The seminal vesicles are two glands present only in the male reproductive system. The seminal vesicles together with the prostate and the bulbourethral glands form the group of the accessory sex glands. They are located above the prostate, one on each side. Their job is to secrete a sticky substance that constitutes semen, along with the sperm produced by the testes and a complex product secreted by the prostate gland and the bulbourethral glands.

The seminal vesicles release a fluid that is rich in sugars, particularly fructose, which feeds the sperm. The fluid also contains clotting factors that cause the sticky characteristic of semen. This substance facilitates the semen to stay inside the vagina enough time for the sperm to travel to the egg. Another fluid produced by the seminal vesicles is prostaglandins, which may facilitate fertilization by increasing the receptiveness to sperm of the mucous lining of the cervix. Moreover, prostaglandins may aid the movement of the sperm toward the ovum.

Overall, the seminal vesicles provide approximately 60% of the fluids that are passed from the male human body during ejaculation.

What are the seminal vesicles?

The seminal vesicles are two glands that belong to the male reproductive system. These two egg-shaped glands are members of the sperm transport, they have a length of about 5 cm and extend the excretory ducts, which in turn, flow into the vas deferens. Moreover, the seminal vesicles are blind pouches that are rounded on the most superior portion and taper on the inferior portion where they become narrower and form short ducts. These short ducts joint the lateral portion of the ducts deferens creating the ejaculatory ducts at the base of the prostate.

The size and functions of the seminal vesicles are regulated by hormones such as androgen. Androgen is the major hormone that regulates the development and activity of the seminal vesicles and its production begins during puberty and begins to decline around the age of 30. Without this hormone, the seminal vesicles will eventually atrophy.

There are three diseases in particular that can affect the seminal vesicles and cause reduced fertility or complete infertility: infections, hemospermia (condition characterized by bleeding of the mucous membranes lining the vesicles involving the presence of blood in the semen) and tumours (rare cases).

The primary arterial supply of the seminal vesicles originates from the anterior division of the internal iliac artery, which provides three sources of blood supply: the inferior vesical, internal pudendal and middle rectal arteries. Moreover, the innervation of the seminal vesicles comes from the sympathetic nervous system, whose nerve fibres originate from the inferior hypogastric plexus.

What function do the seminal vesicles serve?

The main function of the seminal vesicles is to produce a sticky substance that makes up the sperm, which makes up about two-thirds of the total volume. During ejaculation the two seminal vesicles undergo a contraction, thanks to which they can convey their content in the vas deferens; once it reaches the vas deferens, the secreted vesicular substance mixes with sperm produced from the testicles.