Male Reproductive System: Duct System and Sperm Maturation

Male Reproductive System: The Duct System

Introduction

• The presentation focuses on the male reproductive system, specifically the duct system or reproductive tract.
• The presenter is Mario Ritchie, a professor in the Faculty of Health and Medical Sciences at the University of Adelaide.
• Questions can be emailed or posted on the discussion board.

Testis Function

• The testis produces sperm and hormones like testosterone.
• Sperm production occurs within the lobules of the testes in the seminiferous tubules.

Sperm Maturation

• Sperm have a head and tail but are functionally immature when produced in the testes. They are immotile (cannot swim).
• Functional maturation, including the ability to gain motility, occurs within the duct system of the testis.
• Motility is essential for sperm to reach and penetrate an oocyte for fertilization.

Duct System Overview

• The duct system includes:
  • Seminiferous tubules.
  • Rete testis.
  • Efferent ducts.
  • Epididymis (a long duct on one side of the testis).
  • Ductus deferens (vas deferens, starts at the base of the testis and extends into the pelvic cavity).

Functions of the Duct System

• Functional Maturation: Provides sperm with motility.
• Nutrient Supply: Provides nutrients and oxygen to sperm, which can reside in the duct system for extended periods (10 days to months).
• Storage: Stores sperm while awaiting ejaculation.
• Concentration: Resorbs fluid to concentrate sperm.
• Transport: Transports sperm through fluid movement and smooth muscle contractions.
• Ejaculation: Smooth muscle contractions expel sperm during ejaculation.

Duct System Components

Seminiferous Tubules

• Site of sperm production.
• Leiden cells surrounding the tubules produce hormones.

Rete Testis

• A network of interconnecting tubules that collect sperm from the seminiferous tubules.
• Transports sperm to the efferent ducts.

Efferent Ducts

• Carry sperm to the epididymis.

Epididymis

• Sits on the posterior side of the testis and can be felt through the scrotum.
• One long, tightly coiled tube, approximately 7 meters in length.
• Divided into three regions: head, body, and tail.
• Sperm take about 12 to 16 days to travel through the epididymis.

Functions of the Epididymis

• Monitors and Adjusts Fluid Composition: Resorbs fluid from seminiferous tubules to concentrate sperm; can also secrete fluid with specific proteins.
• Recycles Damaged Sperm: Epididymal cells phagocytose and break down abnormal sperm.
• Storage and Protection: Stores sperm for weeks or months, primarily in the tail region.
• Concentration: Resorbs fluid to concentrate sperm.
• Functional Maturation: Site of sperm maturation, where sperm gain motility.

Functional Maturation in Detail

• Sperm from the seminiferous tubules are immotile.
• Motility develops in the epididymis as sperm move through it.
• Functional maturation involves gaining motility and the ability to fertilize an egg.
• Capacitation: Further maturation occurs in the female reproductive tract.

How Functional Maturation Occurs

• Epididymal cells secrete proteins that bind to the sperm plasma membrane.
• These proteins trigger flagellum movement, leading to motility.
• Some proteins stabilize the sperm plasma membrane, providing strength to withstand shearing forces during ejaculation.

Hormonal Dependence

• The maturation of sperm depends on androgens like testosterone.
• Androgens stimulate epididymal cells to produce proteins that facilitate motility and stabilization.

Ductus Deferens (Vas Deferens)

• Extends from the tail of the epididymis into the pelvic cavity.
• The duct cut or ligated during a vasectomy.
• Approximately 40 to 45 centimeters long.
• Ascends along the posterior side of the testis and becomes part of the spermatic cord (bundle of vessels, nerves, and lymphatic vessels).
• Passes through the inguinal canal into the abdominal cavity.
• Curves over the superior and posterior part of the prostate gland.

Ampulla of the Ductus Deferens

• The terminal end of the ductus deferens enlarges to form the ampulla.

Wall of the Ductus Deferens

• Contains a thick layer of smooth muscle.
• Smooth muscle contractions propel sperm out during ejaculation.

Functions of the Ductus Deferens

• Storage: Stores sperm for several months.
• Like epididymal cells, Duct cells break them down after they become too old.

Ejaculatory Duct

• A small duct (about 2 cm long) connecting the ampulla of the ductus deferens with the duct from the seminal vesicles.
• The ejaculatory duct contains fluid from the ductus deferens and seminal vesicles.

Urethra

• Approximately 20 centimeters long in males.
• Extends from the bladder through the penis.
• Composed of three segments:
  • Prostatic Urethra: Within the prostate.
  • Membranous Urethra: Passes through the floor of the pelvis, surrounded by the external urethral sphincter.
  • Spongy Urethra: Within the penis.

Function of the Urethra

• A passageway for both urine and semen to exit the body.