H.1 homestasis summary
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HOMEOSTASIS &
CONTROL SYSTEMS
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Objectives
• H - Explain the importance of maintaining a constant
internal environment
• How do the different systems interact together to maintain
homeostasis?
Guiding Question
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Important variables are regulated within
the body:
• Blood sugar
• Fluid balance
• Body temperature
• Oxygen levels
• Blood pressure
• pH
• These variables must stay within certain ranges
• Changes in the external environment can cause shifting within
these ranges
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Homeostasis
• The process by which a constant internal environment is
maintained despite changes in the external environment.
• Body maintains a constant balance, or steady state,
through a series of monitored adjustments.
• This balance requires constant monitoring and feedback
about body conditions
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Components of a Control System:
Component Function
Monitor Detects a change
Coordinating Centre Receives a message from the
monitor
Directs a response via a regulator
Regulator Carries out the response initiated by
the coordinating centre
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Hypothalamus & Pituitary Glands
• Hypothalamus:
• Often serves as the coordinating centre to either tell the pituitary to
work more or work less depending on the message
• Receives messages from monitors
• Initiates a hormonal/nervous response
• Attempts to keep the body within accepted ranges
• Pituitary:
• Master gland
• Receives communications from hypothalamus and tells other
glands what to produce
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How to Maintain Homeostasis
• Via use of feedback systems
• Two types of feedback systems:
• Negative feedback
• Positive feedback
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The clapping game
• Player 1: Clap half the number of player 3’s claps.
• Player 2: Clap twice the number of player 1’s claps.
• Player 3: Clap twice the number of player 2’s claps.
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The clapping game
• Player 1: Clap half the number of player 3’s claps, unless
you hear “Inhibit”, then clap a quarter the number of
player 3’s claps.
• Player 2: Clap twice the number of player 1’s claps.
• Player 3: Clap twice the number of player 2’s claps.
• Player 4: When player 3 claps 8 times or more, say
“Inhibit”
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Negative Feedback
• Change in condition triggers a response to reverse the
change
• e.g. Body’s response to increase in temperature
• Most responses are under this category
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Positive Feedback
• Change in conditions triggers to response, and reinforces
the change
• Less common in biological systems
• e.g. uterine contractions during birth of baby, mosquito bites, drug
addictions
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Ben’s Story
• Work on the following module about how the body
maintains homeostasis and how all systems interact
• http://ats.doit.wisc.edu/biology/ap/ho/ho.htm
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Internal Factors to Monitor
1. Temperature:
• Liver and muscle contractions are primarily responsible for generating heat within the body.
• When the temperature of the body is greater than the surroundings, the skin loses heat.
• Evaporation is also a means of cooling down the body temperature and getting rid of excess heat.
• The brain also produces a lot of heat.
• The system of blood vessels comprising the head, allow the excess heat to escape and cool the head off.
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2. Osmoregulation:
• The body makes sure that the water content within the
body does not become too diluted or too concentrated.
• Kidneys help by removing excess ions from the blood.
This is then excreted as urine and affects blood pressure
3. Sugar:
• The pancreas secretes two hormones essential to
regulating blood sugar levels (glucagon and insulin).
• ↑ sugar levels = pancreas ↑ insulin = glucose is stored as
glycogen = ↓ blood sugar levels
• Reverse is true when blood sugar is low
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4. Calcium:
• ↓ calcium regulation = detection bh receptors in
parathyroid gland.
• This releases PTH which ↑ blood calcium levels by
release of calcium from bones.
• Thyroid gland releases calcitonin, which helps lower
calcium levels by absorption of calcium into the bones.
• 5. Balance of Fluids:
• adequate balance of fluids within the body includes both
the gain as well as loss of fluids.
• Antidiuretic hormone (ADH) and aldosterone are two
major hormones that help maintain a fluid balance.
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ORGAN SYSTEMS:Their Role in Maintaining Homeostasis
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• The proper functioning of the body requires all systems to
work together and in proper condition.
• Many diseases can affect the various organs and organ
systems of the body.
• When homeostasis within the body cannot be maintained
it can lead to death.
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A person is stuck in icy water and
loses heat faster than they can
generate it. Their body temperature
drops below 35°C
Enzymes become less active.
Exergonic reactions that release
heat become less active.Less heat is released.
The body cools down.
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A person loses 2+ litres of blood in an accident
Arterial blood pressure falls
Flow of blood to
the heart
vessels
decreasesThe heart weakens
The heart pumps less blood
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Baroreceptors signal
the medulla that the
blood pressure is too
high
The medulla signals
the heart to
decrease rate,
which decreases
cardiac output.
The medulla
signals blood
vessels to dilate
(vasodilation)
This also decreases
venous return, which
decreases cardiac
output.
This lowers
blood pressure.
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Baroreceptors signal
the medulla that
blood pressure is
too low.
The medulla signals
the heart to increase
rate, which
increases cardiac
output.
The medulla signals
blood vessel to
constrict
(vasoconstriction).
This also increases
venous return which
increases cardiac
output.
This raises
blood pressure.
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Head of fetus pushes against cervix
Nerve impulse from
cervix transmitted to
brain.
Brain stimulates
pituitary gland to
secrete oxytocin
Oxytocin carried in
bloodstream to
uterus
Oxytocin
stimulates
uterine
contractions and
pushes fetus
towards cervix.
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Kidneys detect reduced
O2 carrying capacity of
blood
When less O2 is delivered
to the kidneys they
secrete erythropoietin
into the blood
Erythropoietin
stimulates red blood
cell production
(erythropoiesis) by
bone marrow
Additional red
blood cells
(erythrocytes)
increase O2
carrying capacity
of blood
Increased O2 carrying
capacity of blood stops
erythropoietin secretion
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Fever!
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• What sets body temperature? what can change the set
point for body temperature?
• How does stress affect body temperature?
• How is fever different from a simple rise in body
temperature?
• What role might fever play in fighting infection?
• Why does the body sweat when a fever breaks?
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Hypothermia