Excretion by the Nephron

 

(Image source: http://www.ivy-rose.co.uk/HumanBody/Urinary/Urinary_System_Nephron_Diagram.php)

- The renal artery coming from the heart, divides into afferent arterioles, then into a network of capillaries called Glomerulus inside the Bowman's capsule

- Blood is forced into the Bowman's capsule under high pressure ( Ultrafiltration). The high pressure is created because the efferent arterioles are wider in diameter than the afferent arterioles.

-Small molecules such as glucose, water, salt, amino acids and urea are filtered through the membrane of the Glomerulus and Bowman's capsule. Large molecules such as proteins and RBC cannot pass through the membrane.

-At the first proximal convoluted tubule, water (about 80%) and other useful substances (e.g. most glucose) are reabsorbed. (Solutes by active transport or diffusion, and water by osmosis)

-The reabsorbed substances then pass into the capillaries that wrap around the tubule

- In the loop of Henle, reabsorption of water (osmosis) and ions (such as Na+, P+ ) take place (by active transport mainly)

- Final reabsorption takes place in the distal convoluted tubule. The remaining mixture is now called urine, and it enters into the collecting duct. 

-Urine then flows through the ureter, into the bladder, where it is temporarily stored. When the bladder is almost full, the sphincter muscles open, and urine flow along the urethra and out of the body.