The membranous urethra or intermediate part of male urethra is the shortest, least dilatable, and, with the exception of the
urinary meatus, the narrowest part of the
urethra
The urethra (: urethras or urethrae) is the tube that connects the urinary bladder to the urinary meatus, through which Placentalia, placental mammals Urination, urinate and Ejaculation, ejaculate.
The external urethral sphincter is a striated ...
. It extends from the apex of the prostate proximally to the
bulb of urethra distally. It measures some 12 mm in length. It traverses the pelvic floor. It is surrounded by the
external urethral sphincter, which is in turn envelopped by the
superior fascia of the urogenital diaphragm.
Anatomy
The mucosal internal lining of the membranous urethra features some longitudinal folds which disappear when the urethra becomes distended.
Relations
It extends downward and forward, with a slight anterior concavity, between the apex of the
prostate
The prostate is an male accessory gland, accessory gland of the male reproductive system and a muscle-driven mechanical switch between urination and ejaculation. It is found in all male mammals. It differs between species anatomically, chemica ...
and the
bulb of the urethra, perforating the
urogenital diaphragm
Older texts have asserted the existence of a urogenital diaphragm, also called the triangular ligament, which was described as a layer of the pelvis that separates the deep perineal sac from the upper pelvis, lying between the inferior fascia of ...
about 2.5 cm below and behind the
pubic symphysis.
The hinder part of the urethral bulb lies in apposition with the inferior fascia of the urogenital diaphragm, but its upper portion diverges somewhat from this
fascia
A fascia (; : fasciae or fascias; adjective fascial; ) is a generic term for macroscopic membranous bodily structures. Fasciae are classified as superficial, visceral or deep, and further designated according to their anatomical location.
...
: the anterior wall of the membranous urethra is thus prolonged for a short distance in front of the urogenital diaphragm; it measures about 2 cm in length, while the posterior wall which is between the two fasciæ of the diaphragm is only 1.25 cm long. The anatomical variation in membranous urethral length measurements in men have been reported to range from 0.5 cm to 3.4 cm.
The membranous portion of the urethra is surrounded by the fibers of the
sphincter urethrae membranaceae.
In front of it the
deep dorsal vein of the penis enters the
pelvis
The pelvis (: pelves or pelvises) is the lower part of an Anatomy, anatomical Trunk (anatomy), trunk, between the human abdomen, abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also c ...
between the
transverse ligament of the pelvis and the
arcuate pubic ligament; on either side near its termination are the
bulbourethral glands.
Additional images
File:Illu penis.jpg, Structure of the penis
File:Gray1156.png, Vertical section of bladder, penis, and urethra.
References
External links
* - "The Female Pelvis: The Urethra"
* - "The Male Pelvis: The Urethra"
*
Male urethra
{{Portal bar, Anatomy