Ultra-filtration is the separation of different sized molecules under pressure. This process happens in the glomerulus.

The renal artery supplies the cortex of the kidney with blood. The artery then splits into smaller arterioles and again into capillaries, Each bundle of capillaries forms a knot, called a glomerulus, which is enclosed by the Bowman’s capsule. The afferent (carrying blood towards something) arterioles take blood into the glomerulus. The afferent arterioles are WIDER than the efferent arterioles, which take blood out of the glomerulus. This causes a high-pressure difference, and forces molecules such as water, urea, plasma, glucose and salts out through the capillary wall of the Bowman’s capsule. Larger molecules such as protein cannot pass through and therefore stay in the blood.

(the filtrate is know as the glomerular filtrate)  

 

Selective Re-absorption is the process by which useful substances are re-absorbed into the blood. This process happens in the proximal convoluted tubule the distal convoluted tubule, the loop of Henele and the collecting duct. The PCT contains many mitochondria to produce ATP for use in active transport.   The glomerular filtrate passes into the PCT where all the sugars are re-absorbed into the blood via active uptake. Sufficient amounts of ions (salts), are reabsorbed into the blood, again this is via active uptake. In the Loop of Henele, and the collecting duct, water is re-absorbed back into the blood. The amount of water re-absorbed depends on the level of the hormone ADH. Water is re-absorbed via the process of Osmosis. Any substances that are not reabsorbed are lost as urine. (goes into ureta à bladder à excreted). Urine usually contains excess water, ions (salts), dissolved urea, hormones soluble vitamins. ALL RE-ABSORBED SUBSTANCE ARE REGULATED

 

Osmoregulation – is the process of keeping things at the right level. Osmoregulation stops urine from become too concentrated or not concentrated enough. It does this by releasing the hormone ADH.

ADH makes the walls of the collecting duct permeable to water, and hence the more ADH released, the more water is absorbed. The body will do this if it does not have enough water.

If the supplies of water are plentiful, then the amount of ADH released will be reduced, so less water will be withheld.

ADH basically controls the amount of water in the blood!

 

 

 

Found in
Substance	Blood	Filtrate in first tubule	Filtrate in second tubule	Urine
Protein	Yes	No	No	No
Water	Yes	Yes	Yes	Yes
Urea	Yes	Yes	Yes	Yes
Glucose	Yes	Yes	No	No
Salts	Yes	Yes	Yes	Yes