renal lecture 3 Flashcards
how is water secreted or reabsorbed?
either paracellularly or transcellularly (through osmosis driven by osmolarity)
where is osmolarity higher?
on the capillary/blood side, so water moves towards that
where is water reabsorbed?
in the proximal tubule, and late distal/collecting duct
where is water reabsorption regulated?
only in the late distal/collecting duct
what is water regulated by?
ADH - antidiuretic hormone
what is water diuresis?
water becomes more dilute (reduces osmolarity with increased volume) to keep solute levels constant
what happens when ADH is low?
hypoosmotic (dilute) urine, high flow, low osmolarity
what happens when ADH is high?
hyperosmotic (concentrated) urine, low flow, high osmolarity
where does ADH come from?
synthesized in hypothalamus, secretion is stimulated by osmoreceptors (detect increased plama osmolarity in hypothalamus) and baroreceptors (detect low blood pressure/volume in left atrium, pulmonary vessels, and aortic arch)
what happens when there is low water intake?
increased plama osmolarity
osmoreceptors in anterior hypothalamus is stimulated
ADH secretion for posterior pituitary increases
increased water reabsorbed
lower volume higher concentration urine
how does ADH increase reabsorbtion?
increases permeability by increasing amount of aquaporin-2 water channels in apical membranes
how does ADH increase aquaporin channels specifically?
V2 receptors couple to G proteins to activate cAMP
PKA is activated and phosphorylates AQP2-P, which increases traffic to membrane
what is a corticocapillary osmotic gradient?
when NaCli is reabsorbed without water in the ascending loop of henle it forms a gradient which decreases using osmolarity in desc limb because it matches osmolarity in interstitial fluid
what happens to the corticocapillary osmotic gradient with low ADH?
urine osmo increases in descending limb because of equilibrium with interstitial fluid, and decreases in ascending limb as salt is reabsorbed
salt is reabsorbed with very little water int eh duct, and final urine is high volume/low osmo
what happens to the corticocapillary osmotic gradient with high ADH?
water permeability in distal tubule and collecting duct increases, allowing water to be reabsorbed (increasing osmotic gradient), urine osmo in desc limb increases, decreases in asc limb, water is reabsorbed in collecting duct, final urine is low volume/high osmo
what is diabetes insipidus?
causes thirst, dehydration, and polyuria
what are the two types of diabetes insipidus?
central and nephrogenic
what is central diabetes insipidus?
failure to secrete ADH from pituitary, caused by head trauma or mutations in ADH gene
what is nephrogenic diabetes insipidus?
failure of kidney to respond to ADH, caused by mutations in V2 receptors or AQP2 water channel genes
