2011 Lab 8 - Postnatal

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2011 Lab 8: Introduction | Sex Determination | Early Embryo | Late Embryo | Fetal | Postnatal | Abnormalities | Quiz | Online Assessment


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


Newborn uterus.jpg

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.
Infant ovary.jpg * 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 growth.jpg 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

Female - Hypothalamus Pituitary Gonad (HPG) Axis

Menstrual cycle.png


  • menarche (the first menstruation or a period) usually occurs after the other secondary sex characteristics
  • cycles 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.

Male - Testosterone

Male testosterone and AMH level graph.jpg


Testosterone and Anti-Müllerian Hormone (AMH) relative levels[1]

  • Sertoli cells - AMH production.
  • Leydig cells - Testosterone production
  • Spermatogonia - mitosis
  • Spermatozoa - maturation

Additional Information

Endocrinology: An Integrated Approach. Nussey S, Whitehead S. Oxford: BIOS Scientific Publishers; 2001.


  1. <pubmed>16544032</pubmed>| Arq Bras Endocrinol Metabol.

2011 Lab 8: Introduction | Sex Determination | Early Embryo | Late Embryo | Fetal | Postnatal | Abnormalities | Quiz | Online Assessment

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Cite this page: Hill, M.A. (2024, June 14) Embryology 2011 Lab 8 - Postnatal. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/2011_Lab_8_-_Postnatal

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