Overview
This lecture explains the biology of male reproductive anatomy and the process of sperm production, maturation, and transport, emphasizing hormonal regulation and anatomical adaptations.
Differences in Reproductive Investment
- Female gametes (ova) are large, rare, and require high biological investment and time to produce.
- Male gametes (sperm) are small, numerous, produced quickly, and involve minimal resource investment.
Testicular Anatomy and Function
- Testes (male gonads) produce sperm and the hormone testosterone.
- Testes are located outside the body in the scrotum to maintain a temperature below core body temperature, necessary for sperm production.
- Each testis contains about 250 lobules with seminiferous tubules, the site of sperm production.
- Sertoli cells in tubules nourish developing sperm; Leydig cells outside tubules secrete testosterone.
Spermatogenesis (Sperm Production)
- Hormonal cascade starts at puberty: hypothalamus releases GnRH, stimulating pituitary to release LH and FSH.
- LH stimulates Leydig cells to release testosterone; FSH triggers Sertoli cells to release androgen-binding protein (ABP).
- Spermatogonia (stem cells) divide to maintain the stem cell pool (type A) and produce primary spermatocytes (type B).
- Primary spermatocytes go through meiosis I and II, resulting in four haploid spermatids.
- Spermiogenesis transforms spermatids into motile sperm with a tail.
- Full spermatogenesis takes about five weeks; mature males produce ~1500 sperm per second.
Sperm Maturation and Transport
- Sperm are moved from seminiferous tubules to the epididymis via peristalsis.
- In the epididymis (about six meters if uncoiled), sperm mature and gain mitochondria.
- Sperm become motile only after exposure to glandular secretions during ejaculation.
- Pathway: epididymis → vas deferens → ejaculatory duct → prostate → urethra → exit.
Role of Accessory Glands
- Seminal vesicles add fluid with coagulating enzymes, fructose, and prostaglandins to nourish sperm and facilitate movement.
- Prostate gland secretes citric acid and enzymes to keep semen liquified.
- Bulbo-urethral glands flush acidic urine from the urethra before ejaculation.
Penis Structure and Function
- Penis consists of a shaft ending in the glans, surrounded by foreskin; contains erectile tissues that fill with blood for erection.
- Primary reproductive role is sperm delivery during intercourse.
Key Terms & Definitions
- Spermatogenesis — The process of sperm cell development.
- Sertoli cells — Cells in seminiferous tubules that nourish developing sperm.
- Leydig cells — Cells between tubules that secrete testosterone.
- Gonadotropin-releasing hormone (GnRH) — Hormone from hypothalamus triggering pituitary to release LH and FSH.
- Luteinizing hormone (LH) — Pituitary hormone stimulating testosterone production.
- Follicle-stimulating hormone (FSH) — Pituitary hormone aiding sperm development.
- Spermatogonia — Sperm stem cells in testes.
- Spermiogenesis — Transformation of spermatids into mature sperm.
Action Items / Next Steps
- Review the steps and hormones involved in spermatogenesis.
- Prepare for upcoming lecture on fertilization and the union of male and female gametes.