seminal vesicle

Seminal vesicle
Human Male Anatomy
Prostate with seminal vesicles and seminal ducts, viewed from in front and above.
Latin	vesiculæ seminales
Gray's	subject #260 1246
Artery	Inferior vesical artery, middle rectal artery
Lymph	external iliac lymph nodes, internal iliac lymph nodes
Precursor	Wolffian duct
MeSH	Seminal+Vesicles

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

Anatomy

Each seminal gland spreads approximately 5 cm, though the full length of seminal vesicle is approximately 10 cm, but it is curled up inside of the gland's structure. Each gland forms as an outpocketing of the wall of ampulla of each vas deferens.

The excretory duct of seminal gland opens into the vas deferens as it enters the prostate gland.

Function

The seminal vesicles secrete a significant proportion of the fluid that ultimately becomes semen. Lipofuscin granules from dead epithelial cells give the secretion its yellowish color. About 60% of the seminal fluid in humans originates from the seminal vesicles, but is not expelled in the first ejaculate fractions which are dominated by spermatozoa and zinc-rich prostatic fluid. The excretory duct of each seminal gland opens into the corresponding vas deferens as it enters the prostate gland.

Prostatic secretion is acidic while seminal vesicle fluid is alkaline, and this results in human semen having a mildly alkaline pH.^[1] The alkalinity of semen helps neutralize the acidity of the vaginal tract, prolonging the lifespan of sperm. Acidic ejaculate (pH <7.2) may be associated with blockage of seminal vesicles.

The thick secretions from the seminal vesicles contain proteins, enzymes, fructose, mucus, vitamin C, flavins, phosphorylcholine and prostaglandins. The high fructose concentrations provide nutrient energy for the spermatozoa when stored in semen in the laboratory. Spermatozoa ejaculated in the vagina are not likely to have contact with the seminal vesicular fluid but transfer directly from the prostatic fluid into the cervical mucus as the first step on their travel through the female reproductive system. The fluid is expelled under sympathetic contraction of the muscularis muscle coat.

In vitro studies have shown that sperm expelled together with seminal vesicular fluid show poor motility and survival, and the sperm chromatin is less protected. Therefore the exact physiological importance of seminal vesicular fluid is not clear. It has been speculated that it is a developmental rest, still seen among some rodents where the last part of the ejaculate form a spermicidal plug which reduces the chances for sperm from a later arriving male to proceed to the oocyte.^{[citation needed]}

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

Additional images

Male reproductive system.	Coronal section of pelvis, showing arrangement of fasciae. Viewed from behind.	Male pelvic organs seen from right side.	Fundus of the bladder with the vesiculae seminales.
Vesiculae seminales and ampullae of ductus deferentes, seen from the front.	Vertical section of bladder, penis, and urethra.	Cross section of seminal vesicle through a microscope.

External links

• Histology at BU 17501loa - "Male Reproductive System: prostate, seminal vesicle"
• SUNY Labs 44:04-0202 - "The Male Pelvis: The Urinary Bladder"
• SUNY Labs 44:08-0103 - "The Male Pel

References

1. ^ "SEMEN ANALYSIS". www.umc.sunysb.edu. http://www.umc.sunysb.edu/urology/male_infertility/SEMEN_ANALYSIS.html. Retrieved 2009-04-28.