Plan
► Concept of excretory system and its basic functions. Excretory organs.
► Kidney as the main excretory organ. Functions of kidneys.
► Nephron as structural and functional unit ofkidney. Structure of nephron.
► Peculiarities of supply of kidney with blood.
► Juxtaglomerular apparatus.
► Mechanisms of urine formation.
► Neuro-humoral regulatory mechanisms of kidney function.
Concept of Excretory System and of its Basic Functions
During life a living organism produces large amounts of products of metabolism no longer needed by cells and to be removed, or excreted, from the body. Besides, the body must rid itself of toxic and foreign materials, excessive water, salts, medical drugs. Sometimes before being excreted from the body, some toxic substances are neutralized in the liver. For example, such substances as phenol, indole, scatole bind with glucuronic acid and HCl and partly lose their toxicity.
Organs that perform excretory functions, are called excretory organs. They are the kidneys, lungs, skin, liver and gastrointestinal tract. The main function of excretory organs is to maintain constant internal environment in the body. Excretory organs are functionally interrelated which means that a change in the functional condition of one organ affects activity of other organs. For example, excessive evaporation of fluid from the skin at high temperature reduces diuresis. Disorders in excretory processes are fraught with inevitable shifts in homeostasis that may be fatal for an organism.
Lungs and upper airways remove CO2 and water from the body. Besides, most aromatic substances leave the body through lungs, e.g., ether and chloro-
form vapors given in anesthesia, grain oils in alcoholic intoxication. If for some reason kidney fails to perform its excretory function, urea starts to be excreted through mucosa of the upper airways where it breaks down causing a specific smell of ammonia from the mouth. Mucosa of the upper airway can excrete iodine from the blood.