The kidney is a pair of bean-shaped organs located in the abdominal cavity one on each side of the spine. The right kidney being slightly lower than the left which is slightly bigger than the right.
The kidneys perform many vital functions. The kidneys regulate electrolytes, blood pressure, acid-base balance, extra-cellular fluid volume, blood pressure and other homeostatic functions. This is done independently or in collaboration with other vital organs like the urinary bladder, the heart and the brain.
They are natural blood filters and channel wastes removed to the urinary bladder for excretion in the urine. Kidneys produce hormones like renin, erythropoietin and calcitriol. Renin is a hormone that affects blood pressure. The long term blood pressure regulation depends mostly upon the kidney. Even though the kidneys do not directly determine blood pressure, the increase or decrease in sodium chloride absorption of the kidney affects the blood pressure. Erythropoietin is a hormone that stimulates erythropoiesis or the production of red blood cells in the bone marrow. Those who lack erythropoietin become anemic and in some cases require blood transfusion. Calcitriol is a form of Vitamin D responsible for the intestinal and renal reabsorption of phosphate. They are also responsible for the reabsorbtion of water, glucose and amino acids.
Among human, one kidney can be enough to sustain him. However, when the kidney function is inefficient a condition known as chronic kidney disease will develop. This will require painful and expensive dialysis or kidney transplant if a suitable match is found.