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The anatomy of the human urinary system differs between males and females at the level of the urinary bladder. In males, the urethra begins at the internal urethral orifice in the trigone of the bladder, continues through the external urethral orifice, and then becomes the prostatic, membranous, bulbar, and penile urethra.
The external genitalia of both males and females have similar origins. They arise from the genital tubercle that forms anterior to the cloacal folds (proliferating mesenchymal cells around the cloacal membrane). The caudal aspect of the cloacal folds further subdivides into the posterior anal folds and the anterior urethral folds.
Neurogenic bladder dysfunction can involve a malfunctioning urethral sphincter. [8] Urge incontinence can happen when the urethra cannot hold the urine in as the bladder contracts uncontrollably. [9] Retrograde ejaculation can occur in men when the internal urethral sphincter fails to adequately contract during ejaculation. [3]
The female urethra is located between the bladder neck to the external urethral orifice and is behind the symphysis pubis. [4] The urethral wall is composed of an inner epithelial lining, a sub-mucosa layer containing vascular supply, a thin fascial layer, and two layers of smooth muscle.
The walls of the bladder have a series of ridges, thick mucosal folds known as rugae that allow for the expansion of the bladder. The detrusor muscle is the muscular layer of the wall made of smooth muscle fibers arranged in spiral, longitudinal, and circular bundles. [ 8 ]
The muscle helps maintain continence of urine along with the internal urethral sphincter which is under control of the autonomic nervous system.The external sphincter muscle prevents urine leakage as the muscle is tonically contracted via somatic fibers that originate in Onuf's nucleus and pass through sacral spinal nerves S2-S4 then the pudendal nerve to synapse on the muscle.
The vesicles are 5–10 cm in size, 3–5 cm in diameter, and are located between the bladder and the rectum. They have multiple outpouchings, which contain secretory glands, which join together with the vasa deferentia at the ejaculatory ducts. They receive blood from the vesiculodeferential artery, and drain into the vesiculodeferential veins.
The rectovesical pouch is a space between the rectum and the bladder in men. [1] It lies above the seminal vesicles. [2] It is lined by peritoneum and at its base is the rectoprostatic fascia (Denonvillier's fascia). When a man is upright or supine, it is the lowest part of his peritoneal cavity. [3]