Male Reproductive System and Temperature Regulation

Male Reproductive System: Regulation of Testis Temperature

Introduction

• Testes produce sperm and hormones (e.g., testosterone). Sperm is essential for fertilization and continuation of the species.
• Hormones like testosterone are required all around the body
• The location of the testes external to the body in the scrotum is unusual but crucial for temperature regulation.
• During embryonic/fetal development, testes initially develop near the kidneys inside the pelvic cavity, later descending into the scrotum.

Why External Location?

• Core body temperature is approximately 37 degrees Celsius.
• This temperature is too high for normal sperm development (spermatogenesis).
• Testis temperature needs to be about 2-3 degrees lower than core body temperature, around 35 degrees Celsius, for normal sperm production.

Effects of Elevated Testis Temperature

• If testis temperature is at core body temperature (37 degrees Celsius):
  • Reduced sperm count.
  • Abnormal sperm morphology (e.g., tail defects, multiple heads).
  • Arrested or slowed spermatogenesis.
  • Abnormal sperm metabolism.
  • Increased risk of testicular cancer.
• Doctors check for descended testes in infants to avoid cryptorchidism, where testes do not descend properly. This may require monitoring, hormone treatment, or surgery.

Importance of Maintaining Optimal Temperature

• Temperature that is too low is also bad (e.g. 33 degrees Celsius). It's really important to maintain a testis temperature that's about 35 degrees.
• Endocrine activity (hormone production, such as testosterone) is generally unaffected by temperature, but sperm production is highly sensitive.

Mechanisms for Maintaining Testis Temperature

1. Scrotum

• External location of the scrotum keeps testes outside the pelvic cavity's 37 degrees Celsius environment.
• Scrotal skin contains temperature receptors and sweat glands.
• Sweat glands release sweat to cool the skin surface through evaporation.

2. Cremaster Muscle

• A skeletal muscle that surrounds the testis.
• Originates from the abdomen and wraps around the testes.
• Contracts when testes are too cold, lifting them closer to the warmer pelvic cavity (at 37 degrees Celsius).
• Relaxes when testes are too warm, allowing them to drop further away from the pelvic cavity into the cooler scrotum.
• This muscle is not under conscious control; its action is autonomic.

3. Dartos Muscle

• A smooth muscle located within the dermis, just beneath the scrotal skin.
• Causes the scrotal skin to wrinkle.
• Contracts when testes are too cold, increasing wrinkling in the scrotal skin and reducing surface area for heat loss, thus retaining heat.
• Relaxes when testes are too warm, flattening out the wrinkles in the scrotal skin to increase surface area and promote heat loss.

4. Countercurrent Heat Exchange

• Involves the testicular artery and testicular veins (pampiniform plexus).
• The testicular artery carries blood from the pelvic cavity (37 degrees Celsius) to the testis.
• The testicular veins form a meshwork (pampiniform plexus) that surrounds the testicular artery.
• Testicular veins form like a kind of network of kind of veins that wrap themselves around this testicular artery.
• Heat is transferred from the warmer arterial blood to the cooler venous blood.
• Cools the arterial blood entering the testis to approximately 35 degrees Celsius.
• Warms the venous blood returning to the pelvic cavity back to approximately 37 degrees Celsius.

Summary

• Maintaining testis temperature at around 35 degrees Celsius is crucial for normal sperm production and overall testicular health.
• Mechanisms include scrotal location, cremaster muscle, dartos muscle, and countercurrent heat exchange in the pampiniform plexus.