Thursday Oct 14

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Thursday Oct 14
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• Roles of Hormones
• Influence all basic drive states eating,
  drinking, sexual activity
• Help maintain homeostasis relatively constant
  internal environment
• Influence mood and behavior
• Influence brain development and development of
  other organ systems
• Influence bodily (incl. brain) changes in puberty
• Influence aging
• Thus, hormones influence anatomy, physiology, and
  behavior.

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• Principles of Hormone Action
• Gradual and slow responses may come minutes,
  hours, or weeks after hormones are released
• Hormones act on probabilities of behaviors
  occurring making you more or less likely to
  take some action depending on hormonal state
  (hunger thirst sexual activity)
• Hormones and behavior act reciprocally hormones
  alter behavior, behavior alters hormones
• A single hormone effects multiple tissues and
  behaviors
• Hormones are secreted in small amounts and often
  in bursts (pulsatile secretion)

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• Principles of Hormone Action
• Hormones are secreted in small amounts and often
  in bursts (pulsatile secretion)
• Hormone levels may vary rhythmically throughout
  the day with levels controlled by circadian
  clocks within the brain
• The effects of hormones are highly interactive
  action may depend on the ratios of what is
  present
• The same sets of chemicals are used as hormones
  across all vertebrate species, but the responses
  to the hormones may vary across species
• Hormones act via binding with receptors
• Hormonal secretions are monitored and regulated
  by feedback control systems

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• Principles of Hormone Action
• Hormonal secretions are monitored and regulated
  by feedback control systems
• Glands manufacture, detect, evaluate effects and
  participate in regulation of hormones
• Regulation may be within the gland or based on
  the glands response to products released from
  other cells or under neural control by actions of
  hypothalamus alone or plus pituitary gland

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• Types of Hormones
• Reproductive hormones control the menstrual
  cycle, child birth, breast feeding (activational
  effects). Also organizational effects instruct
  the body to develop as male or female.
• Homeostatic hormones maintain internal bodily
  environment relevant to life itself the balance
  of sugars, proteins, carbohydrates, salt and
  water in the bloodstream and all body cells
  (activational effects that cells can respond to
  from early life)
• Stress Hormones control behavioral and
  physiological responses to stress (best
  understood re. activational effects)

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Hormones act by 1. Promoting the proliferation,
growth and differentiation of cells In early
development, this applies to brain tissue as
well as the reproductive tissues. At puberty,
hormones trigger physical changes. (Development
al roles) 2. Modulating the rate of cell
function may promote metabolic activity may
promote hormone release (Homeostatic and
rhythmic/cyclical controls)
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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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Pituitary is master controller of the rest of the
bodys endocrine system. Hypothalamus - area of
brain that controls the pituitary. Certain
neurons in the hypothalamus respond to neural and
hormonal signals by secreting hormones (releasing
hormones and inhibiting hormones).
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Hormones from the Hypothalamus Releasing
hormones influence the pituitary to release
hormones that act on other glands in body (tropic
hormones). Inhibiting hormones influence the
pituitary to inhibit release of certain hormones.
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• I. Role of Hypothalamus-Posterior Pituitary
• Axons from hypothalamus travel to Posterior
  Pituitary (PP) where their axon terminals
  terminate and release Oxytocin and Vasopressin
  into the capillaries inside the PP
• from here, the hormones enter the general blood
  stream
• Examples
• Oxytocin acts on receptors (when present) in
  breasts and uterus --- milk ejection uterine
  contractions at end of pregnancy
• Vasopressin acts to constrict blood vessels in
  kidney, influences resorption of water and
  minerals

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Feedback system Levels of hormones in blood are
detected by cells in hypothalamus. Result is to
release releasing or inhibiting hormones to
pituitary This keeps hormonal levels at proper
balance like a thermostat
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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 from the Hypothalamus ----- 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
brain where the hypothalamus reads levels
----- Then, Hypothalamus secretes releasing or
inhibiting factors -----
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• Example 1 - Reproductive Hormones in Females
• Hypothalamus releases Gonadotropin releasing
  hormone (GRH).
• Anterior Pituitary releases Follicle Stimulating
  Hormone and Luteinizing Hormone.
• FSH acts on receptors in ovaries to stimulate
  development of egg LH causes rupture of egg.

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• Example 1 - Reproductive Hormones in Females
• FSH acts on receptors in ovaries to stimulate
  development of 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 - may then 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.
• BCP 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
• Phenotype is determined by gene-environment
• interactions
• Phenotype depends on hormones present at
• specific points in time

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Reproductive systems are made up of 3 categories
of sex organs I. Gonads - testes or
ovaries II. Internal sex organs Female -
uterus, fallopian tubes, vagina Male -
epididymis, vas deferens, 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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