LM 4.2: Sexual Differentiation and Physiology of Human Sexual Function Flashcards
what does species survival require?
- reproduction by parents
- rearing of offspring
- offspring reproduction
what is species survival insured by?
- sex drive and attraction
- social roles and values
- love
what is the general role of a male in species survival?
- relatively non-selective mating
2. goal is to spread genes
what is the general role of a female in species survival?
- generally selective mating
2. goal is reliable partner to assure success raising offspring
when do the gonads differentiate?
weeks 6-9
testis begins by 6 weeks –> sex determining region on Y chromosome (SRY gene) causes testis to develop
in absence of Y chromosome ovaries develop (weeks 7-9)
when do the internal reproductive ducts develop?
8-12 weeks
there are separate sets of primordia that transiently coexist in embryos of both sexes so there is potential for development of either
male offspring requires the positive influences of testosterone to grow Wolffian ducts and Müllerian Inhibiting Substance (MIS) to prevent Müllerian duct development
absence of testosterone and presence of MIS yields female ducts
when do external genitalia develop?
8-12 weeks
maleness requires the positive effect of Dihydrotestosterone (DHT) –> when androgen effect is intermediate, newborn male shows only partial virilization
if androgen (DHT) not present in first 12 weeks, masculinization never completed
genetic females with androgen over-stimulation may have complete phallic urethra and prostatic tissue
differentiation complete by 16th week
when do the biopotential hypothalamic neurons in the brain develop?
after week 16
certain hypothalamic neurons in the preoptic area and some limbic and cortical brain areas of both sexes are initially undifferentiated and are capable of becoming functionally male or female
then during 2nd trimester, androgen presence causes permanent, irreversible biochemical changes in these neurons and their connectivity
regardless of genetic sex, androgen presence prevents cyclic LH release that is required for normal menstruation –> androgen absence during this time would allow for a cyclic LH release pattern to develop
what conditions does chromosomal nondisjunction during meiosis lead to?
- Klinefelter syndrome
2. Turner Syndrome
what is Klinefelter syndrome?
XXY
47 chromosomes with male phenotype
1 in 500 male births
normal phenotypically as a child, but usually tall and with small testes
incomplete post pubertal virilization and gynecomastia due to low T and elevated E
an adult has azoospermia
what is Turner syndrome?
XO
45 chromosomes with female phenotype
1 in 2500 females
short stature, streak gonads (no ovaries), primary amenorrhea and sexually-undeveloped appearance due to low E
associated with many congenital abnormalities
what are some of the abnormal gonadal developments that can occur even in the presence of XX or XY?
- pure gonadal dysgenesis
- gene mutation based gonadal dysgenesis
- vanishing testis syndrome
what is pure gonadal dysgenesis?
an abnormal gonadal development despite presence of XX or XY
patients will present with streak gonads with a normal female phenotype due to absence of MIS and androgens
what is gene mutate based gonadal dysgenesis?
46 XY with mutations in one of the following:
- SRY
- WT1 (Wilms Tumor Related 1)
- SF1 (steroidogenic factor 1)
- SOX9
- DAX1
what is vanishing testis syndrome?
46 XY with absent or rudimentary testes
androgen present for some portion of gestation
effects vary from complete failure of virilization to normal male with anorchia
what is genetic XX with ambiguous or male phenotypic genitalia?
this is females with ovaries and normal Mullerian derivatives, but with excessive androgens during gestation
external genitalia at birth can range from simple clitoral enlargement to complete scrotum and penile urethra
most common cause is Congenital Adrenal Hyperplasia (CAH)
