Biology - 6.4.1 Principles of homeostasis

Describe homeostasis in mammals

• Maintenance of stable internal environment within restricted limits

• By physiological control systems (normally involves negative feedback)

Core temperature, blood pH, blood glucose conc., blood WP

Explain the importance of maintaining stable core temperature

If temperature is too high:

• H bonds in tertiary structure of enzymes break

• Enzymes denature; active sites change shape and substrates can’t bind

• So fewer E-S complexes

If temperature is too low:

• Not enough kinetic energy so fewer E-S complexes

Explain the importance of maintaining stable blood pH

• Above or below optimal pH / H bonds in tertiary structure break

• Enzymes denature; active sites change shape and substrates can’t bind

• So fewer E-S complexes

Explain the importance of maintaining stable blood glucose conc.

Too low → hypoglycaemia

• Not enough glucose (respiratory substrate) for respiration

• So less ATP produced

• Active transport can’t happen → cell death

Too high → hyperglycaemia

• Water potential of blood decreases

• Water lost from tissue to blood via osmosis

• Kidneys can’t absorb all glucose → more water lost in urine causing dehydration

Describe the role of negative feedback in homeostasis

1. Receptors detect change from optimum

2. Effectors respond to counteract change

3. Returning levels to optimum / normal

Control of blood glucose conc., blood pH, core temperature, blood water potential

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

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

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

Describe positive feedback

1. Receptors detect change from normal

2. Effectors respond to amplify change

3. Producing a greater deviation from the normal

NOT involved in homeostasis

Contractions during childbirth (oxytocin), blood clotting