Monday Mar 6

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Monday Mar 6
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• II. Role of Hypothalamus - Anterior Pituitary
• Hormones from hypothalamus travel in special
  blood system (portal system) to Anterior
  Pituitary
• Bind with receptors in Anterior Pituitary gland
• Release of AP hormones is increased or decreased
  (examples reproductive hormones stress
  hormones)
• AP hormones then travel in blood and find
  receptors on major organs (gonads, adrenals, etc)
  - tropic actions

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Hormones released from the Hypothalamus into the
portal system ? Bind receptors in AP ?
in response, AP releases hormones ?
Hormones travel in blood to receptors on
target organs? Target organs respond
in multiple ways that effect release of
hormones? Hormones travel to hypothalamus
where cells read levels ? Then,
Hypothalamus secretes releasing or
inhibiting factors
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• Example 1 - Reproductive Hormones in Females
• Hypothalamus releases Gonadotropin Releasing
  Hormone (GRH)
• binds with receptors in AP
• Anterior Pituitary releases Follicle Stimulating
  Hormone and Luteinizing Hormone
• travel in blood to site of action
• FSH acts on receptors in ovaries to stimulate
  development of the egg LH causes rupture of egg.
• Rupture of egg triggers production of estrogens
  and progestogens (from remaining tissues of
  follicle)
• These hormones travel in blood to the brain
• Hypothalamus senses levels, then may decrease
  release of GRH

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• Drugs can alter hypothalamic-pituitary control
  systems ex Birth Control Pills
• Mature egg and its rupture trigger release of
  estrogens and progestogens.
• Result is that hypothalamus detects high levels
  and shuts down secretion of FSH releasing hormone
  and LH releasing hormone.
• BCPs contain estrogens and progestogens - fool
  brain into thinking levels are high due to egg
  production

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Developmental role of hormones Organizational
effects - permanent effects on tissue
differentiation of body and brain Activational
effects - effects that occur later in life
mostly beginning at puberty
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• Development of Reproductive Systems
• Chromosomal sex is determined at fertilization
• XX - defines female
• XY - defines male
• BUT
• Phenotype is determined by gene-environment
• interactions
• Phenotype depends on hormones present at
• specific points in time and receptor responses

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Reproductive systems are made up of 3 categories
of sex organs I. Gonads - testes or ovaries
make eggs or sperm II. Internal sex organs
travel host pathways Female - fallopian tubes,
uterus, inner vagina Male - epididymis,
seminal vesicles, prostate III. External sex
organs Female - labia, clitoris, outer
vagina Male - penis, scrotum
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• I. Development of Gonads
• A. Males and females have identical immature
  gonads during first month of gestation
• B. During 2nd month, differentiation of immature
  gonads is controlled by presence/absence of
  hormones.
• MALES
• a gene on the Y chromosome causes production of
  testis-determining factor (tdf) - early 2nd month
• testis-determining factor tells the immature
  gonad to become testes (male)
• in absence of gene and tdf, immature gonads
  become ovaries
• in presence, gonads become testes

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II. Development of Internal Sex Organs A.
1st and part of 2nd month - embryo has bisexual
internal organs In same person (male or female),
the precursors for both male and female internal
organs are present. Tissues that can become
female internal organs - Mullerian system
Tissues that can become male internal organs -
Wolffian system B. Whether male or female
internal parts development depends on the
hormonal environment ! At end of 2nd month, this
is set.
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C. 3rd month (fetal period) MALE - To develop
male internal organs, testes (male gonads) must
begin to produce hormones and receptors must
respond! 1. Anti-mullerian hormone - tells the
Mullerian (potentially female) system not to
develop Mullerian tissues have receptors for
anti-Mullerian hormone - when bound, tissues do
not develop into female internal sex organs 2.
Androgens - tell the Wolffian system to
develop into internal male sex organs Wolffian
tissues have receptors for androgens when bound
by androgens, male internal organs develop
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C. 3rd month (fetal period) - continued FEMALE
To develop female internal organs, hormones must
be absent. In absence of hormones, Mullerian
system develops into female internal sex organs.
Wolffian tissues disappear. No hormonal
stimulation is required (default
setting). Mullerian system develops into
fallopian tubes, uterus, internal vagina
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• III. Development of External Sex Organs
• A. In first 2 months of gestation, males and
  females have the same external appearance.
• B. During the 3rd month, male or female
  external sex organs develop.
• 1. MALES
• testes (gonads) produce dihydrotestosterone
• this triggers development of external sex organs
  - the penis and scrotum

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• III. Development of External Sex Organs
• A. In first 8 weeks of gestation, males and
  females have the same external appearance.
• B. During the 3rd month, male or female
  external sex organs develop.
• 2. FEMALES
• in absence of hormones, female external parts
  develop - the labia, clitoris and outer vagina

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