URINARY SYSTEM
All of the organs involved in the secretion and elimination of urine
Urine
The waste material that is secreted by the kidneys
Functions of the urinary system
1. Filters the blood by removing various toxins, metabolic waste products, and
some water
2. Manufactures and excretes urine
3. Assists in regulation of water, electrolyte, and acid-base balance of the body
4. Influences blood pressure
Major organs and structures of the urinary system
1. Kidney
One of a pair of bean-shaped urinary organs in the dorsal
part of the abdomen, one on each side of the vertebral
column
2. Ureter
One of a pair of thick-walled tubes that carries urine
from the kidney into the urinary bladder
3. Urinary bladder
The muscular membranous sac in the pelvis that stores
urine for discharge through the urethra
4. Urethra
The small, tubular structure that drains urine from the
bladder
Characteristics and external structure of the kidneys.
1. The kidneys lie behind the peritoneum, against the posterior wall of the abdomen.
2. Each kidney measures about ½ by 4 ½ inches (6 to 11 centimeters), but the left
kidney is usually slightly larger than the right kidney
3. The right kidney is usually a little lower than the left kidney because of the large space occupied by the liver.
4. Each kidney and its vessels are embedded in a pocket of fatty tissue called the adipose capsule, which protects the
kidney from external blows and helps hold
it in position.
5. The kidney and adipose capsule are suspended in a web of fibrous tissue called the renal fascia, which anchors the
kidney to surrounding structures and also helps hold it in position.
6. The depression on the inner (medial) border of each kidney is called the hilum.
7. The renal artery enters and the renal vein exits each kidney at the hilum
Renal
Relating to the kidneys
8. The renal artery carries blood containing waste products to microscopic structures in the kidney that filter out the
waste products.
9. Filtered blood leaves a kidney through the renal vein.
Major internal macroscopic structures of a kidney
1. Renal cortex
The soft, granular, outer layer of a kidney
2. Glomerulus
A structure composed of capillaries
3. Renal medulla
The middle portion of the kidney that lies beneath the
renal cortex and contains the cone-shaped structures
called renal pyramids
4. Renal pelvis
The funnel-shaped inner portion of the kidney that
contains the cuplike cavities called calyces where urine
is collected before it is sent to the ureter major internal
macroscopic structures of a kidney
Characteristics Microscopic Structures of a Kidney
1. A nephron is one of the approximately 1 million funnel-shaped microscopic structures located along the interface
of the renal cortex and the renal medulla
2. Each nephron consists of two major structures called the renal corpuscle and
the renal tubule.
3. A renal corpuscle consists of a glomerulus of renal capillaries enclosed within a funnel-shaped renal tubule called
Bowman's capsule
4. The renal tubule consists of four sections
(1) the proximal convoluted tubule,
(3) the distal convoluted tubule, and
(2) the loop of Henlie,
(4) the collecting tubule
5. The renal corpuscles and the convoluted portions of the renal tubules are located in the renal cortex
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6. The loop of Henlie and the collecting tubules are located in the renal medulla
7. Urine is formed in the renal corpuscle and in the renal tubule by filtration, reabsorption, and secretion.
Functions of the kidneys
1. Filter the liquid portion of blood in the distal part of the nephrons
2. Manufacture urine
3. Excrete urine from the proximal portion of the nephrons
4. Influence blood pressure
5. Regulate the fluid content of the blood by separating out the constituents of urine from the blood
6. Regulate the concentration of the various salts circulating in the blood
7. Extract foreign substances from the body, such as toxins, whether formed in the body or taken into the body from
the outside
8. Regulate osmotic pressure of extracellular fluid
9. Regulate electrolyte and acid-base balance
Characteristics and structure of the ureters.
1. Each ureter is approximately 10 to 12 inches (250 to 300 millimeters) long and ¼ inch (6.5 millimeters) in
diameter.
2. The ureters begin as calyces in the renal pelvis and end in the posterior floor of the urinary bladder.
3. The ureters consist of three tissue layers: an inner mucous membrane, a middle layer of smooth muscles, and an
outer wall of fibrous tissue.
4. Urine is carried through the ureters by peristalic waves of the muscular-tissue layer
Characteristics and structure of the urinary bladder.
1. The urinary bladder is a hollow, muscular, membranous, collapsible sac located in the pelvis directly behind the
symphysis pubis.
Symphysis pubis
The slightly movable interpubic joint of the pelvis, consisting of two pubic bones separated by a disc of
fibrocartilage
2. The urinary bladder is held in position by a peritoneal fold or fascia.
3. The urinary bladder has rugae to allow it to expand or collapse, depending on how much urine is present.
4. The urinary bladder has an average capacity of 18 to 30 cubic inches (300 to 500 cubic centimeters).
5. The three openings on the floor of the bladder form a triangle called the trigone area with a ureter on each side
and the urethra in the front
6. Urine is emptied from the bladder through the urethra by contractions of its muscular walls.
Characteristics and structure of the female urethra.
1. The female urethra is a short tube approximately 1 1/2 inches (40 millimeters) long and 1/4 inch (6.5 millimeters)
in diameter that lies behind the symphysis pubis and is embedded in the wall of the vagina.
2. The urethra acts as a passageway for urine from the urinary bladder to the urinary meatus
Vagina
The canal in a female that leads from the uterus to the external opening of the genital
canal
Urinary meatus
The external opening of the urethra
3. The urethra contains an internal and an external sphincter.
4. The Skene's glands open into the urethra at its termination to secrete lubricating fluid.
Skene's glands
The largest glands opening into the urethra of women
Characteristics and structure of the male urethra.
1. The male urethra acts as a passageway for both urine and seminal fluid.
2. The male urethra is a modified S-shaped tube approximately 8 to 10 inches (200 to 250 millimeters) long that
consists of three divisions: the prostatic division, the membranous division, and the cavernous division.
3. After exiting the bladder from below, the prostatic division passes through the center of the prostate gland.
4. The membranous division extends from the apex of the prostate and the bulb of the urethra between two sheets of
white fibrous tissue that connect the pubic bones and is surrounded by the external sphincter muscle.
5. The cavernous (anterior) division extends from the pelvic walls through the penis to the urinary meatus.
Normal physical characteristics of urine
1. Urine is a clear, straw-colored watery solution containing the waste products of metabolism.
2. Urine is straw-colored as a result of the excreted bile pigments it contains.
3. Urine has an average pH of 6.0, with a normal range of 5.5 to 6.5 and is, thus, slightly acidic.
4. Urine is slightly heavier than water, with a specific gravity of 1.015 to 1.025.
5. The amount of urine excreted is dependent on the amount of fluid intake and the amount of fluid lost through
other mechanisms, such as respiration and perspiration; on the average, a person will excrete 61 to 110 cubic inches
(1000 to 1800 cubic centimeters) of urine per 24-hour period.
6. After standing for a short period of time, urine has the characteristic odor of ammonia.
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7. The normal constituents of urine are water, organic substances, and inorganic substances.
8. Normal urine is approximately 95 percent water.
9. The organic substances in urine are largely protein waste products, including uric acid, urea, creatinine, ammonia,
and hormones.
Creatinine
The by-product of cellular respiration formed from creatinine phosphate
10. The inorganic substances are primarily mineral salts, and include sodium chloride, sulfates, phosphates,
potassium, magnesium, and calcium.
Processes for producing and expelling urine
1. Blood carrying wastes flows into the kidneys.
2. The high blood pressure within the glomeruli forces blood plasma into the Bowman's capsules to filter it,
producing a fluid called renal filtrate.
3. Nutrients, water, and minerals are reabsorbed from the filtrate and into the bloodstream of the peritubular
capillaries.
4. The capillaries secrete additional wastes and hydrogen into the filtrate.
5. Hormones influence the amount of water that is reabsorbed to help maintain normal blood volume and pressure.
6. The waste products in the filtrate are carried from the body in excreted urine. Processes for producing and
expelling urine
7. The process of expelling urine is variously known as urination, voiding, or micturition.
8. For an average person, as the volume of urine in the bladder approaches 12 to 15 cubic inches (200 to 250 cubic
cm), the pressure of bladder expansion creates an impulse in the central nervous system indicating a need to urinate.
Processes for producing and expelling urine
9. Although urination is dependent on involuntary reflexes, humans learn partial voluntary control over urinating.
10. Expulsion of urine from the bladder is accomplished by contracting the walls of the bladder and relaxation of the
sphincter muscles at the junction of the urinary bladder and the urethra.
11. The external sphincter of the urethra controls the release of urine.
12. The inability to control urination, called incontinence, occurs in young children until control is learned and in the
elderly in whom the sphincter has weakened
Common Abnormal Constituents of Urine
1. Glucose
3. Blood
5. Acetone
2. Albumin
4. Pus cells
Characteristics of calculi
1. Calculi may form in the kidneys or any other part of the urinary tract.
2. Because they contain calcium, calculi are usually radiopaque.
3. Calculi usually form as a result of excessive amounts of calcium, sodium, or other mineral salts; a decrease in the
amount of water; or excessively acidic or alkaline urine.
Calculus
A particle found in the kidney or urinary tract that forms as a result of mineral deposits, generally of salts formed
from ingested materials; also called kidney stones
Radiopaque
Referring to a substance that is capable of reducing the amount of x-ray energy that passes through it, thus making it
visible in a radiograph
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