The permeability of the walls of the DCT and collecting duct changes in response to ADH hormone.
The DCT filtrate has a high water potential, as ions moved out of ascending limbs, so water leaves the DCT and enters capillaries by osmosis and is carried away.
Down the CD there is an increasing ion concentration (decreasing water potential) in the interstitial fluid moving down the medulla, so there is always an osmotic gradient. Water moves out of the CD by osmosis along the whole length.
Water leaves the CD through aquaporins (channel proteins specific to water).
The filtrate, now called urine, has most of its water, enters the ureter and is stored in the bladder.
Explain how urea is concentrated in the filtrate.
Reabsorption if water by osmosis, at the PCT or descending limb on Loop of Henle.
