Human Sexual Differentiation
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Transcript of Human Sexual Differentiation
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Human Sexual Differentiation
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BrainGonads and
Internal Duct Systems
External Genitalia
All mammals including humans begin life as embryos that have the potential to be
either male or female in three ways
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Gonads and Internal Duct Systems
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A male has one X and one Y chromosome. The Y chromosome has an SRY gene, that produces a substance called H-Y antigen. H-Y antigen causes the undifferentiated gonads to become testes.
Male DifferentiationTestes and Ducts
SRY Gene
H-Y antigen
Testes
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A female has two X chromosomes. There is no SRY gene, because that gene only exists on a Y chromosome. In the absence of the SRY gene, no H-Y antigen is produced. In the absence of H-Y antigen, the undifferentiated gonads become ovaries.
Female DifferentiationOvaries and Ducts
No
Antigens
produced
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Development of External GenitaliaDevelopment of External Genitalia
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Male Differentiation External Genitalia
The testes produce testosterone. The testosterone circulates in the bloodstream and is converted to dihydrotestosterone by a substance called 5 alpha reductase. Dihydrotestosterone causes the undifferentiated external genital tissue to develop into the penis and scrotum.
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Adult Male External Genitalia
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Male Adult Gonads and Ducts
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Female Differentiation External Genitalia
The Ovaries produce no testosterone. In the absence of testosterone, the undifferentiated external genital tissue develops into the clitoris, labia minora and labia majora.
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Adult Female Anatomy
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Adult Female Gonads and Ducts
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Male DifferentiationBrain and Behavior
Estradiol
4. The Presence of estradiol in the brain causes it to become masculinized.Blood-Brain Barrier
1. The testes produce testosterone.
Testosterone
Aromatase
2. Testosterone crosses the blood brain barrier into the brain.
3. A substance present in the brain called aromatase converts the testosterone to estradiol, a type of estrogen.
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Female DifferentiationBrain and Behavior
Estradiol
2. Estradiol from the Mother crosses the Placenta into the baby’s blood stream
3. Alpha-fetoproteins present in the baby’s system cannot cross the blood-brain barrier. They bind with the estradiol and prevent it from crossing into the brain.
4. The absence of estradiol in the brain causes it to become feminized.
Blood-Brain Barrier
1. There are no testes to produce testosterone that can be converted to estradiol in the brain Alpha-fetoproteins
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Four Examples of Ways Sexual Differentition Can Go Wrong
1. A genetically male embryo lacks the ability to sense the presence of testosterone.
2. The mother of a genetically male embryo is producing large amounts of adrenaline, which floods the embryo’s body. The adrenaline binds to the receptors that usually detect testosterone, preventing it from being recognized by the body, even if it is present in large amounts.
3. Lack of 5 alpha reductase that converts testosterone to dihydrotestosterone.
4. A genetically female embryo is exposed to external sources of testosterone, or substances that are mistaken for testosterone in the body. Eg. Diethylstilbestrol
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X & Y Chromosomes
DNA
SRY gene
H-Y antigen
Gonad
Mesonephros
Mullerian ducts
Wolffian ducts
Testosterone
Key Terms5 alpha reductase
Dihydrotestosterone
Aromatase
Alpha-fetoprotein
Estradiol
Ovary
Fallopian tubes
Uterus
Vagina
Sexual Differentiation
Testis
Seminal vesicle
Prostate
Vas deferens
Epididymis
Penis
Clitoris
Scrotum
Vulva (Labia)
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Ambiguous Genitalia
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Hermaphrodite Genitalia
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Surgical Reconstruction to Female
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Surgical Reconstruction to Male