Principles of homeostasis and negative feedback (A-level only) Flashcards
Homeostasis
Maintenance of the internal environment within an optimum range.
Homeostasis is necessary to control the following factors:
High temperature
Low temperature
Blood pH
High blood glucose concentration
Low blood glucose concentration
High temperature
Homeostasis maintains optimum core body temperature.
This is approximately 37°C in humans.
If body temperature rises above the optimum range, enzymes denature.
The higher temperature causes the hydrogen bonds that maintain the enzyme structure to break.
This alters the enzyme active site so the enzyme can no longer catalyse reactions (e.g. respiration).
Low temperature
If temperature falls below the optimum range, enzyme activity declines.
Decreased enzyme activity causes the rate of important reactions (e.g. respiration) to slow down.
Blood pH
Homeostasis maintains blood pH.
If blood pH rises above (too alkaline) or falls below (too acidic) the optimum range, enzymes denature.
Denatured enzymes can no longer catalyse important reactions.
Optimum pH range is normally around pH 7.
Some enzymes have very different optimum ranges (e.g. enzymes in the stomach have a very acidic optimum pH).
High blood glucose concentration
Homeostasis maintains blood glucose concentration.
If blood glucose levels rise above the optimum range, the water potential of the blood is reduced.
Low water potential in the blood causes water to diffuse out of the cells by osmosis and into the blood.
This makes the cells flaccid and they die.
Low blood glucose concentration
Homeostasis maintains blood glucose concentration.
If blood glucose levels fall below the optimum range, there is not sufficient glucose for respiration.
Respiration rate declines and energy levels fall.
Negative feedback
Mechanism that restores systems to the original level.
Stages of negative feedback:
Detect change
Counteract change
Detect change
Change in the internal environment (stimulus) is detected by receptors.
Receptors (e.g. thermoreceptors) are stimulated when the level is too high or too low (e.g. temperature).
Counteract change
Receptors send a signal to the effectors through the nervous system.
The effectors counteract the change (e.g by restoring body temperature to 37°C).
Negative feedback can only maintain the internal environment within a specific range.
If a change is too dramatic, negative feedback may not be able to prevent it.
Multiple negative feedback mechanisms provide a greater degree of control of the internal environment such as:
More control
Faster response
More control
Multiple feedback mechanisms provide more control because the body can respond to multiple changes away from the optimum.
E.g. Body temperature can be reduced or increased by multiple mechanisms.
Faster responses
Multiple feedback mechanisms also provide a faster response because the body can respond in more ways to a change away from the optimum.
E.g. If body temperature decreases, negative feedback can increase body temperature by both shivering and vasoconstriction.
