Puberty Notes

Genetic sex is determined by the combination of sex chromosomes at the time of conception, forming either XX (female) or XY (male).

Gonadal sex refers to the type of gonads that develop, which can be either testes or ovaries.
The Y chromosome is critical in driving male differentiation and development.

Phenotypic sex is the apparent anatomical sex of the individual, which is determined by the gonadal sex.

The reproductive system starts as undifferentiated, involving:
- Müllerian ducts which can develop into female reproductive structures.
- Wolffian ducts which can develop into male reproductive structures.

The male reproductive tract forms from the Wolffian ducts under the influence of testosterone and other hormones. Major events include:
- Regression of Müllerian ducts, which are unnecessary for male development.
- Development of the epididymis, ductus deferens, and ejaculatory duct from the Wolffian duct.
- Testes formation and the maturation of Sertoli and Leydig cells which produce hormones such as AMH and testosterone.
- Dihydrotestosterone (DHT) influences the development of external male genitalia (e.g., penis, scrotum).

In the absence of the SRY gene and male hormones, female pathways develop. Major events include:
- Regression of Wolffian ducts.
- Müllerian ducts promote development of female reproductive structures such as the uterus and oviducts.
- Development of ovaries from the bipotential gonad.
- Formation of internal genitalia and external structures (e.g., labia, clitoris) without the presence of DHT.

Intersex conditions illustrate the complexities of biological sex, demonstrating that sex is not strictly binary (male or female).
Conditions like 5-alpha reductase deficiency show that individuals with XY chromosomes can develop female characteristics at birth but may later develop male characteristics during puberty due to testosterone surges.

Examples include:
- Turner Syndrome, Klinefelter Syndrome, and androgen insensitivity syndromes.
- These conditions underscore the diverse pathways of sexual development.

Some terms include:
- Transgender: An individual whose gender identity does not align with sex assigned at birth.
- Nonbinary: Individuals who do not identify strictly as male or female.
- Cisgender: Individuals whose gender identity aligns with their assigned sex at birth.

Leydig cells mature and increase androgen secretion from approximately 0.2 ng/ml to 6 ng/ml between ages 10 to 15.
Testicular volume increases from 2 ml to 20-25 ml during ages roughly 9 to 13.
- There is an increase in diameter and tortuosity of tubules as well as maturation of Sertoli cells and proliferation of germ cells.

Initial development involves primordial and small pre-antral follicles prior to puberty.
Estradiol increases around ages 8-10 which leads to breast development and increases uterine volume.
Menarche typically occurs approximately 2-3 years after breast development, around 12.5 years of age, with cycles that may range from 21-45 days in the initial years.
Menstrual cycles may also be frequently anovulatory.

Stage 1: Prepubescent characteristics.
Menarche: The first menstrual cycle marks significant development, usually around 9.5 to 14.5 years of age.

FSH (Follicle Stimulating Hormone) and LH (Luteinizing Hormone) levels vary with age, showing an increase during puberty.
Changes in plasma testosterone and estradiol concentrations are significant during this period.

Hormonal profiles change throughout different life stages, including childhood, puberty, and adulthood.

The onset of pubertal changes is determined by the maturation of a somatic component that is independent of the gonad itself.
The development of central neural mechanisms that control GnRH (Gonadotropin-releasing hormone) is vital in this process.
- GnRH serves as a reproductive hormone that has a 'brake' during the juvenile period, preventing premature gonadal activation.