Human Reproductive Systems and Pregnancy Development

The Male Reproductive System and Gametes

• Testicles: Glands in the scrotum that produce sperm.
• Prostate Gland: A walnut-sized gland surrounding the urethra. It produces a prostatic fluid that protects the sperm against the acidity of the urethra and vagina.
• Ductus Deferens (Vas Deferens): Tubes that are a continuation of the epididymis and converge in the urethra.
• Seminal Vesicles: Glands that produce seminal fluid, in which sperm swim. This fluid empties into the ductus deferens.
• Urethra: Duct that communicates with the outside. Its muscular walls contract rhythmically during ejaculation, propelling the sperm.
• Epididymis: A long, very thin, coiled tube located on each testicle. Sperm mature inside it.
• Penis: A cylindrical organ, whose widened end, the glans, is covered by the foreskin, which is retractable skin.
• Scrotum: A pouch formed by skin and membranes that lines and houses the testicles outside of the abdomen. This skin has many sebaceous glands.

Male Gametes: Sperm

Sperm are produced continuously in the seminiferous tubules. From there, they travel to the epididymis, where they complete their maturation and develop a long flagellum (tail) that allows them to swim very lightly.

Every day, several hundred million sperm mature in the testicles. Their release occurs through ejaculation, which expels semen – a fluid formed by sperm, lubricating fluid, seminal fluid, and prostatic fluid.

The Female Reproductive Cycle

The female sex hormones are estrogen and progesterone. Estrogen is produced in the ovaries and is responsible for the development and maintenance of secondary sexual characteristics. It also induces the formation of the Graafian follicle in the ovary. The maturation of an egg occurs within this follicle.

After releasing the egg (ovulation), the follicle produces progesterone, which induces the growth and maturation of the endometrium (the tissue lining the uterus) where the fertilized egg implants. When the progesterone level is maximal, the endometrium is completely developed.

If fertilization does not occur, the egg dies. The follicle degenerates, progesterone production ceases, and the endometrium is shed, causing menstruation (the period or rule).

Development of Pregnancy

Gestation, or pregnancy, is the process that begins with fertilization and ends with delivery. During this time, very significant changes occur. What began as a single cell, the zygote, becomes an embryo, then a fetus, and finally, a human being.