Kidney (Excretory) System

The Excretory (Urinary / Kidney) System consists of two kidneys, two ureters, one urinary bladder and one urethra. After the kidneys filter blood plasma, they return most of the water and solutes to the blood stream. the remaining water and solutes constitute urine,which passes through the ureters and is stored in the urinary bladder until it is excreted from the body through the urethra. The kidneys do the major work of the urinary system.

The paired kidneys are reddish, kidney-bean-shaped organs located just above waist between the peritoneum and the posterior wall of the abdomen.

Functions of kidneys are: 1. Regulating blood ionic composition: sodium (Na+), potassium (K+), calcium (Ca+2), chloride (Cl-), and phosphate (HPO4-2). 2. Regulating blood pH: The kidneys excrete a variable amount of hydrogen ions (H+) into the urine and conserve bicarbonate ions (HCO3-), which are an important buffer of H+ in the blood. Both of these activities help regulate blood pH.