Endocrine Hypothalamus

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Endocrine Hypothalamus

• JP Slovak

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Hormones

• Thyrotropin-Releasing hormone
• Controls TSH secretion
• Post-translationally processed
• 3 a.a.
• Some evidence that neurons release TRH
• Other functions
• Stimulates release of PRL in humans
• Somatostatin
• 14 aa
• GH released in pulses
• SST inhibits release
• Inhibits TSH release
• Lowers blood glucose levels

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Hormones

• GHRH
• Somatocrinin
• Formed in arcuate nucleus of median eminence
• Increase release of GH
• GnRH
• Controlled by regular neurons
• Controls secretion of FSH and LH
• FSH and LH produced in same cells
• CRH
• Stimulates secretion of ACTH
• Beta endorphin also
• Highly conserved

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Hormones

• PIF
• Inhibits PRL secretion
• dopamine
• PRH
• ?

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Control

• Neurohormones
• Sensory neurons?hypothalamus?HTA?median eminence
• CRH
• Stress increases ACTH
• Cholinergic pathways likely control ACTH
  secretion
• PIF
• Suckling causes inhibition of neurons that
  release PIF
• 5-HT may stimulate PRL secretion
• GH
• Several forms(alternative splicing)
• If you inhibit SST?
• Inhibit GHRH?
• Ghrelin also stimulates
• SST receptors on GHRH neurons
• Receptors for GHRH, grherlin and SST all
  G-proteins

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Feedback

• ACTH
• Stressor induced
• Cortisol and corticosterone on ACTH
• At level of pituitary and hypothalamus
• GnRH
• Gonadal steroids on GnRH
• Act on hypothalamus
• May work at pituitary
• FSH and LH may act on pituitary(auto inhibition)
• PRL
• Similar to GH(gene duplication)
• PRL receptors found on ovaries
• Upregulates immune function
• PRL increases PIF
• Short loop

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Feedback

• GH
• GH acts to increase SST
• IGFs also stimulate SST production
• Growth hormone effects
• Lower blood aa conc
• Lower blood urea nitrogen
• Positive nitrogen balance
• Increase in synthesis of protein, DNA and RNA
• Increase blood glucose
• Increase lipolysis
• Growth of cartilage and bone
• Growth effects mediated by insulin like growth
  factors
• TSH
• T4 and T3 inhibit TRH

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Mechanisms of action of RH

• Most cAMP
• Protein kinase
• Arachidonic Acid
• Promotes exocytosis
• Prostaglandins
• GH and ACTH
• Can activate Phospholipase C

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Physiological Roles of Neurohypophysial Hormones

• Oxytocin
• Milk release
• Nerve endings in nipple
• Stimuli conducted to neurohypophysis
• Dilation of cervix
• Stimulates OT release
• Milk release during coitus
• Sensory stimuli may affect milk release
• Uterine Contraction
• Used to induce labor
• Cause myometrium to contract
• Binding of OT to uterine receptors increase
  during labor
• Estrogen increases number of oxytocin receptors

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Physiological Roles of Neurohypophysial Hormones

• Maternal Behavior
• Inhibits ACTH secretion
• Mating behavior
• Human sexual response
• Increase in both males and females
• AVP(vasopressin)
• Osmoregulation
• Fluid osmolarity down ? AVP levels fall
• Excretion of hypotonic urine
• Osmoreceptors lie near neurohypophysis
• 1 change is enough to cause AVP changes

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Physiological Roles of Neurohypophysial Hormones

• Blood Volume-pressure regulation
• Baroreceptors in left atrium, aorta
• Vagal nerves reach brainstem
• Increase in AVP occurs when blood volume reduced
  by 8
• Arterial pressure drops by 5 ?AVP secretion

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The varied pathways to increased renin
secretion are illustrated in this chart, as are
the subsequent steps leading to increased levels
of angiotensin II in the blood. Note that the
vasoconstrictor action of angiotensin II allows
it to decrease GFR as a direct result
of decreasing blood flow through the glomerular
capillaries.
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An abnormal increase in blood volume stretches
out the atria, stimulating secretion of ANP
(atrial natriuretic peptide). ANP promotes
vasodilation, thus increasing GFR, and inhibits
sodium reabsorption in the distal tubule,
leading to natriuresis (increased levels of
sodium in urine), which increases urine volume
as it decreases blood volume.
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An abnormal decrease in blood volume and pressure
activates baroreceptor neurons in the aorta and
carotid sinuses, leading to increased secretion
of vasopressin, also known as anti-diuretic
hormone (ADH) which increases water permeability
in the collecting ducts, which decreases the
volume of excreted urine.
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