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The human male urethra laid open on its anterior (upper) surface. In the human male, the urethra is on average 18 to 20 centimeters (7 to 8 inches) long and opens at the end of the external urethral meatus. [10] The urethra is divided into four parts in men, named after the location: [10]
Male urinary meatus Drawing of male internal sexual anatomy. The male external urethral orifice is the external opening of the urethra, normally located at the tip of the glans penis, [1] at its junction with the frenular delta.
The male urethra enters the penis at the superior aspect of the anterior part of the bulb (most of the bulb is thus situated inferoposteriorly to the urethra), and the arteries of bulb of penis enter near the urethra. [2] The bulb of penis is homologous to the vestibular bulbs in females. [3]
The female or male external sphincter muscle of urethra (sphincter urethrae): located in the deep perineal pouch, at the bladder's distal inferior end in females, and inferior to the prostate (at the level of the membranous urethra) in males. It is a secondary sphincter to control the flow of urine through the urethra.
The spongy urethra (cavernous portion of urethra, penile urethra) is the longest part of the male urethra, and is contained in the corpus spongiosum of the penis. It is about 15 cm long, and extends from the termination of the membranous portion to the external urethral orifice .
Inside the penis is the urethra, which is used to ejaculate semen and to excrete urine. Both substances exit through the meatus. When a male becomes sexually aroused, erection occurs because sinuses within the erectile tissues of the penis (corpora cavernosa and corpus spongiosum) become filled with blood.
The prostatic urethra, the widest and most dilatable part of the urethra canal, is about 3 cm long.. It runs almost vertically through the prostate from its base to its apex, lying nearer its anterior than its posterior surface; the form of the canal is spindle-shaped, being wider in the middle than at either extremity, and narrowest below, where it joins the membranous portion.
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.