Urinary System Health Article

Definition

The urinary system consists of organs, muscles, tubes, and nerves that are responsible for producing, transporting, and storing urine. The major structures of the urinary system include the kidneys, the ureters, the bladder, and the urethra.

The kidneys

The two kidneys are located lateral (to each side) to the spinal column, along the posterior (back) wall of the abdominal cavity. Each kidney is bean-shaped and approximately the size of one's fist (4 to 5 in, or 10 to 13 cm in length). The hilus is the indentation found along the medial side (the side closest to the midline of the body) of the kidney and is the point at which blood vessels (the renal artery and renal vein), nerves, and the ureter enter and exit the organ. The outer layer of the kidney is called the renal cortex, and the inner region of the organ is called the renal medulla.

The individual filtering unit of the kidney is called a nephron, of which there are approximately one million in each kidney. Each nephron extends from the renal cortex into the renal medulla and empties into the funnel-like reservoir of the kidney called the renal pelvis. There are three major components of the nephron: Bowman's capsule, the glomerulus (plural, glomeruli), and the renal tubule. Bowman's capsule is a structure that contains the glomerulus, a cluster of capillaries that is the main filtering device of the nephron. The afferent arteriole brings blood from the branches of the renal artery into Bowman's capsule, where fluid is filtered through the glomerulus. Blood exits the glomerulus by way of the efferent arteriole, passing through the persitubular capillaries and eventually entering the renal vein. The renal tubule has four main sections: the proximal tubule, the loop of Henle, the distal tubule, and the collection tubule. The end closest to Bowman's capsule is called the proximal tubule. The loop of Henle extends from the proximal tubule in the renal cortex to the medulla and back to the cortex, into the distal tubule. The distal tubule empties

into a collecting duct which in turn empties into the renal pelvis.

The ureters

Urine is transported from the renal pelvis of each kidney to the urinary bladder by way of a thin muscular tube called the ureter. The ureter of an adult is typically 8-10 in. (21-26 cm) long and approximately 0.25 in.(0.75 cm) in diameter. The walls of the ureter are muscular and help to force urine toward the bladder, away from the kidneys.

The bladder

The urinary bladder is a hollow organ with flexible, muscular walls; it is held in place with ligaments attached to the pelvic bones and other organs. Its primary function is to store urine temporarily until urination occurs, when urine is discharged from the body. When the bladder is empty, its inner wall retracts into many folds that expand as the bladder fills with fluid. The bladder of a healthy adult can typically hold up to 2 cups (0.5 L) of urine comfortably for two to five hours. Circular muscles called sphincters are found at bladder

openings—from the ureters and to the urethra—and control the flow of urine out of the bladder by closing tightly around the opening.

The urethra

The urethra is a tube that leads from the bladder to the body's exterior. In females, the urethra is typically about 1.5 in. (4 cm) in length and carries only urine; its opening is found anterior (in front of) the opening to the vagina. In males, however, the urethra is much longer—approximately 8 in. (20 cm) in length—and extends from the bladder to the tip of the penis. It passes through the prostate gland; semen is directed into the urethra via the ejaculatory ducts of the prostate. The male urethra therefore alternately transports urine (during urination) and semen (during ejaculation).