General Structure and Function of the Urinary SystemThe urinary system is a special excretory system that plays several roles in maintaining homeostasis. A primary function is the excretion of urea, a major nitrogen-containing waste product derived from the catabolism of amino acids. More generally, this system regulates the chemical composition and pH of the blood by analyzing and adjusting the levels of major ions (including H+), nutrients, and other important substances in the blood. Finally, the urinary system is responsible for maintaining the proper amount of water in the body, a major determining factor in the concentrations of all solutes present in an organism. Anatomically, the urinary system consists of the following (see Figure 16.3):
- Kidneys: The kidneys, located dorsally behind the stomach and liver, are the major organs of the urinary system. They filter blood, analyze its composition, and form urine that will ultimately be expelled from the body. Each kidney is divided into an outer cortex region, and an inner medulla.
- Ureters: These tubes transport urine from each kidney to the urinary bladder.
- Urinary bladder: This sac-like structure stores the urine until enough of it has collected to be expelled
- Urethra: The urethra is the tube through which the urine ultimately exits the body