Question

How do the kidneys determine which solutes to reabsorb and the quantity of solvent to reabsorb? Please provide an explaination of any processes involved.

Answer 1

* Various portions(PCT, Loop of henle, DCT and collecting duct) of nephron differ in their capacity to reabsorb water and specific solutes. The reabsorbtion and secretion process occurs passively based on concentration gradients and water is directly regulated by ADH and aldosterone and indirectly by renin.

*The various processes involved for substances move across membranes for reabsorption or secretion includes active transport, diffusion, facilitated diffusion, secondary active transport and osmosis.

* Active transport utilizes energy from phosphate bond of ATP to move a substance across membrane from lower concentration to higher concentration.An appropriately shaped receptor is needed for the transport . For example, Na+/K+ Pump for sodium efflux and potassium influx by using energy from lower concentration to higher concentration.

* Simple diffusion is a process in which substance moves from higher concentration to lower concentration down its concentration gradient. It does not requires energy for transport.

* Facilitated diffusion is similar to diffusion in which movement is down its concentration gradient and requires membrane receptors for movement. It is described in terms of dymport and antiport.