lecture 18 (T3)- renal regulation of ion concentrations Flashcards
Where does most potassium reabsorption occur
proximal convoluted tubule
what cell plays a major role in the secretion of potassium
principal cells
what plays a major role in stimulating potassium excretion by the kidney tubule
aldosterone
approximately how much of the body’s supply of calcium is stored in bone
99%
what does metabolic acidosis due to extracellular potassium concentration
increases it
how much of filtered calcium is excreted by the kidneys
1%
what cell reabsorbs potassium during potassium depletion
intercalated cells
what effect would high potassium intake have on potassium excretion associated with increased renal tubule flow rate
potassium excretion would increase with increased tubular flow rate
what is extracellular potassium normally precisely regulated at
4.2mEq/L
how much of total body potassium is in extracellular fluid
2%
what is the normal intracellular concentration of potassium ion
140mEQ/L
what does an increase in extracellular potassium do to aldosterone
increases aldosterone secretion
where does reabsorption of potassium occur
proximal tubule and ascending limb of henle
where does secretion of potassium occur
late tubule and collecting duct
what is potassium secretion by principal cells stimulated by
potassium concentration and aldosterone
what does blockage of the aldosterone system impair
regulation of potassium concentration
how much of plasma calcium is in the ionized form
50%
define acidosis
less calcium is bound to the plasma proteins
define alkalosis
more calcium is bound to the plasma proteins
what are parathyroid glands directly stimulated by
low calcium levels
what are the effects of PTH
stimulates bone reabsorption
stimulates activation of vitamin D
indirectly increases tubular calcium reabsorption
how is most of the calcium reabsorption in distal tubule done
via active transport (calcium ATPase pump in basolateral membrane that is stimulated by PTH)
what factors regulate tubular calcium reabsorption
increased level PTH
plasma concentration of calcium
metabolic acidosis
what happens if phosphate concentration is less than 0.1
all filtered phosphate is reabsorbed
what happens if phosphate concentration is greater than 0.1
excess phosphate is secreted
what pathway is 75-80% of phosphate reabsorbed in proximal tubule
transcellular pathway
what effect does insulin have on regulating extracellular potassium
stimulates potassium uptake by cells
define hypokalemia
excess secretion of aldosterone (conn’s syndrome)
low potassium in blood
define hyperkalemia
deficiency in aldosterone secretion (addison’s disease)
high potassium in blood
what does aldosterone do in regards to potassium
increases potassium uptake by cells
stimulates active reabsorption of Na+ by principal cells via Na+k+ ATPase pump
increases permeability of luminal membrane for K+
increases extracellular K+
what do catecholamines do in regards to regulating extracellular potassium
beta-adrenergic stimulation (epinephrine): stimulates potassium uptake by cells
beta-adrenergic receptor blockers: hyperkalemia
what are things that can cause hyperkalemia
cell lysis
strenuous exercise
increased extracellular fluid osmolarity
what is the normal rate of potassium filtration
756 mEq/day
what is the normal rate of potassium reabsorption
65% in proximal tubule
25-30% in loop of Henle
where are principal cells found
late distal tubule and cortical collecting tubules
what does increased tubular flow rate do to K+ secretion
stimulates it
how do intercalated cells reabsorb K+ during K+ depletion
possibly through a H+K+ ATPase pump
secrete H+ into tubular lumen
what does high levels of angiotensin II do to arterial pressure
increases it and this is necessary to increase sodium excretion
how can normal levels of sodium be maintained when there is reduced angiotensin II levels
maintained at reduced arterial pressures
