The Proximal Tubule Flashcards
How is the apical membrane specialised for transport?
Microvilli to increase surface area
High endocytic concentration
How is the basolateral membrane specialised for transport?
Infolding to increase surface area
Describe sodium coupled nutrient reuptake
A sodium gradient is set up across the basolateral membrane via Na/K/ATPase
Sodium coupled cotransport of nutrients occurs across the apical membrane
Describe reabsorption of carbonate ions
A sodium gradient is set up across the basolateral membrane via Na/K/ATPase
The Na/H exchanger exchanges sodium for hydrogen ions across the apical membrane
Membrane bound carbonic anhydrase in the lumen converts carbonate and a proton to carbon dioxide and water
Carbon dioxide and water diffuses through the membrane
Intracellular carbonic anhydrase converts carbon dioxide and water back into a proton and carbonate
The proton is pumped into the lumen via Na/H exchanger and H ATPase
The Na/carbonate and Cl/carbonate channels pump carbonate out of the cell across the basolateral membrane
Describe the process of chloride handling
A sodium and potassium gradient is set up across the basolateral membrane via Na/K/ATPase
Sodium is exchanged for hydrogen across the apical membrane
Hydrogen cation is converted to a hydrogen anion in the lumen and diffuses back into the cell
The hydrogen anion is exchanged for chloride using an anion exchanger
Potassium and chloride are cotransported across the basolateral membrane
Chloride will also be diffused paracellularly with sodium
What affect does chloride handling have on luminal charge?
The luminal contents are slightly positively charged compared to the cell contents
Describe the process of organic anion secretion
A sodium gradient is set up across the basolateral membrane via Na/K/ATPase
Sodium is brought back into the cell via cotransport with alpha ketoglutarate
Alpha ketoglutarate is exchanged for an organic anion at both the apical and basolateral membrane, causing the organic anion to enter then leave the cell
The organic anion may leave the cell via facilitated diffusion, or become protonated to diffuse freely
Describe the process of organic cation secretion
The organic cation is brought into the cell via facilitated diffusion
The organic cation leaves across the apical membrane either by facilitated diffusion or exchange for a proton
What may alter bioavailability of drugs in relation to organic ion secretion?
The ion transporters can become saturated which reduces their rate of secretion
Describe how protein is reabsorbed and processed
Any protein filtered will be collected by vesicles and endocytosed
The protein will be then degraded in the cell
Describe what happens to chloride concentration in the proximal tubule
It increases
Bulk sodium reabsorption causes water reabsorption
Less water = higher chloride concentration
Describe what happens to sodium concentration in the proximal tubule
It remains constant due to water following sodium
Define clearance
A volume of plasma that is cleared of a substance in a given time
When does clearance = GFR
When absorption and secretion rates are 0
What substances are not secreted or reabsorbed?
Inulin and creatinine
