Reproduction and Development - The Male Reproductive System

Humans reproduce through sexual reproduction involving specialized sex cells produced in male and female reproductive systems.
Male gonads (testes) produce sperm; female gonads (ovaries) produce eggs.
Fertilization occurs in the female reproductive system, creating a zygote that develops into an embryo and eventually into a fetus.

Origin: Male and female sex organs develop in the abdominal cavity and become distinguishable around the third month of embryonic development due to genetic influences.
Testes Decent:
- Testes descend into the scrotum (a pouch below the pelvic region) during fetal development.
- A membrane over the canal prevents re-entry into the abdominal cavity; injury may lead to inguinal hernia, which can compress the testes or intestine.
- Cooler temperatures in the scrotum (several degrees lower than body temperature) are crucial for sperm development; failure to descend leads to sterility.
Vas Deferens:
- A tube that carries sperm from the testes to the ejaculatory duct.
- Blockage may prevent sperm transport.
- A vasectomy cuts and ties the vas deferens as a birth control method.
Ejaculatory Duct & Urethra:
- The ejaculatory duct transports sperm and seminal fluids (semen) into the urethra, which also conducts urine.
- A sphincter ensures urine and semen do not mix; only one at a time is conducted through the urethra.
Erection Mechanism:
- During sexual excitement, erectile tissue in the penis fills with blood due to nerve stimulation, resulting in an erection.
- Damage to the parasympathetic nerve can lead to impotence.

Inside each testis, seminiferous tubules (250 meters long in total) are where spermatogenesis occurs.
Process of Spermatogenesis:
- Spermatogonia (sperm-producing cells) divide into spermatocytes, which then develop into spermatids that become mature sperm.
- Spermatids have 23 chromosomes (half the somatic cell count), taking 9-10 weeks to mature.
- Sertoli cells nourish developing sperm and form a blood-testis barrier to protect sperm from the immune system.
Maturation in Epididymis:
- Sperm mature in the epididymis where they develop swimming motions in four days.
- They are streamlined for movement and have limited cytoplasm that restricts energy reserves.
- An acrosome caps the sperm head, containing enzymes for penetrating the egg.

Ejaculation Process:
- Sperm leave the body in semen (3-4 mL containing 500 million sperm cells) transmitted through contractions of various glands.
Glandular Contributions:
- Seminal Vesicles: Secrete fructose (energy) and prostaglandins (promote muscular contractions in females).
- Prostate Gland: Produces an alkaline buffer to protect sperm from the vagina’s acidity.
- Cowper’s Gland: Releases mucus-rich fluids that protect sperm from urethral acids.
Sperm Lifespan: In body temperature, sperm live 24-72 hours but can remain viable for years when frozen at -100 °C.

Testes Structure and Function:
- Testes produce sperm and testosterone; seminiferous tubules generate immature sperm.
Hormonal Regulation:
- Testosterone (primary male hormone) facilitates spermatogenesis, secondary sexual characteristics, and affects sex drive.
Gonadotropins:
- Follicle-stimulating hormone (FSH) from the pituitary stimulates sperm production; luteinizing hormone (LH) promotes testosterone production.
Feedback Mechanisms:
- Inhibin regulates FSH production when sperm levels are high, while testosterone levels inhibit both LH and GnRH.

Structures: Testes, seminiferous tubules, epididymis, vas deferens, seminal vesicles, prostate gland, Cowper’s gland, urethra, and penis.
Functions include sperm and testosterone production, and seminal fluid facilitation during ejaculation.
Gonadotropins regulate sperm production, with negative feedback systems maintaining hormonal regulation.