1 B io F actsheet September 1997 Number 1 The kidney: excretion and osmoregulation Kidneys have two main functions. 1. They are excretory organs, removing nitrogenous and other waste from the body. 2. They play an important part in maintaining a constant internal environment by helping to regulate pH, water and sodium ion concentrations in the blood and tissues. This Factsheet will focus on the role of the kidney in excretion and osmoregulation. Excretion Surplus nitrogen-containing compounds such as amino acids have to be broken down in the body because they are toxic and are then excreted as ammonia, urea or uric acid (Table 1). Table 1. Nitrogenous excretory products Renal corpuscle Proximal convoluted tubule Distal convoluted tubule Collecting duct Ascending limb