Urethra
In a male, the urethra is the tube that conveys both urine and semen to the outside of the body, at different times.
ANATOMY:
The urethra is the only exit to the urinary bladder. The proximal portion of the urethra is open to the inside of the urinary bladder where urine is stored. The distal end of the urethra is open to the outside of the body.
In a male, the urethra has 3 regions:
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Prostatic urethra- the proximal portion of the urethra is continuous with bladder superiorly, and surrounded by the prostate gland. The right and left ejaculatory ducts and numerous prostatic ducts open into the prostatic urethra.
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Membranous urethra- a short segment of the urethra that passes through the muscular pelvic floor, located between the prostatic and spongy urethra.
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Spongy urethra- also known as the penile or pendulous urethra, is the portion of the urethra distal to the membranous urethra. It travels through the corpus spongiosum, a column of erectile tissue in the penis and opens on the body’s external surface.
Figure 1: A labeled diagram of a midsagittal view of the urethra.
PHYSIOLOGY:
The urethra conveys urine to the outside of the body from the urinary bladder.
During ejaculation, the urethra conveys semen to outside of the body. The autonomic reflex regulating ejaculation closes the muscular exit to the bladder, so urine cannot enter the urethra during ejaculation.