Human Anatomy - Kotsan I. Y. 2009

Urogenital system
Urinary organs
Urinary bladder

The Urinary Bladder (vesica urinaria) is an unpaired, hollow organ that acts as a urine reservoir (Fig. 172). Its shape varies depending on the degree of distension. An empty bladder is flattened, whereas a full bladder assumes an ovoid or pear-like shape. The average capacity of the bladder in adults ranges from 250 to 750 ml.

The urinary bladder is divided into the apex, body, fundus, and neck. The apex (apex vesicae) is directed upward and forward toward the anterior abdominal wall. The median umbilical ligament (lig. umbilicale medianum), which represents the obliterated remnant of the embryonic urachus, extends from the apex to the umbilicus. The body (corpus vesicae) forms the broad central portion, which transitions without a clear boundary into the lower part — the fundus (fundus vesicae). The fundus is directed downward and backward, tapering into the neck (cervix vesicae). The internal urethral orifice (ostium urethrae internum) is located in the lower region of the neck.

The urinary bladder is situated within the lesser pelvis, posterior to the Pubic Symphysis. Its anterior surface faces the pubic symphysis, separated from it by a layer of loose Connective Tissue. When filled with urine, the bladder apex rises above the pubic symphysis and comes into contact with the anterior abdominal wall. In males, the posterior surface of the bladder is adjacent to the rectum, Seminal Vesicles, and ampullae of the Ductus Deferentes, while the fundus rests on the Prostate Gland. In females, the posterior surface abuts the anterior wall of the uterine cervix and Vagina, and the fundus is related to the urogenital Diaphragm. The lateral surfaces in both sexes border the levator ani Muscle. The superior surface is related to loops of the Small Intestine in males and the Uterus in females. A distended bladder lies mesoperitoneally, whereas an empty bladder is retroperitoneal. The Peritoneum covers the superior, lateral, and posterior aspects of the bladder, and then reflects onto the rectum in males (forming the rectovesical pouch) and onto the uterus in females (forming the vesicouterine pouch). The peritoneum covering the bladder is loosely connected to its wall.

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Fig. 172. Urinary bladder

a — posterior view: 1 — apex of the bladder; 2 — Ureter; 3 — body of the bladder; 4 — Ductus deferens; 5 — Seminal Vesicle; 6 — Cytology/practical/108.html">Fundus of the bladder; 7 — prostate gland; b — internal view: 1 — muscular layer; 2 — submucosa; 3 — mucosa; 4 — ureteric orifices; 5 — trigone of the bladder; 6 — internal urethral orifice

The urinary bladder is anchored to the walls of the lesser pelvis and connected to adjacent Organs by fibrous cords. The apex is attached to the umbilicus by the median umbilical ligament. The lower portion of the bladder is secured to the pelvic walls by ligaments formed from the fibers of the pelvic fascia. These include the puboprostatic ligament (lig. puboprostaticum) in males and the pubovesical ligament (lig. pubovesicale) in females. In addition to these ligaments, the bladder is supported by muscle bundles that form the pubovesical muscle (musculus pubovesicalis) and the rectovesical muscle (musculus rectovesicalis), the latter being present exclusively in males. In both sexes, the bladder is further stabilized by the proximal Urethra and the distal ends of the Ureters, as well as by the prostate gland in males and the urogenital diaphragm in females.

The wall of the urinary bladder consists of a mucous membrane, submucosa, muscular layer, adventitia, and partially a serosa. Where the serosa is absent, the adventitia serves as the outer layer of the bladder. The bladder wall is highly distensible. Its thickness reaches 12—15 mm when empty, but stretches and thins down to 2—3 mm when filled with urine.

The mucosa (tunica mucosa) lines the interior of the urinary bladder. It has a pinkish hue and is covered by transitional epithelium. In an empty bladder, the mucosa forms numerous folds that smooth out as the organ fills. Folds are absent only in a small triangular area located in the region of the fundus, known as the trigone of the bladder (trigonium vesicae). This region lacks a submucosal layer, and the mucosa is firmly fused with the underlying muscle. In the anterior part of the fundus (near the apex of the bladder trigone), the mucosa features the internal urethral orifice (ostium urethrae internum), while the right and left ureteric orifices (ostia ureterum dextrum et sinistrum) are located at the posterolateral corners of the trigone. Extending between the right and left ureteric orifices along the Base of the trigone is a mucosal fold known as the interureteric fold (plica interureterica). Posterior to the internal urethral orifice on the inner surface of the male bladder, there is an elongated elevation called the uvula of the bladder (uvula vesicae), which is formed by the underlying prostate gland.

The submucosa (tela submucosa) is well-developed within the bladder wall. It is rich in Fibrous connective tissue interspersed with fine and coarse elastic fibers. Thanks to the submucosa, the mucosa of an unfilled bladder can gather into folds that mirror the contours of the muscular layer. The submucosa is entirely absent in the region of the bladder trigone.

The muscular layer (tunica muscularis) of the urinary bladder is prominent and consists of three interwoven layers of smooth muscle: inner and outer longitudinal layers, and a middle circular (transverse) layer. The interweaving of these muscle bundles ensures uniform contraction of the bladder wall during urination, expelling urine into the urethra. The middle circular layer is especially well-developed; it thickens in the region of the bladder neck and internal urethral orifice to form the sphincter vesicae muscle or internal urethral sphincter (musculus sphincter vesicae s. musculus sphincter urethrae internus). The weakest layer is the inner muscular layer, which consists of longitudinal and partially oblique bundles and is developed only in the region of the fundus. The fibers of this inner layer encircle the ureteric orifices, forming sphincter-like structures that prevent the backflow of urine. During contraction, the muscular layer reduces the volume of the organ and forces urine out through the urethra. Due to this primary function, the muscular layer is also referred to as the detrusor muscle of the bladder (musculus detrusor vesicae).

The outer coat of the urinary bladder is a thin connective tissue adventitia. The peritoneum covers the bladder anteriorly and laterally, as well as superiorly and partially posteriorly.

Blood supply to the urinary bladder. The superior vesical Arteries (Branches of the umbilical artery) supply the apex and body of the bladder. The lateral walls and fundus are supplied by branches of the inferior vesical artery (a branch of the internal iliac artery). Venous blood from the bladder walls drains into the vesical venous plexus, as well as via vesical Veins directly into the internal iliac veins.

Lymphatic drainage from the urinary bladder leads to the internal iliac Lymph Nodes.

The urinary bladder is innervated by branches of the inferior hypogastric plexus (sympathetic innervation), visceral nerves (parasympathetic innervation), and branches of the Sacral Plexus (sensory innervation).