormone secretion.

3. II. Anterior pituitary (=Adenohypophysis)
Cells:
Chromophobes: (50% of cells) = precursor cells.
Acidophils (alpha cells): (40% of cells) & secrete: Growth hormone (GH) & Prolactin (PRL).
Basophils (Beta cells): (10% of cells) & secrete:
Thyriod stimulating hormone (TSH) or Thyrotropin.
Adrenocorticotrophic H. (ACTH) or Corticotropin.
Follicle stimulating hormone (FSH).
Luteinizing hormone (LH).

4. Anterior Pituitary hormones
Growth Hormone (GH)
Prolactin (PRL)
Thyroid Stimulating Hormone (TSH)
Follicle Stimulating Hormone (FSH)
Luteinizing Hormone (LH)
AdrenoCorticoTropic Hormone (ACTH)

6. Hypothalamo - Hypophyseal portal system
Vascular connection between hypothalamus & anterior pituitary.
Hypothalamus secretes polypeptide hormones (= hypothalamic releasing or inhibiting factors) absorbed into hypothalamic-hypophyseal portal capillaries to be carried to anterior pituitary.

7. Hypothalamic
- hypophyseal
Portal system

8. Vascular Link Between the Hypothalamus and Anterior Pituitary

11. Anterior Pituitary Hormones

12. Anterior pituitary hormones

13. Thyroid Stimulating Hormone (TSH) = Thyrotropin
Actions:
Stimulates development of thyroid structure and function.
Stimulates formation and secretion of thyroxine.
Control:
1- Feedback mechanism:
*  Thyroxine   thyrotropin releasing factor (=TRF) &  TSH.
*  Thyroxine   TRF &  TSH.
2- Neural: TRF is stimulated mainly by neural reflexes.

14. ADRENOCORTICOTROPIC HORMONE (ACTH) = Corticotropin
Actions:
Stimulates adrenal cortex (except zona glomerulosa).
Stimulates adrenocortical hormones (except aldosterone).
It has melanocyte stimulating& fat mobilizing effects.
Control:
1- Feedback mechanism:
Cortisol   corticotropin releasing factor (CRF) &  ACTH.
 Cortisol   CRF &  ACTH.
2- Neural:
Emotion, Excitement, pain and fear   CRF   ACTH.
Circulatory stresses as hemorrhage stimulate anterior pituitary directly.

15. Follicle Stimulating Hormone Luteinizing Hormone (LH)
GONADOTROPINS
Follicle Stimulating Hormone
Luteinizing Hormone (LH)
Female
Stimulates growth & maturation of Graffian Follicle  secretion
of estrogen.
Stimulates ovulation and formation of corpus Luteum   secretion of progesterone from it.
Male
Stimulates Spermatogenesis.
Stimulates Sertoli cells estrogen.
Stimulates interstitial cells of Leydig   testosterone.

16. PROLACTIN
Prolactin is a protein hormone of the anterior pituitary gland that was originally named for its ability to promote lactation in response to the suckling stimulus of hungry young mammals. 
Based on its genetic, structural, binding and functional properties, prolactin belongs to the prolactin/growth hormone/placental lactogen family.
The mature human prolactin is composed of 199 amino acids

17. CONTROL OF SECRETION 1- Hypothalamic control:
Prolactin Inhibiting Factor (predominant): Dopamine & GABA
Prolactin Releasing Factor (PRF): Thyrotrophin releasing Factor (TRF) & VIP.
2-  Thyroxin   prolactin via  TRF secretion (by -ve feedback mech.).
3-  Estrogens   prolactin secretion via  TRF receptors on lactotrophs.

18. Functions of PROLACTIN
It is involved in MILK formation. In the process of lactogenesis, prolactin stimulates uptake of some amino acids, the synthesis of the milk proteins casein and α-lactalbumin, uptake of glucose, and synthesis of the milk sugar lactose as well as milk fats.
Prolactin stimulates MILK secretion from already formed mammary gland and prepared by estrogen and progesterone. During pregnancy, prolactin stimulates Breast Growth with no lactation; only colostrum is produced. As estrogen and progesterone (secreted from placenta)  inhibit prolactin action at receptor sites in alveolar cells. ↓ Estrogen & progesterone after delivery  initiation of milk production.

19. Other functions of prolactin
3) It is involved in Regulation of Gonadal function 4) It plays an important role in maternal behavior
N.B. ↑ Prolactin secretion in:
Strenuous exercise (exercise amenorrhea in ♀)
Sleep
Suckling,
Stress conditions

20. HYPERPROLACTINAEMIA Causes: 1-Hypothalamic Dopamine deficiency due to:
Stress  hypothalamic Dopamine.
Drugs e.g. Alpha methyldopa ( central dopamine stores).
2- Defective Dopamine transport: due to pituitary tumors.
3- Lactotroph insensitivity to Dopamine:
Dopamine receptor blockers as Phenothiazines.
Effects:
1- Galactorrhoea: In 80% of Females & 30% of Male (due to inhibitory effect of androgens).
2- Hypogonadism: : menstrual abnormalities (in Female), impotence (In Male) & infertility in both.
Hypogonadism in hyperprolactinaemia may be due to:
1- Suppression of pituitary gonadotrophins secretion.
2- Blockade of receptors of gonadotrophins at gonadal level.

21. Endocrine Control Three Levels of Integration
Hypothalamus
Pituitary stimulation from hypothalamic trophic hormones
Endocrine gland stimulation from pituitary trophic hormones

22. Hormones of hypothalamic-anterior pituitary pathway

23. Negative Feedback Loops
Regulate amount of hormones in blood
Hormone levels stay within range needed for appropriate responses
Eliminates waste of hormones.
A) long loop –ve feedback:
1) Direct -ve feedback
Anterior pituitary hormones  stimulate target gland ( TSH   Thyroxin).
E.g. ↓ Thyroxin  ↑ TSH from Ant. pituitary
↑ Thyroxin  ↓ TSH.

24. 2) Indirect -ve feedback
When hypothalamus is indirectly involved in regulation of hormone secretion from target gland via releasing or inhibitory factors {TRF   TSH   Thyroxin}.
E.g. ↑ Thyroxin  ↓ TRF ↓ Thyroxin  ↑ TRF.
B) Short loop -ve Feedback:
Some anterior pituitary hormones e.g. Somatotropin (= GH) can regulate its own release by a short loop -ve feedback on the secretion of its hypothalamic releasing or inhibitory factors. E.g. Somatotropin and Somatotropin RF or Somatostatin.

25. Negative Feedback Loops

29. (طريق الخير صعوبته في سلوكه، وطريق الشر صعوبته في عاقبته، فاللهم أعنّا على الخير، وعافنا من الشر).
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