This document provides information about homeostasis and examples of homeostasis in mammals. It begins by defining homeostasis as the maintenance of a stable internal environment regardless of external changes. It then outlines the objectives of explaining key terms, regulatory mechanisms, and giving examples using diagrams. Several examples of homeostasis in mammals are provided, such as temperature regulation and glucose regulation, along with diagrams illustrating the negative feedback loops involved. Sensors, effectors, and integrators that make up these feedback mechanisms are also described.

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OBJECTIVES
Module 3 Unit 8 Lesson 3
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OBJECTIVES
After reviewing the slides and doing the
activities you will be able to:
1.explain the term ‘homeostasis’ and its
importance.
2.outline the regulatory mechanisms involved in
homeostasis.
3. give examples of homeostasis in mammals,
using a diagram to explain each.
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OBJECTIVES
What is it?
Homeostasis is the maintenance of a constant or stable
internal environment, regardless of internal/external
changes.
Why do it?
Homeostasis is important to provide a suitably stable
environment for metabolic activity in cells.
When is it done in humans?
Homeostasis involves regulating and maintaining such
things as salt, water, glucose, Carbon dioxide and body
temperature at a ‘normal’ level.
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OBJECTIVES
 The thickening of an animal’s fur in
winter.
 The darkening or “tanning” of skin
in sunlight.
 Regulation of body temperature.
 Regulating the levels of Carbon
dioxide.
 Regulating the water concentration
in the body or osmoregulation.
 The production of more red blood
cells at high altitude.
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5. X
OBJECTIVES
 Homeostasis can be controlled/regulated
either by a process known as a ‘negative
feedback mechanism’ or by a ‘positive
feedback mechanism’.
 Within the human body, most homeostatic
activities are regulated by a negative
feedback mechanism.
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OBJECTIVES
A negative feedback mechanism is any
process which detects a change from the
normal or ‘set point’ in the internal
environment, that brings a response which
reverses that change so as to restore normal
conditions.
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OBJECTIVES
Every negative feedback mechanism has the
following inter-related components:
A detector or sensor
which identifies the
change (stimulus)
An effector which
corrects the change
An integrator or a
controller which
regulates the sensor and
effector
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OBJECTIVES
Effectors
EffectorsReceptors
Factor
Norm
Message
Corrective Response
Corrective Response
Factor Decrease
Factor
Norm
Message
Receptors
Factor Increase
No change in factor
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Discuss this flow diagram with your teacher.

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OBJECTIVES
 In humans, detectors/sensors are sense
organs and sensory receptor cells found
throughout the body.
 Effectors are various muscles and glands
that carry out corrective measures/respond.
 The integrator or controller is the brain.
Quite often it is the master control endocrine
gland in the brain (Pituitary gland) that is the
controller.
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OBJECTIVES
 Glucose is a respiratory substrate.
 Excess glucose is normally stored in the liver
as glycogen or ‘animal starch’.
 If the blood/cellular glucose level gets too
low, the energy level of the cells will be
reduced.
 If the level gets too high, the osmotic balance
of the cells will be affected.
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OBJECTIVES
1. If the level of glucose rises too much,
special receptors (called hepatocytes)
detect this.
 A message is sent to the pancreas which
secretes insulin. This insulin converts
glucose to glycogen, which is stored in the
liver, and also in skeletal muscles, until
required.
Follow that sequence in the next slide by clicking
the ANIMATE button.
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OBJECTIVES
If there is too much
glucose in the blood,
Insulin converts some
of it to glycogen
Glycogen
Glucose in the blood
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ANIMATE

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OBJECTIVES
2. If the level of blood glucose falls too low,
special receptors (especially hepatocytes)
detect this.
A message is sent to the pancreas which
secretes glucagon. This glucagon converts
glycogen stored in the liver/body muscles to
glucose, and it is released to the blood/cells.
What are the sensors, effectors and integrators in
this feedback mechanism?
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OBJECTIVES
If there is not enough
glucose in the blood,
Glucagon converts
some glycogen into
glucose.
Glycogen
Glucose in the blood
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ANIMATE

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OBJECTIVES
 Now, let’s look at those two situations together
in one flow chart!
 On the next slide, follow what happens starting
from the stimulus on the left when food with
carbohydrates is eaten.
 Did you notice the opposite effects of insulin and
glucagon?
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OBJECTIVES
http://www.biologymad.com/resources/A2%20Homeostasis.pdf
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OBJECTIVES
Here is a
simple diagram
that you can
learn how to
draw !
Try it now.
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http://www.worldofteaching.com/powerpoints/biology/Blood%20sugar.ppt#257,7,Slide7

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OBJECTIVES 18

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OBJECTIVES
 The level of Carbon dioxide in the blood will be
increased if there is much physical activity and
increased cellular respiration.
 If allowed to accumulate, CO2 will lower the pH of
the cells.
 If levels fall too low, CO2 will diffuse down the
concentration gradient across the alveoli into the
blood.
 A rise is detected by chemoreceptors in blood
vessels, namely the Carotid and Aortic vessels.
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20. X
OBJECTIVES
 These chemoreceptors send messages to the
Medulla oblongata of the brain which signals the
breathing rate to increase.
 If the level falls, probably due to inactivity, the same
chemoreceptors in the blood vessels detect this.
 Messages are sent to the Medulla oblongata and the
breathing rate decreases.
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OBJECTIVES
 Talk with your teacher about the structure of the
human skin shown in 3D section on the next two
slides.
 In the first diagram, note the capillary networks
just below the epidermis, sweat glands, sweat
pores and hair muscles.
 In the second diagram of the skin, note the
various types of receptors including those for
sensing heat and cold.
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OBJECTIVES 22
Note the capillary
networks just below
the epidermis, sweat
glands, sweat pores
and hair muscles.

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OBJECTIVES 23
http://universe-review.ca/I10-13-senses.jpg
Note the various
types of receptors
including those for
sensing heat and
cold.

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OBJECTIVES
 In humans, body temperature is controlled by the
thermoregulatory centre in the hypothalamus of the
brain. It receives input from: (1) receptors in the
hypothalamus itself which monitors the temperature
of the blood as it passes through the brain and (2) from
skin receptors that monitor the external temperature.
Both sets of information are needed so that the body
can make appropriate adjustments.
 The thermoregulatory centre sends impulses to several
different effectors (e.g. muscles in blood vessels, hair
muscles) to adjust body temperature.
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OBJECTIVES 25
http://www.biologymad.com/resources/A2%20Homeostasis.pdf

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OBJECTIVES
 Body temperature increases due to internal
cellular activity. External temperatures also
affect body temperature.
 Body temperature falls due to low cellular
activity and a fall in external temperature.
 When the body temperatures falls,
thermoreceptors in the skin detect this.
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OBJECTIVES
 A message is sent to the Hypothalamus in the brain
which implements several mechanisms to increase
temperature.
 These mechanisms include: vasoconstriction,
increased fat respiration, contraction of hair erector
muscles.
The next two slides show how skin capillary loops
contract and dilate during temperature regulatory
processes.
Why would those changes occur?
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28. X
OBJECTIVES
When body temperature rises:
 Blood flow to the surface is
increased.
 (a) is closed and (b) and (c) arterioles
are open.This is vasodilation.
 Blood flows closer to the skin
surface.There is a larger surface area
for the heat to escape through the
skin surface.
 More heat is lost to the external
environment.
 Body temperature is reduced.
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29. X
OBJECTIVES
When body temperature falls:
 Blood flow to the surface via
arterioles is reduced.
 (a) is dilated but (b) and (c)
arterioles are
vasoconstricted.
 Blood flow to the surface is
reduced.
 Less heat is lost to the
external environment by
radiation.
 Body heat is retained.
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OBJECTIVES
In the next slide, notice that the diagrams show the
sweat glands, and you can see how the openings
(pores) come right up to the surface.
 The sweat can easily escape to the surface of the
skin through the pores.
 When sweat evaporates (changing from liquid to
gas), the process needs heat energy to do this; so,
heat is removed from the sweat to do so.
The result? Your body gets cooler!
 The hairs are moved by the action of the muscle,
and lie flat against the skin surface.
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OBJECTIVES 31

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OBJECTIVES
http://scienceaid.co.uk/biology/humans/homeostasis.html
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OBJECTIVES
Homeostasis is an organism’s ability to regulate its
internal environment, keeping cellular processes
and contents at a ‘set point’ which thereby enables
the organism to obtain and use resources, feed,
grow, reproduce, excrete waste and generally
maintain stable internal conditions while living in a
constantly changing external environment.The
various
receptors and effectors within the organism’s body
enable it to use negative and positive feedback
mechanisms for homeostasis.
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