Human Reproductive System: Anatomy, Fertilization, and Pregnancy

Male Reproductive System

The male reproductive system is responsible for producing sperm and testosterone. It is involved in the fertilization process and shares several organs with the urinary system. Some organs are external, while others are located in the abdominal cavity.

Spermatozoa Production

Sperm production occurs in the seminiferous tubules of the testes. It begins at puberty and continues throughout life, though production decreases with age. Sperm travel through the vas deferens to the urethra, where they mix with fluids from the seminal vesicles and prostate. In each ejaculation, 200 to 300 million sperm are expelled; within the female reproductive tract, they can live for 2–4 days.

• Head: Contains a nucleus with chromosomes and an acrosome (hood) with enzymes.
• Midpiece: A cylinder containing mitochondria to provide energy for movement.
• Tail: A flagellum that enables movement.

Female Reproductive System

The female reproductive system is responsible for producing eggs (ova), estrogen, and progesterone. It supports fertilization and fetal development, is located in the pelvic cavity, and is independent of the urinary system.

The Egg (Ovum)

Eggs are produced in the ovaries within follicles, beginning at puberty and continuing until menopause. They travel through the fallopian tubes to the uterus. Ovulation occurs monthly when a mature follicle ruptures and releases an egg.

• Core: Contains chromosomes and cytoplasm with nutritious substances.
• Mobility: Eggs are motionless; they move through the tubes via cilia and stay alive for 1–2 days.

The Menstrual Cycle

• Days 1–4: Menstruation occurs.
• Days 5–13: The follicle matures and the uterine wall thickens.
• Day 14: Ovulation occurs; a new egg is released from the ovary.
• Days 15–28: The uterine wall continues to thicken. If the egg is not fertilized, a new cycle begins.

Fertilization and Pregnancy

Fertilization

Fertilization is the union of an egg and a sperm. It is possible if intercourse occurs several days before or during ovulation. Only one sperm penetrates the protective layer of the egg; once inside, the egg wall prevents the entry of others. The merger of the two cells results in a zygote (a single-celled embryo).

Pregnancy

The zygote divides and feeds on nutrients from the egg and maternal secretions. 7–8 days after fertilization, the embryo implants in the uterine wall. Gestation lasts approximately 9 months. By the 3rd month, the embryo is called a fetus.

• Absence of menstruation and new ovarian follicles.
• Increase in breast volume.
• Weight gain and physical silhouette changes.

Childbirth

Childbirth is the process of delivering the fetus after approximately 40 weeks. If a natural birth is not possible, a cesarean section (a surgical opening in the abdomen and uterus) is performed.

Stages of Labor

• Expansion: The cervix dilates to 10 cm (8–14 hours).
• Expulsion: The fetus is expelled through the vagina, and the umbilical cord is cut, forming the navel (30 minutes).
• Placental Stage: The placenta is expelled approximately 15 minutes after the baby's birth.