Urine Formation

Filtration: removing maximum waste from the blood At the Glomerulus there is very high pressure that filters a lot of stuff out of the blood stream and into the nephron (at the bowman’s capsule) Things that move out of the blood stream: o Water o NaCl (and other salt/ions) o Glucose o Amino Acids o H+ o Urea/Uric Acid Things that stay in the blood: o Plasma proteins (to big to fit through the “filter”) o Blood cells (also too big) o Some water, salts, glucose, amino acids and H+ stay in behind in the blood

Reabsorption: bringing as much “good stuff” back into the blood as possible All along the Proximal Convoluted Tubule and Loop of Henle your nephron actively transports glucose, amino acids and Na+ ions BACK into the blood (Negative ions, such as Cl-, will also move back into the blood because they are following the Na+) All of this material moving back into the blood concentrates the blood, which them causes water to follow the osmotic gradient and ALSO move back into the blood.

This is GREAT because it makes sure you have most of the good stuff in your blood stream, and your urine is mostly concentrated waste with a bit of water. Unfortunately, reabsorption accidentally brings some wastes back into the blood stream (urea, uric acid, ammonia, some extra H+)

Secretion: bringing as much “bad stuff” back out of the blood as possible Along the distal convoluted tubule the nephron actively transports that small amount of waste that snuck into the blood during reabsorption BACK out of the blood again Some water also goes into the urine during this process, and so does histamine, excess minerals and any drugs in your system. Then the urine is all collected in the collecting ducts, and carried to the bladder through the ureters (to eventually leave the body)