Male & Female Reproductive Systems: Fertilization
Male Gametes
Sperm cells are produced continuously in the seminiferous tubules. They move up to the epididymis, at which time they complete their maturation and develop a flagellum with which they swim very quickly. They are small and numerous, unlike the eggs. Hundreds of millions mature daily. Output is performed by ejaculation, in which semen is expelled. Semen is a liquid formed by sperm and prostatic seminal lubricant. Sperm remain alive between 3 and 5 days in the vagina, at which time fertilization can occur.
Fertilization and Early Pregnancy
Ovulation occurs approximately 14 days before the menstrual period. The egg released from the Graafian follicle is driven along the length of the fallopian tube to the uterus. It takes more than a week. A single egg can be fertilized for 24 hours after ovulation. Intercourse involves the introduction of the penis into the vagina. Upon ejaculation, sperm are released into the vagina. The genetic material of the sperm and egg fuse, and fertilization occurs. The resulting cell is the zygote, or egg cell.
Beginning of pregnancy: The formation of a zygote produces a substance that prevents the Graafian follicle from degenerating, producing progesterone. Nesting occurs when the zygote attaches to the endometrium. From that moment, it is called an embryo and develops:
- Placenta: An organ that develops in the endometrium and serves as a connection between the mother and the embryo.
- Umbilical cord: Connects the embryo with the placenta and consists of a tube through which two arteries pass, carrying nutrients to the embryo, and a vein that carries waste from the embryo to the mother.
- Amniotic sac: A bag of amniotic fluid where the embryo develops.
Changes Towards Sexual Maturity (Post-Embryonic Development)
This is the time from birth until early adulthood. It is divided into:
- Childhood (0-10 years): Sex organs (penis, scrotum, and vulva) are formed, which are the primary sexual characteristics.
- Puberty (10-14 years): The first period occurs in females, and males start producing sperm. Secondary sexual characteristics appear. Breasts grow, hips widen in females. Bone density increases, and the voice becomes more recorded in males. Beard growth and hair in the pubic area and armpits appear in both sexes.
- Adolescence (14 to 20 years): Sexual desire appears, emotional support is sought in friends, conflict situations with adults may arise, and adolescents may feel misunderstood. The body is prepared for reproduction.
- Maturity or Adulthood (20/25 – Death): Individuals adapt to emotional changes and may choose to form a family.
Female Reproductive System
- Ovaries: Have the shape and size of an almond. They are attached to the uterus by a ligament. They produce mature eggs.
- Fallopian Tubes: Ducts that connect each ovary with the uterus. Their interior is carpeted with cilia that push the egg.
- Clitoris: An organ with many nerve terminations, making it very sensitive. It is located at the junction of the labia minora.
- Uterus: A hollow organ with the inside covered with a highly vascular epithelium, the endometrium, where the fertilized egg implants. It has a narrowing called the cervix, which connects to the vagina.
- Vagina: A muscular duct that connects the uterus to the exterior (vaginal opening).
- Labia Majora: Skin folds between the thighs, covering the external genitalia.
- Labia Minora: Folds of fine, sensitive skin covered by the labia majora.
Female Gametes (Eggs)
The egg is the female reproductive cell or gamete. It is a very large cell, about 1 mm in diameter, that ripens in the ovary, in a capsule called a Graafian follicle. This follicle opens and pours the egg into the fallopian tube. The expelled egg remains fertile for 24 hours. If it is not fertilized during that time, it dies.
Female Reproductive Cycles
Female sex hormones, estrogen and progesterone, induce the formation of the Graafian follicle. Estrogen formation follows a cycle of 28 days. When its quantity in the blood is greatest, ovulation occurs (rupture of the follicle and release of the egg into the fallopian tube). After the egg is released, the Graafian 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 at its maximum, the endometrium is fully developed. If there is no fertilization, the egg dies, the follicle degenerates, progesterone production stops, and the endometrium is shed, resulting in menstruation.