980
UNIT 4
Maintenance of the Body
25
Most calculi are under 5 mm in diameter and pass through the
urinary tract without causing problems. However, larger calculi
can obstruct a ureter and block urine drainage. Increasing pres-
sure in the kidney causes excruciating pain, which radiates from
the flank to the anterior abdominal wall on the same side. Pain
also occurs during peristalsis when the contracting ureter wall
closes in on the sharp calculi.
Predisposing conditions are frequent bacterial infections of
the urinary tract, urine retention, high blood levels of calcium,
and alkaline urine. Surgical removal of calculi has been almost
entirely replaced by
shock wave lithotripsy
, a noninvasive pro-
cedure that uses ultrasonic shock waves to shatter the calculi.
Te pulverized, sandlike remnants of the calculi are then pain-
lessly eliminated in the urine. People with a history of kidney
stones are encouraged to drink enough water to keep their
urine dilute.
Lumen
Adventitia
Muscularis
Longitudinal
layer
Circular
layer
Mucosa
Transitional
epithelium
Lamina
propria
Figure 25.19
Cross-sectional view of the ureter wall (10
3
).
The prominent mucosal folds seen in an empty ureter stretch and
flatten to accommodate large pulses of urine.
Urinary Bladder
Describe the general location, structure, and function of
the urinary bladder.
Te
urinary bladder
is a smooth, collapsible, muscular sac that
stores urine temporarily.
Urinary Bladder Anatomy
Te bladder is located retroperitoneally on the pelvic floor just
posterior to the pubic symphysis. Te prostate (part of the male
reproductive system) lies inferior to the bladder neck, which
empties into the urethra. In females, the bladder is anterior to
the vagina and uterus (see Figure 27.12 on p. 1035).
Te interior of the bladder has openings for both ureters and
the urethra
(Figure 25.20)
. Te smooth, triangular region of
the bladder base outlined by these three openings is the
trigone
(tri
9
gōn;
trigon
5
triangle), important clinically because infec-
tions tend to persist in this region.
Te bladder wall has three layers: a mucosa containing tran-
sitional epithelium, a thick muscular layer, and a fibrous ad-
ventitia (except on its superior surface, where it is covered by
the peritoneum). Te muscular layer, called the
detrusor
(de-
tru
9
sor; “to thrust out”), consists of intermingled smooth mus-
cle fibers arranged in inner and outer longitudinal layers and a
middle circular layer.
Urine Storage Capacity
Te bladder is very distensible and uniquely suited for its func-
tion of urine storage. When empty, the bladder collapses into its
basic pyramidal shape and its walls are thick and thrown into
folds (
rugae
). As urine accumulates, the bladder expands, be-
comes pear shaped, and rises superiorly in the abdominal cav-
ity. Te muscular wall stretches and thins, and rugae disappear.
Tese changes allow the bladder to store more urine without a
significant rise in internal pressure.
A moderately full bladder is about 12 cm (5 inches) long
and holds approximately 500 ml (1 pint) of urine, but it can
hold nearly double that if necessary. When tense with urine, it
can be palpated well above the pubic symphysis. Te maximum
Table 25.2
Abnormal Urinary Constituents
SUBSTANCE
NAME OF CONDITION
POSSIBLE CAUSES
Glucose
Glycosuria
Diabetes mellitus
Proteins
Proteinuria, albuminuria
Nonpathological: excessive physical exertion, pregnancy
Pathological (over 150 mg/day): heart failure, severe hypertension, glomerulonephritis,
often initial sign of asymptomatic renal disease
Ketone bodies
Ketonuria
Excessive formation and accumulation of ketone bodies, as in starvation and untreated
diabetes mellitus
Hemoglobin
Hemoglobinuria
Various: transfusion reaction, hemolytic anemia, severe burns, etc.
Bile pigments
Bilirubinuria
Liver disease (hepatitis, cirrhosis) or obstruction of bile ducts from liver or gallbladder
Erythrocytes
Hematuria
Bleeding urinary tract (due to trauma, kidney stones, infection, or cancer)
Leukocytes (pus)
Pyuria
Urinary tract infection
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