📊
Chapter 16: Homeostasis
6.4.1 Principles of homeostasis and negative
feedback
💡 Homeostasis is the maintenance of a constant internal environment within
restricted limits by physiological control systems
Importance of homeostasis
1. 🌡 Temperature- crucial for enzymes. If it's too high, enzymes are denatured, making
metabolic reactions less efficient. If it's too low, enzyme activity is reduced, slowing
metabolic reactions.
2. 🧪pH- again, enzymes are denatured if pH strays too far from their optimum because
their hydrogen bonds are broken
3. 🍬 Blood glucose- if it is too high, water potential is reduced so cells shrivel and die. If
it's too low, there isn't enough respiratory substrate.
Negative feedback systems
In negative feedback, corrective mechanisms are applied when the internal environment
deviates from its normal level, in order to restore it.
Chapter 16: Homeostasis 1
, Having separate negative feedback systems that control departure from the norm in both
directions (eg blood glucose decrease- glucagon or increase- insulin) allows a greater degree
of homeostatic control.
Positive feedback systems
In positive feedback, a deviation from normal internal conditions is amplified.
Neurones use positive feedback to produce rapid action potentials- the small influx of sodium
ions increases permeability which causes more diffusion of ions.
For example, in hypothermia, the homeostatic system of thermoregulation breaks down,
causing further falls in body temperature when the brain stops working and shivering stops.
💡 Examples of positive feedback are generally more rare because they tend to create
unstable conditions that can be harmful.
6.4.2 Control of blood glucose concentration
Chapter 16: Homeostasis 2
Chapter 16: Homeostasis
6.4.1 Principles of homeostasis and negative
feedback
💡 Homeostasis is the maintenance of a constant internal environment within
restricted limits by physiological control systems
Importance of homeostasis
1. 🌡 Temperature- crucial for enzymes. If it's too high, enzymes are denatured, making
metabolic reactions less efficient. If it's too low, enzyme activity is reduced, slowing
metabolic reactions.
2. 🧪pH- again, enzymes are denatured if pH strays too far from their optimum because
their hydrogen bonds are broken
3. 🍬 Blood glucose- if it is too high, water potential is reduced so cells shrivel and die. If
it's too low, there isn't enough respiratory substrate.
Negative feedback systems
In negative feedback, corrective mechanisms are applied when the internal environment
deviates from its normal level, in order to restore it.
Chapter 16: Homeostasis 1
, Having separate negative feedback systems that control departure from the norm in both
directions (eg blood glucose decrease- glucagon or increase- insulin) allows a greater degree
of homeostatic control.
Positive feedback systems
In positive feedback, a deviation from normal internal conditions is amplified.
Neurones use positive feedback to produce rapid action potentials- the small influx of sodium
ions increases permeability which causes more diffusion of ions.
For example, in hypothermia, the homeostatic system of thermoregulation breaks down,
causing further falls in body temperature when the brain stops working and shivering stops.
💡 Examples of positive feedback are generally more rare because they tend to create
unstable conditions that can be harmful.
6.4.2 Control of blood glucose concentration
Chapter 16: Homeostasis 2
