Urinary (excretory) system of Man

It consists a pair of bean shaped organs called kidneys, a pair of ducts called ureters which arise from each kidney, a muscular sac like organ the urinary bladder and a tubule called urethra which arises from bladder and empties urine outside the body. The bladder end of urethra has a sphincter valve, which controls release of urine from the bladder.Structure of kidney:Each kidney is bean shaped organ which is about 10 cm long. They lie in the abdominal cavity being attached with dorsal body wall on either side of vertebral column. Each kidney is enclosed by a thin membranous covering called peritoneum and located on the top of each kidney is adrenal gland. The kidneys receive blood through paired renal arteries which directly arise from dorsal aorta. The blood is drained out from each kidney by a renal vein. Both renal arteries enter and renal veins leave kidney at the site called hilns.Nephron:Each kidney is composed of about a million microscopic tubules or nephrons. It is regarded as structural and functional unit of kidney which performs osmoregulation as well as excretion.

Function:Kidney performs regulatory functions by different processes viz filtration, re-absorption, tubular secretions and counter current exchange. These processes are carried on at the level of each nephron.Kidneys play vital role in osmoregulation as well as excretion of nitrogenous wastes.