Urinary system

From ArticleWorld

The urinary system is the part of the body that filters out metabolic products from the blood, produces urine by combining metabolic products, salts and water, carries and stores urine, and finally, removes the urine from the body. There are several connected organs and tubes that make up this system.

Anatomy

In humans, the kidneys come in a pair (normally) and are located in the back of the mid abdominal cavity. Each kidney is encapsulated in a fibrous covering and is about the size of a human fist. They are shaped like a kidney bean. Approximately a million filtering nephrons make up the internal structure of the kidney. The urine is collected into the renal pelvis which acts like a funnel to send the urine into a downward path.

The ureters are a pair of tubes that connect the renal pelvis in the kidney to the bladder. Each ureter is approximately 20-25 cm long and uses smooth muscle peristaltic contractions to pass the urine along its length.

The bladder is a hollowed out organ that stores the bladder prior to urination. It contains muscle fibers within its wall that contract at the time of emptying. The bladder can hold in excess of one liter but normally will give the urge to the brain to void prior to 500 milliliters.

There are sphincters or circular muscles that must relax in order for the bladder to empty. The relaxation of the sphincter muscles must happen at the same time as the contraction of the bladder detrusor muscle in order for normal bladder emptying. The urethra is the tube through which the urine passes to the outside.

Function

The function of the urinary system is to filter out products of metabolism, medication metabolites and some toxins from the blood via a complex system of nephrons that consist of filtering glomeruli and tubules in the kidneys. The glomerulus is in close contact with the capillary system and the metabolites and some salts are diffused into the urinary system. The tubules will reabsorb some of the nutrients, water and salts that will go back into the blood stream.

Over 1.5 liters of urine is made per day. This is why the bladder is necessary for the holding of urine until the urge is passed to the brain that voiding is necessary.

Conditions

There are many conditions that can affect the urinary tract. The kidney can become damaged and fail to function. Kidney stones can develop in the renal pelvis and block the ureter. The bladder can lose its supporting structures, especially in women after childbirth, resulting in incontinence. The opposite problem, urinary retention is more common in men and can be due to prostate enlargement. The muscles of the bladder in either gender can be either overactive or underactive, resulting in urinary problems.

Any cell in the body can become cancerous; however, bladder cancer is probably the most common urinary tract cancer, followed by cancer of the kidneys. The bladder interior is exposed to carcinogens (toxins) all of the time, particularly in smokers. This is why most cancers of the bladder affect the inner lining of transitional cells in the bladder.