Hypophysis-Anterior Pituitary

Prof. K. Sivapalan

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Location.

• It is located in Sella Turcica, under Diaphragma Sella.

• It weighs 0.5g.• In pregnancy it hypertrophies to 1g.• 75% of the gland is anterior lobe- anterior

pituitary.• 25% is posterior pituitary.

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Development.

• Rathke's pouch- anterior pituitary.

• Floor of the third ventricle- posterior pituitary.

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Anterior Pituitary.[Adenohypophysis]

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Blood supply

• Anterior lobe: superior hypophysial artery and Hypothalamic Hypophysial Portal system from hypothalamic nuclei.

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ACTH

• Single chain, 39 amino acids, parts resembling MSH and stimulates Melanocyte activity.

• Half life- 3-4 minutes.• Regulation of secretion- studied under

glucocorticoids.• ACTH and β-LPH- lipotropin are synthesized as

one molecule and split before release.• Lipotropin resembles Endophins and

Enkephalins which act like opiates.• ?use in stress.

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Gonodotrophins- FSH + LH.

FSH- follicular stimulating hormone.• Glycoprotein, 25000mw, a and b chains. • Action on testis and ovaries.• Secretion at puberty.LH- Luteinizing hormone.• Glycoprotein, 40000mw, a and b chains.

– Action on testis and ovaries.• Secretion starts at puberty.

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TSH

• Glycoprotein, 30000mw, a and b chains. • Control- TRH• Action on thyroid gland.

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Prolactin.

• Structure- similar to GH.• Human Prolactin- 198 amino acids.• Control- Prolactin Inhibiting Hormone

(Dopamine, - only inhibitory factor from hypothalamus)

• Chlorpromazine stimulates secretion by reducing Dopamine receptors.

• Regulation-– exercise and stress- surgical or psychological.– stimulation of nipple by nerves to hypothalamus.

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Actions of Prolactin• Secretion of milk in breast prepared by estrogen,

progesterone, growth hormone and corticoids.• At high concentrations, similar metabolic actions

as Growth Hormone.• (Ejection of milk -by oxytocin)• Hyperprolactinaemia:

– Inhibition of menstruation in females– Impotence and hypogonadism in males.

• Mechanism not known. ? Inhibition of gonadotropins by nervous stimuli from breast or prolactin