One quarter of the total ~blood~ output from the |heart| comes to the |kidneys| along the ~renal~ arteries. The incoming |artery| divides up repeatedly inside the |kidney|, eventually forming |arterioles|, each one of which leads to the |Bowman's capsule|. The tiny, thin walled |capillaries| branch from the |arterioles| and form a compact ball known as the glomerules. These |capillaries| then reunite to form the |arterioles| which leaves the |capsule|. The capillary walls of the |kidney| consist of many minute pores, which are so small that they act, in effect, like a filter, allowing water, glucose, salts, amino acids, |vitamins|, and ~urea~ from the ~blood~ to pass through into a tubule, but preventing the passage of |blood cells| and |proteins|. Every minute 125 ccs (1/4 pint) of fluid is filtered through the |capillaries|. This fluid contains about one kilo (2 1/2 pounds) of sodium chloride, .45 kilo (1 pound) of sodium bicarbonate, and .15 kilo (1/3 pound) of glucose. The body then reabsorbs about 99% of the fluid back into the ~blood~ stream. The |kidney| filters and reabsorbs the body's ~blood~ supply nearly fifteen times every day, which results in a remarkably thorough cleaning operation.
