What does it mean when the male urethra is narrowed in three places and has two bends?

The structure of the human body is truly amazing. One word to describe it is the work of God. Every tissue in the human body is so perfectly connected that even the slightest difference is not acceptable. Take the male urethra for example. In medicine, there is a saying that it has two bends and three strictures. However, male friends who have not studied medicine will definitely not understand it very well. So the question is, what does the three strictures and two bends of the male urethra mean?

Two physiological curves: pubic hypocurvature (convex downward and backward, located 2 cm below the pubic symphysis, constant); pubic anterior curvature (concave downward, located below the pubic symphysis, disappears when the penis is erect or lifted upward).

There are three strictures: internal urethral opening, membranous urethra, and external urethral opening.

Components

Prostate

The prostatic part is the part of the urethra that passes through the prostate. It has the widest lumen and is about 2.5 cm long. There is a longitudinal bulge on the posterior wall, called the urethral crest. The part that bulges in the middle of the crest 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. There are many openings of the 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 part 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.

Membrane

Membranous part is the part of the male urethra that passes through the urogenital diaphragm. It is about 1.5 cm long and is the shortest part of the male urethra. It is surrounded by the membranous urethral sphincter, which is a transverse muscle that controls urination and is also called the external urethral sphincter. The position of the membranous part is relatively fixed and it is easy to be injured when the pelvis is fractured. In clinical practice, the prostatic part and the membranous part of the urethra are combined to form the posterior urethra.

Cavernous body

The cavernous part is the part of the urethra that passes through the cavernous body of the urethra. It is the longest part of the urethra, 12 to 17 cm long, and is clinically called the anterior urethra. The urethra inside the bulbus urethra is the widest, called the bulbus urethra, where the bulbourethral glands open. The urethral dilation inside the glans penis is called the navicular fossa of urethra. There are many mucous glands in the submucosal layer of the urethra, called urethral glands, whose excretory ducts open in the urethral mucosa.

Shape during the trip

The male urethra varies in size 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.