Costanzo Renal Physiology: Phosphate, Calcium, and Magnesium Regulation Flashcards
What proportion of filtered Urea is reabsorbed in the proximal tubule?
about 50%
Other than in the proximal tubule where can urea be absorbed?
ADH can increase the urea permeability of the inner medullary collecting ducts thus contributing to urea cycling of inner medulla.
What factor substantially influences urea excretion?
Water reabsorption and thus urine flow rate influence urea excretion.
(1) high urine flow rate increases urea excretion
(2) low urine flow rate decreases urea excretion
What proportion of filtered phosphate is reabsorbed in the proximal tubule?
About 85%
What proportion of filtered phosphate is excreted?
About 15% (only the proximal tubule reabsorbs phosphate)
What hormone influences the reabsorption of phosphate?
parathyroid hormone activates adenylate cyclase which through cAMP production inhibits the Na+/phosphate co-transporter. This leads to phosphaturia and urinary cAMP.
What proportion of Ca2+ is filtered across the glomerulus?
About 60%
What proportion of filtered Ca2+ is reabsorbed?
More than 90% of filtered Ca2+ is reabsorbed by the proximal tubule and thick ascending loop.
What effect do Loop diuretics have on Ca2+?
loop diuretics inhibit Na+ reabsorption which also inhibits Ca2+ reabsorption because their transport is linked.
What proportion or Ca2+ is reabsorbed in the distal tubule and collecting ducts?
About 8% by an active process.
How is Ca2+ reabsorbed in the distal tubule?
(1) PTH activates adenylate cyclase which leads increased Ca2+ reabsorption in the distal tubule.
(2) Thiazide diuretics increase Ca2+ reabsorption in the distal tubule
Where is Mg2+ reabsorbed?
In the proximal tubule (30%), Thick ascending loop (60%), and distal tubule (5%)
Why does hypermagnesemia cause an increase in Ca excretion and vice versa?
Because Mg2+ and Ca2+ compete for reabsorption in the thick ascending loop of Henle.
