Transcript Human Sexual Anatomy & Physiology (Part 1)

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.
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Courting
Mating
Parental behavior
Aggressive behavior
Without these behaviors most
species would not survive
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 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
Initially, there are more males than females
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 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 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 Development
Gonads become ovaries
in females
Ovaries- endocrine glands that
produce
• female hormones
(e.g.estrogen)
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 Development
Wolffian Ducts - later
become
• epididymis
• vas deferens
• seminal vesicles
Mullerian Ducts - later
become
• uterus
• fallopian tubes
• upper part of vagina
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
Undifferentiated External Genitalia
(<7 weeks)
Partially differentiated external
male & female genitalia
Fully developed male & female
external genitalia
Fetal External Genitals: Female
11-12 weeks
19 weeks
Fetal External Genitals: Female
5 months
Fetal External Genitals: Male
15 weeks
16 weeks
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 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 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.
• Nutrition affects age of puberty
– Reduced in developing countries
– Thin girls reach puberty later
• Due to the presence of leptin
Hormonal
Changes in
Puberty
Hypothalamus
FSHRF
LHRF
Anterior Pituitary
Hormonal
Changes in
Puberty
Hypothalamus
FSHRF
LHRF
Anterior Pituitary
FSH
FSH
LH
OVARIES
ICSH(LH)
TESTES
Hormonal
Changes in
Puberty
Hypothalamus
FSHRF
LHRF
Anterior Pituitary
FSH
FSH
LH
OVARIES
Ovum
Growth
Ovulation
Corpus Luteum
Estrogen
(estradiol)
Progesterone
ICSH*(LH)
TESTES
Testosterone
Spermatogenesis
* Interstitial-cell stimulating hormone
Sexual Maturation
• Secondary sex characteristics (onset of puberty)
– Females (estradiol)
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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)
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Facial, underarm, and pubic hair
Deep voice
Alter hairline (baldness)
Muscle development
Maturation of genitalia
– Males (estradiol)
• Enlarged breasts
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