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COGNITIVE SCIENCE 17 Why Sex is Necessary Part 1 Jaime A. Pineda, Ph.D. PowerPoint Presentation
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COGNITIVE SCIENCE 17 Why Sex is Necessary Part 1 Jaime A. Pineda, Ph.D. Why is Sex Necessary ?. Sexually dimorphic behaviors Anatomical, physiological, and behavioral differences between males and females of the same species. Courting Mating Parental behavior

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slide1

COGNITIVE

SCIENCE

17

Why Sex is

Necessary

Part 1

Jaime A. Pineda, Ph.D.

why is sex necessary
Why is Sex Necessary?
  • Sexually dimorphic behaviors
    • Anatomical, physiological, and behavioral differences between males and females of the same species.
      • Courting
      • Mating
      • Parental behavior
      • Aggressive behavior

Without these behaviors most species would not survive

is sexual identity learned
Is Sexual Identity Learned?
  • The case of Bruce who became Brenda who became David
    • Socialization over biology?
  • XX (female) and XY (male) genes
    • A person’s genetic sex is determined by the father
    • SRY gene on short arm of Y chromosome- dictates the development of the fetal testis (testis-determining factor) and triggers action of receptors to receive chemical message hormone brings
is sexual identity learned4
Is Sexual Identity Learned?
  • The Y chromosome controls the development of the glands that produce the male sex hormones
  • The default sex (if the Y chromosome isn’t present or doesn’t work) is female
sexual development
Sexual Development
  • Three categories of sex organs (primary sex characteristics)
    • Gonads (testes or ovaries)
      • Develop first (Sry  testes; otherwise ovaries)
      • Produce ova/sperm and secret hormones
      • Critical Period of sexual development: Gestational weeks 7-12
    • Internal sex organs
    • External sex organs
sexual development7
Sexual Development

Gonads can become either Testes or Ovaries

Develop as a function of the presence or absence of SRY gene

In males, at 7th week, outer portions of gonads degenerate and inner portions develop into testes

In females, at 11th week, inner portions of gonads degenerate and outer portions develop into ovaries

sexual development8
Sexual Development

Gonads become testes in males

Testes - endocrine glands that produce

• male hormones

(androgens)

• Mullerian Inhibiting

Substance

Most changes reflect the presence or absence of androgen

sexual development9
Sexual Development

Gonads become ovaries in females

Ovaries- endocrine glands that produce

  • female hormones (e.g.estrogen)
sexual development10
Sexual Development

Internal sex organ precursors

  • Mullerian system  female
    • Develops into fimbriae, fallopian tubes, uterus, and vagina
  • Wolffian system  male
    • Develops into epididymis, vas deferens, seminal vesicles
  • Develop as a function of hormones released by testes
    • Mullerian inhibiting hormone or anti Mullerian hormone(defeminizing effect)
    • Androgens (masculinizing effect): testosterone/dihydrotestosterone
sexual development11
Sexual Development

Wolffian Ducts - later become

• epididymis

• vas deferens

• seminal vesicles

Mullerian Ducts - later become

• uterus

• fallopian tubes

• upper part of vagina

sexual development12
Sexual Development
  • External sex organs
    • Penis and scrotum in males
    • Labia, clitoris, and outer vagina in females
    • Female development is the default
      • “Nature’s impulse is to create a female”
    • Male development requires androgens
sexual development dysfunctions
Sexual Development Dysfunctions
  • Androgen insensitivity syndrome
    • Genetic mutation that prevents the formation of androgen receptors
      • Gonads become testes (normal process)
      • Defeminization (normal process)
      • Lack of masculinization (abnormal process)

An XY male with female external genitalia;

have a woman’s body but not internal female sex organs

sexual development dysfunctions20
Sexual Development Dysfunctions
  • Persistent Mullerian duct syndrome
    • Failure to produce anti-Mullerian hormone
    • Absence of receptors for this hormone
      • In an XY male, defeminization does not occur but masculanization does
      • Person is born with both sets of internal sex organs
  • Turner’s syndrome
    • Individuals have only one sex hormone: an X chromosome
      • Essentially develop into females (normal internal/external sex organs)
      • However, no ovaries since two XX chromosomes needed
puberty development of secondary sex characteristics
PUBERTY - development of secondary sex characteristics
  • Puberty occurs when hypothalamus begins to secrete gonadotropin-releasing hormones (GnRH) causing pituitary to release
    • Follicle-stimulating hormone (FSH)
    • Luteinizing hormone (LH)

In males, these hormones stimulate testes to produce sperms and secrete testosterone (androgens)

In females, they stimulate the ovaries to produce estradiol (estrogens)

puberty cont
Puberty – cont.
  • Nutrition affects age of puberty
    • Reduced in developing countries
    • Thin girls reach puberty later
      • Due to the presence of leptin
hypothalamus
Hypothalamus

Hormonal

Changes in Puberty

FSH-

RF

LH-

RF

Anterior Pituitary

hypothalamus24
OVARIES

TESTES

Hypothalamus

Hormonal

Changes in

Puberty

FSH-

RF

LH-

RF

Anterior Pituitary

FSH

FSH

LH

ICSH(LH)

hypothalamus25
OVARIES

TESTES

Hypothalamus

Hormonal

Changes in

Puberty

FSH-

RF

LH-

RF

Anterior Pituitary

FSH

FSH

LH

ICSH*(LH)

Ovulation

Corpus Luteum

Ovum

Growth

Testosterone

Spermatogenesis

Progesterone

Estrogen

(estradiol)

* Interstitial-cell stimulating hormone

sexual maturation
Sexual Maturation
  • Secondary sex characteristics (onset of puberty)
    • Females (estradiol)
      • Enlarged breasts
      • Growth of the lining of the uterus
      • Widened hips
      • Maturation of genitalia
    • Females (androgens)
      • Underarm and pubic hair (face as well)
    • Males (androgens)
      • Facial, underarm, and pubic hair
      • Deep voice
      • Alter hairline (baldness)
      • Muscle development
      • Maturation of genitalia
    • Males (estradiol)
      • Enlarged breasts
hormonal control of reproductive cycle
Hormonal Control of Reproductive Cycle
  • Menstrual cycle
    • Begins with secretion of FSH to stimulate growth of ovarian follicles (epithelial cells surrounding each ovum)
    • As ovarian follicles mature they secrete estradiol causing the growth of the lining of the uterus (preparation for fertilization)
    • Increasing levels of estradiol triggers the release of LH causing ovulation (release of ovum)
    • Ovum enters a Fallopian tube and starts migrating towards uterus.
    • If it meets sperm and becomes fertilized it begins to divide and then attaches itself to uterus wall
    • If it is not fertilized, the ruptured ovarian follicle (corpus luteum) and the lining of the uterine wall will be expelled – menstruation commences