Distribution of the male urethra

The male urethra is composed of the glans penis, prostate, and cavernous body tissues. The prostate and the membrane belong to the posterior urethra, while the cavernous body needs to be separated. The prostate is the tissue through which the urethra passes. There must also be vas deferens on both sides, which are connected to the seminal vesicles. Only by conducting an anatomical analysis of the male reproductive organs can we fully understand the distribution of the urethra and the functions of the male reproductive organs.

The male urethra is both a urinary and sperm excretion channel. It starts 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 for adults and can be divided into three parts: the prostatic part (the part that passes through the prostate), the membranous part (the part that passes through the urogenital diaphragm, about 1.2 cm long) and the cavernous body (the part that passes through the urethral cavernous body). Clinically, the prostatic part and the membranous part are collectively called the posterior urethra, and the cavernous body is called the anterior urethra.

1. Physiological structure:

1. 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 24~26 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.

(ii) Membrane part:

The membranous part of the male urethra is the part of the 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. Clinically, the prostatic part and the membranous part of the urethra are combined to form the posterior urethra.

(iii) Cavernous body:

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

2. Urethra 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.