The nephron is the basic, functional unit of the kidney. Each kidney has 1 million nephrons packed into the cortex. It has three main parts: the glomerulus, the Bowman's Capsule, and the tubule (divided into the proximal tubule, distal tubule, the Loop of Henle). The nephron restores essential nutrients and water into the bloodstream, and removes waste products from the blood through tubular reabsorption and tubular secretion. In tubular reabsorption, proximal tubule cells remove water and nutrients from the filtrate and they are returned to the bolood while wastes are kept in the tubule. IN tubular secretion, wastes not filtered in the Bowman's Capsule are removed from the blood by the distal tubule. The filtrate flows through the proximal tubule to the Loop of Henle, which concentrates the flitrate by removing more water from it, and the concentrated filtrate then flows through the distal tubule to the collecting duct. The filtrate is now called urine and the collecting duct prepares the urine for transport. Afterwards, it is collected in the renal pelvis and goes through the ureter to the bladder.
The way the nephron works is similar to countercurrent exchange. Solutes are exchanged as the nephron returns nutrients to the blood and removes wastes from the blood. The kidney has a countercurrent multiplier system where it allows the kidney to maintain high concentrations of solutes, which is essential to the kidney's function of removing wastes from the blood.
Below is a mind map on kidney function:
Sources:
information from: Campbell and Reece's Biology, Sixth Edition
nephron picture from: http://www.irvingcrowley.com/cls/nephron.htm
countercurrent picture from: http://en.wikipedia.org/wiki/Countercurrent_exchange
hydrostatic skeleton picture from: http://www.emc.maricopa.edu/faculty/farabee/biobk/biobookmusskel.html
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