longitudinal and an inner circular layer of smooth muscles. Close to the lumen lies the mucosa consisting of a columnar epithelium with cuboidal cells along the lamina propria. The height of the cells mirrors their activity depending on the serum testosterone level. Excretory ducts open into the ductus ejaculatorius of the ductus deferens as it enters the prostate.

In former times,seminal vesicles were thought to store semen – hence their name. However, this turned out to be wrong. The secretion is strongly acidophilic and constitutes 60–80% of the ejaculate volume. It contains several proteins and enzymes, as well as mucus and vitamin C. The yellow fluorescing pigment flavin is of use in forensic medicine for the detection of semen stains.Prostaglandins stimulate smooth muscles of the female genital tract to enhance the migration of sperm from the vagina to the uterus. The large amount of fructose serves as an energy source for the sperm.

Blood supply via arteria vesicalis inferior,arteria rectalis media, and arteria ductus deferentis. Veins open into the plexus vesicoprostaticus. Lymphatic drainage occurs via nodi lymphatici iliaci interni et externi et hypogastrici. Nerves originate from plexus hypogastricus superior et inferior.

Clinic: The fructose concentration within the seminal plasma serves as indicator for the function of the seminal vesicles (reference >13 mmol ejaculate12;), especially in patients with a central

obstruction of the seminal pathways and agenesis of the glands.

Bulbourethral Glands

Bulbourethral glands or Cowper’s glands are homologous to Bartholin’s glands in the female. They are located posterior-lateral to the membranous portion of the urethra at the base of the penis. Glandular units are surrounded by smooth muscles originating from the musculus transversus perini profundus. Excretory ducts open into the ampulla of the urethra releasing a clear viscous secretion known as pre-ejaculate.

Penis

The human penis is made up of three columns of tissue (Fig. 4.15). Two corpora cavernosa are located next to each other on the dorsal side and one corpus spongiosum lies between them on the ventral side. The end of the corpus spongiosum is enlarged and forms the glans, which supports the foreskin or prepuce, a loose fold of skin that in adults can retract to expose the glans. The area on the underside of the penis, where the foreskin is attached, is called the frenulum. The urethra traverses the corpus spongiosum and its opening lies on the tip of the glans. It is a passage for both urine and semen. The raphe is the visible ridge between

the lateral halves of the penis, found underside of the penis running from the meatus (opening of the urethra) across the scrotum to the perineum (area between scrotum and anus).

The glans penis is homologous to the clitoral glans, the corpora cavernosa are homologous to the body of the clitoris and the corpus spongiosum is homologous to the vestibular bulbs beneath the labia minora. The raphe does not exist in females because there the two halves are not connected.

Blood supply via arteriae pudenda interna dextra et sinistra from which there originate three branches: (1) Arteria dorsalis penis to skin, prepuce and glans; (2) Arteria profunda penis which give rise to several arteriae helicinae that opens into the chambers of the corpora cavernosa; (3) Arteria bulbi penis to urethra and corpus spongiosum. Many venae circumflexae merges to the vena dorsalis penis that opens into the plexus vesicoprostaticus. Lymphatic

drainage occurs via nodi lymphatici inguinales. Sensoric nerves originate from the nervus pudendus. The sympathicus is responsible for vasoconstriction, while the parasympathicus causes vasodilation.

Erection and Ejaculation

Erection is caused by the parasympathic (S3 of spinal cord) dilation of the arteriae helicinae that supply blood to the chambers of the corpora cavernosa. As a consequence, more and more blood fills the chambers causing the penis to lengthen and stiffen. The now engorged erectile tissue presses against and constricts the veins that carry blood away from the penis. As a consequence, more blood enters than leaves the penis until an equilibrium is reached where an equal volume of blood flows into the dilated arteries and out of the constricted veins.