For example, they convert a precursor of vitamin D to its active form, calcitriol and synthesize the hormones erythropoietin and renin.Ĭhronic kidney disease (CKD) has been recognized as a leading public health problem worldwide. The kidneys also carry out functions independent of the nephrons. Each adult human kidney contains around 1 million nephrons, while a mouse kidney contains only about 12,500 nephrons. The nephron is the structural and functional unit of the kidney. Examples of substances secreted are hydrogen, ammonium, potassium and uric acid. Examples of substances reabsorbed are solute-free water, sodium, bicarbonate, glucose, and amino acids. Filtration occurs in the glomerulus: one-fifth of the blood volume that enters the kidneys is filtered. The kidney participates in the control of the volume of various body fluids, fluid osmolality, acid–base balance, various electrolyte concentrations, and removal of toxins. Each kidney is attached to a ureter, a tube that carries excreted urine to the bladder. They receive blood from the paired renal arteries blood exits into the paired renal veins. They are located on the left and right in the retroperitoneal space, and in adult humans are about 12 centimetres ( 4 + 1⁄ 2 inches) in length. The kidneys are two reddish-brown bean-shaped organs found in vertebrates.

Interstilial fluid image