Principles of Homeostasis and Negative Feedback

Describe homeostasis in animals

Maintenance of a stable internal environment within restricted limits, by physiological control systems (negative feedback) e.g. core temperature, blood pH, blood glucose concentration and blood water potential

Explain the importance of maintaining a stable core temperature

Temp too HIGH:

• Hydrogen bonds in tertiary structure of enzymes will break

• So the active site changes shapes and substrates can’t bind. so the enzyme has denatured

• And fewer enzyme-substrate complexes

Temp too LOW:

• Not enough kinetic energy so fewer enzyme substrate complexes

Explain the importance of maintaining stable blood pH

• Above or below optimal pH, the ionic'/ hydrogen bonds in tertiary structure of enzymes will break

• So active sites changes shape and substrates can’t bind as enzyme has denatured

• So fewer enzyme substrate complexes form

What happens if blood glucose concentration is too low (hypoglycaemia)?

• Not enough glucose for respiration

• So less ATP produced overall

• And active transport can’t occur/ occurs less so could lead to cell death

What happens if blood glucose concentration is too high (hyperglycaemia)?

• Water potential of blood decreases

• Water lost from tissue to blood via osmosis

• Kidneys can’t absorb all the glucose, so more water lost in urine causing dehydration

Describe the role of negative feedback in homeostasis

• Receptors detect change from optimum level

• Effectors (e.g. muscle/ gland) respond to counteract change in internal conditions

• To return levels back to optimum/ normal

• e.g. blood glucose falls and hormones are released to concert glycogen to glucose to bring it back to normal levels

Explain the importance of conditions being controlled by separate mechanisms involving negative feedback

• Departures in different directions from original state can all be controlled/ reversed

• Giving a greater degree of control over changes in internal environment

Describe positive feedback

• Receptors detect change from normal

• Effects respond to amplify/ increase change

• Producing a greater deviation from normal

• Not involved in homeostasis e.g. contractions in childbirth and blood clotting