Flashcards in Lecture 9: Regulation of Water Balance and Body Fluid Osmolality (Bolsor) Deck (28):
what structures sense a change in blood pressure? What do they signal to effect a change in BP?
osmoreceptors and baroreceptors. Signal the hypothalamus to "make a decision" about whether an action is needed to regulate BP
What does hypothalamus secrete to cause kidney to change body water content?
see flow charts pg. 82/83 scavma notes
what part of kidney does ADH act on?
late distal tubule and collecting ducts on the peritubular side
What does ADH do specifically?
activates adenylate cyclase which causes insertion of water channels into the luminal membrane of the distal nephron
2 main compartments of body fluid. Which is larger?
intracellular and extracellular. Intracellular compartment is larger
How does body compensate when there is a loss of volume from the extracellular compartment?
Water moves into the extracellular compartment from the intracellular compartment to compensate for the loss. Therefore, hemorrage involves loss of volume from BOTH extracellular and intracellular compartments
Primary controlling factor in how the kidney handles water
Where is ADH stored? Where is it released?
Stored: posterior pituitary
Released: supraoptic nucleus projecting from the post. pituitary
What happens if the thirst area of the hypothalamus has a lesion?
Animal will not have sensation to drink
Most potent stimulus of ADH release
plasma osmolality. Increased plasma osmolality increases ADH release.
What is unique about the osmoreceptors in the anterior wall of the third ventricle?
Area lacks a blood-brain barrier. These osmoreceptors signal plasma osmolality for ADH release
How does blood volume effect ADH release?
Increased blood volume inhibits ADH secretion, decreased blood volume increases ADH secretion
T or F: decreased blood volume elicits greater ADH amounts released than osmolality
Where are sensory receptors responsive to blood volume located? How do they function?
atria and large veins. The receptors
About how much blood loss (%) can be tolerated before large amts of ADH are release?
hyposmotic plasma --> thirst/intake of water
hyperosmotic plasma --> thirst/intake of water
Once body water content is normalized, what happens to osmoreceptors and baroreceptors?
They stop signaling hypothalamus to make a change
Where does ADH act?
peritubular side of late distal tubules and collecting ducts of kidney
HOW does ADH act?
1) activates adenylate cyclase via a G protein mediated system on the basal membrane of collecting duct principal cells
2) triggers increased formation of cAMP
3) triggers cAMP-dependent protein kinase C to release vesicles with aquaporins that bind to apical membrane of cell. This ultimately increases water absorption from lumen of collecting duct into collecting duct principal cells.
T or F: only the apical/luminal membrane of the collecting duct principal cells is variably permeable to water depending on how much ADH is present.
True. The basolateral membrane is not effected by ADH; its conductance of H2O is always high.
Verney experiment: Explain what happens to urine flow if pituitary gland NOT removed (normal state) and 1) ingestion of H2O increases, 2) NaCl injected IA (into carotid a.) and 3) ADH injected IV
1) urine flow increases
2) urine flow decreases, even though the animal is not dehydrated
3) urine flow decreases, even though the animal is not dehydrated
Verney experiment: Explain what happens to urine flow if pituitary gland is removed (abnormal state) and 1) ingestion of H2O increases, 2) NaCl injected IA (into carotid a.) and 3) ADH injected IV
1) urine flow increases
2) urine flow doesn't change (normally it would decrease)
3) urine flow decreases (kidney was able to respond even though PP was removed)
How do you differentiate primary polydipsic, hypothalamic, or nephrogenic causes for high urine flow in a patient?
Withhold water from the patient and measure urine osmolality with and without ADH:
-If urine osmolality goes up without adding ADH, animal is primary polydipsic (they have an excessive need to drink but can in fact concentrate urine normally; result of various disease states)
-If urine osmolality only goes up after ADH is added, animal's problem is hypothalamic (in the hypothalamus) and the kidneys can only concentrate urine when ADH given
-If urine osmolality doesn't go up at all even with addition of ADH, problem is nephrogenic (in the nephrons of the kidney)
see graph on bottom of p.85
excretion of large volumes of urine