| Anatomy
of the Urinary System
How does the urinary system work?
The body takes nutrients from food and converts them to energy. After the
body has taken the food that it needs, waste products are left behind in
the bowel and in the blood.
The urinary system keeps the chemicals and water in balance by removing
a type of waste called urea from the blood. Urea is produced when protein,
found in meat products, are broken down in the body.
Urinary system parts and their functions:
- two kidneys - a pair of purplish-brown organs
located below the ribs toward the middle of the back. Their function
is to:
- remove liquid waste from the blood in the form of urine.
- keep a stable balance of salts and other substances in the
blood.
- produce erythropoietin, a hormone that aids the formation of red
blood cells.
The kidneys remove urea from the blood through tiny filtering units
called nephrons. Each nephron consists of a ball formed of small blood
capillaries, called a glomerulus, and a small tube called a renal
tubule. Urea, together with water and other waste substances, forms
the urine as it passes through the nephrons and down the renal tubules
of the kidney.
- two
ureters - narrow tubes that carry urine from the kidneys to
the bladder. Muscles in
the ureter walls continually tighten and relax forcing urine downward,
away from the kidneys. If urine backs up, or is allowed to stand
still, a kidney infection can develop. About every 10 to 15 seconds,
small amounts of urine are emptied into the bladder from the ureters.
- bladder - a triangle-shaped, hollow organ located
in the lower abdomen. It is held in place by ligaments that are
attached to other organs and the pelvic bones. The bladder's
walls relax and expand to store urine, and contract and flatten to
empty urine through the urethra. The typical healthy adult
bladder can store up to two cups of urine for two to five hours.
- two sphincter muscles - circular muscles that help
keep urine from leaking by closing tightly like a rubber band around
the opening of the bladder.
- nerves in the bladder - alert a person when it
is time to urinate, or empty the bladder.
- urethra - the tube that allows
urine to pass outside the body. The brain signals the bladder muscles
to tighten, which squeezes urine out of the bladder. At the same time,
the brain signals the sphincter muscles to relax to let urine exit the
bladder through the urethra. When all the signals occur in the correct
order, normal urination occurs.
|
Facts about
urine:
- Adults pass about a quart and a
half of urine each day, depending on the fluids and foods
consumed.
- The volume of urine formed at
night is about half that formed in the daytime.
- Normal urine is sterile. It
contains fluids, salts and waste products, but it is free of
bacteria, viruses and fungi.
- The tissues of the bladder are
isolated from urine and toxic substances by a coating that
discourages bacteria from attaching and growing on the
bladder wall.
|
Click here to view the
Online Resources page of this web. |
