Communication, Homeostasis, Negative Feedback notes

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  • Created on: 10-03-16 17:25
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Communication Homeostasis
Learning objective(s):
Define the terms negative feedback , positive feedback and homeostasis
Explain the principles of homeostasis in terms of receptors, effectors and negative
Establish the ideal conditions required for cells to work correctly ­ maintaining the
constant internal environment despite changes to the external environment
Mechanisms which act to keep conditions within the body constant
What causes changes to these ideal conditions in the body?
How does the body respond to these changes to maintain the ideal conditions for cells to
work correctly?
Homeostasis can be defined as keeping the internal environment constant despite external
changes . Many living organisms have to keep a great number of conditions constant inside the
body. These may include:
Body temperature ­ ideal conditions for enzymes (pH)
Blood glucose concentration ­ hyperglycaemic (peak blood glucose), hypoglycaemic (low
blood glucose)
Blood salt concentration
Water potential of blood ­ osmoregulation
CO 2 concentration
[Blood pressure]
Cells have an optimal:
Water content
Oxygen and carbon dioxide concentration
Glucose concentration
In the lining of the stomach, goblet cells secrete mucus to protect cells lining the stomach
from the low pH inside the stomach.
What causes changes to ideal conditions?
Activity ­ body temperature, water levels, CO2 and O2 concentration
Eating and drinking ­ glucose levels

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Organs involved in homeostasis:
Hypothalamus ­ receptors to monitor blood temperature and water content and then
sends nerve impulses to the skin and to the pituitary gland ; also monitors CO2 levels
Lungs ­ removes carbon dioxide and prevents hypercapnia
Pituitary gland ­ produces many vital hormones , including ADH for controlling water
Skin ­ adjusts body temperature by erecting hairs
Muscles ­ can produce heat by shivering
Liver and pancreas ­ work together to adjust blood sugar level
Kidneys ­ Remove urea…read more

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Negative feedback is a process that brings about a reversal of any change in conditions . It ensures
that an optimum steady state can be maintained , as the internal environment is returned to its
original set of conditions after any change .
For negative feedback to work effectively there must be a complex arrangement of structures that
are all coordinated through cell signalling. These structures are a part of a standard pathway that
is used to produce a suitable response to a stimulus .…read more

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Enzyme action and temperature regulation
As core body temperature rises the increase will affect the activity of enzymes . This can lead to
heat exhaustion and even death . When temperature increases, enzymes gain kinetic energy and
begin to move faster, causing more collisions between enzymes and substrates hence more
successful collisions . This initially increases the activity of an enzyme until it reaches the optimum
temperature for the enzyme to be working.…read more

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Endotherms include birds and mammals ­ their core body temperature is kept nearly constant by
thermal homeostasis , largely independent of the external temperature .…read more


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