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A2 Biology Revision: Homeostasis and the Kidney
Homeostasis and the Kidney
Homeostasis: Maintenance of a constant internal environment by regulating physical
and chemical processes of the body
The Norm: A set or ideal level
Deviation: Any change from the norm
Homeostatic control processes:
Deviation (there is a change)
Deviation acts as a signal to the control centre
The control centre sets off a CORRECTIVE RESPONSE
This response cancels out the change (DEVIATION) and returns the factors back to
the norm
What is the internal environment?
Immediate surroundings of a cell e
...
plasma and tissue fluid
It provides the medium in which cells have to live and it MUST be KEPT CONSTANT
Factors that must be kept constant are:
-

pH of the blood PLASMA
temperature
conc of sodium ions
conc of GLUCOSE
water potential

For Homeostasis to work there must be:
-

A control SYSTEM
-A sensor or receptor that monitors the factors being controlled

-

A corrective MECHANISM which brings about change resulting in the
monitoring of these factors
Negative Feedback sensor which stops the corrective mechanism to avoid
over correction

HOW is HOMEOSTASIS brought about?
4 things:
-

Stimulus
Receptors
Effectors
Sensory Neurones

Ok so we need a stimulus- changes in the environment capable of causing a response
through the nervous system
Receptors are specialised cells, nervous cells which detect the stimulus (the change
in the environment)
The effector responds to the receptor and carries out the corrective response
The sensory neurone transmits the impulse from the receptor to the CNS

Homeostasis requires RECEPTORS, CORRECTIVE MECHANISMS AND EFFECTORS
Corrective mechanisms are carried out by effectors, they restore factors to the norm
The effectors are what carries out the corrective response

Homeostasis is brought about by NEGATIVE FEEDBACK SYSTEMS
(when a negative response comes back to say the factors have been restored to the
norm homeostasis is then)
NEGATIVE FEEDBACK is a CORRECTIVE MECHANISM that RESTORES THE FACTOR TO
THE NORM



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