Fetus -- Adrenal Gland produces Cortisol and DHEAS .
Cortisol from fetus converted to prostaglandins in placenta--these begin contractions.
DHEAS from fetus converted to estriol in placenta--these promote oxytocin in mother.
Oxytocin (from Posterior pituitary ) in mother begins labor.
Cervical stretching--positive feedback.
Both male and female embryos are indifferent.
That means they have the ability to be both male and female.
Wolfian--will form male genetalia.
Mullarian--will form female genitalia.
How does this work? All embryos start on a neutral or "indifferent" path. The 4 week old embryo is indifferent
By 7 weeks, the SRY gene encoded by the short arm of the Y chromosome begins to roar.
Indifferent embryos have two sets of ducts:
Müllerian ducts- -will be come the future oviducts--thus female.
Wolfian ducts- -will become the future vas deferens--thus male.
How does SRY determine which duct will develop? SRY causes testes to develop.
The Wolfian duct is dependent on testosterone for its continued development. It needs testosterone produced from the testes to grow.
The testes also produce an anti-Müllerian hormone that promotes regression of the Müllerian ducts.
So without SRY, the indifferent embryo will naturally develop into a female.
Sex Chromosomal Disorders
Turner Syndrome – XO only one sex chromosome
Short, thick neck and stature
Do not undergo puberty, or menstruate,
no breast development
Kleinfelter Syndrome – XXY
Testis and prostate underdeveloped
No facial hair
Long arms and legs: big hands and feet
Can be mentally retarded
Two copies of DAX (double X) inactivate SRY, thus this individual would be genetically male, but look female.
An XY Individual with Androgen Insensitivity Syndrome Androgen Insensitivity Syndrome is a sex reversal condition where XY individuals look female. These individuals have the Y chromosome and functional SRY. These individuals have testis which generate AMH and testosterone. However, the genetic mutation results in a lack of the testosterone receptor. Estrogens are made in the adrenal gland which drive phenotypic development. As adults, these individuals have testes in the abdomen and lack a uterus and oviducts.