Posterior PItuitary Flashcards
The primary determinant of free water excretion in humans is the regulation of urinary water excretion by circulating levels of
arginine vasopressin (AVP) [antidiuretic hormone {ADH}] in plasma.
where is ADH stored?
In the posterior pituitary in large amounts
The supraoptic and paraventricular nuclei of the anterior hypothalamus synthesize AVP, package it into granules, and transport the granules along their axons to nerve terminals in the
posterior lobe of the pituitary (the magnocellular neurons).
Levels of circulating AVP depend on both the
rate of AVP release from the posterior pituitary and the rate of AVP degradation.
The major factor controlling AVP release is _____The half-life of AVP in the circulation is 18 minutes. Diseases of the liver and kidney may impair AVP degradation and may thereby contribute to water retention.
plasma osmolality.
ADH binds to the V 2 receptor (a G-protein-linked receptor) on the basolateral membrane of the _______, and activates adenylyl cyclase increasing the intracellular concentration of cyclic adenosine monophosphate (cAMP).
renal collecting tubule
cAMP binds to the regulatory subunits of protein kinase and induces a conformational change, causing these subunits to dissociate from the catalytic subunits. These activated subunits (C) as shown here are anchored to an ______containing endocytic vesicle via an A-kinase anchoring protein (AKAP).
aquaporin-2 (AQP2)
When AVP is not available, what happens to AQP2?
AQP2 water channels are retrieved by an endocytic process, and water permeability returns to its original low rate. AQP3 and AQP4 water channels are expressed constitutivelyat the basolateral membrane
What is the end result of ADH release?
increase AQP2 translocation to the renal tubulels to REABSORB water into the body thus you should get hypertonic urine in normal perso
The release of ADH in response to changes in volume or pressure is less sensitive than the release in response to osmoreceptors, and generally a ______ reduction in blood volume or pressure is needed to stimulate the release of ADH
. However, once arterial pressure falls below this threshold, the stimulated response is exponential, and plasma levels of ADH are markedly greater than those from osmotic stimulation.
10 to 15%
The collecting duct is the primary site of ADH response, which leads to
urine concentration
Increases in plasma osmolality above approximately 290 to 295 mOsm/kg result in increases in plasmaADH but no further concentration of the urine, which is limited by
the maximal osmolality in the inner medulla.
• Urine volume does not change substantially until there is nearly absent ADH secretion, after which urine volume
increases dramatically.
defined by continuous inappropriate secretion of ADH, despite normal or increased plasma volume, causing impaired water excretion and resulting in hyponatremia and hypo-osmolality
SIADH
Symptoms associated with SIADH
depend upon the rate of onset and degree of hyponatremia.
Rapid or severe hyponatremia/hypo-osmolality leads to acute edema of the brain cells. :neurological symptoms that range from headache, apathy, agitation, muscle cramps, weakness, and may develop into confusion, seizures, and coma
Etiologies of SIADH
Cerebral, Drugs, lung disease, miscellaneous
The cardinal feature of SIADH is______, and often this is an incidental lab finding without any obvious clues in the history or physical examination.
hyponatremia
You order labs for a pt and notice they are HYPOnatremic, you know this can be caused by SIADH, What lab would you order next?
Measure pts serum osmolality:
are they isotonic, hypertonic or hypotonic
*PT with SIADH will have HYPOtonic serum osmolality
YOu are doing a work up on a pt while rotating through endocrinology. They are hyponatrermic and has a HYPOtonic serum osmolality. What would you do next if you suspect SIADH?
Assess pts volume status
for SIADH, most are Euvolemic
Pt is:
HYPOnatremic
HYPOtonic (<275) serum osmolality
Euvolemic
what is the next step of your work up for SIADH?
Get urine osmolality:
>100 = SIADH/hypothryoidism or adrenal insuffuciency
If <100 they have water intoxication
What do we expect for pt with SIADH
Hypo/hypernatremic
serum osmolality:
volume status:
urine osmolality:
HYPOnatremic
Hypotonic (<275) for serum
Euvolemic
>100 for urine osmolality