lecture 22: water balance

Question 1

aquaporins (AQPs)

Answer 1

transmembrane channel proteins, allows water to pass through lipid membrane

Question 2

AVP (arginine vasopressin) / ADH (antidiuretic hormone)

Answer 2

changes water permeability of collecting tubules to promote reabsorption

causes vessel constriction

Question 3

osmoreceptors

Answer 3

sensitive to changes in extracellular fluid osmolarity
increased osmolarity > sensed by osmoreceptors > AVP secretion > water reabsorption

Question 4

describe the process in which AVP has an antidiuretic effect

Answer 4

AVP binds to receptors
adenylate cyclase is activated and produces cAMP
cAMP translocates AQP-2 from intracellular vesicles to the apical plasma membrane, allowing for water reabsorption

AQP-2 reinternalized when AVP is removed

Question 5

AQP-3 and AQP-4

Answer 5

exit channels for water that is not absorbed into cells
AQP-4 not affected by AVP

Question 6

baroreceptors

Answer 6

detects increase in blood volume > inhibits AVP secretion > low water reabsorption, high excretion

hypovolemia > baroreceptors not stimulated > secretion of AVP

Question 7

Describe the process of AVP-mediated water reabsorption.

Answer 7

AVP binds to receptors > Adenylate cyclase activated > produces cAMP > cAMP promotes AQP-2 translocation to apical membrane, allowing water reabsorption > AQP-2 reinternalized in the cell, when AVP removed, stopping water reabsorption.
AVP also stimulates AQP-3 which is the exit channel for water absorbed in cells