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27 Cards in this Set
- Front
- Back
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What is a neurosecretory cell?
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Has all the capacities of a nerve cell but with additional ability to secrete hormone
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What two nuclei regulate the hypothalamo-neurohypophyseal system?
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Supraoptic and paraventricular nuclei
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What is the posterior pituitary's main function?
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Storage and release of oxytocin and ADH. Comprised of terminals of the neurosecretory cell.
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How are ADH and oxytocin similar?
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Small peptides; homologues of each other, 6 member ring with 3 member side chain.
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How are ADH and oxytocin store and cleared?
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Circulate unbound and are cleared by liver and kidney (T 1/2 2-18 minutes)
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What are the physiological actions of ADH?
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1) Vasopressor action - contraction of vessels. Released in response to 10% drop in blood volume
2) Antidiuretic action - promotes reabsorption of water in distal tubule and collecting ducts (major physiological action) |
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What's the mechanism of vasopressor action?
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Involves V1 receptor (G protein coupled) and Ca2+ dept form of signal transduction.
Involves PLC generation of IP3 and DAG |
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What's the mechanism of antidiuretic action of ADH?
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Involves V2 receptors (GPCR) located in basolateral membrane. They bind hormone, increase cAMP --> PKA --->etc leads to insertion of aquaporins (and activation by phosphorylation of existing aquaporins) for passive water absorption in late distal and collecting ducts.
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What's the more potent but less sensitive stimulus for ADH secretion?
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Hypovolemia (as opposed to hyperosmolarity)
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What mediates the hypovolemic response (transduces the signal)?
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Left Atrial Stretch receptors. When they are stretched they lead to increased firing of vagal inhibitory neurons leading to decreased vasopressin release.
Decrease of stretch has reverse effect - increased vasopressin release |
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What mediates the hyperosmolar response (transduces the signal)?
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Hypothalamic osmoreceptors sense change in osmolarity.
These are NOT SON or PVN |
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T/F Hypothalamic osmoreceptors are in the supraoptic nucleus/paraventricular nucleus
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F
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What kind of interaction can occur between osmotic and volume controls of vasopressin secretion?
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Angiotensin II can sensitize osmotic receptors indicating that volume depletion can enhance sensitivity of osmotic stimuli
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What other things can stimulate vasopressin release?
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pain, nausea, anxiety, nicotine etc
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What other things can inhibit vasopressin release?
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alcohol
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What is diabetes insipidus?
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Deficiency in vasopressin secretion.
Symptoms only manifest when anterior pituitary hormones are present (related to maintenance of GFR) |
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How much vasopressin must be lost before there are symptoms? What does this indicate?
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about 80%. indicates there is a large reserve
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What can cause nephrogenic diabetes insipidus?
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Vasopressin is unresponsive in target cells of nephron, due to receptor dysfunction or defect in gene that inserts water channel
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What happens to ADH in pregnancy?
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There is enhanced ADH clearance and metabolism --> cleared too rapidly
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Dipsogen - defn
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something that causes drinking
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functions of oxytocin in female
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1) Milk let down
2) Parturition 3) Sperm transport (?) involve contraction of myoepithelial cells |
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functions of oxytocin in male
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Sperm transport?
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Where are the ADH and oxytocin precursors made?
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SON and PVN
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What happens in the hypothalamo-neurohypophyseal tract?
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Prohormone is transported by axoplasmic flow, and post ribosomal processing (proteolytic cleavage) to actual hormone and its associated products
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What are neurophysins?
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Neurophysins are carrier proteins for oxytocin and vasopressin (ADH). Oxytocin and vasopressin are carried by unique neurophysins from their site of production in the cell bodies of the paraventricular and supraoptic nuclei to their site of release in the axon terminals of the posterior pituitary.
Glycoprotein enriched material transported by axoplasmic flow. Also called "neurosecretory material" |
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Does anything happen chemically to ADH or ocytocin in post pituitary?
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No, they're just stored and release there
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How are ADH and oxytocin first produced and where?
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As pre-prohormones (Pre-propressophysin and pre-prooxyphysin).
Initial processing involves N terminal cleavage to pro-hormones. Proteolytic processing to final hormone occurs in hypothalamo-hypophyseal tract. ONLY storage and release in post pituitary |
