RENAL TUBULE

Three components of the renal tubule

PCT, loop of Henle, and DCT.

Renal tubule transport processes

Reabsorption and secretion involve a combination of diffusion, osmosis, and cell transport to facilitate movement across the plasma membrane.

PCT

Proximal Convoluted Tubule.

PCT function

Reabsorption of water, ions (K+, Cl- and Na+), and all organic nutrients (glucose and amino acids).

PCT reabsorption

Substances are reabsorbed from the filtrate and diffuse back into the blood.

PCT tissue

Simple cuboidal endothelial cells.

PCT cell adaptations

Microvilli facilitate osmosis and diffusion.

Loop of Henle

Consists of descending and ascending limbs.

Loop of Henle: tubular fluid

Filtrate is now called tubular fluid (not yet urine).

Descending limb

Reabsorption of a lot of water; increases solute concentration in tubular fluid.

Ascending limb

Reabsorption of more ions (Cl- and Na+).

DCT

Distal Convoluted Tubule.

DCT function

Reabsorption and secretion.

DCT reabsorption

Reabsorption of ions (Na+).

DCT secretion

Secretion of organic wastes (acids, ammonia, drugs) from blood into the tubular fluid.

DCT and RAAS

The DCT is a key site of regulation for the renin-angiotensin-aldosterone system (RAAS) that adjusts blood volume and pressure.

Collecting duct function

Continues some reabsorption of water and ions from the tubular fluid.

Collecting duct drainage

Drains tubular fluid into the calyces, renal pelvis, and ureter where it is called urine.

Collecting duct pH adjustment

Final pH adjustment is made here.

Collecting duct and blood pH

Bicarbonate ions and H+ are used to maintain blood pH.