04 Tubular Function Flashcards
(10 cards)
Define osmolarity
a measure of the osmotic pressure exerted by a solution across a perfect semi-permeable membrane
True or false: active transport does not have maximum rate of transport as long as there is unlimited energy supply
False. Every transporter/carrier protein has its own capacity. Only passive diffusion has no rate limit
What are the substances that are secreted
K+, H+, creatinine, choline, penicillin and other drugs
How much of solutes are reabsorbed in PCT
How much Na+ is reabsorbed in descending loop of Henle and DCT
Overall: 60 - 70%
Na+: 65%
Glucose: 100%
Bicarbonate: 90%
Na+: 20% and 8%
What is the significance of PCT in homeostasis of acid
There are carbonic anhydrase in the lumen and epithelial cells with Na+/H+ exchanger. Reabsorption of Na+ is coupled to removing H+ into the lumen for excretion
Describe the ion transporter in ascending loop of Henle and explain its significance clinically
Cl- is actively reabsorbed which drag Na+ in and bicarbonate. This triple transporter is blocked by loop diuretics to reduce reabsorption
What are the transporters on DCT that can be clinically important
Luminal: Na+/Cl- symporter; Ca2+ channel
Basolateral: Na+/K+ ATPase; Na+/Ca2+ exchanger
Thiazide diuretics bind to Na+/Cl- symporters which will result in the reduction of Na+ in the cytosol. In order to regain the concentration, Na+/Ca2+ exchanger has to increase its activity and cause more reabsorption of Ca2+ into plasma
What causes renal tubular acidosis and what causes it
Hypercholermic metabolic acidosis, hypokalaemia and impaired growth
Caused by the impaired Na+/Cl- exchanger in late PCT
What is Barrter syndrome
Impairment of triple cotransporter resulting in excessive electrolyte secretion and moderate metabolic alkalosis
What is Dent disease
Fanconi syndrome
Increased excretion of larger molecules such as proteins due to impairment of CICR-5 which is a H+/Cl- exchanger on endosome
