Human Reproduction: From Gametes to Birth

Reproduction of Human Beings

It is comprised of the following processes:

• The production of gametes: In specialized reproductive organs.
• Fertilization: Is the union of two gametes within the female reproductive system, forming a single cell, the zygote.
• Zygote development: Inside the female reproductive system.
• Birth: A fully formed baby is born.

Development to Sexual Maturity

Changes from infancy to sexual maturity:

• Primary sexual characters: Are present at birth. These are the sexual organs: the penis in boys, and the vulva and excretory system in girls.
• Secondary sexual characters (Puberty):
  • In children: Deep voice, beard, pubic and underarm hair, increased bone and muscle mass.
  • In girls: High voice, growth of breasts and hips, and pubic and underarm hair.
• Adolescence: Sexual maturity to adulthood.

Gametes

Female Gametes (Ovules)

The egg is the reproductive cell or female gamete. It is a very large cell that matures inside the ovary, in a capsule called the Graafian follicle.

Male Gametes (Spermatozoids)

Many are smaller and more numerous than the eggs. Every day, several hundred million mature in the testicles. Their exit is done by ejaculation to be deposited inside the vagina. They remain alive for 3 to 5 days.

Hormonal Cycle (Female)

Female sex hormones are estrogen and progesterone.

• Estrogen: Ovaries produce estrogen, according to a cycle of 28 days duration, and are responsible for the development and maintenance of secondary sexual characteristics. Estrogen produces the maturation of a Graafian follicle into an egg.
• Progesterone: The follicle produces an egg maturation and produces progesterone. Progesterone prepares the uterus for the implantation of the zygote. If no fecundation occurs, the follicle dies, and the endometrium is shed, causing menstruation.

Pregnancy elements

• Placenta: Organ that develops in the endometrium and serves as a connection between mother and embryo.
• Umbilical cord: Connects the embryo with the placenta and consists of a tube through which 3 blood vessels run: 2 arteries carrying nutrients from mother to embryo, and a vein of waste substances from the embryo to the mother.
• Amniotic sac: A bag filled with a liquid called amniotic fluid, remains inside the embryo.

Intercourse

It involves inserting the penis into the vagina. To ejaculate, the spermatozoids are released inside the vagina.

Gestation or Pregnancy

It is the process that begins with fertilization and ends with childbirth. Significant changes occur.

Delivery

Consists of 3 steps:

1. Dilatation: The cervix begins to dilate. The vaginal muscles relax and dilate. The amniotic sac breaks and the amniotic fluid comes out.
2. Expulsion: The fetus is pushed outward by contractions of the uterus and by the force exerted by the mother pushing with the diaphragm. This usually lasts about 15 or 30 minutes. When air comes in, the baby cries for the first time, and the umbilical cord is cut.
3. Birth: Between 5 or 15 minutes after the expulsion, the placenta comes out, along with the remains of the endometrium.

Childbirth Complications

• Poor posture, inadequate dilatation of the cervix and the vagina: To avoid this problem, the mother is given a serum with the hormone oxytocin, which causes the dilation and contraction of the uterus.
• Umbilical cord clamping: If the umbilical cord is compressed, it cuts the flow of blood between mother and fetus, and suffers from lack of oxygen, which, if it lasts more than 5 minutes, can cause brain damage.

Fertilization, Pregnancy and Childbirth

Fertilization occurs in one of the fallopian tubes. The zygote reaches the uterus, implants in the endometrium, and the embryo is formed. The placenta, umbilical cord, and amniotic sac develop. At 3 months, its heart beats, and it is renamed the fetus. At six months, the fetus has developed the nervous, circulatory, and excretory systems. Sex is recognized. At 9 months, development ends.