The sebaceous secretion called sebum is not only protective, but also serves as a conduit for excretion of hydrocarbons, sterols and waxes. The main function of sweat is to cool the body down, but it also contains sodium chloride, urea and lactic acid, which are removed from the body in small amounts through sweat. The lungs are responsible for the excretion of carbon dioxide produced by our cells. Saliva has a secretory function, as it carries small amounts of nitrogenous wastes.