Problem 22 - Anatomy and Physiology of Animals

Question

What do each of the three male accessory glands contribute to the semen?

Step-by-Step Solution

Answer

Seminal vesicles provide nutrients and alkalinity; the prostate gland adds citrate and PSA; bulbourethral glands produce lubrication and neutralize urine.

Step 1: Seminal Vesicles

The seminal vesicles are a pair of glands that contribute approximately 60% of the total volume of semen. They secrete a viscous, alkaline fluid that contains fructose, prostaglandins, and other substances. Fructose provides an energy source for sperm, prostaglandins help stimulate contractions in the female reproductive tract, and the alkaline nature helps neutralize the acidity of the female vagina.

Step 2: Prostate Gland

The prostate gland surrounds the urethra just below the bladder and contributes about 30% of the semen volume. It secretes a slightly acidic fluid that contains citrate (a nutrient for sperm) and prostate-specific antigen (PSA), which helps to liquefy the semen after ejaculation, making it easier for sperm to swim.

Step 3: Bulbourethral Glands

The bulbourethral glands, also known as Cowper's glands, contribute a small portion of the semen. They secrete a clear, mucous fluid that serves as a lubricant during sexual activity and neutralizes traces of acidic urine in the urethra prior to ejaculation.

Key Concepts

Seminal Vesicles

The seminal vesicles play a crucial role in the male reproductive system by significantly contributing to the composition of semen. These paired glands are located near the base of the bladder and are responsible for producing about 60% of the semen's total volume.

The fluid secreted by the seminal vesicles is alkaline and viscous, and it contains several key components:

• Fructose: This sugar provides energy for sperm, enabling them to be motile and active.
• Prostaglandins: These hormone-like substances aid in stimulating muscle contractions in the female reproductive tract, assisting in the transportation of sperm toward the egg.
• Alkaline nature: Helps neutralize the acidity of the vagina, creating a more favorable environment for sperm survival.

Understanding these contributions is essential for appreciating how sperm are supported and protected in their journey through the female reproductive system.

Prostate Gland

Situated just below the bladder and encircling the urethra, the prostate gland adds approximately 30% to the total volume of semen. This gland is particularly notable for secreting a fluid that is slightly acidic, countering the alkaline secretions from the seminal vesicles in a careful balance.

• Citrate: Serves as a nutrient for sperm, providing them with the necessary energy to propel through the female reproductive system.
• Prostate-specific antigen (PSA): Besides its diagnostic importance in clinical settings, PSA has an essential role in semen liquidity. It helps break down the thick consistency of the ejaculate, allowing sperm to swim more freely.

By facilitating the smooth motility of sperm and protecting them with this nutrient-rich fluid, the prostate gland is fundamental to effective male fertility.

Bulbourethral Glands

The bulbourethral glands, also known as Cowper's glands, are pea-sized glands located beneath the prostate. Before ejaculation occurs, these glands secrete a clear, mucous fluid into the urethra.

• Lubrication: This fluid acts as a lubricant during sexual activity, which can enhance comfort and decrease friction during intercourse.
• Neutralization: It neutralizes any acidic residues from urine in the urethra, protecting sperm as they pass through.

Although the bulbourethral glands contribute only a small volume to semen, their secretions play important roles in preparing the sperm's passage through the male reproductive system.

Sperm Physiology

Sperm physiology is central to the understanding of male fertility, addressing how sperm develop, function, and survive. Each sperm cell is highly specialized and is designed with the goal of achieving fertilization.

• Structure: Sperm are streamlined for efficiency and contain a head, midpiece, and tail. The head houses genetic material, the midpiece contains mitochondria to fuel movement, and the tail propels the sperm toward the egg.
• Environment: Sperm require a specific environment to maintain motility, which is why the contributions of the seminal vesicles, prostate gland, and bulbourethral glands are crucial. These glands provide energy, protection from acidity, and necessary lubrication.
• Energy Source: Fructose from the seminal vesicles is a primary energy source for sperm, facilitating their active movement once in the female reproductive tract.

Understanding sperm physiology is essential for comprehending how the male reproductive system supports the complex journey sperm must embark on to achieve successful fertilization.