Ovary Development

From Embryology

Introduction

The ovary and uterus

The female gonad is the ovary and is closely associated with female internal genital (reproductive) tract development. In humans, these laterally paired organs lie within the peritoneal cavity. Genes such as Wnt-4 and DAX-1 necessary for initiation of female pathway ovary development, female gonad is not considered a default process.

Initial gonad development in females and males is virtually identical with germ cells migrating into an indifferent gonad. In females with XX, the ovary then begins to develop and the subsequent structure and timecourse of germ cell then differs between males and females. In the ovary oocytes proliferate prior to birth and arrest in meiosis 1.

Links: Menstrual Cycle | Lecture - Genital Development | X Chromosome | Testis Development | System - Female | Week 1 - Oogenesis

Human Timeline

Approximate dates listed below.

24 days - intermediate mesoderm, pronephros primordium

28 days - mesonephros and mesonephric duct

35 days - uteric bud, metanephros, urogenital ridge

42 days - cloacal divison, gonadal primordium (indifferent)

49 days - paramesonephric duct, gonadal differentiation

56 days - paramesonephric duct fusion (female)

100 days - primary follicles (ovary)

Oogenesis

Human ovary oocyte number

This graph shows the changes in human germ cell numbers in the ovary with age.

Total numbers peak at about 7 million (occuring in early fetal development) 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.

Infant Ovary

Histology of the female infant ovary

This image shows a region (see inset) of the infant ovary cortex.

There are a large number of developing oocytes which will eventually form a dense primordial germ layer at the ovary periphery.

Later stages of follicle development are completely absent and will begin to only appear just prior to puberty.



References


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Additional Images