Difference between revisions of "Reproductive System Development"
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Development of the reproductive system is a complex process relying on numerous systems and conditions to ensure appropriate structures and rate of development are maintained within the embryo. There are several important criteria that determine appropriate reproductive system development; '''genetic sex''' which determines the sex of the embryo, '''gonadal sex''' and '''phenotypic sex''' which both determine sexual differentiation. Genetic sex determines gonadal sex which in turn determines phenotypic sex. Sex determination relates to the genetic or environmental process which determines the sex of an individual whilst sexual differentiation represents the development of internal and external genitalia. | Development of the reproductive system is a complex process relying on numerous systems and conditions to ensure appropriate structures and rate of development are maintained within the embryo. There are several important criteria that determine appropriate reproductive system development; '''genetic sex''' which determines the sex of the embryo, '''gonadal sex''' and '''phenotypic sex''' which both determine sexual differentiation. Genetic sex determines gonadal sex which in turn determines phenotypic sex. Sex determination relates to the genetic or environmental process which determines the sex of an individual whilst sexual differentiation represents the development of internal and external genitalia. | ||
==Sex Determination in Mammals== | ==Sex Determination in Mammals== | ||
| − | In mammals the male is the heterogametic species (XY chromosomes) and females are the homogametic species (XX chromosomes) and this is the first stage in the development of the reproductive system. This stage occurs in the zygote and genes in the Y chromosome regulate the development of gonads towards the male phenotype. Therefore the Y chromosome must be present for the development of the male gender, regardless of the number of X chromosomes (see Developmental Abnormalities section below). Each Y chromosome contains a '''Sex Determining Region''' (SRY). | + | In mammals the male is the heterogametic species (XY chromosomes) and females are the homogametic species (XX chromosomes) and this is the first stage in the development of the reproductive system. This stage occurs in the zygote and genes in the Y chromosome regulate the development of gonads towards the male phenotype. Therefore the Y chromosome must be present for the development of the male gender, regardless of the number of X chromosomes (see Developmental Abnormalities section below). Each Y chromosome contains a '''Sex Determining Region''' (SRY) and testes must be present for the formation of male characteristics. Sex hormones produced by the developing gonads affect the further development of the reproductive organs and the nervous system and are therefore crucial. |
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==EMBRYOLOGICAL DEVELOPMENT OF THE GENITAL TRACT== | ==EMBRYOLOGICAL DEVELOPMENT OF THE GENITAL TRACT== | ||
Revision as of 14:16, 19 August 2011
Introduction
Development of the reproductive system is a complex process relying on numerous systems and conditions to ensure appropriate structures and rate of development are maintained within the embryo. There are several important criteria that determine appropriate reproductive system development; genetic sex which determines the sex of the embryo, gonadal sex and phenotypic sex which both determine sexual differentiation. Genetic sex determines gonadal sex which in turn determines phenotypic sex. Sex determination relates to the genetic or environmental process which determines the sex of an individual whilst sexual differentiation represents the development of internal and external genitalia.
Sex Determination in Mammals
In mammals the male is the heterogametic species (XY chromosomes) and females are the homogametic species (XX chromosomes) and this is the first stage in the development of the reproductive system. This stage occurs in the zygote and genes in the Y chromosome regulate the development of gonads towards the male phenotype. Therefore the Y chromosome must be present for the development of the male gender, regardless of the number of X chromosomes (see Developmental Abnormalities section below). Each Y chromosome contains a Sex Determining Region (SRY) and testes must be present for the formation of male characteristics. Sex hormones produced by the developing gonads affect the further development of the reproductive organs and the nervous system and are therefore crucial.
EMBRYOLOGICAL DEVELOPMENT OF THE GENITAL TRACT
Early embryo
- Small indifferent gonads.
- Primitive structures which will become gonads and genital tract are identical at this stage.
- Paired mesonephric ducts (Wolffian) or paramesonephric (Mullerian) ducts fuse caudally with urogenital sinus.
(Metanephros - becomes the kidney).
Gonadal differentiation
- Determined by the presence of the SRY gene of the Y chromosome (sex determining region of the Y chromosome) which encodes “testicular determining factor” protein (SRY protein).
- Lack of SRY gene (i.e. XX females) leads to ovarian differentiation.
Development of phenotypic sex
- The sex of the embryonic gonad normally determines which reproductive duct system develops.
- Testes induce development of mesonephric (Wolffian) duct system in to epididymis and vas deferens and cause regression of paramesonephric (Mullerian) duct by ”mullerian inhibitory substance”, (MIS).
- Absence of testes in presence of ovaries allows paramesonephric ducts to develop under influence of oestrogen to oviduct, uterus, cervix and cranial vagina.
Summary of determinants of sexual development
Chromosomal or genetic sex = sex chromosomes
Gonadal sex = ovary or testis
Phenotypic sex = usually determined by gonad
Information by permission of Professor RW Else
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This article is still under construction. |