Prepubertal period: initial changes
In prepuberty, the development of secondary sexual characteristics begins. The process follows a strict order: first, the mammary glands (mamma) enlarge and pubic hair appears (pubis), followed by hair growth in the axillary region (axillaris).
The anatomy of the reproductive organs also undergoes changes:
- Vulva and vagina: The invagination of the vulva decreases, the labia minora grow, and the hymen thickens. The vaginal mucosa becomes velvety, the number of epithelial layers increases, and rugae develop.
- Secretion and smear: The pH shifts from neutral to acidic, and the volume of discharge increases. Superficial and intermediate cells of the squamous epithelium predominate in the vaginal smear.
- Uterus: The organ actively enlarges (length changes from 3.7 cm at age 7 to 6.5 cm by ages 12–13). The ratio of the size of the uterine body to the cervix reaches a proportion of 1:1.
- Ovaries: Increase in mass. They already contain follicles at various stages of development, but none reach maturity, so ovulation is absent.
Pubertal period: menarche and cycle establishment
The pubertal period is counted from the first menstruation (menarche) and continues until age 15. During this time, hypothalamic structures mature, and connections form between cells secreting liberins (including GnRH, somatoliberin, and corticoliberin).
- Endocrine regulation: The release of gonadotropin-releasing hormone (GnRH) becomes rhythmic. Initially, a circadian (daily) rhythm is established with surges during nocturnal sleep. This stimulates the pituitary gland to rhythmically produce LH and FSH, which prompt the ovaries to synthesize estrogens.
- Receptor apparatus: In all organs of the reproductive system, the number of sex steroid receptors increases sharply, and their sensitivity to estradiol changes. However, receptors in the uterus are still insufficiently developed, creating a risk of uterine bleeding of puberty.
- Cycle characteristics: In the first 0.5–1.5 years, the rhythm is often irregular (delays up to 1–2 months). In 20% of girls, anovulatory cycles are observed during the first two years (follicles undergo atresia). Even if ovulation occurs, the corpus luteum may be inadequate due to progesterone deficiency. Menstruation-like bleeding may occur without secretory transformation of the endometrium.
- Anatomy and somatics: The uterus undergoes a growth spurt, with the body-to-cervix ratio reaching 3:1. The typical position—anteflexio versio—is established. The uterine arteries become tortuous. The formation of the female morphotype (widening of the pelvis, distribution of adipose tissue) is completed, along with changes in voice timbre and psychological patterns.
Adolescent period: full synchronization
The main characteristic of the adolescent period is the activation and absolute synchronization of pituitary and ovarian function. Reproductive function completes its formation.
- Circannual rhythm: A stable hourly rhythm of GnRH secretion is established, ensuring adequate release of LH and FSH.
- Mechanism of ovulation: The negative feedback mechanism, which has existed since the antenatal period, is supplemented by a positive feedback mechanism. Now, reaching peak estradiol levels triggers a massive ovulatory surge of gonadotropins.
- Summary: The constant rhythm of hormone secretion is restored, and the final transition to regular ovulatory menstrual cycles occurs.
The order of appearance of secondary sexual characteristics is easy to remember using the rule "from top to bottom, then to the sides": first, Mammary glands (Ma) enlarge and Pubic hair (Pb) appears, followed by Axillary hair (Ax). Abbreviation: MPA.
Class and exam questions
Why is the cycle often irregular in the first years after menarche?
In the first 1.5–2 years of puberty, the uterine receptor apparatus is insufficiently developed. Cycles frequently occur without ovulation, and if ovulation does take place, the corpus luteum may be functionally inadequate due to reduced progesterone secretion.
How do uterine proportions change during maturation?
During the prepubertal period, the uterus grows actively, and the ratio of its body size to the cervix reaches 1:1. During puberty, a rapid growth spurt occurs, and this proportion changes to the adult female norm of 3:1.
What triggers full ovulation in the adolescent period?
Formation of the positive feedback mechanism. When blood estradiol levels reach peak values, it triggers a powerful response surge of luteinizing (LH) and follicle-stimulating (FSH) hormones, leading to the release of the oocyte.
What else to study on this topic
- Stages of mammary gland development (Ma0–Ma4) and timelines for their formation
- Assessment of axillary hair development (Ax0–Ax3) and pubic hair (Pb0–Pb3)
- Mechanisms of pubertal uterine bleeding
- Changes in the cellular composition of the vaginal smear in prepuberty
- Formation of the female morphotype and psychological patterns
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