Transcript Homeostasis - Science Website

Homeostasis
Learning Objective
 Discuss
the importance of
homeostasis in mammals, and explain
the principles of homeostasis in terms
of receptors, effectors and negative
feedback.
Think about the following:
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What happens if .......
Your body loses too much water?
You eat a bag of sweets?
You get too hot?
Homeostasis
Homeostasis means “controlling internal conditions”:
Waste products that need to be removed + how
CO2
Produced by respiration, removed via lungs
Urea
Produced by liver breaking down amino acids,
removed by kidneys and transferred to bladder
Internal conditions that need controlling + how
Temperature
Increased by shivering, lost by sweating
Ion content
Increased by eating, lost by sweating + urine
Water content
Increased by drinking, lost by sweating + urine
Blood glucose
Increased and decreased by hormones
A Steady State
In order to survive, an organism has to be able to
keep its internal environment within tolerable
limits. The internal environment of a multicellular
organism is the tissue fluid bathing the cells.
Keeping these conditions constant is called
Homeostasis.
 The features of the environment which affect the
functioning of the cell are: temperature, amount of
water and amount of glucose.
Q) How do you think these conditions affect the
functioning of the cell? Write down your ideas.
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Temperature
 Low
temperatures slow metabolic
reactions, while high temperatures
cause denaturation of proteins,
including enzymes.
Amount of Water
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Lack of water in the tissue fluid causes
water to be drawn out of cells by
osmosis, causing metabolic reactions in
the cell to slow or stop, while too much
water entering the cell may cause it to
swell and burst.
Amount of Glucose
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Glucose is the fuel for respiration, so
lack of it causes respiration to slow or
stop, depriving the cell of an energy
source, while too much glucose may
draw water out of the cell by osmosis.
Negative Feedback
Negative
feedback is an important type of
control that is found in homeostasis. A
negative feedback control system responds
when conditions change from the ideal or
set point and returns conditions to this set
point. There is a continuous cycle of events
in negative feedback.
Stages in negative feedback
An example
 An
increase in the internal body
temperature causes the body to lose
more heat; a decrease in body
temperature causes the body to
generate more heat.
Places where regulation takes
place
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Blood Sugar Concentration – Insulin and
Glucagon
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Osmoregulation – hypothalamus and pituitary
gland
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Temperature regulation - hypothalamus
Task
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Hot Day
Running a Marathon
Lazy Day at Home
Suggest how your fluid intake and urine output
would vary under these different circumstances
and why.