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Endocrine Anatomy The Pituitary Gland The Hypothalamic Control

Endocrine Anatomy The Pituitary Gland The Hypothalamic Control. The Pituitary gland ( hypophysis ):.  Small gland (  1cm diameter;  0.5 to 1 gm weight).  Lies in sella turnica , a bony cavity at the base of the brain.  Connected to the hypothalamus by the pituitary stalk or

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Endocrine Anatomy The Pituitary Gland The Hypothalamic Control

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  1. Endocrine AnatomyThe Pituitary GlandThe Hypothalamic Control

  2. The Pituitary gland (hypophysis):  Small gland ( 1cm diameter;  0.5 to 1 gm weight).  Lies in sella turnica, a bony cavity at the base of the brain.  Connected to the hypothalamus by the pituitary stalk or (hypophysial; infundibulum).  Structurally & functionally divided into 2 lobes: 1) Anterior lobe )2/3(, 2) Posterior lobe )1/3(.

  3. The anterior pituitary lobe (adenohypophysis) •  Master gland (adenohypophysis). •  Consists of 2 parts in adults: 1. Pars distalis… known as the anterior pituitary. rounded portion & the major endocrine part of the gland. 2. Pars tuberalis… thin extension in contact with the infundibulum. Pars intermedia… Avascular tissue b/w anterior & posterior lobes, exists in fetus (no longer present in adults). Much more functional in some lower animals, such as fish, amphibians, & reptiles.

  4. The anterior pituitary gland cells  Embryologically derived from a pouch of epithelial tissue (Rathke’s pouch), that is derived from pharyngeal epithelium(mouth).  Histologically, contains many types of secretary cells (Chromophils): • Acidophils (epsilon ) • Somatotropes– (hGH) … 30-40% • Lactotropes– (PRL)  3-5% • Basophils (delta ) • Corticotropes– (ACTH) … 20% • Thyrotropes– (TSH)  3-5% • Gonadotropes–gonadotropic hormones (LH, FSH)  3-5% (at least one cell type for each major hormone)

  5. The anterior pituitary gland cells

  6. 2) The posterior pituitary lobe (neurohypophysis)  Is the neural part of the pituitary gland.  Embryologically derived from a down growth of the hypothalamus.  In contact with the infundibulum & adenohypophysis. Consists of Pars Nervosa, also called the posterior pituitary.

  7. Relationship between the Hypothalamus & the Pituitary gland

  8. Hypothalamic control of pituitary secretions Almost all secretions by the pituitary are controlled by either hormonal or nervous signals from hypothalamus

  9. Hypothalamic Control of I: Anterior Pituitary Gland

  10. Relationship with anterior pituitary gland  There are both anatomical & physiological relationship: I: Anatomical relationship: Anterior pituitary gland is connected to hypothalamus by portal system: “hypothalamic-hypophysial portal vessels”. Remember: Anterior pituitary gland is NOT innervated by hypothalamus.

  11. Relationship with the anterior pituitary gland … (continued) “Superior hypophysial artery”  1st capillary network (at the median eminence)  “Hypophysial portal vessels”  2nd capillary network (in the anterior pituitary)  Venous flow to the heart

  12. Relationship with the anterior pituitary gland … (continued) II: Physiological linkagediscovered by Harris in 1947. Hypophysectomized (removed pituitary gland) of animals; divided them into 2 groups: Group 1:Transplanted new pituitary below hypothalamus (normal position):a. new blood vessels developed between hypothalamus & new pituitary gland; b. Pituitary was living & provided its normal fx. Group 2:Transplanted new pituitary into either kidney or eye: a. Pituitary was living; b. Does not fx normally (since blood from hypothalamus to kidney or eye is not direct & is diluted with blood of other tissues).

  13. Hypothalamic control of anterior pituitary secretions  Hypothalamus secrete hormones called “hypothalamic releasing & inhibitory hormones” that regulate anterior pituitary secretions.

  14. Hypothalamic control of anterior pituitary secretions

  15. Hypothalamic hormones Hypothalamus GnRH GHRH GHIH/SS TRH PRIH PRH CRH + + + + - - - + + ACTH Prolactin FSH & LH GH TSH Anterior Pituitary

  16. Hypothalamic Control of II: Posterior Pituitary Gland

  17. Relationship with the posterior pituitary gland  Posterior pituitary gland is connected to hypothalamus by “unmylenated” nerve fibers.  Cell bodies of nerves that secrete posterior pituitary hormones are located in supraoptic & paraventricular nuclei of hypothalamus , & NOT in posterior pituitary gland itself.  Nerve fibers extend through the infundibulum along with small neuralgia-like cells called pituicytes to the posterior pituitary.

  18. Relationship with the posterior pituitary gland … cont.

  19. Relationship with the posterior pituitary gland… (continued) Synthesized hormones are then transported to the posterior pituitary gland in the axoplasmic flow of neuron’s nerve fibers passing from hypothalamus to be stored in the posterior pituitary gland. Posterior pituitary gland stores & releases hormones that are secreted from hypothalamus

  20. Control of Hypothalamic Secretions

  21. Control of hypothalamic secretions Neural signals: e.g. pain, depression, exciting, smell, etc. Hormonal concentration feed back mechanism: Chemical stimuli: e.g. nutrients, electrolytes, & [water] in the blood.

  22. General Functions of Hypothalamus

  23. General Functions of the hypothalamus 1. Controls body temperature. 2. Controls the cardiovascular system. 3. Controls food intake & body weight. 4. Controls thirst & water balance. 5. Involved in sleep & wakefulness. 6. Involved in emotional reactions. 7. Involved in reactions to stress. 8. Controls ovarian secretions during ovarian cycle. 9. Controls testicular secretions.

  24. Anterior Pituitary Gland hormones

  25. Anterior Pituitary Hormones  Called trophic hormones; ‘trophic’ means “feed”. High[hormone] causes target organ to hypertrophy. Low [hormone] causes target organ to atrophy. When names applied to the hormones, it is shortened to ‘tropic’, meaning “attracted to”. That’s why APH end with the suffix –tropin.

  26. Anterior Pituitary Hormones

  27. Anterior pituitary hormones Anterior Pituitary FSH & LH GH TSH Prolactin ACTH + + + + + Gonads Most tissues Thyroid gland Mammary glands Adrenal cortex  estrogen; progeterone; + testosterone +gametes; +ovulation; +corpus Lut. protein synthesis; Lipolysis; &  blood glucose +T4; +T3 + thyroid growth +milk; + breast dvlp. regulate ♂ reproductive system glucocorticoids

  28. Anterior Pituitary Hormones

  29. The anterior pituitary hormones… (continued) • Pars intermedia: In fetus & some lower animals, secretes melanocyte stimulating hormone (MSH). In adults, some cells of adenohypophysis derived from fetal pars intermedia  a large polypeptide prohormone called pro-opiomelanocortin (POMC), whose major products are β-endorphin, MSH, & ACTH.

  30. Feedback Control of the Anterior Pituitary • Anterior pituitary & hypothalamic secretions are controlled by negative feedback inhibition by their target gland hormones. • Negative feedback at 2 levels: • Target gland hormone can act on the hypothalamus & inhibit secretion of its releasing hormones. • Target gland hormone can act on the anterior pituitary & inhibit its response to the releasing hormone.

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