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Introduction to homeostasis

General summary of biological principles involved in Homeostasis
by

Lisbeth Ricciardi

on 8 September 2013

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Transcript of Introduction to homeostasis

LESSON OBJECTIVES

Outline the need for communication systems within multicellular organisms, with reference to the need to respond to changes in the internal and external environment and to coordinate the activities of different organs.
State that cells need to communicate with each other by a process called cell signalling.
State that neuronal and hormonal systems are examples of cell signalling.
Define the terms negative feedback, positive feedback and homeostasis.
Explain the principles of homeostasis in terms of receptors, effectors and negative feedback.

Homeostasis
Keeping Cells Active
All living things need to maintain a certain set of conditions inside their cells:
External Environment
Internal Environment
In multicellular organisms most cells are not in contact with the external environment. In animals internal cells are bathed in tissue fluid - this is the internal environment.
Multicellular organisms are more efficient because cells can specialise for particular functions and thus form tissues and organs. This means sensory cells tha monitor the blood will be separate from effector cells that can alter its composition, so a communication system is required.
Coordination
Maintaining the Internal Environment
Stimulus and Response
The composition of tissue fluid is maintained by the blood. Wastes or toxins accumulating in tissue fluid will diffuse into the blood and be carried away to be excreted
The accumulation of waste or toxins acts as a stimulus to cause their removal so that cells can survive.

This may act directly on the cells to inhibit activity in order to reduce waste production, but this may not be good for the organism as a whole
For example, the build up of lactic acid in skeletal muscle tissue produced by anaerobic respiration will inhibit contraction of skeletal muscle cells

All living organisms have an external environment: the air, water or soil around them. As this changes it can put stress on the organism, so changes need to be monitored and compensated for if the organism is to
survive....
....eg. a co
oler
environm
ent
will cause great
er
heat loss
.
The organism must
cha
nge its
beh
aviour or physiology
t
o reduc
e s
tress
Cell metabolism changes the internal environment : substrates diffuse into cells, waste products diffuse out of cells, changing the composition of tissue fluid
eg. one waste product is carbon dioxide. If this is allowed to build up it will affect the pH of the tissue fluid, potentially disrupting enzyme activity
Maintaining tissue fluid
The composition of tissue fluid is maintained by the blood: waste/toxins will enter the blood and be transported to where they can be excreted.

Similarly, substrates will be transported by the blood to the sites where they are required.

Concentration of all substances must be closely monitored to ensure useful substances aren't excreted with the toxins, and needed substrates don't run out.
Cell Signalling
This is a process where one cell releases a chemical which causes a response in another cell
NEURONAL
Rapid conduction via neurones and synapses, allows for rapid response to fast changing stimuli
HORMONAL
Hormones are secreted by endocrine glands, transported by the blood all over the body but only specific target cells will recognise them and respond.
Enables coordination of long-term responses
Questions
1 (a) Give three examples of a
stimulus and corresponding
response
(b) For each of your examples
state which communication
system is used, and why
2 Outline the likely
communication pathways used by
the arctic fox to produce its
winter coat
Negative Feedback
Positive Feedback
An effective communication system must:
cover the whole body
enable intercellular communication
enable specific communication
enable rapid communication
enable both short- and long-term responses
suitable temperature
suitable pH
aqueous environment to keep substrates and products in solution
freedom from toxins and excess inhibitors
Full transcript