2. Introduction to the Urinary System
• The urinary system, also known as the
renal system or urinary tract, consists of
the kidneys, ureters, bladder, and the
urethra. The purpose of the urinary
system is to eliminate waste from the
body, regulate blood volume and blood
pressure, control levels of electrolytes
and metabolites, and regulate blood ph.
• The body takes nutrients from food and
converts them to energy. After the body
has taken the food components that it
needs, waste products are left behind in
the bowel and in the blood.
4. Introduction to the Urinary System
• The principal function of the urinary system is to maintain the volume and
composition of body fluids within normal limits. One aspect of this function is to
rid the body of waste products that accumulate as a result of cellular
metabolism, and, because of this, it is sometimes referred to as the excretory
system.
• Although the urinary system has a major role in excretion, other organs
contribute to the excretory function. The lungs in the respiratory system excrete
some waste products, such as carbon dioxide and water. The skin is another
excretory organ that rids the body of wastes through the sweat glands. The liver
and intestines excrete bile pigments that result from the destruction of
hemoglobin. The major task of excretion still belongs to the urinary system. If it
fails the other organs cannot take over and compensate adequately.
• In addition to maintaining fluid homeostasis in the body, the urinary system
controls red blood cell production by secreting the hormone erythropoietin. The
5. Components of the Urinary System
The urinary system consists of the kidneys, ureters, urinary bladder, and urethra.
The kidneys form the urine and account for the other functions attributed to the
urinary system. The ureters carry the urine away from kidneys to the urinary
bladder, which is a temporary reservoir for the urine. The urethra is a tubular
structure that carries the urine from the urinary bladder to the outside.
• Kidneys
• Ureters
• Urinary Bladder
• Urethra
6. Kidneys
• The kidneys are the primary organs of the
urinary system. The kidneys are the organs
that filter the blood, remove the wastes, and
excrete the wastes in the urine. They are the
organs that perform the functions of the
urinary system. The other components are
accessory structures to eliminate the urine
from the body.
• The right kidney usually is slightly lower than
the left because the liver displaces it
downward. The kidneys, protected by the
lower ribs.
• Each kidney is held in place by connective
tissue and is surrounded by a thick layer of
adipose tissue, which helps to protect it. A
tough, fibrous, connective tissue renal
capsule closely envelopes each kidney and
7. Kidneys
• In the adult, each kidney is approximately 3 cm
thick, 6 cm wide, and 12 cm long. It is roughly
bean-shaped.
• Two kidneys. This pair of purplish-brown organs is
located below the ribs toward the middle of the
back. Their function is to:
Remove waste products and drugs from the body
Balance the body's fluids
Release hormones to regulate blood pressure
Control production 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.
8. Ureters
Two ureters. These narrow tubes 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 can 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.
9. Urinary Bladder
• The urinary bladder is a temporary storage reservoir for urine. It is
in the pelvic cavity. The size and shape of the urinary bladder
varies with the amount of urine it contains and with the pressure it
receives from surrounding organs.
• 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. These circular muscles help keep urine
from leaking by closing tightly like a rubber band around the
opening of the bladder.
• Nerves in the bladder. The nerves alert a person when it is time
to urinate or empty the bladder.
10. Urethra
• This tube 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.
• The internal urethral sphincter surrounds the beginning of the
urethra, where it leaves the urinary bladder. This sphincter is
smooth (involuntary) muscle. Another sphincter, the external
urethral sphincter, is skeletal (voluntary) muscle and encircles the
urethra where it goes through the pelvic floor. These two sphincters
control the flow of urine through the urethra.
• In females, the urethra is short, only 3 to 4 cm (about 1.5 inches)
long. In males, the urethra is much longer, about 20 cm (7 to 8
inches) in length
11. Facts about urine
• Normal, healthy urine is a pale straw or
transparent yellow color.
• Darker yellow or honey colored urine means you
need more water.
• A darker, brownish color may indicate a liver
problem or severe dehydration.
• Pinkish or red urine may mean blood in the
urine.
• You may suffer from stress if the muscles
supporting the bladder are weakened. You can
help to strengthen these by doing pelvic floor
exercises.
• If one kidney fails to function and is removed,
the other kidney can increase in size by 50%
within two months to handle the entire task of
filtration.
• The kidneys can clean more than 1 million gallon
12. Review: Introduction to the Urinary
System
Here is what we have learned from Introduction to the Urinary
System:
• The urinary system rids the body of waste materials,
regulates fluid volume, maintains electrolyte concentrations in
body fluids, controls blood pH, secretes erythropoietin, and
renin.
• The components of the urinary system are the kidneys,
ureters, urinary bladder, and urethra.
• The primary organs of the urinary system are the kidneys.
• The functional unit of the kidney is a nephron.
• The ureters transport urine from the kidney to the urinary
bladder.
• The urinary bladder is a temporary storage reservoir for urine.
• The urethra is the final passageway for the flow of urine.
• The flow of urine through the urethra is controlled by an
involuntary internal urethral sphincter and voluntary external
urethral sphincter.
