Male Gonads: Testes

Spermatogenesis

The creation of sperm (genesis: creation)
Occurs inside seminiferous tubules.
Sperm development begins with a diploid cell called the spermatogonium located near the outer wall of the seminiferous tubules.
Sperm development ends when a haploid motile sperm cell sloughs off the inner wall of the seminiferous tubule.

Mitosis
- Spermatogonium (diploid cell)
  - Located near the outer wall of the seminiferous tubules.
  - Reproduce by mitosis to produce cells that will eventually enter meiosis to become sperm.
  - Three million differentiate into primary spermatocytes each day.
Meiosis
- Primary spermatocyte (diploid cell)
  - One is produced from mitosis of one spermatogonium.
  - Located a little closer to the lumen of the seminiferous tubules.
  - Undergoes the first meiotic division which reduces the chromosome number by half, producing secondary spermatocytes.
- Secondary spermatocytes (haploid cells)
  - Two are produced from meiosis of one primary spermatocyte.
  - Located a little closer to the lumen of the seminiferous tubules.
  - Undergoes the second meiotic division, producing spermatids.
Final differentiation
- Spermatids (haploid cells)
  - Four total are produced from one spermatogonium.
  - Located a little closer to the lumen of the seminiferous tubules.
  - Develop into sperm.
- Sperm (haploid cells)
  - Four total are produced from one spermatogonium.
  - Have tails and are therefore motile (can move).

Head
- Haploid nucleus
- Acrosome: tip of head; has enzymes that help the sperm penetrate the egg.
Middle piece
- Packed full of mitochondria to convert glucose energy into ATP to provide an energy source for tail movement.
Tail
- A flagellum (not a cilium).

Figure 46.11, page 922, Campbell's Biology, 5th Edition

Cilia (Latin for “eyelash”) and flagella (Latin for “whip”) are both extensions of the plasma membrane.
They share the same anatomy:
- Ring of nine fused pairs of microtubules with one unfused pair of microtubules in the center (called the “9+2” arrangement)
- Basal body
  - Located at the base
  - Nine fused microtubule triplets
  - No microtubules in the center

Figure 4.23, Purves's Life: The Science of Biology, 7th Edition

Cilia
- Short
- Numerous
- Provide a force parallel to the plasma membrane (like oars in a canoe).
Flagella
- Long
- Few in number
- Provide a force perpendicular to the plasma membrane (like the engine on a motorboat).

Figure 7.23, page 121, Campbell's Biology, 5th Edition

Leydig cells
- Located between the seminiferous tubules.
- Produce testosterone.
Epididymis
- Storage tubules outside of the testes in which sperm mature.
- Sperm remain here until they leave the body.
Scrotum
- A sac of skin that hangs outside the main body cavity.
- Contains the testes and epididymis.
- Keeps sperm 2 °C cooler than normal body temperature.
Vasa deferentia (singular: vas deferens)
- Two total, one from each testis
- Duct that runs from the epididymis up and behind the urinary bladder, eventually joining a duct from the seminal vesicle.
Ejaculatory duct
- Two total, one from each vas deferens
- Short duct that begins where the vas deferens meets the duct from the seminal vesicle and ends when it meets the urethra.
Urethra
- The tube that drains both the reproductive and excretory systems
Three accessory glands
- Seminal vesicles
- Prostate gland
- Bulbourethral glands
- Provide substances which help sperm on their journey.
  - Fructose: for energy
  - Alkaline fluid: to help neutralize any acidic urine in the urethra.

Part of Figure 43.9, Purves's Life: The Science of Biology, 7th Edition; Figure 46.8, page 919, Campbell's Biology, 5th Edition

Hypothalamus: releases gonadotropin-releasing hormone (GnRH).
- Stimulates the release of FSH and LH from the anterior pituitary.
Anterior pituitary gland: releases FSH and LH.
- Follicle stimulating hormone (FSH): acts on the seminiferous tubules to increase sperm production (spermatogenesis).
- Luteinizing hormone (LH): acts on the Leydig cells to increase androgen production.
Testes: release androgens (e.g. testosterone).
- Cause development of primary sex characteristics: all anatomical structures associated with male reproductive system.
- Cause development of secondary sex characteristics: all things not directly associated with male reproductive system (deepening of voice, body hair, muscle growth, sex drive, male aggressiveness, etc.)
- Provide negative feedback to:
  - Anterior pituitary by inhibiting LH.
  - Hypothalmus by inhibiting GnRH.

Figure 46.14, page 925, Campbell's Biology, 5th Edition