Page 1044 - Fundamentals of anatomy physiology

bladder, and urethra) transports, stores, and eliminates urine.
A pyelogram (PI.-el-o. -gram) is an image of the urinary system
(Figure 26–17). It is obtained by taking an x-ray of the kidneys
after a radiopaque dye has been administered intravenously.
Such an image provides an orientation to the relative sizes
and positions of the main structures. Note that the sizes of
the minor and major calyces, the renal pelvis, the ureters, the
urinary bladder, and the proximal portion of the urethra are
somewhat variable. These regions are lined by a transitional
epithelium that can tolerate cycles of distension and contraction
without damage. p. 146
The Ureters
The ureters are a pair of muscular tubes that extend from the
kidneys to the urinary bladder—a distance of about 30 cm
(12 in.). Each ureter begins at the funnel-shaped renal pelvis
(Figure 26–4). The ureters extend inferiorly and medially, passing
over the anterior surfaces of the psoas major muscles (Figure 26–3).
Figure 26–17 A Pyelogram. This anterior-posterior view
of urinary system structures is color-enhanced. ATLAS: Plate 62b
11th and 12th ribs Minor calyx Major calyx
Ureter Urinary bladder Renal pelvis Kidney
Chapter 26 The Urinary System 1031
The ureters are retroperitoneal and are firmly attached to the
posterior abdominal wall. The paths taken by the ureters in men
and women are different, due to variations in the nature, size,
and position of the reproductive organs. In males, the base of the
urinary bladder lies between the rectum and the pubic symphysis
(Figure 26–18a). In females, the base of the urinary bladder sits
inferior to the uterus and anterior to the vagina (Figure 26–18b).
The ureters penetrate the posterior wall of the urinary blad-
der without entering the peritoneal cavity. They pass through
the bladder wall at an oblique angle. The ureteral openings
are slit-like rather than rounded (Figure 26–18c). This shape
helps prevent the backflow of urine toward the ureter and
k­ idneys when the urinary bladder contracts.
Histology of the Ureters
The wall of each ureter consists of three layers (Figure 26–19a):
(1) an inner mucosa, made up of a transitional epithelium and
the surrounding lamina propria; (2) a middle muscular layer
made up of longitudinal and circular bands of smooth muscle;
and (3) an outer connective tissue layer that is continuous with
the fibrous capsule and peritoneum. About every 30 seconds,
a peristaltic contraction begins at the renal pelvis. As it sweeps
along the ureter, it forces urine toward the urinary bladder.
The Urinary Bladder
The urinary bladder is a hollow, muscular organ that serves as a
temporary reservoir for urine (Figure 26–18c). The dimensions
of the urinary bladder vary with its state of distension. A full
urinary bladder can contain as much as a liter of urine.
A layer of peritoneum covers the superior surfaces of the
urinary bladder. Several peritoneal folds assist in stabilizing
its position. The median umbilical ligament extends from
the anterior, superior border toward the umbilicus (navel).
The lateral umbilical ligaments pass along the sides of the
bladder to the umbilicus. These fibrous cords are the vestiges of
the two umbilical arteries, which supplied blood to the placenta
26during embryonic and fetal development. p. 798 The urinary
bladder’s posterior, inferior, and anterior surfaces lie outside
the peritoneal cavity. In these areas, tough ligamentous bands
anchor the urinary bladder to the pelvic and pubic bones.
In sectional view, the mucosa lining the urinary bladder is
usually thrown into folds, or rugae, that disappear as the bladder
fills. The triangular area bounded by the openings of the ureters
and the entrance to the urethra makes up a region called the
trigone (TRI.-go. n) of the urinary bladder. There, the mucosa is
smooth and very thick. The trigone acts as a funnel that channels
urine into the urethra when the urinary bladder contracts.
The urethral entrance lies at the apex of the trigone, at the
most inferior point in the urinary bladder. The region surround-
ing the urethral opening is known as the neck of the urinary
bladder. It contains a muscular internal urethral sphincter.