Seminal vesicle

The seminal vesicles are a pair of simple tubular glands posteroinferior to the urinary bladder of males.

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Anatomy

They are approximately 5 cm in length, though the full length of the gland is approximately 10 cm and curled up inside of the structure. Both glands form as an outpocketing of the wall of the ampulla of the vas deferens.

The ducts of the seminal vesicles open into the vas deferens as it enters the prostate gland.

Function

They secrete a significant proportion of the fluid that ultimately becomes semen. About 70% of the seminal fluid in humans originates from the seminal vesicles.

The thick secretions contain proteins, enzymes, fructose, mucus, vitamin C, flavins, phosphorylcholine and prostaglandins. The high fructose concentrations provide nutrient energy for the spermatozoa as they travel through the female reproductive system. The fluid is expelled under sympathetic contraction of the muscularis muscle coat.

Histology

Histologically, the seminal vesicles are notable for their tortuous pathways, diverticula, pseudo-stratified columnar epithelium and cuboidal cells along the basal layer.

The height of these columnar cells, and therefore activity, is dependent upon testosterone levels in the blood.

The lumen is large and stores the fluid secretions (but not spermatozoa) between ejaculations.

From inside to out, the layers are:

• Mucosa - arranged into convoluted folds, significantly increasing surface area
• Muscular - well-developed layer composed of an inner circular and outer longitudinal layer of smooth muscle
• Connective tissue

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