Skin hygiene and the urinary system

Metabolic waste leaves the body through several organs: the lungs (carbon dioxide and water), skin (sweat), intestine (undigested residue), but the main excretory organ is the kidney. The urinary system consists of two kidneys, two ureters, the bladder and the urethra. There are two bean-shaped kidneys; they lie at the back of the waist, to the left and right of the vertebrae, each about the size of a fist and weighing about 150 g. In section there are an outer cortex and an inner medulla (pyramids); from the medulla urine passes to the renal calyces and pelvis, then into the ureter. The kidney’s working unit is the nephron; each kidney has over a million nephrons. A nephron consists of a capsule (Shumlyansky–Bowman) containing a capillary tuft and a long tubule. The ureter is a tube 25–30 cm long that carries urine to the bladder. The bladder is a sac with muscular walls where urine collects; a ring muscle (sphincter) in the urethra controls urination.