sexuality study guide

Gonad Development

• Ovaries for females.

• Testes for males.

• No sexual differentiation until the 6th week of development.

  • Homologous structures.

• At 6 weeks, SRY becomes active.

  • The sex determining region of the Y-chromosome.

• The SRY gene develops the male gonads.

• Without activation of the SRY gene, ovaries will develop.

• In a research study, the SRY gene was inserted into female mice, resulting in testis development.

Internal Organ Development

• At 3 months of development, male fetuses obtain the Wolffian system, while female fetuses obtain the Müllerian system.

• In male fetuses, testosterone causes the full development of the Wolffian system.

  • The anti-Mullerian hormone degenerates the female system.

• In female fetuses, the lack of testosterone degenerates the Wolffian system.

• Without the anti-mullerian hormone, the female system will fully develop.

External Genitalia Development

• In male fetuses, testosterone and 5-alpha-reductase (cousin of testosterone) combine to form 5-alpha-dihydrotestosterone.

  • 5-alpha-dihydrotestosterone develops the penis and scrotum.

• In female fetuses, no hormone activity is needed.

  • Therefore, the lack of activity forms the labia, clitoris, and outer part of the vagina.

Puberty

• Spermarche: first ejaculation for males.

• Menarche: first menstrual period for females.

Pfeiffer & The Pituitary Gland

• Pfeiffer’s research shows that testicular implants in neonatal female rats block ovulation.

  • Concluded there are hormonal differences between males and females.

• Since the pituitary gland releases reproductive hormones, males and females must have different pituitary glands.

• A later study transplanted adult male rat pituitary glands into adult females.

  • Ovulation continued normally in the female rats.

• Female and male pituitary glands can produce the same hormones; therefore, the difference must be in the signals from the brain to the pituitary gland.

Rat Studies & Sexual Development

• Castrated adult male rats cannot ovulate even when a female system is surgically implanted.

• Castrated baby male rats can ovulate if a female system is surgically implanted.

• Testosterone treatment in adult female rats stops ovulation, but can be overcome with brain stimulation.

• Testosterone treatment in baby female rats stops ovulation and cannot be reversed.

Rat Studies & Behavior

• Lordosis:

  • Female animals arch their spine when touched on the back to aid copulation.

• Mounting:

  • Male animals mount other animals to aid copulation.

• Castration of baby male rats:

  • Suppresses mounting and increases lordosis.

• Testosterone exposure for female baby rats:

  • Suppresses lordosis and increases mounting.

Organizational Effect

• Hormones permanently shape the brain and body during critical development periods. These changes are structural and long-lasting.

• For example, testosterone masculinizes the developing brain and body.

Activation Effect

• Hormones temporarily activate behaviors in a time-specific manner, such as puberty or reproductive cycles.

• For example, testosterone stimulates mounting.

Menstrual Cycle & Hormones

• FSH is secreted at the beginning of a cycle.

  • FSH causes the ovaries to develop follicles, which contain an ovum.

• One follicle develops more rapidly than others, and estrogens are released.

  • Estrogen prevents the other follicles from developing.

• High estrogen levels stimulate the release of LH.

  • High LH levels cause ovulation.

• The remaining empty follicle is now the corpus luteum.

• The corpus luteum releases progesterone, which prevents the formation of more follicles and thickens the uterine lining.

• If fertilization hasn’t occurred, progesterone levels fall and the cycle repeats.

  • Menstruation will occur.

Turner Syndrome

• XO female, usually infertile.

• Sperm properly fertilizes the egg, but has lost the X chromosome.

• Affects cognitive functioning and sexual maturation.

• Short stature is common.

Klinefelter’s Syndrome

• XXY male with low testosterone.

• The Y chromosome stimulates the growth of male genitalia, but the additional X chromosome inhibits this development.

• Increased breast development, wider hips, infertility, and low testosterone.

• Hormone therapy can help with symptoms.

Congenital Adrenal Hyperplasia

• Females exposed to excess androgens prenatally will be born with ambiguous genitalia.

• Cognitive abilities are more similar to males.

• Increased rate of homosexuality.

Androgen Insensitivity Syndrome

• Chromosomes: XY

• Insensitive to androgens and develops externally as a female.

• Gonads are typically testes.

• Anti-mullerian hormone prevents the internal female system from developing.

5 Alpha Reductase Deficiency

• No 5-alpha-dihydrotestosterone.

• XY born with female genitalia.

• At puberty, high testosterone levels develop male genitalia.

Brain Differences Between Men & Women

• Males have larger inferior parietal lobes, associated with spatial tasks.

• Females have larger language structures, such as Broca’s area.

  • For example, women are better at multitasking.

• Male brain activity patterns are more likely to be lateralized than female brain activity patterns.

• Generally, there are larger differences within the genders than there are between the genders, though.

• INAH-3. Interstitial nuclei of the anterior hypothalamus are 40% larger in males than in females.

  • Structure is tiny, though, so many believe this difference is unimportant.

Testosterone & Sexual Behavior

• Testosterone is linked to aggression and sex drive.

  • Strongly correlated in animals.

  • Weakly correlated in humans.

• High testosterone levels happen after/during a competition, such as sporting events.

  • Even watching your team increases testosterone levels.

• Single men also have higher levels of testosterone.

• Castrated males have low testosterone levels, capable of erections, and sex drive eventually drops.

• Testosterone treatments increase sexual activity in men and women.

Brain Areas & Sex Drive In Animals

• The hypothalamus has been linked to animals.

• Lesions of the medial preoptic area in rats will not impact sexual interest, but the animal is unable to copulate.

• Changing androgen exposure can increase or decrease sexual motivation in males.

• Lordosis behaviors in females are linked to the ventromedial hypothalamus.

• Damage to the amygdala can cause hypersexuality or less sexual motivation.

Biological Links For Homosexuality

• Genetic link for homosexuality.

  • Solid concordance rate for identical twins; 52% for males; 48% for females.

• Females exposed to excess androgens early in development see higher rates of lesbianism.

  • 1/3 of XX individuals with Congenital Adrenal Hyperplasia identify as homosexual.

  • However, the majority of women exposed to androgens are still heterosexual.

• Males exposed to low levels of androgens show higher levels of homosexuality.

• Androgen insensitivity syndrome.

  • Not perfectly predictive, though.

Biological Links For Transgenders

• Transgender women are more likely than transgender men.

  • Possibly a 3:1 ratio.

  • Prevalence has increased in the last 50 years.

• Research suggests feminization of the brain is also another process, like masculinization.

• The stria terminalis, which connects the amygdala and hypothalamus, is found to be “female-like” in size for transgender women.