The Anatomy of the Male Pelvis
The anatomy of the pelvis varies depending on whether you are male or female. The male pelvic organs include the penis and various glands and ducts. The testicles and scrotum are also important male structures.
The male urethra and the penis
The male urethra is a muscular tube that runs through the prostate, perineal membrane and muscles, and the penis from the internal urethral orifice of the urinary bladder to the external urethral orifice located at the tip of the glans penis (the bulbous structure at the distal end). It conveys urine, as well as semen, out of the body.
The urethra is divided into the following four parts:
Preprostatic part: Surrounded by the internal urethral sphincter, which prevents semen from entering the bladder during ejaculation (the release of semen through the urethra)
Prostatic part: Surrounded by the prostate gland
Intermediate (membranous) part: Surrounded by another sphincter called the external urethral sphincter
Penile (spongy) part: Runs through the penis
The prostatic nerve plexus provides innervation to the first three parts of the urethra. The penile (spongy) urethra is innervated by the dorsal nerve of the penis. The first two parts of the urethra get their blood supply from the inferior vesical and middle rectal arteries, while the rest of the urethra gets its blood flow from the internal pudendal artery. Blood is returned through their accompanying veins. Lymph drainage is mostly through the internal iliac lymph nodes, but some also goes to the external iliac lymph nodes and the deep inguinal lymph nodes.
The penis consists of three parts:
Root: The root contains three groups of erectile tissue called the bulb and the left and right crura. The bulb surrounds the urethra and is covered by bulbospongiosus muscles. Each crus is covered by ischiocavernosus muscle, which is attached to the pubic arch.
Body: The body contains the corpus spongiosum, which is a cylindrical continuation of the bulb, and the corpora cavernosa, which are formed by continuations of the two crura. All three cylinders of erectile tissue are surrounded by Buck’s fascia.
Glans: The corpus spongiosum expands distally to form the glans penis. The glans forms the corona of the glans, which is separated from the body by the neck of the glans. The external urethral orifice is the slit-like opening at the tip.
The glans penis is covered by a double layer of skin called the prepuce, or foreskin. The frenulum is a fold of skin that runs from the prepuce to the urethral surface of the glans.
The pudendal nerve via the dorsal nerve of the penis innervates the skin and glans. Parasympathetic innervation from the inferior hypogastric plexus supplies the vasculature of the erectile tissue. Blood is supplied to the penis by the branches of the internal pudendal arteries called the deep arteries of the penis, the arteries of the bulb, and the dorsal arteries of the penis. Blood returns via the pudendal veins. Lymph drains into the superficial inguinal nodes and internal iliac nodes.
Internal male organs
The internal male organs, or genital organs, include the testes, epididymides, vasa deferentia (ductus deferentia), seminal vesicles, ejaculatory ducts, prostate gland, and the bulbourethral glands.
The vas deferens is a long tube that carries sperm from the epididymis to the ejaculatory duct. It starts from the epididymis, goes through the inguinal canal, crosses the external iliac vessels, and enters the pelvis. It runs along the lateral wall of the pelvis and ends its course with a dilation called the ampulla of the vas deferens, and joins the duct of the seminal gland on the medial side of the seminal vesicle to form the ejaculatory duct. Each seminal vesicle lies on the posterior surface of the urinary bladder. They secrete thick fluid into the ejaculatory duct, which mixes with the sperm.
Blood supply to the vasa deferentia is from the superior vesicle arteries, and blood supply to the seminal vesicles comes from the inferior vesicle and middle rectal arteries and returns via the internal iliac veins. Lymph drains into the internal iliac nodes.
The prostate gland surrounds the prostatic part of the urethra. It’s about the size of a walnut. Its base sits near the neck of the urinary bladder, and its apex is next to the urogenital diaphragm. It’s covered in a thick fibrous capsule, which houses the prostatic plexuses of nerves and veins. The prostate has five lobes, the anterior, middle, posterior, and two lateral lobes. The prostate secretes a milky fluid that’s added to the seminal fluid at the time of ejaculation. Blood is supplied to the prostate by the inferior vesical, internal pudendal, and middle rectal arteries. Blood is returned via the prostatic venous plexuses, which is located around the base and sides of the prostate.
The fluids produced by the glands are alkaline in pH, which helps to neutralize the acidity of the female vagina.
The bulbourethral glands are two small glands located within the external urethral sphincter. They secrete a mucus-like fluid into the urethra during sexual arousal.