Human Reproduction: Gamete Formation and Fetal Development

Female Reproductive Anatomy

The Uterus

The uterus is a pear-shaped organ, inverted. Its walls are formed by a muscular layer lined by an epithelial layer, the uterine lining or endometrium.

The Vagina

The vagina is an elastic conduit connected to the uterus.

Sperm and Spermatogenesis

Sperm Structure

Sperm cells are tiny, highly specialized cells. The front portion, known as the head, contains the nucleus with the parental genetic material. They also have a long thread called the flagellum (or scourge).

Formation of Sperm

Sperm are formed within the testes in small tubes called seminiferous tubules. Each testis contains many seminiferous tubules inside.

Ovules and Oogenesis

Ovules (Egg Cells)

Ovules are large cells containing hereditary information and nutrients. The cytoplasm holds yolk reserve substances designed to nourish the embryo during the earliest stages of development.

Formation of Eggs

Unborn girls already have ovules and are born with thousands of immature eggs. At 10 years of age, the follicles remain unchanged. Upon reaching puberty, cyclical maturation begins.

The Ovarian and Menstrual Cycles

1. Follicular Phase

   Characterized by the rapid growth and maturation of the follicle.

2. Ovulation

   This occurs when the follicle opens and the egg is expelled from the abdominal cavity.

3. Luteal Phase (Corpus Luteum)

   The rest of the follicle becomes a residual structure called the corpus luteum (yellow body).

Reproductive Processes

Fertilization

Fertilization is the process where a sperm and an egg join. It takes about 36 to 60 hours and takes place in the fallopian tubes.

Nidation (Implantation)

Once the embryo reaches the uterus, it enters the uterine mucosa where it is finally implanted. This process is called nidation or implantation.

Placentation

The placenta is formed when the embryo emits tree-like extensions (villi) into the uterine lining. The placenta is attached to the embryo through the umbilical cord, which contains blood vessels responsible for the transport of substances.

Stages of Pregnancy (Fetal Development)

First Month

In the first days, the embryo measures 1 mm. The nervous system and heart begin to form.

Second Month

The creation of the brain begins. By the end of the second month, the embryo measures 30 mm.

Third Month

The fetus is 56 mm long and can perform movements.

Fourth Month

The circulatory system is formed.

Fifth Month

Completes the maturation of the nervous system.

Sixth Month

The bronchi and lungs are almost fully formed.

Seventh Month

The fetus has vital organs necessary for life outside the womb.

Eighth and Ninth Months

Complete fetal growth and development.