SEX HORMONESSEX HORMONES

Endocrine glands:Endocrine glands: glands that secrete internally (into glands that secrete internally (into

bloodstream)bloodstream) Exocrine glands:Exocrine glands:

secrete externally (i.e. sweat glands)secrete externally (i.e. sweat glands) Endocrine glands secrete hormonesEndocrine glands secrete hormones Hormone:Hormone:

complex chemical with specific actions for complex chemical with specific actions for specific organs onlyspecific organs only

SEX HORMONESSEX HORMONES (CONT’D)(CONT’D)

Pituitary gland:Pituitary gland: called master gland butcalled master gland but

Hypothalamus controls pituitary:Hypothalamus controls pituitary: Dual function: as a gland, and as a part of the Dual function: as a gland, and as a part of the

CNS.CNS.• As a gland, it reacts to hormonal levels in the As a gland, it reacts to hormonal levels in the

bloodstream. As CNS, it reacts to higher brain bloodstream. As CNS, it reacts to higher brain functions (perceptions, thoughts, feelings, moods).functions (perceptions, thoughts, feelings, moods).

The pituitary stimulates the The pituitary stimulates the gonads: gonads: ovaries ovaries and testesand testes

SEX HORMONES (CONT’D)SEX HORMONES (CONT’D)

Pituitary produces:Pituitary produces: FSHFSH LHLH oxytocin (orgasm, birth, milk release)oxytocin (orgasm, birth, milk release) prolactinprolactin

Testes produce:Testes produce: testosteronetestosterone estrogenestrogen inhibininhibin

SEX HORMONES (CONT’D)SEX HORMONES (CONT’D)

Ovaries produce:Ovaries produce: estrogenestrogen progesteroneprogesterone testosteronetestosterone inhibininhibin

InhibinInhibin regulates levels of FSHregulates levels of FSH

LH is regulated by levels of either LH is regulated by levels of either testosterone (males) or estrogen (females)testosterone (males) or estrogen (females)

SEX HORMONES (CONT’D)SEX HORMONES (CONT’D)

Follicle-Stimulating Hormone (FSH) – Follicle-Stimulating Hormone (FSH) – pituitarypituitary In Women:In Women:

• stimulates the ovary to activate a follicle, maturing stimulates the ovary to activate a follicle, maturing an eggan egg

In Men:In Men:• stimulates spermatogenesisstimulates spermatogenesis

SEX HORMONES (CONT’D)SEX HORMONES (CONT’D)

Luteinizing Hormone (LH) – pituitary:Luteinizing Hormone (LH) – pituitary: In Men:In Men:

• stimulates Leydig cells in testes to produce stimulates Leydig cells in testes to produce testosteronetestosterone

In Women:In Women:• stimulates rupture of follicle, releasing egg, and stimulates rupture of follicle, releasing egg, and

creating corpus luteus to produce progesterone.creating corpus luteus to produce progesterone.

SEX HORMONES (CONT’D)SEX HORMONES (CONT’D)

Gonadotropin-Releasing Hormone (GnRH):Gonadotropin-Releasing Hormone (GnRH): released by the hypothalamus in response to sensory released by the hypothalamus in response to sensory

receptors or thoughts.receptors or thoughts. stimulates the pituitary to release its hormonesstimulates the pituitary to release its hormones

Estrogen:Estrogen: hormone produced by the ovaries. Thickens hormone produced by the ovaries. Thickens

endometrium, starting a week after menstruationendometrium, starting a week after menstruation

SEX HORMONES (CONT’D)SEX HORMONES (CONT’D)

Progesterone:Progesterone: hormone produced by the corpus luteum of hormone produced by the corpus luteum of

the ovaries after ovulationthe ovaries after ovulation Both estrogen and progesterone drop to Both estrogen and progesterone drop to

lowest levels at the end of menstrual lowest levels at the end of menstrual cycle. cycle.

The low levels of estrogen stimulate the The low levels of estrogen stimulate the beginning of another cycle.beginning of another cycle.

SEX HORMONES (CONT’D)SEX HORMONES (CONT’D)

Testosterone:Testosterone: produced by gonads and adrenals in both produced by gonads and adrenals in both

sexes. sexes. Responsible for male characteristics, and for Responsible for male characteristics, and for

sex drive in both sexes.sex drive in both sexes.

SEX HORMONES (CONT’D)SEX HORMONES (CONT’D)

Hormonal Output Regulation:Hormonal Output Regulation: Homeostasis:Homeostasis:

• state of perfect equilibrium of all physiological state of perfect equilibrium of all physiological states. It’s constantly being broken and restored. states. It’s constantly being broken and restored. E.g. thirst. Hypothalamus central role in E.g. thirst. Hypothalamus central role in homeostasis.homeostasis.

SEX HORMONES (CONT’D)SEX HORMONES (CONT’D)

Hormonal Output Regulation (Cont’d):Hormonal Output Regulation (Cont’d): Negative feedback loops:Negative feedback loops:

• When something is low (sodium, estrogen, When something is low (sodium, estrogen, glucose, etc. etc.) hypothalamus gets signal via glucose, etc. etc.) hypothalamus gets signal via bloodstream and activates mechanisms to bloodstream and activates mechanisms to increase substance.increase substance.

• When something is too high, another negative When something is too high, another negative feedback loop signals to stop production or feedback loop signals to stop production or ingestion.ingestion.

• The hypothalamus signals all other endocrine The hypothalamus signals all other endocrine glands to either step up or decrease production.glands to either step up or decrease production.

SEX HORMONES (CONT’D)SEX HORMONES (CONT’D)

THE ROLE OF TESTOSTERONE IN SEXTHE ROLE OF TESTOSTERONE IN SEX Testosterone mediates sexual response in Testosterone mediates sexual response in

both sexes.both sexes. It comes in two forms:It comes in two forms:

• bound and freebound and free Men: 95% bound, not active for sexual desireMen: 95% bound, not active for sexual desire

5% free5% free Women: 97-99% boundWomen: 97-99% bound

1-3% free1-3% free

SEX HORMONES (CONT’D)SEX HORMONES (CONT’D)

THE ROLE OF TESTOSTERONE IN SEX THE ROLE OF TESTOSTERONE IN SEX (Cont’d)(Cont’d) Amount needed varies in individuals of both Amount needed varies in individuals of both

sexes. Women more sensitive.sexes. Women more sensitive. More testosterone does not produce more More testosterone does not produce more

sexual desiresexual desire

SEX HORMONES (CONT’D)SEX HORMONES (CONT’D)

THE ROLE OF TESTOSTERONE IN SEX (CONT’D)THE ROLE OF TESTOSTERONE IN SEX (CONT’D)

Additional testosterone has adverse Additional testosterone has adverse effects:effects: Men:Men:

• hair loss, salt and fluid retention, possible testicular hair loss, salt and fluid retention, possible testicular cancer, acne, digestive problems, irritability, cancer, acne, digestive problems, irritability, aggressionaggression

Women:Women:• facial and body hair, muscle mass, smaller facial and body hair, muscle mass, smaller

breasts, larger clitoris, voice deeperbreasts, larger clitoris, voice deeper

SEXUAL DIFFERENTIATIONSEXUAL DIFFERENTIATION

Gestational Development of Genitals:Gestational Development of Genitals: First seven weeks: undifferentiatedFirst seven weeks: undifferentiated

• two gonadstwo gonads• two sets of ducts (Mullerian and Wolffian)two sets of ducts (Mullerian and Wolffian)• genital tuberclesgenital tubercles• genital foldsgenital folds• genital swellinggenital swelling

77thth week: week:• Y chromosome, if present, turns gonad into Y chromosome, if present, turns gonad into

testicle.testicle.

SEXUAL DIFFERENTIATION (CONT’D)SEXUAL DIFFERENTIATION (CONT’D)

1010thth-11-11thth week: week:• in absence of Y chromosome, ovaries develop.in absence of Y chromosome, ovaries develop.

Both types of gonads start producing their Both types of gonads start producing their respective hormones.respective hormones.

Female:Female: absence of testosterone causes degeneration absence of testosterone causes degeneration

of Wolffian ducts. Mullerian ducts form of Wolffian ducts. Mullerian ducts form internal sex organs (uterus, etc.)internal sex organs (uterus, etc.)

Sexual Differentiation (Cont’d)Sexual Differentiation (Cont’d)

Gestational Development of Genitals Gestational Development of Genitals (Cont’d):(Cont’d): Female:Female:

• absence of testosterone causes degeneration of absence of testosterone causes degeneration of Wolffian ducts. Mullerian ducts form internal sex Wolffian ducts. Mullerian ducts form internal sex organs (uterus, etc.)organs (uterus, etc.)

Male:Male:• testes produce anti-Mullerian hormone, so they testes produce anti-Mullerian hormone, so they

disappear. Wolffian ducts become internal sex disappear. Wolffian ducts become internal sex organs (epididymis, etc.)organs (epididymis, etc.)

SEXUAL DIFFERENTIATION (CONT’D)SEXUAL DIFFERENTIATION (CONT’D)

Gestational Development of Genitals Gestational Development of Genitals (Cont’d):(Cont’d): Tubercle, folds and swelling develop into Tubercle, folds and swelling develop into

external genitals for each sex.external genitals for each sex. The default model is female. In the absence The default model is female. In the absence

of any step to go to the male model, the child of any step to go to the male model, the child will be female.will be female.

EFFECTS ON BRAIN DEVELOPMENT EFFECTS ON BRAIN DEVELOPMENT

While sex hormones are directing gonadal While sex hormones are directing gonadal differentiation, they also affect brain differentiation, differentiation, they also affect brain differentiation, particularly in the hyothalamus. particularly in the hyothalamus.

The hypothalamus has neurons that are estrogen The hypothalamus has neurons that are estrogen sensitive, they bind to estrogen. sensitive, they bind to estrogen.

If testosterone is present, these cells become If testosterone is present, these cells become insensitive to estrogen. insensitive to estrogen.

Conversely, if estrogen is present, these cells become Conversely, if estrogen is present, these cells become sensitive to estrogen. sensitive to estrogen.

This difference is crucial for the hormonal feedback This difference is crucial for the hormonal feedback loops in the hypothalamus - pituitary - gonads circuit. loops in the hypothalamus - pituitary - gonads circuit.

Hormone disruptors (chemicals in the environment) Hormone disruptors (chemicals in the environment) could significantly alter this plan of development. could significantly alter this plan of development.

Some Variations of the Usual Sex Some Variations of the Usual Sex Differentiation PathDifferentiation Path

Hermaphrodite, pseudohermaphroditeHermaphrodite, pseudohermaphrodite Congenital adrenal hyperplasia (CAH)Congenital adrenal hyperplasia (CAH) Progestin-induced pseudohermaphroditismProgestin-induced pseudohermaphroditism Androgen insensitivity:Androgen insensitivity:

• genetic male with female phenotypegenetic male with female phenotype 5-alpha reductase syndrome (girls that turn 5-alpha reductase syndrome (girls that turn

into boys at puberty)into boys at puberty)

Hermaphrodite:Hermaphrodite: Someone with both male and female Someone with both male and female

reproductive organs, both internal and reproductive organs, both internal and external.external.• The majority (60%) are XX.The majority (60%) are XX.• 33% are XX but with SRY (sex determining region 33% are XX but with SRY (sex determining region

on the Y) present.on the Y) present.• 7% are XY.7% are XY.• Where SRY not present, mutation is suspected, Where SRY not present, mutation is suspected,

but not known yet.but not known yet.

Pseudohermaphrodite:Pseudohermaphrodite: Only the external sex organs are either ambiguous or Only the external sex organs are either ambiguous or

do not correspond with the chromosomal profile of XX do not correspond with the chromosomal profile of XX or XY. Various causes, e.g. CAH (see below).or XY. Various causes, e.g. CAH (see below).

Congenital Adrenal Hyperplasia (CAH) or Congenital Adrenal Hyperplasia (CAH) or Adrenogenital Syndrome:Adrenogenital Syndrome: XX (girls) whose adrenal glands secrete too much XX (girls) whose adrenal glands secrete too much

testosterone during gestation, which causes testosterone during gestation, which causes masculinization of the external genitals and, it is masculinization of the external genitals and, it is suspected, of certain regions of the brain, resulting in suspected, of certain regions of the brain, resulting in more masculine behaviour (“tomboys”). Normal more masculine behaviour (“tomboys”). Normal female development and fertility.female development and fertility.

Progestin Induced Pseudohermaphroditism:Progestin Induced Pseudohermaphroditism: Iatrogenic effect of progestin given to pregnant women to Iatrogenic effect of progestin given to pregnant women to

prevent miscarriage. In XX fetuses, effects similar to prevent miscarriage. In XX fetuses, effects similar to CAH. Progestin seemed to have an androgenic effect, in CAH. Progestin seemed to have an androgenic effect, in varying degrees. No longer used.varying degrees. No longer used.

Androgen insensitivity:Androgen insensitivity: XY (genetic male) with female phenotype. During XY (genetic male) with female phenotype. During

gestation, fetal tissues are insensitive to testosterone, so gestation, fetal tissues are insensitive to testosterone, so they develop with female external genitals, but have no they develop with female external genitals, but have no female internal organs because the Mullerian ducts have female internal organs because the Mullerian ducts have been eliminated. Testicles are initially formed but don’t been eliminated. Testicles are initially formed but don’t descend. Reared as girls, female gender identity.descend. Reared as girls, female gender identity.

5-Alpha Reductase Syndrome (5-ARD):5-Alpha Reductase Syndrome (5-ARD): 5-alpha reductase is an enzyme that catalyzes 5-alpha reductase is an enzyme that catalyzes

conversion of testosterone to dihydrotestosterone conversion of testosterone to dihydrotestosterone during fetal development, necessary for normal during fetal development, necessary for normal development of external and internal genitals. When development of external and internal genitals. When absent, feminized external genitals are present at absent, feminized external genitals are present at birth and the internal genitals have varying degrees of birth and the internal genitals have varying degrees of abnormality. The cause of the absence of 5-ARD is a abnormality. The cause of the absence of 5-ARD is a recessive gene. At puberty, the large amounts of recessive gene. At puberty, the large amounts of testosterone produced promote a masculine testosterone produced promote a masculine phenotype, but the individual is infertile. Generally, phenotype, but the individual is infertile. Generally, male gender identity.male gender identity.

These variations highlight the complex These variations highlight the complex nature of masculinity and femininity, both nature of masculinity and femininity, both biological and social.biological and social.

According to John Money, eight variables According to John Money, eight variables interplay to arrive at an individual’s gender interplay to arrive at an individual’s gender (see text).(see text).