Kidney The kidney is a paired organ which strongly reminds of a bean. The main task of the kidney is the formation of urine. In addition, the kidney is involved in important physical regulation. This includes regulation of the water and electrolyte balance and regulation of acid base balance. The kidney is an endocrine organ involved in blood pressure regulation and, roughly speaking, erythrocytes (erythrocyte red blood cells) formation. The kidney is found below the diaphragm in the so-called retroperitoneal space (posterior abdominal wall) and is approx. 120-200 g heavy (per kidney). Since every human has 2 kidneys it is a perfect organ to donate (you can get along well with a kidney)