slide 9: Sexual determination and differentiation

steroid hormones bind to receptors inside cells and can

alter gene expression, increasing and decreasing the production of various proteins

the effect of steroid hormones in adulthood are __________ but ________ during early development

short term (or transient) but permanent

sex determination is driven by

chromosome

sex differentiation is driven by

hormone

gonadal hormones direct

sexual differentiation of brain and behavior

sex determination is the process by which the

decision is made for a fetus to develop as a male or female

sexual differentiation is a process by which

individuals develop either male or female bodies and behaviors

sex determination focuses on _____________ sex and ________ sex

chromosomal sex and gonadal sex

sex differentiation focuses on ______________ sex , _____________ sex, and ___________ sex

hormonal sex, morphological sex, and behavioral sex

when gonads are first made they are biopotential which means that the

same gonad can become either testes or ovaries

the SRY gene on the Y chromosome codes for the

development of testes from the biopotential gonad

without the SRY gene an

ovary forms

hormones secreted early on by the gonads direct sexual

differentiation of internal and external sex organs

in males the Wolffian ducts develop into the

epididymis, vas deferens, and seminal vesicles, and the Mullerian system shrinks

in females, the Mullerian ducts develop into the

oviducts, uterus, and vagina and the wolffian system degenerates

if testes are present the anti-mullerian hormone causes

regression of the mullerian system

if testes are present the testosterone masculinizes the

internal organs by promoting development of the Wolffian system

testosterone can be converted to ______________ by the enzyme 5-reductase

dihydrotestosterone (DHT)

if testes are present then dihydrotestosterone (DHT) masculinizes the

external structure

testosterone can be aromatized to

estradiol via aromatase

estradiol masculinizes the

brain

sexual differentiation of external genitalia is also biopotential and based on the presence or lack of

DHT

small changes in hormonal exposure early in development can

change the appearance of genitalia

Turners syndrome

person only have one sex chromosome (X)

someone with Turners syndrome will develop as a

female due to lack of SRY gene and will have abnormal ovaries

Klinefelter’s syndrome

person has an extra chromosome (XXY)

someone with Klinefelter’s syndrome will develop a

masculine body with abnormally small testes and penis with low testosterone production (little to no sperm are produced)

CAH starts with the

hypothalamic pituitary adrenal axis

patients with CAH lack the enzyme that produces

cortisol so there is no negative feedback

patients with CAH have higher hormone production which leads to the

adrenal gland becoming enlarged

cortisol buildup leads to the adrenal glands turning 17-OHP into

other androgens like testosterone

external genitalia in female is partially masculinized because of

exposure to increased DHT during development

exogenous cortisol is given after birth to

halt excess androgen production

Androgen insensitivity syndrome occurs in

XY people with defective androgen receptors

ovaries don’t produce hormones until

puberty

sexual dimorphism is the condition in which

male and females exhibit marked sex differences in appearance

sex differences in the brain refers to the

number or density of neurons, dendritic branching, or connectivity

in rats, the pre-optic area is called the

sexually dimorphic nucleus of the POA is larger in males than in females

organizational effect of estradiol can

permanently alter the brain by doing things like altering cell death, changing synaptic connectivity, and affecting densities

organizational effects occur early in development during the

critical period when the brain is still developing

a hormone can be both

organizational and activational

the deciding factor for what kind of effect the hormone will have is the

timing of its action

steroid hormones have an organizational effect only when

present during the critical period of development

the critical period can be before birth or

just afterwards in the neonatal period

no steroid is found exclusively in either

males or females

female brains aren’t masculinized during fetal development because

ovaries aren’t active until puberty and maternal estrogen in developing females doesn’t enter the brain (due to alpha-fetoprotein)