Male urethra structure

The urethra of both men and women carries the function of normal urination, and the male urethra opening is a magical place, because their urethra opening can both urinate and ejaculate. This urethra opening has dual functions, which leads to a much higher probability of disease in the male urethra opening than in women. And every normal man should have some understanding of the relevant structure of the male urethra opening.

Male urethra

The male urethra has a dual function of both urination and ejaculation.

The male urethra is about 16-22 cm long, from the urethral opening at the neck of the bladder to the external urethral opening. The average diameter is 5-7 mm. It can be divided into the penis part (cavernous body part), bulb part, membranous part and prostatic part. Clinically, the prostatic part and membranous part are called the posterior urethra.

The anterior urethra starts from the urethral opening and ends at the bulb. It is about 15 cm long and is covered by the corpus cavernosum. It is attached to the two shallow grooves of the corpus cavernosum of the penis. This section of the urethra is movable and therefore not easily injured. The two ends of the anterior urethra are enlarged, one at the urethral opening, called the fossa navicularis, and the other at the bulbus urethra.

The posterior urethra starts from the membranous urethra and ends at the neck of the bladder, and is about 4 cm long. The membranous urethra is the shortest, only about 1 cm, and is located between the two layers of triangular ligaments. It is surrounded by the striated muscle, the external sphincter, and is the most fixed and weakest section. It is easy to get injured if the urethra instrument is used improperly, and it is also the most vulnerable part when the perineum is violently squeezed. The prostatic urethra is about 3 cm long, starting from the triangular ligament, passing through the entire gland, to the neck of the bladder. It is the widest part of the entire urethra. In the center of the posterior wall of this section of the urethra, there is a protrusion called the urethral ridge or the seminal colliculus, and there is a crypt in the middle of it. The ejaculatory ducts open on both sides of the crypt, and the prostatic tubules open in the grooves on both sides of the seminal colliculus.

Prostate

The prostatic part is the part of the urethra that passes through the prostate. The lumen is the widest and is about 2.5 cm long. There is a longitudinal bulge on the posterior wall, called the urethral ridge, and the part that bulges in the middle of the ridge is called the colliculus. There is a small depression in the center of the colliculus, called the prostatic cyst. There is a pair of small ejaculatory duct openings on both sides, and there are many openings of prostatic excretory ducts on the urethral mucosa near the colliculus; the membranous part is the part of the urethra that passes through the urogenital diaphragm. It is surrounded by the membranous urethral sphincter and has a narrow lumen. It is the shortest of the three parts and is about 1.2 cm long; the cavernous body is the part of the urethra that passes through the urethral cavernous body. The urethra inside the urethral bulb is the widest, called the bulbous urethral part, where the bulbourethral gland opens. The urethra at the glans penis expands into the fossa scaphoidae. There are many mucous glands under the urethral mucosa called urethral glands, and their excretory ducts open in the mucosa.

The urethra has three anatomical narrow parts and dilated parts. The former are located at the external opening, membranous part and internal opening respectively, and the latter are located at the navicular fossa, bulbous part and prostatic part. The diameters of normal adult urethra vary slightly, with an average of about 8 mm. The commonly used urethral instruments are about 24 to 26 in size. When using a cystoscope or urethral dilation, size 24 can be used as the maximum standard. There are two bends in the entire urethra, which are "S" shaped. The first bend is in the membranous part of the urethra, called the subpubic bend, with an angle of 93°. The second bend is located in the prepubic bend. When the penis is moved forward toward the abdominal wall, the anterior pubic curvature disappears, but the inferior pubic curvature cannot be straightened artificially. Therefore, when inserting the instrument, it should be inserted gently along this curvature, and not roughly to avoid injury.

Shape during the trip

The male urethra varies in thickness along its course, with three narrowings, three dilations, and two bends.

The three strictures are located at the internal urethral opening, the membranous part, and the external urethral opening. When inserting instruments or catheters into the urethra, it is most difficult to pass through the stricture of the membranous part of the urethra. Care should be taken to prevent damage to the urethra during the operation. The stricture of the urethra is also the place where urethral stones are easily entrapped.

Three enlargements are located in the prostatic part, bulbar urethra, and fossa navicularis.

When the penis is sagging, the urethra has two bends along its entire length: one bend is the inferior pubic bend, located below the pubic symphysis, 2 cm below the pubic symphysis, concave forward and upward, including the prostate, membranous part and the starting section of the cavernous body. The position of this bend is fixed and cannot be changed. The other bend is the anterior pubic bend, located below the pubic symphysis, concave backward and downward, between the root and body of the penis. When the penis is lifted, this bend can disappear and become straight. In clinical practice, this feature is used to lift the penis, and the entire urethra has only one concave upward bend, so that instruments or catheters can be smoothly inserted into the bladder.

Urethral wall tissue

The urethral wall is composed of the mucosal layer, submucosa layer and muscle layer. On the outside of the anterior urethra, there is also the urethral cavernous body which is rich in elastic fibers and smooth muscle fibers. The urethral mucosal epithelium is transitional epithelium in the prostatic part (near the bladder), and part of it is multi-row or stratified columnar epithelium. In the part of the urethra with the urethral cavernous body, it is mainly stratified columnar epithelium, and there is also single-layer columnar epithelium on the folds. There are many circular cells in the navicular fossa in particular, and non-keratinized stratified squamous epithelium begins to appear at the distal end of the navicular fossa. The submucosa has a rich blood supply and is mainly connective tissue. The muscle layer has longitudinal muscles and external circular muscles.

Urethral glands

Urethral glands are scattered throughout the urethra, mainly concentrated in the anterior urethral cavernous body, called paraurethral glands. During erection, they can be squeezed and secrete clear mucus to lubricate the surface of the urethral mucosa. In chronic infection, they actually secrete sticky threads. A pair of bulbourethral glands are located between the two layers of the triangular ligament, opening in the bulb of the urethra. They secrete clear and slightly gray mucus, rich in protein, and form part of the semen during ejaculation. The blood of the urethra is supplied by the internal pudendal artery and the superior vesical artery. Venous blood returns to the pudendal and perivesical venous plexus. The nerve innervation is mainly the pudendal nerve, genitofemoral nerve and sympathetic nerve.