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Summary Notes on homeostasis and thermoregulation
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A levels notes on homeostasis and thermoregulation in ectotherms and endotherms
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HomeostasisLiving cells need to maintain:
a suitable temperature
a suitable pH
an aqueous environment that keeps substrates and products in solution
freedom from toxins and excess inhibitors
- In multicellular organisms, cells are specialized and rely upon another; therefore they must be able to
communicate in order to coordinate their activities (coordination of activities of different organs)
- The environment of organism and cells changes, so need to maintain constant internal environment.
e.g. Respiration in cells produces CO2, which causes pH to become more acidic if it builds up
disrupts the action of enzymes and other proteins
Cell signaling - one cell releases a chemical which is detected by another cell (binds to complementary
shaped receptors on CSM); this causes a change in the second cell (response)
A good communication system will:
cover the whole body
enable cells to communicate with each other
enable specific communication
enable rapid communication
enable short-term and long-term responses
Two major systems using cell signaling are the neuronal and hormonal systems:
Neuronal Hormonal
Cells involved neurons Cells in endocrine organs
Interconnected network of neurons that Hormones travel in blood and are
Where/how signal
signal to each other across synapse only recognized by specific targets
travels
junctions (complementary shapes receptors)
Very rapid responses to stimuli that may
Effects Longer-term response
be changing quickly
, Homeostasis – maintaining a constant internal environment, through coordination by cell signalling,
despite changes in external and internal factors
Need to maintain:
body temperature
blood glucose concentration
blood salt concentration
water potential of the blood
blood pressure
CO2 concentration
Standard response pathway
Stimulus Receptor Communication pathway (cell signalling) Effector Response
Location Details
- on surface of body (skin)
- monitor changes in external environment
Sensory receptors
- internal (e.g. in
- monitor changes in internal environment
hypothalamus)
- signaling between cells
- used to transmit a message from receptor
- neuronal system
cells to the effector cells via a coordination
Communication system
center (brain)
- hormonal system
- messages are input (from receptor) and
output (to effector)
- muscle cells
Effectors - bring about a response
- liver cells
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