Urinary system is the group of organs that produce urine and remove it from the body. The urinary system is one of the body’s major organ systems.
The kidneys are the main organs of the urinary system. Their primary role is to filter waste from the blood and to produce and concentrate urine. From the kidneys, urine enters the urinary tract. The urinary tract carries urine away from the kidneys and stores it for later excretion (removal from the body).
The kidneys
are a pair of purplish-brown organs on each side of the spine in the lower back. Each kidney includes about 1 million nephrons. The nephrons produce urine. A nephron consists of a network of tiny blood vessels, called the glomerulus, surrounded by a two-layered membrane called Bowman’s capsule. As blood flows through the glomerulus, pressure forces much of the plasma (fluid portion of the blood) through the glomerulus wall and into Bowman’s space, the area between the two layers of Bowman’s capsule. The fluid that collects in Bowman’s space contains water and dissolved chemicals. It passes from Bowman’s space into a duct called the convoluted tubule.
The portion of blood that remains in the glomerulus flows into small vessels called capillaries that surround the convoluted tubule. As fluid flows through the tubule, the cells of the tubule wall absorb substances needed by the body. These substances include amino acids , glucose , and about 99 percent of the water. They rejoin the blood in the capillaries and are returned to the body.
Substances not absorbed in the tubule are wastes that the body cannot use. Other wastes are secreted into this fluid by cells in the tubule. The wastes—which include ammonia , urea , uric acid , and excess water—make up urine.
The urinary tract.
Ducts collect urine from the convoluted tubules and carry it to a region of the kidney called the renal pelvis. A long, slender tube called a ureter drains urine from the renal pelvis to the urinary bladder. The urinary bladder is a hollow, stretchable sac that holds urine. During urination, also called micturition, the muscular walls of the urinary bladder contract, forcing urine into the urethra. The urethra is a narrow tube that carries urine out of the body.
