ⓘ Seminal vesicle. The seminal vesicles, vesicular glands, or seminal glands, are a pair of simple tubular glands posteroinferior to the urinary bladder of some m ..

                                     

ⓘ Seminal vesicle

The seminal vesicles, vesicular glands, or seminal glands, are a pair of simple tubular glands posteroinferior to the urinary bladder of some male mammals. Seminal vesicles are located within the pelvis. They secrete fluid that partly composes the semen.

                                     

1. Structure

The seminal vesicles are a pair of glands that are positioned below the urinary bladder and lateral to the vas deferens. Each vesicle consists of a single tube folded and coiled on itself, with occasional diverticula in its wall.

The excretory duct of each seminal gland unites with the corresponding vas deferens to form the two ejaculatory ducts, which immediately pass through the substance of the prostate gland before opening separately into the verumontanum of the prostatic urethra.

Each seminal vesicle spans approximately 5 cm, though its full unfolded length is approximately 10 cm, but it is curled up inside the glands structure.

                                     

1.1. Structure Development

Each vesicle forms as an outpocketing of the wall of the ampulla of one vas deferens. The seminal vesicles develop as one of three structures of the male reproductive system that develops at the junction between the urethra and vas deferens. The vas deferens is derived from the mesonephric duct, a structure that develops from mesoderm.

                                     

1.2. Structure Histology

Under microscopy, the seminal vesicles can be seen to have a mucosa, consisting of a lining of interspersed columnar cells and a lamina propria; and a thick muscular wall. The lumen of the glands is highly irregular and stores secretions from the glands of the vesicles. In detail:

  • The epithelium is pseudostratified columnar in character, similar to other tissues in the male reproductive system.

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

  • A muscular layer, consisting of an inner circular and outer longitudinal layer of smooth muscle, can also be found.
  • The lamina propria, containing underlying small blood vessels and lymphatics. Together with the epithelia, this is called the mucosa, and is arranged into convoluted folds, increasing the overall surface area

Spermatozoa may occasionally be found within the lumen of the glands, even though the vesicles are blind-ended in nature. This is thought to be because of slight reflux due to muscular contractions of the urethra during ejaculation.



                                     

2. 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 70-85% 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. Seminal vesicle fluid is alkaline, resulting in human semen having a mildly alkaline pH. The alkalinity of semen helps neutralize the acidity of the vaginal tract, prolonging the lifespan of sperm. Acidic ejaculate (pH