Reabsorption and Secretion Flashcards
What limits how much of a substance can be reabsorbed?
Transport capacity. The transporters can become saturated
What is the renal threshold?
When the transporters are saturated and can’t absorb all the substrate at high concentrations
What are the primary sites for reabsorption and secretion?
Proximal and distal tubules
What are the 2 substances reabsorbed by the proximal tubule?
Glucose and Na+
Which transporter on the apical surface of the proximal tubule transports glucose?
Na+/glucose symporter. Secondary active transport
What is the other transporter besides the Na+/glucose symporter that brings sodium into the proximal tubule cells?
Na+/H+ antiporter
Where do the protons powering the Na+/H+ antiporter in the proximal tubule cells come from?
Metabolism
How does chloride get into the proximal tubule cells?
Follows the sodium into the blood through the paracellular path
How does glucose in the proximal tubule get into the bloodstream?
Glucose permease on the basolateral membrane
What do the proximal tubules secrete?
Organic ions, water soluble toxins and drugs
What are the 3 transporters in the proximal tubules that secrete drugs?
Organic cation transporters (OCT), ATP-dependent multidrug resistant transporters (MDR), organic anion transporting polypeptide transporters (OATP)
What do the distal tubules reabsorb?
Calcium and some Na+ and Cl-
What are the transporters on the apical membrane of the distal tubule cells?
Calcium channels, Na+/Cl- symporter, K+ channel into the urine
What are the transporters on the basolateral membrane of the distal tubule cells?
Na+/K+ ATPase, chloride channels, Ca2+/Na+ antiporter, calcium active transport
What does the loop of Henle do?
Generates an osmotic gradient to concentrate the urine and pull out most of the water
