USMLE Guide: Seminal Vesicles

Introduction

The seminal vesicles are male reproductive organs that play a vital role in the production and ejaculation of semen. This guide aims to provide a comprehensive overview of the seminal vesicles, including their anatomy, function, and clinical significance, in preparation for the United States Medical Licensing Examination (USMLE).

Anatomy

1. Location: The seminal vesicles are paired structures located behind the bladder and in front of the rectum.
2. Structure: Each seminal vesicle is a convoluted, sac-like structure measuring approximately 5-10 cm in length.
3. Relation to other structures:
   • Anteriorly: Posterior surface of the urinary bladder
   • Posteriorly: Rectum
   • Inferiorly: Prostate gland
   • Medially: Vas deferens (ductus deferens)

Histology

1. Epithelium: Pseudostratified columnar epithelium lines the inner surface of the seminal vesicles.
2. Glands: The seminal vesicles contain numerous branched tubular glands that produce the majority of the seminal fluid.

Function

1. Production of Seminal Fluid: Seminal vesicles contribute approximately 60-70% of the total volume of semen.
2. Composition of Seminal Fluid: Seminal fluid secreted by the seminal vesicles contains:
   • Fructose: Provides an energy source for spermatozoa.
   • Prostaglandins: Aid in sperm motility and fertility.
   • Fibrinogen: Promotes the clotting of semen after ejaculation.

Clinical Significance

1. Seminal Vesicle Infection: Seminal vesiculitis is an infection of the seminal vesicles usually caused by ascending urinary tract infections. It may present with lower abdominal pain, dysuria, and ejaculatory pain. Treatment involves antibiotics.
2. Obstruction or Seminal Vesicle Agenesis: Congenital absence or obstruction of the seminal vesicles may lead to infertility or ejaculatory dysfunction. Imaging studies, such as transrectal ultrasound or MRI, can help diagnose such conditions.
3. Prostate Cancer: Seminal vesicles are commonly involved in advanced prostate cancer. Palpable or fixed seminal vesicles during a digital rectal examination may indicate local spread of prostate cancer.

Summary

The seminal vesicles are paired male accessory reproductive organs located behind the bladder and in front of the rectum. They produce a significant portion of seminal fluid, contributing to sperm viability and fertility. Understanding the anatomy and function of seminal vesicles is crucial for evaluating infertility, diagnosing infections, and assessing prostate cancer.

Note: This guide provides a concise overview of seminal vesicles for the USMLE. For in-depth knowledge, refer to standard textbooks and additional resources.