The Seminal Vesicles
What could a submarine possibly have in common with the seminal vesicles? Yup, you guessed it – they’re both full of semen. Located in the pelvis and intimately linked with the vas deferens, the seminal vesicles spend their time chugging out most of the constituent ingredients of semen, providing around 70% of its final volume.
In this article we’ll learn a little about the anatomical relations of the gland, its functions, neurovascular relations and clinical significance.
Anatomical Position and Structure
The seminal glands are a pair of small (5cm long) tubular glands. They are located between the bladder fundus and the rectum (separated from the latter by the rectovesicle pouch). Their most important anatomical relation is with the vas deferens, which combines with the duct of the seminal gland to form the ejaculatory duct, which subsequently drains into the prostatic urethra.
Internally the gland has a honeycombed, lobulated structure with a mucosa lined by pseudostratified columnar epithelium. These columnar cells are highly influenced by testosterone, growing taller with higher levels, and are responsible for the production of seminal secretions.
The Seminal glands, along with the Ejaculatory ducts, Epididymis and Ductus (vas) deferens, are derived from the mesonephric ducts, the precursor structure of male internal genitalia. These structures can easily be remembered using the handy acronym SEED.
The secretions of the seminal gland have a key role in the normal functioning of semen, none least as they make up 70% of its total volume. The secretions contain;
- Alkaline fluid – neutralises the acidity of the male urethra and vagina in order to facilitate the survival of spermatazoa.
- Fructose – provides an energy source for spermatozoa and helps ‘em keep on swimming.
- Prostaglandins – have a role in suppressing the female immune response to foreign semen.
- Clotting factors – designed to keep semen in the female reproductive tract post-ejaculation.
The remaining volume of semen is made up of testicular spermatozoa, prostatic secretions and mucus from the bulbourethral gland.
The arteries to the seminal gland are derived from the inferior vesicle, internal pudendal and middle rectal arteries, all of which stem from the internal iliac artery.
The innervation of the gland, like much of the male internal genitalia, is sympathetic in origin.
You can use the classic memory aid Point and Shoot to remember this. Erection, or pointing, receives parasympathetic innervation, while ejaculation (including contraction of the smooth muscle of the seminal vesicles) receives sympathetic innervation.
The lymphatic drainage of the gland is the external and internal iliac lymph nodes.
Seminal Gland Abscess
Abscess formation in the seminal glands can allow pus to enter the peritoneal cavity in the event of rupture. Swollen glands can be detected through digital rectal examination (DRE).
The seminal glands can be felt most easily through DRE, especially when the bladder is almost at full capacity. This palpability can allow the glands to be massaged to release their secretions, which can be collected and used for the microscopy of certain STIs such as gonnorhoea.