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The perineum: boundaries, triangles, muscles, blood and nerves supply, lymphatic drainage. Pelvic diaphragm, urogenital diaphragm, their structure in female and male

Is area corresponding to the pelvic outlet and is filled with striated muscles, which are invested in fasciae and form together with them two diaphragms: urogenital diaphragm and the pelvic diaphragm. Both diaphragms transmit to the exterior canals of the urogenital and digestive systems for which they form sphincters closing the external openings of these canals.

The peritoneum can be compared with a diamond shaped figure whose four angles correspond with the following four points: the pubic symphysis in front, the apex of the coccyx behind, and the ischial tuberosity on the right and left. The area is made up of two triangles, an anterior one filled by the urogenital diaphragm and a posterior triangle filled by the pelvic diaphragm.

Both diaphragms contain muscles arranged in two layers, deep and superficial. The urogenital diaphragm consists of muscles which had initially surrounded the opening of the cloaca. After the cloaca seperates into the rectum and the urogenital sinus. The sphincter muscle of cloaca also separates into two parts: posterior part and anterior.

The perineal region is supplied with the arterial blood from the internal pudendal artery. The veins pass in attendance to the arteries. Lymph drained into the superficial inguinal lymph nodes.

Urogenital diaphragm: the deep transverse perinea m, the sphincter urethrae m, bulbospongiosus m, ischiocavernosus m.

The pelvic diaphragm: m.levator ani, m.coccygeus

The urogenital hiatus is necessary to allow the passage of the urethra in both males and females and the vagina in females. However, the opening in the pelvic diaphragm is too large to remain uncovered. Without the presence of the muscles and fascia of the urogenital diaphragm, it would be easy for pelvic structures to collapse through the hiatus (prolapse).

In the male, the urogenital diaphragm contains the second (membranous) portion of the urethra, nerves and vessels, and the bulbourethral. Although these glands are located on either side of the membranous urethra, their ducts penetrate the perineal membrane to enter the third portion of the urethra, the spongy urethra.

In the female, the urogenital diaphragm is penetrated by the vagina and contains the membranous urethra and neurovascular structures. The vagina is located just posterior to the membranous urethra and is attached to this portion of the urethra by means of connective tissue.

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