Blood is got to the kidney via renal artery. The renal artery divides into a great number of arterioles and capillaries, mostly in the cortex. Each arteriole leads to a glomerulus. The pressure in the glomerulus causes part of the blood plasma to leak the capillary walls. The RBC's and proteins in plasma r too big to pass out. The fluid that moves out contains mainly water with dissolved salts, urea, glucose and uric acid. The process by which the fluid is filtered out of the blood by the glomerulus is called ultrafiltration. The filtrate from the glomeruls collects in the renal capsule and trickles down the renal tubule. As it does so, the capillaries which surround it absorb the substance the body needs. All the glucose is absorbed, with much of the water(depends on the state of hydration). The some salts r taken back to keep the correct con in the blood. This process of taking back the required substances is called selective reabsorption.
Substances that r not needed pass further down to the collecting duct into the pelvis of the kidney. From here the fluid, now called urine, passes down the ureter to the bladder.
Nephron- A single glomerulus with its renal artery, renal tubule and blood capillaries
visit the site for a good animation
http://www.biologymad.com/resources/kidney.swf
