Blog 4: Nephron

Nephrons and blood vessels that are associated in the process are the functional units of mammal kidney. A nephron consists of a single long tubule and a ball of capillaries called the glomerulus. Each human kidney has about a million nephrons. Excretory tubules that contains nephrons and collecting ducts and associated blood vessels are packed inside the kidney. Fluid from several nephrons flows into a collecting duct and from there a ureter conveys urine from the renal pelvis to the urinary bladder. The nephrons control the composition of the blood by filtration, secretion, and re-absorption. The counter current system present in the loop of henle is able to dilute or concentrate urine depending on what the body needs. In the descending limb, ions such as salts has very little permeability, only water is permeable here. The water moves by osmosis into the hyper osmotic interstitial fluid and salt diffuses out of the concentrated filtrate as t moves through the salt-permeable ascending limb of the loop of Henle.

SOURCES: Campbell book
http://science.howstuffworks.com/environmental/life/human-biology/kidney.htm