Male urethra anatomy

The male urethra is the urinary passage and the ejaculation passage. It originates from the internal urethral opening and ends at the external urethral opening at the tip of the glans penis. It is about 18 cm long in an adult and can be divided into three parts: the male prostate part (the part that passes the male prostate), the membranous part (the part that passes the urogenital diaphragm, about 1.2 cm long) and the corpus cavernosum (the part that passes the corpus cavernosum of the urethra). In clinical medicine, the male prostate part and the membranous part are collectively referred to as the posterior urethra, and the corpus cavernosum is called the anterior urethra.

Components

Male prostate

The male prostate part is the part of the urethra that passes through the male prostate. The lumen is the widest and is about 2.5cm long. There is a longitudinal protrusion on the posterior inner wall, called the urethra crest, and the part of the protrusion in the middle of the crest is called the spermatic colliculus. There is a small indentation in the center of the spermatic colliculus, called the male prostate cyst. There is a pair of tiny vas deferens openings on both sides. There are many openings of male prostate metabolic ducts on the urethra mucosa around the spermatic colliculus; the membranous part is the part of the urethra that passes through the urogenital diaphragm, and is surrounded by the urethral membranous part. The lumen is narrow and is the shortest section of the three parts, about 1.2cm long; the penis cavernous body part is the part of the urethra that passes through the urethra cavernous body. The urethra inside the urethra bulb is the widest, called the urethral bulb, where the urethral gland opens. The urethral opening at the glans penis expands into the fossa navicularis. There are many mucous glands under the mucosa of the urethral opening, called urethral glands, whose metabolic ducts open into the mucosa.

The urethral opening has three anatomical narrow and wide 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 urethral openings in adults vary slightly, with an average of about 8 mm. The size of the urethral opening instruments used in theory is about 24 to 26. When using a ureteroscope or urethral dilation, No. 24 can be a larger standard. There are two bends along the entire line of the urethral opening, which are "S" shaped. The first bend is in the membranous part of the urethra, called the subphalangeal bend, with an angle of 93°. The second bend is located in the anterior phalangeal bend. When the male genitals are moved forward to the abdominal cavity, the anterior bend of the phalanges will disappear, but the posterior bend of the phalanges cannot be straightened artificially. Therefore, when inserting the equipment, it should be inserted gently along this bend, and not roughly to prevent 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 urethral membranous dilatation muscle, which is a transverse muscle and has the function of controlling urination. It is also called the external dilatation of the urethra. The membranous part is relatively fixed and is easily damaged when the pelvis is fractured. In clinical medicine, the male prostatic part and the membranous part of the urethra are combined into the posterior urethra.

Corpus cavernosum

The cavernous part of the penis is the part of the urethra that passes through the urethral cavernous body. It is the largest part of the urethra, 12~17cm long, and is clinically called the anterior urethra. The urethra in the urethral bulb is the widest, called the urethral bulb, where the urethral gland opens. The urethral opening in the glans penis is called the navicular fossa of urethra. There are many mucous glands under the mucosa of the urethra, called urethral glands, whose metabolic ducts open in the urethral mucosa.

Itinerary

The male urethra varies in size throughout its course, with three constrictions, three dilations, and two bends.

The three narrow parts are located at the internal urethral opening, the membranous part and the external urethral opening. In clinical medicine, it is most difficult to insert instruments or catheters into the urethra through the narrow part of the membranous part of the urethra. During actual operation, care should be taken to avoid damaging the urethral opening. The narrow part of the urethra is also the place where urethral stones are easily trapped.

In men, there are three dilations in the prostate, bulbar urethra, and fossa navicularis.

When the penis is flaccid, the urethral opening has two bends in total length: one bend is the inferior bend of the phalanges, located below the ischial tuberosity, 2 cm below the ischial tuberosity, concave forward and upward, including the start and end sections of the prostate, the membrane and the cavernous body of the penis. This bend is fixed and cannot be changed. The other bend is the anterior bend of the phalanges, located below the ischial tuberosity, concave backward, in the middle of the root and body of the penis. When the glans penis is lifted, this bend can be straightened. In clinical medicine, this feature is used to lift the glans penis, so that the entire urethral opening has only one concave upward bend, which is convenient for instruments or catheters to be inserted smoothly into the bladder.

Urethral wall tissue

The wall of the urethral opening is composed of the mucosal layer, the submucosal layer and the muscle layer. Outside the anterior urethra, there is also the urethral cavernous body, which is rich in elastic fibers and smooth muscle fibers. The epithelial cells of the urethral opening mucosa are transitional epithelial cells in the male prostate (near the bladder), and some are two-row or stratified columnar epithelial cells. In the part of the urethral opening with the urethral cavernous body, the main cells are stratified columnar epithelial cells, and there are also single-sided columnar epithelial cells on the wrinkle wall. There are many annular cells in the navicular fossa, and the distal part of the navicular fossa begins to have non-keratinized stratified squamous epithelium. The blood supply of the submucosal layer is rich and varied, and the key is connective tissue. The muscle layer has longitudinal muscles and external circular muscles.

Urethral gland

Urethral glands are scattered throughout the urethral opening, and are mainly concentrated in the anterior urethral cavernous body, called paraurethral glands. When erect, they can be squeezed and formed to metabolize clear mucus to moisten the surface of the urethral mucosa. When there is a chronic infection, they metabolize mucus. A pair of bulbourethral glands are located in the middle of the double layer of the triangular ligament, opening in the bulbourethral part, metabolizing clear and slightly grayish mucus, rich in protein, and part of the sperm produced during male ejaculation. The blood of the urethral opening is supplied by the internal aorta of the private part and the superior aorta of the bladder. Venous blood flows back to the private part and the peripheral venous plexus of the bladder. The key nerves for nerve manipulation are the private nerves, genital femoral nerves and central nerves.