The kidneys are paired organs which reside in the dorsal abdomen. One on the left and one on the right. Their role is to filter the blood through the glomerulus to form what is known as the filtrate. This filtrate is then on the whole reabsorbed along the nephron until what is left comprises compounds superfluous to the requirements of the organism. Some compounds, normally fully reabsorbed, are on occasion present in the body in excess. The kidney tubules are able to respond to this excess and excrete such compounds in greater amounts. This is how the kidneys play a major role in the homeostasis of the organism. The kidneys also plays a vital role in the total water balance of the organism. Varying their excretion of water in relation to the hydration status of the animal.
The kidneys receive 25% of the cardiac output. From this they filter 20% of the plasma forming a filtrate of which all but 1% is reabsorbed. This equates to all the circulatory volume being filtered and reabsorbed every 30 minutes. The functions of the kidneys are to maintain the volume and composition of plasma, regulate water, ion and pH levels, retain nutrients and excrete waste, toxins and excess electrolytes. The kidneys achieve these functions via; glomerular filtration, solute reabsorption, tubular secretion, water balance and acid-base regulation.