Obstetrics and Gynecology - A.M. Gromova 2000

Fertilization and Fetal Development

Like most animal organisms, humans reproduce sexually, which means through the Separation of Female Germ Cells (eggs/ova) from the female (maternal) Organism and Male Germ Cells (spermatozoa) from the male (paternal) organism, provided that Fertilization takes place—a process defined as the fusion of male and female germ cells (Gametes). The maturation process of both the egg and the spermatozoon is complex. It culminates in reductional division (Meiosis), As a result of which the chromosome count in the nuclei of both cells is halved, yielding cells with a haploid set of Chromosomes (23 chromosomes, one of which is a sex chromosome).

A mature human spermatozoon is 50–60 μm long and consists of a HEAD containing The Nucleus, a neck, and a tail. Driven by whip-like Movements of the tail, the sperm moves independently at a speed of 2–3 mm/min, though it only acquires motility after entering the secretion of the Seminal Vesicles and the Prostate Gland. This mixture is known as seminal fluid or semen. Semen is a whitish, gelatinous, alkaline substance with a specific odor reminiscent of raw chestnuts. Under normal conditions, the volume of an ejaculate is 3–5 ml (with 1 ml of semen containing 60–120 million spermatozoa). Motile spermatozoa account for 80% of the total, while the proportion of pathological forms should not exceed 20%.

The GROWTH AND DEVELOPMENT of the oocyte take place within primary follicles located in the cortical layer of the Ovary. The egg Cell is practically devoid of autonomous mobility. It is surrounded by the zona pellucida and the corona radiata. Following ovulation (rupture of the follicle), the egg is released into the peritoneal cavity and is immediately captured by the fimbriae of the ampullary region of the fallopian tube.

Spermatozoa penetrate the Uterus and fallopian tubes owing to their intrinsic motility. Upon entering the Vagina, which has an acidic environment, they migrate toward the cervix, reaching it as early as 3 minutes after ejaculation into the vagina. Cervical mucus exhibits the highest permeability to spermatozoa during the few days surrounding ovulation. Within the cervical canal mucus, abnormal spermatozoa—which are constantly present in seminal fluid—are broken down and eliminated. Spermatozoa reach the fallopian tubes 1.5–2 hours after ejaculation into the vagina. In the alkaline environment of the uterus and fallopian tubes, spermatozoa retain their motility for 3–4 days.

During the interaction between male and female germ cells, a series of changes occurs within them; sperm activation is driven by capacitation and the acrosome reaction. Capacitation is the process whereby spermatozoa shed surface Antigens, occurring within the uterus and oviducts under METABOLISM/18.html">The Influence of mucous secretions from glandular cells and follicular fluid. Capacitation is followed by the acrosome reaction, resulting in the release of Enzymes from the spermatozoa (such as hyaluronidase, acrosin, and Trypsin), which facilitate the Digestion of hyaluronic acid and the Proteins of the zona pellucida and corona radiata of the egg cell.