Seminal Vesicles and Accessory Glands

The seminal vesicles and bulbourethral glands are accessory sex glands that, together with the prostate, supply most of the fluid volume of semen. The paired seminal vesicles add a fructose-rich, alkaline secretion, while the bulbourethral glands contribute a pre-ejaculatory mucous secretion. This topic covers their anatomy and secretory functions.

Definition

The seminal vesicles are paired sacculated glands posterior to the bladder whose ducts join the vasa deferentia to form the ejaculatory ducts; they secrete a fructose-rich, alkaline fluid containing semenogelins that constitutes the largest fraction of seminal plasma and forms the semen coagulum.

Scope

The entry covers the gross anatomy and relations of the seminal vesicles, their union with the vas deferens to form the ejaculatory ducts, the bulbourethral (Cowper's) glands, and the composition and role of their secretions in semen, including semen coagulation. It is a reference description of normal structure and function and does not address disease of these glands. The prostate, the third major accessory gland, is covered in its own topic.

Core questions

• Where are the seminal vesicles located and how do they connect to the ejaculatory ducts?
• What does seminal-vesicle fluid contribute to semen?
• What are the bulbourethral glands and what do they secrete?
• How do accessory-gland secretions affect semen coagulation and sperm function?

Key concepts

• Seminal vesicle and ejaculatory duct
• Fructose as a sperm energy source
• Semenogelins and semen coagulation
• Alkaline seminal plasma
• Bulbourethral (Cowper's) glands
• Seminal plasma composition

Mechanisms

Each seminal vesicle is a coiled, sacculated gland lying posterior to the bladder; its duct joins the ampulla of the vas deferens to form the ejaculatory duct, which traverses the prostate to open at the verumontanum. Seminal-vesicle epithelium secretes a viscous, alkaline, fructose-rich fluid containing semenogelins; the fructose provides an energy substrate for spermatozoa, the alkalinity helps buffer the acidic vaginal environment, and semenogelins cause the ejaculate to coagulate, which is later liquefied by prostatic prostate-specific antigen. The paired bulbourethral glands, below the prostate, secrete a clear mucous fluid into the urethra that precedes ejaculation and lubricates the passage.

Clinical relevance

The secretions of the seminal vesicles and bulbourethral glands determine much of the volume and biochemistry of semen, which is relevant to semen analysis and to the anatomy of pelvic surgery. This entry describes normal structure and function for educational orientation and is not a basis for diagnosing or treating disease of these glands.

Evidence & guidelines

The account of accessory-gland secretions draws on classic biochemical work on human semen and on standard anatomical references. As a normal-anatomy topic it is not governed by disease-specific guidelines.

History

Classic mid-twentieth-century biochemical studies, including work by Huggins and colleagues, characterised the distinct contributions of the prostate and seminal vesicles to semen, establishing fructose as a marker of seminal-vesicle secretion and clarifying the coagulation-liquefaction cycle.

Key figures

• Charles B. Huggins

Seminal works

• huggins-1942

Frequently asked questions

What is the main contribution of the seminal vesicles to semen?

The seminal vesicles supply the largest fraction of seminal-fluid volume: a fructose-rich, alkaline secretion containing semenogelins that causes the ejaculate to coagulate.

What do the bulbourethral glands do?

The paired bulbourethral (Cowper's) glands secrete a clear mucous fluid into the urethra before ejaculation, helping to lubricate and neutralise the urethral passage.