Chapter 33
Physiological Homeostasis
Need to Maintain Conditions within Tolerable Limits
For the human body to function efficiently, our internal environmental must be maintained within tolerable limits.
 Water concentration of blood and the concentration of chemicals in cells must be regulated so they stay at a fairly constant level.

Blood sugar level must be kept within a certain range.
 The body temperature must be kept around 37

C.
Physiological Homeostasis is the maintenance of the body's internal environment within certain tolerable limits, despite changes in the body's external environment.
Negative Feedback Control is the means by which this is maintained.
Draw: fig 33.1
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1.
Receptors are sensory mechanisms which detect a change in the body's internal environment away from the norm.
2.
These receptors send out nervous or hormonal messages which are received by effectors.
3.
The effectors then bring about certain responses which correct the original deviation away from the norm and return the system back to the norm.
Osmoregulation: Control of water content of blood
Draw: Fig 33.3
2

Water content of blood too low:
Complete:
Water content of blood too high:
Complete:
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Control of blood sugar level
All body cells need a continuous supply of energy, most from the oxidation of glucose during respiration , therefore cells are constantly using up the glucose in the blood stream (blood sugar).
The body only obtains glucose on eating, so to maintain an even, regular supply, homeostasis is necessary.
Draw: fig 33.4 or 33.5 (Use whichever is clearer to you)
Glucose is stored in the liver as glycogen and can be added to or removed from as needs demand.
Blood sugar level too high:
Complete:
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Blood sugar level too low:
Complete:
Complete the following table:
Control
Receptor Hormone produced
Osmoregulation
Blood Sugar
Blood too conc.
Blood too dilute
Blood too conc
Blood too dilute
Effector Effect brought about
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Thermoregulation
Ectotherm
What is an ectotherm?
Give an example;
Endotherm
What is an endotherm?
Give an example;
Endotherms have a high metabolic rate which means they can generate a lot of heat.
They regulate their body temperature through homeostatic control.
Hypothalamus
How does the hypothalamus act in thermoregulation? (notes or copy fig.33.6)
What are the main mechanisms for cooling the body back down?
What are the main mechanisms for heating the body up?
These are all involuntary responses, what voluntary responses could the body make to warm up or cool down?
Onto a black piece of paper copy fig 33.11 or make bullet points from it, and make a note on the advantages of homeostasis (page288).
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