BGDB Sexual Differentiation - Postnatal

Introduction

This section gives a very brief overview of genital postnatal changes that occur in neonatal, childhood and through to puberty. These topics, particularly puberty, will be revisited in detail in other parts of your course. For sexual development at puberty, we will use resources available online from Endocrinology: An Integrated Approach (NCBI Bookshelf).

Newborn

Newborn uterus anatomy

Female tract abnormalities tend to be rarer and when they do occur are also more difficult to detect.
Male abnormalities are more likely and easily detected asociated with fusion of the urogenital folds, undescended testes or hernia.
This topic will be discussed on the next abnormalities will be discussed in detail on the next page.

Ovary - Primordial follicle numbers are highest late fetal to around birth (estimated 2.5 - 7 million) and then decreasing by apopotic cell death.
At puberty there remain only about 400,000 and only about 10% of these will be released through reproductive life.

(Based on data from: Hassold, etal., Environ Mol Mutagen 1996. 28: 167-175)

Puberty

Latin, pubertas = "adulthood"

In the teen years the endocrine changes that signal sexual development trigger changes in primary sex organs and the development of secondary sexual characteristics.

Hypothalamic expression of gonadotropin releasing hormone (GnRH) is a known puberty trigger.
Recent research suggests that an earlier signal could come from increased neuronal and hypothalamic expression of a peptide family (kisspeptins) and their receptor (G protein-coupled receptor GPR54) in the hypothalamus.
GnRH then signals the pituitary gland to release luteinizing hormone (LH) and follicle-stimulating hormone (FSH) to start sexual development.

Puberty can occur over a broad range of time and differently for each sex:

girls - age 7 to 13
boys - age 9 to 15

Early onset of puberty (precocious) occurs more frequently in girls than boys, in contrast late onset (delayed) occurs more frquently in boys than girls.
The physical characteristics that can be generally measured are: genital stage, pubic hair, axillary hair, menarche, breast, voice change and facial hair.
In 1976, Tanner and Whitehouse established a series of descriptive stages (Tanner Stages) for primary and secondary sexual characteristic development at puberty.

Study the Tanner stages comparing the male and female physiological changes.

Links: Puberty Development | Tanner stages

Hypothalamus Pituitary Gonad (HPG) Axis

In females, menarche (the first menstruation or a period) usually occurs after the other secondary sex characteristics, and will continue until menopause (permanent cessation of reproductive fertility).

The diagram shows the hormonal regulation pathway from the brain to the ovary and subsequent impact on uterine changes during the menstral cycle.

GnRH = gonadotropin-releasing hormone (GnRH). This peptide hormone is a decapeptide (10 amino acids) with a short half life (<15 minutes). LH = Luteinizing Hormone FSH = Follicle Stimulating Hormone

A similar endocrine axis is also found for regulation of the male gonad.

Additional Information

References

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Cite this page: Hill, M.A. (2026, October 1) Embryology BGDB Sexual Differentiation - Postnatal. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/BGDB_Sexual_Differentiation_-_Postnatal

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