HypophysisAnterior Pituitary
Prof. K. Sivapalan
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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Anterior Pituitary
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Development.
• Rathke's pouch- anterior
pituitary.
• Floor of the third ventricleposterior 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
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