Term
| What is the post pit derived from and which two nuclei does it originate from? |
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Definition
Derived from neural tissue.
Infundibulum and posterior pituitary are primarily nonmyelinated nerve fibers.
Originate in the supraoptic and paraventricular nuclei |
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Term
| What is the role of the prohormone in ADH physiology? |
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Definition
ADH:
Nine amino acid peptide, sometimes termed arginine vasopression or AVP.
Synthesized in cell bodies of hypothalamic nuclei as large prohormone.
ADH and the prohormone are packaged in secretory vesicles and transported to nerve terminals in the stalk and posterior pituitary.
The large prohormone, termed neurophysin, appears to play an important role in neural transport. |
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Term
| MECHANISM OF ADH SECRETION |
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Definition
Stimulation of hypothalamic nuclei results in axon potentials to the posterior pituitary.
Resultant calcium influx mediates exocytosis of secretory granules. |
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Term
| QUIZ: Osmolal is body’s way of measuring total water. Water balancing mechs assume Na conc is matched to the water content! Where is this detected? |
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Definition
Osmoreceptors in third ventricle, outside the blood brain barrier, respond to small increases in "effective" osmolality.
Osmoreceptor stimulation results in stimulation of ADH producing cells and release of ADH.
When too much water you get hypoosm/hyponatriemia feedback to hypothalamus. |
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Term
| T/F: When plasma osmolality is below threshold, ADH is not secreted. |
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Definition
T, but Above threshold, ADH secretion is proportional to the increase in osmolality.
Under most circumstances, osmolality is the only important regulator of ADH secretion. |
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Term
| T/F: Decreased activity of only low pressure receptors triggers secretion of ADH. |
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Definition
F:
Decreased activity of low pressure or high pressure receptors can trigger secretion of ADH.
Usually this only happens after substantial changes in blood pressure or volume.
When baroreceptor stimuli are present, they override the effects of osmolality QUIZ this explains SIADH secretion |
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Term
| T/F: Baroreceptors override the effects of osmolal receptors in the 3rd ventricle |
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Definition
| TRUE - this explains SIADH secretion |
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Term
| Name some STIMULATORS OF ADH SECRETION |
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Definition
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Term
| T/F: ADH's effects can last up to 3 hours |
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Definition
F
Circulates in an unbound form
Short half life (4-8 minutes) |
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Term
| Name ADH's renal and vascular effects |
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Definition
Renders collecting duct permeable to water
Increases sodium reabsorption in the thick ascending limb of Henle
Aquaporins are membrane proteins that act as water channels.
ADH stimulates translocation of aquaporin to the membrane of collecting duct cells.
Vascular: Potent vasoconstrictor
Vasoconstrictive effects are probably only important in states of severe hypovolemia or hypotension. |
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Term
| V1 vs. V2 receptors for ADH? |
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Definition
V1 receptors mediate vascular smooth muscle effects
V2 receptors are present in renal tubular cells. Their effects are mediated by cAMP |
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Term
| You give a patient with ADH deficiency dDAVP. T/F: This drug binds to both V1/V2 receptors. |
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Definition
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Term
| T/F: both baroreceptors and osmoreceptors signal thirst |
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Definition
T:
Thirst centers are located in the hypothalamus, near the supraoptic and paraventricular nuclei
Respond to stimulation of osmoreceptors
Increased osmolality is a potent thirst stimulator
Decreased osmolality does not appear to suppress thirst
Decreased baroreceptor stimulation increases thirst
Angiotensin II, within the brain, is a mediator of increased thirst center activity |
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Term
| T/F: An excess of water suppresses ADH secretion, suppresses thirst, and increases renal water excretion. |
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Definition
| F (thirst is usually not suppressed) |
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Term
| OXYTOCIN: SYNTHESIS AND SECRETION |
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Definition
Nine amino acid peptide, all but two amino acids are the same as ADH.
Synthesis and storage are identical to ADH
Oxytocin has a different neurophysin than ADH.
Suckling triggers nerve endings at nipple
Uterine stretch |
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Term
| Mechanism of oxytocin in => labor and lactation: |
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Definition
Labor:
At the end of pregnancy, myometrium is highly sensitive to oxytocin
As labor progresses, increasing oxytocin levels cause uterine contraction
Postpartum, oxytocin induced myometrial contraction is important in minimizing blood loss
Oxytocin is sometimes used to induce labor
Milk:
Milk secretion requires contraction of myoepithelial cells lining alveoli
Oxytocin simulates contraction of myoepithelial cells, without it, lactation does not occur |
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Term
| T/F: ADH levels tell you whether a patient has a deficiency or not. |
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Definition
F: Can’t rely on low ADH level to make the deficiency a diagnosis
So you DEPRIVE the px of water!!! Water depletion => higher plasma osm and Uosm is LOW….px should hae been concentrating it…means ADH deficiency! But if you give them ADH…NOW then it gets more concentrated! |
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