Periods of development of the girl's reproductive system

Classification of age stages

A girl's life from birth to adulthood is divided into several sequential stages. Each is characterized by a unique hormonal profile and anatomical changes:

• Neonatal period: lasts the first 28 days after birth.
• Infancy: continues until the age of 1 year.
• "Neutral" period: covers the age from 1 year to 8 years.
• Prepubertal period: begins at 8 years and ends with the onset of menarche (first menstruation).
• Pubertal period: lasts from menarche to 15 years.
• Adolescent period: the final stage of maturation, occurring at 16–18 years.

Intrauterine development of the hypothalamo-pituitary system

The development of the key links of the reproductive axis occurs in the early stages of embryogenesis. Already at the 5th week, the pituitary gland stands out as an independent structure. By the 8th week of gestation, the paraventricular and supraoptic nuclei of the hypothalamus appear, and the pituitary gland begins to secrete adrenocorticotropic hormone (ACTH) and gonadotropins — follicle-stimulating hormone (FSH) and luteinizing hormone (LH).

At the 9th week, trace amounts of FSH and LH can already be detected in the amniotic fluid and fetal blood. These hormones play an important role in the formation of primary follicles and steroid synthesis. In the 2nd trimester, their concentration drops because the adenocytes of the pituitary gland become highly sensitive to placental estrogens.

By the 16th week, the hypothalamic nuclei acquire the topography characteristic of an adult female and begin to produce neurosecretion. At the 19th week, the anterior pituitary initiates prolactin production, and by the 28th week, the differentiation of the hypothalamic nuclei is largely complete.

Embryogenesis of the gonads and genital tracts

Ovarian development is genetically determined by the 46,XX karyotype. The gonads are formed from mesenchyme, coelomic epithelium, and primordial germ cells. Primary differentiation starts at 6–7 weeks. Interestingly, the gonads, adrenal glands, and kidneys develop from the same region of the primitive mesoderm, which determines their close embryological connection.

The transformation of the primitive gonad directly into the ovary occurs at the 17–20th week. At this point, germ cells turn into oocytes and become surrounded by granulosa cells.

The formation of the reproductive tract takes place from the 4th to the 18th week. The embryonic structures form:

• Genital tubercle — gives rise to the clitoris.
• Genital folds — transform into the labia minora.
• Genital swellings — turn into the labia majora.
• Müllerian ducts — form the uterus, fallopian tubes, and the upper third of the vagina.
• Urogenital sinus — becomes the source of the greater vestibular glands and the upper 2/3 of the vagina.

Hormonal Crisis of Newborns

At the end of pregnancy, high concentrations of maternal estrogens suppress the fetal pituitary gland. After birth, the level of these hormones drops sharply, which leads to a compensatory release of endogenous FSH and LH in the girl. This causes a short-term stimulation of the ovaries — a hormonal crisis.

Its manifestations are most noticeable in the first 10–20 days of life. Hyperestrogenemia stimulates prolactin production, leading to breast engorgement and colostrum secretion. By the 10th day, these symptoms usually subside.

After the decline of estrogenic influence, involutional processes begin: the vaginal mucosa thins to 2–4 layers (predominantly parabasal and basal cells remain), cervical mucus production stops, and the mammary glands flatten. Anatomically, the newborn's vulva looks slightly swollen, the clitoris appears relatively large, and the hymen may have various shapes.

Class and exam questions

What else to study on this topic

• Anatomical and physiological features of the "neutral" period.
• Hormonal restructuring in the prepubertal and pubertal periods.
• Feedback mechanisms in the fetal hypothalamo-pituitary system.
• The process of follicular atresia from the intrauterine period to birth.
• Specifics of the adolescent period of reproductive system development.

Other topics in the "Gynecology" section

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