 | Blood forced through capillary wall into Bowman's capsule under high
pressure |
| Filtrate flows through renal tubule (permeable walls) |
| Network of capillaries wrap around renal tubules |
| Composition of blood and filtrate modified at various points along the
length (proximal convoluted tubule, loop of Henle, distal convoluted tubule and collecting
duct) involving filtration, reabsorption and secretion |
| Filtration
 | Blood plasma (1/5) forced out of glomerulus into Bowman's capsule |
| Pressure forces water, nitrogenous wastes, glucose and minerals ->
walls of tubules -> renal tubule |
|
| Reabsorption
| Filtrate -> capillaries |
| Most reabsorption occurs in proximal convoluted tubule |
| 75% water returned by osmosis |
| Glucose, Na+, K+ and Ca++ by active
transport |
| Additional reabsorption occurs in distal convoluted tubule |
|
| Secretion
| Some substances in blood -> filtrate in distal convoluted tubule |
| Blood pH adjusted by secretion of H+ ions into filtrate |
|
| Loop of Henle
| Maintains high concentration of NaCl in extracellular spaces of medulla |
| Cl- ions actively transported from filtrate |
| Na+ follows negatively charged Cl- ions |
| Promotes reabsorption of water |
|
| Concentration
| Urine from several tubules flow into collecting ducts |
| Urine concentrated by osmosis in collecting duct due to high NaCl
concentration in extracellular fluid |
| 99% of water returned to filtrate |
|
| Urinary system
| Collecting ducts -> ureter-> urinary bladder -> urethra |
|
Encarta (MSN)
used as a reference for many of the articles 