Urinary System

The Urinary System, while seemingly related to the Digestive System, isn’t the same thing. Its primary function is to regulate the composition and concentration of the plasma and tissue fluids surrounding the body cells, and to form urine from the blood plasma in the kidneys.

Regulate volume of blood plasma

The kidneys regulate the volume of blood plasma, contributing to blood pressure. They control the concentration of waste products in the blood. They regulate the concentration of electrolytes and contribute to the pH level of the plasma.

The nephron is the functional unit of the kidney, consisting of small vessels carrying blood, which goes through filtration as the blood reabsorbs many materials of value to the body; it secretes substances to be removed from the body, which ends up in urine. Reabsorption of salts and water occurs separately.

Approximately 95% of urine is water, and 5% is solid organic waste (one being urea—toxic to the body), ions and salts. Urea is a product of liver metabolism, created during the conversion of amino acids to energy-supplying compounds.