Week 9: Reproductive Development & Sexual Behaviour

Question 1

Development of sex organs: Sequence

Answer 1

1. Genetic Sex (XX, XY)
2. Gonads (Testis/Ovaries)
3. Sex Organs (Organizing Effects)
4. Maturation (Organizing and Activating Effects)

Question 2

1. Genetic sex

Answer 2

• Genetic sex is determined

Question 3

2. Gonads

Answer 3

• 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
• SRY gene on the Y chromosome causes gonads to become testes

Question 4

3. Sex organs (organizing effects)

Answer 4

• becoming Female = mullerian system
• becoming Male = wolffian system
• determined by sex hormones

Question 5

mullerian system

Answer 5

The embryonic precursors of the female internal sex organs (fimbriae, fallopian tubes, uterus, inner 2/3 of vagina)

Question 6

wolffian system

Answer 6

The embryonic precursors of the male internal sex organs (seminal vesicles, epididymis, vas deferens,)

Question 7

Sexual development: hormone effects

Answer 7

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.

Question 8

Hormone: organizing effects

Answer 8

• 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

Question 9

Hormone: activating effects

Answer 9

• Sex hormones activated during postnatal stage, e.g., sperm production, erection and ejaculation,
  ovulation, sex drive
• More short-term effects - cyclical

Question 10

organizing effects

Answer 10

determination of internal and external sex organs
7-8 weeks = precursor tissue differentiates

Question 11

2 precursor tissue systems

Answer 11

• Mullerian system - female tissue
• Wolffian system - male tissue

Question 12

testosterone

Answer 12

• Androgen
• Organizing: facial and body hair, lowers voice, muscular development, genital growth,
• Activating: sex drive, reproduction

Question 13

Estradiol

Answer 13

• Estrogen
• Organizing: breast development, lining of uterus, body fat deposition, maturation of female genitalia,
• Activating: sex drive, reproduction

Question 14

“typical” development

Answer 14

XX OR XY = Dichotomy

Question 15

XXY Klinefelter

Answer 15

• 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

Question 16

XX Male Syndrome

Answer 16

• 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

Question 17

Androgen Insensitivity Syndrome (AIS)

Answer 17

• 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

Question 18

Persistent Mullerian Duct syndrome

Answer 18

• 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

Question 19

Turner’s syndrome

Answer 19

• 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

Question 20

Congenital Adrenal Hyperplasia (CAH)

Answer 20

• 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)

Question 21

sexual dimorphism of hypothalamus is due to….

Answer 21

hormone exposure

Question 22

behavioural defeminization

Answer 22

suppression of female neural circuits to prevent female behavior

Question 23

behavioural masculinization

Answer 23

stimulation of male neural circuits to promote male
behavior

Question 24

Bio correlates of Sex Dimorphic Behavior: Males

Answer 24

• 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