Renal urea handling is the part ofrenal physiology that deals with thereabsorption andsecretion ofurea. Movement of large amounts of urea across cell membranes is made possible byurea transporter proteins.
Urea allows thekidneys to createhyperosmotic urine (urine that has more ions in it - is "more concentrated" - than that same person'sblood plasma). Preventing the loss of water in this manner is important if the person's body must save water in order to maintain a suitableblood pressure or (more likely) in order to maintain a suitable concentration ofsodium ions in the blood plasma.
About 40% of the urea filtered is normally found in the final urine,[1] since there is more reabsorption than secretion along thenephron.
It is regulated byantidiuretic hormone, which controls the amount reabsorbed in thecollecting duct system and secreted into theloop of Henle.
| Characteristic | Proximal tubule | Loop of Henle | Distal convoluted tubule | Collecting duct system | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| S1 | S2 | S3 | descending limb | thin ascending limb | thick ascending limb | connecting tubule | initial collecting tubule | cortical collecting ducts | medullary collecting ducts | ||
| reabsorption (% compared to filtered amount) | 50[1] | 50 | |||||||||
| secretion (% compared to filtered amount) | 50[1] | ||||||||||
| reabsorption (mmoles/day) | |||||||||||
| concentration | |||||||||||
| electrical driving force (mV) | -3[2] | +3[2] | +15[2] | -5 to +5[2] | -40[2] | ||||||
| chemical driving force (mV) | |||||||||||
| electrochemical driving force (mV) | |||||||||||
| apical transport proteins |
|
| |||||||||
| basolateral transport proteins |
|
| |||||||||
| other reabsorption features | |||||||||||