SEMINAL VESICLE: CHARACTERISTICS, FUNCTIONS, HISTOLOGY - ANATOMY AND PHYSIOLOGY - 2025

The seminal vesicles, also known under the name of seminal glands, are the structures responsible for the production of approximately half the volume of seminal fluid in men. These consist of a tube folded and rolled on itself.

Anatomically, it is located in a region called the pelvic cup. This is located behind the urinary bladder and in front of the rectum. It is attached to the prostate through the lower end.

The ejaculatory duct is formed by the excretory duct of the seminal vesicle and the vas deferens. Both converge in the urethra. It is a unique organ of the male sex and there is no equivalent or homologous structure in females.

characteristics

General morphology of the seminal vesicle

The normal gallbladder of an average adult is piriform and is in the range of 5 to 10 cm long, and a diameter of 3 to 5 centimeters. However, the vesicles decrease in size over the years.

The gallbladder can store a mean volume of up to 13 mL. A certain pattern has been found in which some men display the right gland slightly larger than the left.

Composition of the seminal vesicle

The vesicle is made up of a tube that is wound multiple times on itself, tripling the length of the seminal vesicle. If we observe a cut of the gallbladder, we will see a significant number of cavities that seem to communicate with each other.

The upper limb is widened and an excretory duct emerges from the lower limb or neck, which is coupled with the ejaculatory duct.

The ejaculatory duct is the junction of a vas deferens, which exits a testicle, and joins a secretory duct of the seminal vesicle. The vas deferens are a pair of tubes made of smooth muscle and can measure up to 45 cm.

In these tubes, mature sperm are transported to another conduit where they mix with other additional fluids and finally leave the male body during the event of ejaculation.

The wall is made up of smooth muscle and is lined by mucous cells that secrete a viscous substance. This product will participate in the constitution of semen.

Histology

Source: Nephron

Each seminal vesicle is an evagination of the efferent duct. The gallbladder is a collection of tightly wound tubes.

Histologically, the sections of the structures show a significant number of lumens or holes. However, all you see is the image of a single tubular light that is continuous - let's try to visualize what it would look like if we cut a rolled tube multiple times.

As we mentioned, the seminal vesicle is lined by a pseudostratified epithelium of the columnar type that is similar to that found in the prostate gland.

The mucosa of the seminal glands is characterized by being wrinkled. These folds differ in size and are generally branched and connected to each other.

The folds that are larger can form recesses with the smaller folds. Thus, when they are sectioned, a kind of arches or villi are observed, depending on the plane of the cut. In certain sections, particularly in the periphery of the lumen, the folds of the mucosa reach a configuration of alveoli.

Features

Currently, not all the physiological functions performed by seminal vesicles have been fully elucidated.

However, what is known is that the fluid that is secreted by these male glands is of vital importance for the motility and metabolism of the sperm transported in the event of ejaculation.

These secretions contribute 50 to 80% of the total ejaculate volume - on average it would be about 2.5 mL. We will now describe in detail the composition of the secretions of these important glands.

Seminal vesicle secretions

It is a discharge with a viscous texture and a white or yellowish hue. The chemical composition of this product is made up of:

Fructose and other sugars

Chemically, the secretion of the seminal vesicle is composed of significant amounts of fructose and other simple sugars.

These carbohydrates are very important to promote sperm motility, since they serve as a nutritional source. The sperm will use these sugars until one of them manages to fertilize the egg.

Prostaglandins

The secretion of the seminal gland is rich in prostaglandins E, A, B and F. Prostaglandins are lipid molecules made up of 20 carbon atoms and contain a cyclopentane ring in their structure.

These molecules have the ability to affect different systems, including the nervous and reproductive systems. They are also involved in pressure and blood clotting.

Prostaglandins are believed to contribute to fertilization as they can react with the female's cervical mucus and make the movement of sperm more fluid.

In the same way, it can stimulate contractions in the female reproductive system that would favor the movement of the sperm to reach the ovaries and thus promote fertilization.

Although prostaglandins were molecules first found in the prostate (for this reason they are known as prostaglandins), they are synthesized within the seminal vesicles in significant quantities.

Semenogelin 1

The seminal vesicle product was found to contain a 52 kDa molecular weight protein called Semenogelin 1. It is speculated that this protein disrupts sperm motility.

During ejaculation, the protein is cleaved by a proteolytic enzyme, called prostate specific antigen. Subsequently, the sperm regain their motility.

Other compounds

In addition, the secretion contains amino acids (the building blocks of proteins), ascorbic acid, and clotting factors.

Diseases

In seminal vesicles, primary pathologies are very rare. However, secondary injuries to structures are common.

Thanks to current diagnostic technologies (ultrasound, MRI, among others), the origin of the lesion studied can be precisely established. The most important pathologies are:

Embryological abnormalities

The pathologies of the seminal vesicle at the embryonic level occur when errors occur in the development of the individual. Errors in the area of ​​birth of the urethral bud cause late resorption of the structure - seminal vesicles begin to form around week 12 of embryogenesis.

According to studies, in half of men the ectopic ureters enter the posterior urethra, while in 30% of cases they join in the seminal vesicle. The remainder enters the vas deferens or ejaculatory ducts.

Infections

The seminal pathway is a region prone to infections caused by the presence of microorganisms. These can lead to an inflammatory process, clogging the ducts.

They can also negatively affect sperm motility. These infections can be easily detected by performing a urine culture.

Seminal vesicle overload

Although it is not a disease or a pathology as such, it is a condition that can cause discomfort in men. Remember that the gallbladder is responsible for generating more than half of the seminal fluid, so that an overload translates into swelling, sensitivity and in some cases, prolonged pain.

It is a common situation due to the infrequency or abstinence when having sex or masturbating. The way to relieve it is by releasing the extra seminal load through ejaculation.

Prolonged overload can have serious long-term consequences, such as rupture of the seminal ducts and sterility.

Gallbladder cysts

The seminal vesicle is prone to cyst development. These do not present symptoms - if their size is small, less than 5 centimeters - and they are generally identified incidentally, since the patient resorts to the study for some other medical reason. This condition is not common in men.

When the cyst is larger, the most common symptoms are pain when urinating and difficulty in performing this action, pain in the scrotum and pain during ejaculation.

Depending on the size of the cyst, the urinary ducts can become blocked. One way to remove it is through surgery.

Tumors

According to the data available in the medical literature, the most common tumors in the seminal vesicle are - in addition to benign ones - carcinomas and sarcomas. The first is reported with an incidence close to 70%, and the remainder is attributed to the presence of sarcomas.

The presence of tumors in the seminal vesicle is much more frequent due to secondary invasion, compared to the appearance of primary tumors in the area. Also, in most cases, primary tumors are detected at a fairly advanced stage, making treatment difficult.

This diagnosis can be made by clinical and radiological means. Subsequently, a histological study of the region is carried out to corroborate the result. Treatment of this pathology includes surgical removal and radiation therapy.

In the case of benign tumors, surgery will only be performed when the tumor volume is considered dangerous or if there are histological doubts.

References

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3. Flores, EE, & Aranzábal, MDCU (Eds.). (2002). Atlas of Vertebrate Histology. UNAM.
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