Wagner-Sexual Differentiation

Front 1

describe sexual, genetic, and gonadal differentiation

Back 1

SEXUAL DIFFERENTIATION-in utero development of reproductive system along male or female lines
1. Genetic differentiation-depends on combination of sex chromosomes. Males have XY chromosomal pattern, females have pair of X chromosome
2. Gonadal differentiation: depends on presence of gene products on Y chromosome
a. SRY gene-“sex-determining region of Y chromosome” that encodes testis-determining factor (TDF)
b. TDF: DNA-binding protein and transcription factor, expressed by primordial gonadal cells; triggers transformation of gonads into testes

Front 2

describe phenotypical differentiation and how it relates to primordial duct systems

Back 2

Phenotypic (anatomic) differentiation-occurs at level of primordial duct systems and external genitalia due to actions of hormones secreted by fetal testes
a. primordial duct systems-present in all embryos
i. Wolffian ducts-testosterone transforms these into male reproductive tract
ii. Müllerian ducts-in developing males; apoptotic regression of these is induced by Müllerian inhibiting substance (MIS); w/out testosterone and MIS, müllerian ducts become female reproductive tract

Front 3

describe external genitalia in phenotypical differentiation

Back 3

bipotential external genitalia-differentiation of external genitalia observed in developing males is dictated by local conversion of testosterone to dihydrotestosterone (DHT)
i. genital tubercle-in males, this becomes shaft and glans of penis; in females, corresponds to clitoris
ii. urethral folds-in males, fuse to help form shaft of penis; in females, becomes labia minora
iii. genital (labioscrotal) swellings-in males, fuse to become scrotum; in females, develop into labia majora

Front 4

Describe brain development in phenotypic differentiation

Back 4

in utero or neonatal androgen exposure predisposes brain toward male pattern of sexual behavior

Front 5

Describe genetic errors in sexual differentiation

Back 5

Primarily result of X chromosomal separation failure (i.e. non-disjunction) during anaphase I of gametogenesis
a. seminiferous tubule dysgenesis (Klinefelter’s syndrome)-characterized by the XXY chromosomal pattern; most common sex chromosome disorder; afflicted individuals have testes that secrete sufficient testosterone to develop male genitalia and other secondary sex characteristics; seminiferous tubules develop abnormally, and mental retardation occurs w/ higher prevalence
b. ovarian agenesis (Turner’s syndrome)-characterized by XO chromosomal pattern, rudimentary gonads, female external genitalia don't mature during puberty, short stature and other congenital abnormalities
c. “superfemale”-XXX chromosomal pattern; 2nd most common non-disjunctional error; exhibit comparatively benign symptomatology
d. true hermaphroditism-haracterized by XX/XY mosaic in primordial gonadal tissue due to faulty mitoses in early zygote, giving rise to individual w/ both ovaries and testes
e. other chromosomal abnormalities-due to sex chromosomal transposition and deletion

Front 6

describe female pseudohermaphroditism as it relates to hormonal abnormalities

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Hormonal abnormalities-result in pseudohermaphroditism, in which person exhibits genetic karyotype and gonads of one sex, and external genitalia of other
female pseudohermaphroditism-development of male external genitalia in genetic females due to in utero exposure to androgens during critical period b/t 8-13 weeks of gestation
i. congenital virilizing adrenal hyperplasia-individuals exhibit excessive circulating levels of dehydroepiandrosterone
ii. systemic maternal exposure to androgens

Front 7

describe male pseudohermaphroditism

Back 7

development of female external genitalia in genetic males
i. defective testicular development-compromises both testosterone and MIS secretion, which results in development of female reproductive tract
ii. androgen resistance-due to inadequate androgen signaling in target tissues
1 example arises from 5α-reductase deficiency; local DHT production reduced, development of external genitalia compromised
Other examples include mutations in androgen receptor gene; symptoms associated range from infertility to testicular feminizing syndrome (aka complete androgen resistance syndrome); w/ latter, both MIS and testosterone are secreted by testes retained in pelvic cavity due to development of female external genitalia; individuals exhibit comparatively large breasts and are taken for normally developing female until medical consult is sought over concern due to lack of menstruation

Front 8

describe other congenital hormonal abnormalities

Back 8

congenital adrenal hyperplasia associated w/ blockade of pregnenolone formation-no adrenal or testicular androgen synthesis (therefore no testosterone-induced differentiating signal)
congenital 17α-hydroxylase deficiency-compromises 17-hydroxysteroid formation, and thus androgen production