Human Anatomy Part 1 - K. A. Dyubenko, A. K. Kolomiytsev, Yu. B. Chaykovsky 2002

Special Part
Urinary System, systema urinarium - General Overview
Urinary organs - Urinary bladder - Structure of the urinary bladder

The wall of the Urinary Bladder consists of (Fig. 313):

- mucous membrane, tunica mucosa;

- submucosa, tela submucosa;

- muscular layer, tunica muscularis;

- fascial or partially peritoneal covering, tunica adventitia (t. serosa).

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Fig. 313. Structure OF THE male urinary bladder in section (anterior view)

The mucous membrane, tunica mucosa, is grayish-red in color and folded. Folds are absent only in the region of the bladder base, where the mucous membrane lacks a submucosal layer and is fused with the muscular coat. This area is called the urinary bladder triangle, trigonum vesicae. It is located between the ureteric orifices, ostium ureteris, and the internal urethral orifice, ostium urethrae internum. The interureteric fold, plica interureterica, extends between the ureteric orifices, preventing the backflow of urine into the Ureter. During cystoscopy (examination of the bladder mucosa using a cystoscope), folds of the mucous membrane and the openings of the Ureters are visible; the latter periodically open (2–3 times per minute) to eject urine into the urinary bladder.

The submucosa, tela submucosa, is composed of loose irregular Connective Tissue. It contains networks of Blood and Lymphatic vessels as well as neural elements.

The muscular coat, tunica muscularis, is quite thick and forms the bulk of the bladder wall. It consists of bundles of smooth Muscle fibers arranged in three layers: external, stratum externum; internal, stratum internum (longitudinal); and middle, stratum medianum (circular). These layers of smooth muscle fibers unite to form the detrusor muscle of the bladder, m. detrusor vesicae. The most developed layer is the stratum medianum, which forms the sphincter of the urinary bladder, m. sphincter vesicae, at the beginning of the Urethra. Sphincters are also formed at the sites where the ureters enter the urinary bladder due to the circular fibers of the muscular layer.

The serous coat (Peritoneum), tunica serosa, covers the superior half of the posterior and lateral surfaces of the urinary bladder, while the remainder of its surface has a fascial covering.

Radiological Anatomy of the urinary bladder. Radiographic examination without the administration of a contrast medium (plain radiograph) can detect the presence of calculi or foreign bodies. When a contrast medium is introduced into the bladder (contrast cystography)—such as iodine-containing substances, barium sulfate, oxygen, or carbon dioxide—its shape and the condition of its walls can be clearly visualized (Figs. 314, 315).

Ultrasonography of the urinary bladder. A distended urinary bladder serves as the primary landmark in pelvic sonography. On sonograms, it appears as an anechoic structure with distinct margins, located directly behind the anterior abdominal wall in the lower floor of the Abdominal cavity. During longitudinal scanning, the lower contour of the urinary bladder is not fully visualized because this portion falls within the acoustic shadow of the pelvic bones. On transverse sonograms, the walls of the urinary bladder are clearly visible, appearing as Kidney-shaped structures. The lower part is rectangular in shape, while the upper part is broader and ovoid.

An empty urinary bladder is not visible on sonograms; therefore, the primary prerequisite for the examination is filling it with 300–400 ml of fluid. The mucosal folds smooth out, and the internal surface becomes smooth. The examination is performed both transabdominally and via the urethra and rectum using specialized probes. The posterior wall of the urinary bladder is visualized more clearly than the anterior wall. Posterior to the urinary bladder, the sonograms clearly show the Uterus in females and the Prostate Gland in males.

Fig. 314. Retrograde urethro-cystogram (30-year-old male) (according to V. V. Zhyla)

Blood supply to the urinary bladder is provided by the superior vesical Arteries, aa. vesicales superiores (from the umbilical artery), and the inferior vesical arteries, a. vesicalis inferior (from the internal iliac artery), which anastomose with one another. In addition, the urinary bladder receives several branches from the internal pudendal, obturator, and middle rectal arteries. Veins OF THE urinary bladder drain blood into the vesical venous plexus, plexus venosus vesicalis. Superior and inferior vesical veins originate from this plexus and empty into the internal iliac vein.

Lymphatic drainage occurs via Lymphatic vessels originating from the capillary lymphatic networks of the subserous and submucosal plexuses, which empty into the internal iliac Lymph Nodes, nodi lymphatici iliaci interni.

Fig. 315. Retrograde urethro-cystogram (5-year-old child) (according to D. A. Seymivsky)

Innervation of the urinary bladder is derived from the inferior hypogastric plexus, plexus hypogastricus inferior. Efferent parasympathetic preganglionic fibers originate in the lateral horns of the II–IV sacral segments, emerge as part of the ventral roots of Spinal Nerves, and then separate to form the pelvic splanchnic nerves, nn. splanchnici pelvici, which enter the pelvic ganglia of the urinary bladder; postganglionic fibers extend from these ganglia to the musculature of the urinary bladder. These fibers stimulate the contraction of the detrusor muscle and relax the bladder sphincter. Efferent sympathetic nerves originate from the lateral horns of the lumbar Spinal Cord, enter the ventral roots, and, upon separating as white rami communicantes, reach the inferior mesenteric ganglion. From here, postganglionic fibers arise which, as part of the hypogastric nerves, nn. hypogastrici, reach the smooth musculature, causing relaxation of the detrusor muscle and contraction of the bladder sphincter. Sensory innervation is supplied to the urinary bladder by the Sacral Plexus (n. pudendus).