Biology major.
Love and fascination of biology since I was a kid.
Basic knowledge of puberty and hormones.
You can look up the info on google.
I did misspeak on one point. Wolffian system is the male system. Mullerian system is the female system. The anti-mullerian hormones is what kills the female reproductive system.
There is a condition called Androgen insensitivity syndrome. It is where a genetic male fetus is immune to male hormones. There are various levels of immunity. Complete Androgen insensitivity syndrome, they are totally immune to androgens. In the absent of the androgens (male hormones) the body continues to develop along it's natural template. Female. The anti-mullerian system cause the default female reproductive system to wither away before it develops into the uterus, cervix and upper vagina. The fetus continues to follow the natural template of female development in the absence of signals from male hormones (because they are immune to them), developing a vagina, labia, clitoris etc.
At puberty, these individuals will develop female secondary sex characteristics. Their bodies respond only to the natural levels of estrogen the testes produce, not the testosterone. If they were identified as AIS and their immature testes removed to prevent cancer risk, they will instead start hormone replacement therapy just like we take. Since they are immune to androgens, testosterone won't work, and so they get estrogen. This cause them to develop as female. hips, breasts, female facial and skeletal structure and denisty.
The only thing different between someone with Complete Androgen insensitivity syndrome and any other genetic male is their body doesn't respond to testosterone. That's it. They are genetically male. But develop as female.
You can google Complete Androgen insensitivity syndrome and see images of how a male in the absence of testosterone will develop.
There is something called the SRY gene. It stands for "the
Sex determining
Region of the
Y chromosome" gene. It is found on the Y chromosome only. It initiates the development of a male fetus. When this gene is mistakenly transcribed onto an X chromosome, a fetus with XX chromosome, female chromosomes will develop into a biological male. They are known as XX male syndrome. You can google that too.
The gonads begin in a state that can develop into either female or male system. It is know as bipotential gonadal ridge. Without the SRY gene to activate male development, which is caused by the release of male hormones to develop the fetus into a male. Or in it's absence flooded with female hormones to develop the fetus into female.
Hormones define our sex before birth.
And again during puberty. Look up what puberty is. As wikipedia confirms "Puberty is the process of physical changes by which a child's body matures into an adult body capable of sexual reproduction to enable fertilisation. It is initiated by hormonal signals from the brain to the gonads: the ovaries in a girl, the testes in a boy. In response to the signals, the
gonads produce hormones that stimulate libido and the growth, function, and transformation of the brain, bones, muscle, blood, skin, hair, breasts, and sexual organs. Physical growth—height and weight—accelerates in the first half of puberty and is completed when the child has developed an adult body. Until the maturation of their reproductive capabilities, the pre-pubertal, physical differences between boys and girls are the genitalia, the penis and the vagina."
"For boys, an androgen called testosterone is the principal sex hormone."
"The hormone that dominates female development is an estrogen called estradiol."
http://en.wikipedia.org/wiki/PubertyIt goes on to list all the changes these hormones cause in both males and females.
Hormones are way our bodies develop. They signal cells and regions of the body to activate and start to grow and divide. When sections of the skull get this signal, the bone cells in that area divide and reproduce a lot more, causing a more noticeable and prominent structure. For example, hormones trigger the bone cells of the brow to divide and reproduce quickly. More cells mean more bone, mean larger region of bone that jets out noticeably from the forehead and bone around it. Think about it as if your were modeling the skull in clay and just kept adding more clay to the brow. The brow would be larger and stick out more. That's what happens to the brow under the influence of testosterone.
All of this can be looked up and confirmed for yourself.
But this is the reason for HRT. Hormones trigger development of secondary sex characteristics in puberty. HRT is used to induce a second puberty that will develop our bodies to match our gender identity and not our biology.
