ANATOMY of URINARY BLADDER Characterized by Its Distensibility

The urinary bladder, a hollow viscus with strong muscular walls, is ANATOMY OF URINARY BLADDER characterized by its distensibility . The urinary bladder is a temporary reservoir for urine and varies in size, shape, position, and relationships according to its content and the state of neighboring viscera. Location : Bladder separated from pubic bones by the potential retropubic space (of Retzius) and lies mostly inferior to the peritoneum, Anterior : pubic bones and pubic symphysis Posterior : the prostate (males) or anterior wall of the vagina posteriorly Relation to other organs free within the extraperitoneal subcutaneous fatty tissue, except for its neck, which is held firmly by the lateral ligaments of bladder and the tendinous arch of the pelvic fascia—especially its anterior component, the puboprostatic ligament in males and the pubovesical ligament in females In females, since the posterior aspect of the bladder rests directly upon the anterior wall of the vagina, the lateral attachment of the vagina to the tendinous arch of the pelvic fascia, the paracolpium, is an indirect but important factor in supporting the urinary bladder Position when empty In infants and young children: in the abdomen even when empty. The bladder usually enters the greater pelvis by 6 years of age; however, it is not located entirely within the lesser pelvis until after puberty. In adult : o almost entirely in the lesser pelvis, lying partially superior to and partially posterior to the pubic bones o As the bladder fills, enters the greater pelvis as it ascends in the extraperitoneal fatty tissue of the anterior abdominal wall When empty, the bladder is somewhat tetrahedral externally has an apex,body, fundus, and neck. The apex of the bladder points toward the superior edge of the pubic symphysis when the bladder is empty. The fundus of the bladder is opposite the apex, formed by ♀ : the fundus is directly related to the superior anterior wall the somewhat convex posterior wall. of the vagina The body of the bladder is the major portion of the bladder The bladder is enveloped by a loose connective tissue visceral between the apex and the fundus. fascia The fundus and inferolateral surfaces meet inferiorly at the neck of the bladder. The walls of the bladder are composed chiefly of the detrusor muscle. Toward the neck of the male bladder, the muscle fibers form the involuntary internal urethral sphincter. This sphincter contracts during ejaculation to prevent retrograde ejaculation (ejaculatory reflux) of semen into the bladder. Some fibers run radially and assist in opening the internal urethral orifice. In males, the muscle fibers in the neck of the bladder are continuous with the fibromuscular tissue of the prostate, whereas in females these fibers are continuous with muscle fibers in the wall of the urethra. The bladder’s four surfaces (superior, two inferolateral, and posterior) are most apparent when viewing an empty, contracted bladder that has been removed from a cadaver, when the bladder appears rather boat shaped. The bladder bed is formed by the structures that directly contact it. On each side, the pubic bones and fascia covering the levator ani and the superior obturator internus lie in contact with the The ureteric orifices and the internal urethral orifice are at the inferolateral surfaces of the bladder angles of the trigone of the bladder (Fig. 3.28C). The ureteric Only the superior surface is covered by peritoneum. orifices are encircled by loops of detrusor musculature ♂ : the fundus is separated from the rectum centrally by only that tighten when the bladder contracts to assist in preventing reflux the fascial rectovesical septum and laterally by the seminal of urine into the ureter. The uvula of the bladder is a slight glands and ampullae of the ductus deferentes elevation of the trigone; it is usually more prominent in older men owing to enlargement of the posterior lobe of the prostate. sphincter to contract, hampering the ability to urinate until Arterial Supply of Bladder. parasympathetic inhibition of the sphincter occurs. The main arteries supply : branches of the internal iliac arteries Anterosuperior : The superior vesical parasympathetic fibers ♂ : inferior vesical arteries supply the fundus and neck of the From sacral spinal cord levels are conveyed by the pelvic bladder. splanchnic nerves and the inferior hypogastric plexus ♀ : vaginal arteries replace the inferior vesical arteries and motor to the detrusor muscle and inhibitory to the internal send small branches to posteroinferior parts of the bladder urethral sphincter of the male bladder. Hence, when visceral .The obturator and inferior gluteal arteries also supply small afferent fibers are stimulated by stretching, the bladder branches to the bladder. contracts reflexively, the internal urethral sphincter relaxes (in Venous Drainage males), and urine flows into the urethra from the bladder correspond to the arteries and are tributaries of the internal iliac veins. Sensory fibers from most of the bladder are visceral; reflex afferents ♂ : the vesical venous plexus is continuous with the prostatic follow the course of the parasympathetic fibers, as do those venous plexus, and the combined plexus complex envelops transmitting pain sensations (such as results from the fundus of the bladder and prostate, the seminal glands, overdistension) from the inferior part of the bladder. The superior the ductus deferentes, and the inferior ends of the ureters. It surface of the bladder is covered with peritoneum and is therefore also receives blood from the deep dorsal vein of the penis, superior to the pelvic pain line; thus pain fibers from the superior which drains into the prostatic venous plexus. The vesical bladder follow the sympathetic fibers retrogradely to the inferior venous plexus is the part of the plexus complex that is most thoracic and upper lumbar spinal ganglia (T11–L2 or L3). directly associated with the bladder itself. It mainly drains through the inferior vesical veins into the internal iliac veins; however, it may drain through the sacral veins into the internal vertebral venous plexuses. ♀ : the vesical venous plexus envelops the pelvic part of the urethra and the neck of the bladder, receives blood from the dorsal vein of the clitoris, and communicates with the vaginal or uterovaginal venous plexus Innervation of Bladder. Sympathetic fibers Conveyed from inferior thoracic and upper lumbar spinal cord levels to the vesical (pelvic) plexuses primarily through the hypogastric plexuses and nerves Stimulates ejaculation simultaneously contraction of the internal urethral sphincter prevent reflux of semen into the bladder. A sympathetic response at moments other than ejaculation(e.g., self-consciousness when standing at the urinal infront of a waiting line) can cause the internal HISTOLOGY OF URINARY BLADDER The mucosa of bladder is lined by unique stratified transitional epithelium or urothelium. This is surrounded by folded lamina propria and submucosa, followed by dense sheath of interwoven smooth muscle layers and adventitia. Urothelium is composed of the following 3 layers : single layer of small basal cells resting on a very thin basement membrane an intermediate region containing from one to several layers or more columnar cells a superficial layer of very large, polyhedral, or bulbous cells called umbrella cells (occasionally bi- or multinucleated and are highly differentiated to protect underlying cells against the cytotoxic effect of hypertonic urin o Umbrella cells well developed in bladder o Up to 100µm in diameter o Have extensive intercellular junctional complexes surrounding unique apical membranes o Most of apical surface consist of assymetric unite membrane (outer lipid layer appear twice as thick as the inner leaflet . Lipid rafts containing uroplakins which assembly into paracrystalline arrays of stiffened plaques 16 µm in diameter impermeable and protect cytoplasm and underlying cells from hyperosmotic effects Bladder’s lamina propria and dense irregular connective tissue of submucosa are highly vascularized. The muscular consist of three poorly delineated layers, call detrusor muscle, which contract to empty the bladder. This detrusor muscle are seen most distinctly at the neck of the bladder near the urethra. The ureter pass through the wall of bladder obliquely, forming a valve prevents backflow of urine into ureters. All the urinary passage are covered externally by an adventitia layer, except for the upper part of bladder which is covered by serous peritoneum..

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