Male Reproductive System

Male Reproductive System Anatomy

• Comprised of primary sex organs (gonads: testes) and accessory organs (ducts, glands).

• Testes produce sex cells (sperm) and secrete hormones (androgens).

• External genitalia include the scrotum and penis.

Sperm Production

• Sperm production occurs in seminiferous tubules of the testes, takes about 64 days, starts at puberty.

• Meiosis I and II reduce chromosome count from diploid (2n) to haploid (n).

• Spermatogonia differentiate into sperm:

  • Head: contains nucleus and acrosome.

  • Midpiece: houses mitochondria for energy.

  • Tail: flagellum for movement.

Semen Composition

• Semen is a mixture of sperm and secretions from accessory glands (70% comes from seminal vesicles).

• Contains fructose, enzymes, prostaglandins, and neutralizing alkaline substances to protect sperm.

Hormonal Regulation

• Controlled by the Hypothalamic-Pituitary-Gonadal (HPG) axis:

  1. GnRH from hypothalamus stimulates FSH and LH from anterior pituitary.

  2. FSH promotes sertoli cell activity, LH stimulates testosterone production by Leydig cells.

  3. Testosterone regulates spermatogenesis and provides negative feedback to the system.

Testosterone Functions

• Critical for spermatogenesis, development of male genitalia, and maintaining libido.

• Influences secondary sexual characteristics: body hair, voice deepening, muscle growth, and metabolic rate.

• Converted to DHT and estradiol in target tissues.

Study Guide Summary

1. Anatomy Ovreview

   • Primary Sex Organs (Gonads): The testes, responsible for producing sperm and secreting androgens (primarily testosterone).

   • Accessory Organs: Include various ducts and glands (such as the seminal vesicles and prostate) that support sperm transport and survival.

   • External Genitalia: The scrotum houses the testes, and the penis serves as the copulatory organ.

2. Spermatogenesis (Sperm Production)

   • Location: Occurs in the seminiferous tubules.

   • Timeline: Takes approximately $64$ days and begins at puberty.

   • Process: Meiosis reduces the chromosome count from a diploid state ($2n$) to a haploid state ($n$).

   • Structure of a Mature Sperm:

     • Head: Contains the genetic material (nucleus) and the acrosome (enzymes for egg penetration).

     • Midpiece: Packed with mitochondria to provide energy ($ATP$) for swimming.

     • Tail: A flagellum that enables movement.

3. Semen Composition

   • Semen is a mixture of sperm cells and glandular secretions.

   • Seminal Vesicles: Contribute about $70\%$ of the total semen volume.

   • Key Components: Fructose (fuel), enzymes, prostaglandins (muscle contraction), and alkaline substances (to neutralize acidic environments).

4. The HPG Axis & Hormones

   • Hypothalamus: Releases Gonadotropin-releasing hormone ($GnRH$).

   • Anterior Pituitary: Responds to $GnRH$ by releasing Follicular Stimulating Hormone ($FSH$) and Luteinizing Hormone ($LH$).

   • FSH: Stimulates Sertoli cell activity (supports sperm development).

   • LH: Stimulates Leydig cells to produce testosterone.

   • Testosterone Functions: Regulates spermatogenesis, maintains libido, and develops secondary sexual characteristics (voice deepening, muscle mass, body hair).

Quiz

1. At what stage of life does sperm production typically begin in males?

2. What is the specific site within the testes where sperm are produced?

3. Which hormone directly stimulates Leydig cells to secrete testosterone?

4. What specialized structure in the sperm head contains enzymes to help penetrate an egg?

5. Approximately what percentage of semen volume is produced by the seminal vesicles?

6. How does the HPG axis maintain hormonal balance if testosterone levels become too high?

7. What is theploidy level ($n$ or $2n$) of a mature sperm cell?

Answer Key

1. Puberty

2. Seminiferous tubules

3. Luteinizing Hormone ($LH$)

4. Acrosome

5. $70\%$

6. Negative Feedback: High levels of testosterone inhibit the release of $GnRH$ from the hypothalamus and $FSH/LH$ from the pituitary.

7. Haploid ($n$)