Week 9: Reproductive Development & Sexual Behaviour Flashcards
Development of sex organs: Sequence
- Genetic Sex (XX, XY)
- Gonads (Testis/Ovaries)
- Sex Organs (Organizing Effects)
- Maturation (Organizing and Activating Effects)
- Genetic sex
- Genetic sex is determined
- Gonads
- 0-6 weeks → sex organs are undifferentiated
- Undifferentiated gonads
- Undifferentiated precursor tissue:
* Mullerian ducts
* Wolffian ducts
- Gonads (testes/ovaries) are the first to be determined
- Important for determining production of
sperm/ova and hormones
- Important for determining production of
- SRY gene on the Y chromosome causes gonads to become testes
- Sex organs (organizing effects)
- becoming Female = mullerian system
- becoming Male = wolffian system
- determined by sex hormones
mullerian system
The embryonic precursors of the female internal sex organs (fimbriae, fallopian tubes, uterus, inner 2/3 of vagina)
wolffian system
The embryonic precursors of the male internal sex organs (seminal vesicles, epididymis, vas deferens,)
Sexual development: hormone effects
steroid hormones = androgens + estrogens
androgens = testosterone + dihydrotestosterone
estrogens = estradiol
Action via:
* Bind to membrane receptors to exert quick effects
* Activate proteins in the cell
* Alter expression of chromosomes to turn genes off/on.
Hormone: organizing effects
- Sex hormones during prenatal development determines structure of sex organs and brain.
- Postnatal development at puberty determines other sexually dimorphic features (e.g., breast development and dropping of testes)
- Long lasting effects
- Sensitive period
Hormone: activating effects
- Sex hormones activated during postnatal stage, e.g., sperm production, erection and ejaculation,
ovulation, sex drive - More short-term effects - cyclical
organizing effects
determination of internal and external sex organs
7-8 weeks = precursor tissue differentiates
2 precursor tissue systems
- Mullerian system - female tissue
- Wolffian system - male tissue
testosterone
- Androgen
- Organizing: facial and body hair, lowers voice, muscular development, genital growth,
- Activating: sex drive, reproduction
Estradiol
- Estrogen
- Organizing: breast development, lining of uterus, body fat deposition, maturation of female genitalia,
- Activating: sex drive, reproduction
“typical” development
XX OR XY = Dichotomy
XXY Klinefelter
- 1/500 newborn males
- Additional X from mother’s egg or father’s sperm
- Diagnosis in adulthood
- 75% never diagnosed
- Taller than average, greater abdominal fat, low muscle tone, less facial/body hair, smaller sex organs, hypogonadal, infertile
XX Male Syndrome
- XX sex-reversal
- 1/25,000 newborn males
- Genetic sex is “female” (XX)
- SRY is translocated to X chromosome
- Y sequences usually located on the distal tip of
the paternal X chromosome - Result: Male gonads (i.e., testes) are formed
- Identify with and physically look male
- Shorter than average, less hair, gynecomastia,
hypogonadal, smaller sex organs, infertile
Androgen Insensitivity Syndrome (AIS)
- Genetic sex is male (XY)
- Receptors do not respond to androgens
- Range from:
- Complete AIS (external genitalia feminized)
- Partial AIS (partial genitalia masculinized)
- Mild (masculinized) AIS
- Present with internal testes, not ovaries or uterus
- Presentation from hypogonadal → Shallow vagina
- Infertile
Persistent Mullerian Duct syndrome
- Genetic sex is male (XY)
- Extremely rare (prevalence unknown; 250 reported cases in medical literature)
- Failure to produce AMH or no receptors for the hormone
- Genetic variation in AMH gene – inherited autosomal recessive gene
- Present with female and male internal sex organs
- Undescended testes
- Underdeveloped uterus
- Hermaphroditism
- Infertile
Turner’s syndrome
- Genetic sex X (aka X0)
- 1/2500 newborn females
- Either entire X, or partial X chromosome is missing
- Result of defective sperm
- Gonads do not develop (non-working ovaries)
- Internal and external organs are female
- No estrogen, puberty must be induced
- Poor breast development, short stature, broad
chested, webbed neck - Other: learning disability, increased risk for CVD,
immune disorders
Congenital Adrenal Hyperplasia (CAH)
- Genetic sex is “female” (XX)
- 1/15,000 newborn females
- Autosomal recessive disorders – dysregulation of the adrenal glands (CYP21 gene)
- Exposure to high androgen levels during development
- Mullerian system activated, but external organs are “intersex” or “ambiguous”
- Masculinization of Behavior
- Early research: Ehrhardt (1975)
sexual dimorphism of hypothalamus is due to….
hormone exposure
behavioural defeminization
suppression of female neural circuits to prevent female behavior
behavioural masculinization
stimulation of male neural circuits to promote male
behavior
Bio correlates of Sex Dimorphic Behavior: Males
- Medial preoptic area (mPOA) of anterior hypothalamus (mPOA/AH)
- Lesion to mPOA abolishes sexual behaviour in male rodents
- Abundance of testosterone receptors
- Important for sexual performance – facilitate erection
- Activation of dopamine receptors – greater activation, more likely to copulate
- Sexual dimorphic nucleus (SDN) = 3rd interstitial nucleus of the anterior hypothalamus (INAH-3)
- Larger in males than females (2x more in males) – important for male copulation
- Neural Pathway: Inhibitory connections between mPOA/AH and motor neurons via periaqueductal
gray matter (PAG) of midbrain and nucleus of the perigigantocellularis (nPGi) in medulla
