Explain how the Proximal Convoluted Tubule reabsorbs solute and solvent out of the urine into the blood.

 

PCT absorb 70% of filtered sodium, chloride, bicarbonate and water and almost 100% of filtered potassoum, aminoacid and glucose

Mechannism of glucose absorbtion

• glucose and sodium bind to same carrier I. E. SGLT 2 in luminal membrane and glucose is carried into cell as sodium move down to electrical and chemical gradient
• SSodium is pumped out of cell into lateral intercellular space and glucose moves intoperotubular capillaries via GLUT 2 by simple diffusion
• GGlucose transport across PCT cell is example of secondary active transport
• EEergy is provided by sodium potassoum pump

Mechanism of sodium reabsorbtion

• Through apical membrane sodium is transport through apical membrane passively down an electrical and chemical gradient by facililated diffusion
• TThrough basolateral membrane intracellulat sodoumnks actively pumped out of cell into lateral intercellular space

MMechanism of potassium reabsorbtion

• ??po?otassium reabsorbtionoccur by active transport

Mechansim of bicarbonate reabsorbtion

• AApp 90% of filtered bicarbonate is reabsorbed into PCT by secondary active transport by sodium -hydrogen exchanger
• Secret hydrogen iom with filtered bicarbonate to form carbonic acid
• CCarbonic annhydrase catalyses the rapid dehydration of bicarbonic acid to form. Carbon dioxide and water
• Both carbon dioxide and water diffuse back into PCT cell which together with carbondioxide derived from cel metabolism is rehydrated by intracellular CA and bicarbonate which dissociate to form Hydrogen ion and bicarbonate ion

mechansim of water reabsorbtionii

• It is active site for reabsorbtion of many substances eg glucose, sodium, bicarbonate, chloride
• IIt act as passive site for reabsorbtion of 75-80% of water by osmotoc gradient set by actuve transport of solute