Seminal Vesicles

Introduction

Introduction to the Seminal Vesicles

The seminal vesicles are paired accessory glands of the male reproductive system located in the pelvis, posterior to the urinary bladder and superior to the prostate gland. They contribute significantly to the volume of seminal fluid, producing an alkaline secretion rich in fructose, prostaglandins, and coagulating enzymes. This fluid provides nourishment and motility support to spermatozoa, facilitating their survival and function during ejaculation.

Anatomical Context in the Male Pelvis

Within the male pelvis, the seminal vesicles are situated in the rectovesical pouch, bounded laterally by the pelvic walls and posteriorly by the rectum. Their anatomical position is critical for surgical and diagnostic procedures, as they lie in close proximity to the ureters, vas deferens, and neurovascular bundles. Understanding their spatial relationships is essential for avoiding iatrogenic injury during pelvic surgeries.

Study

Gross Anatomy and Structure

The seminal vesicles are elongated, lobulated sacs measuring approximately 5–7 cm in length and 1–2 cm in width. Each vesicle consists of a coiled tubular structure with a central lumen lined by pseudostratified columnar epithelium. The walls are composed of an inner mucosal layer, a middle smooth muscle layer, and an outer fibrous adventitia. The convoluted nature of the gland increases its secretory surface area, optimizing fluid production.

Developmental Origin and Embryology

The seminal vesicles develop as outpouchings from the mesonephric (Wolffian) ducts during the 12th week of gestation. Their formation is androgen-dependent, requiring the presence of testosterone and functional androgen receptors. Failure of proper development can result in congenital anomalies such as agenesis or hypoplasia, which may present with infertility or ejaculatory dysfunction in adulthood.

Neurovascular Supply and Lymphatic Drainage

The arterial supply to the seminal vesicles is primarily derived from the inferior vesical and middle rectal arteries, branches of the internal iliac artery. Venous drainage follows the arterial supply, emptying into the internal iliac veins. Lymphatic drainage occurs via the internal iliac lymph nodes, which also receive lymph from the prostate and bladder. Sympathetic innervation arises from the hypogastric plexus, regulating secretory activity and smooth muscle contraction during ejaculation.

Functional Role in Semen Production

The seminal vesicles contribute approximately 60–70% of the total ejaculate volume. Their secretions are alkaline, which helps neutralize the acidic environment of the male urethra and female reproductive tract, enhancing sperm viability. Fructose serves as an energy source for spermatozoa, while prostaglandins promote smooth muscle contraction in the female reproductive tract, aiding sperm transport. Coagulating enzymes facilitate the temporary clotting of semen post-ejaculation, preventing immediate leakage from the vagina.

Clinical Significance and Pathologies

Pathologies involving the seminal vesicles include infections (e.g., seminal vesiculitis), cysts, calculi, and neoplasms. Chronic inflammation may result from bacterial infections or systemic diseases such as tuberculosis. Primary tumors of the seminal vesicles are rare but may include adenocarcinoma or sarcoma. Imaging modalities such as transrectal ultrasound, MRI, or CT scans are essential for evaluating structural abnormalities, while seminal fluid analysis can assess functional impairment.

Summary

Key Takeaways

The seminal vesicles are paired accessory glands in the male pelvis that produce the majority of seminal fluid, which is essential for sperm nourishment, motility, and survival. Their anatomical position and neurovascular supply are critical for surgical planning and understanding potential complications. Developmental anomalies, infections, and neoplasms can impair their function, leading to reproductive or systemic health issues.

Clinical Correlate

Clinically, the seminal vesicles are relevant in the evaluation of male infertility, chronic pelvic pain, and hematospermia. Imaging studies are indispensable for diagnosing structural pathologies, while seminal fluid analysis can reveal functional deficits. Surgical procedures involving the pelvis, such as prostatectomy or rectal resection, require careful consideration of the seminal vesicles to avoid inadvertent injury and preserve reproductive function.