6.7: The principles of homeostasis and negative feedback

What is homeostasis?

Maintaining a stable internal environment within restricted limits by physiological control systems, most often a negative feedback system

What does homeostasis control?

• Core body temperature

• Body pH

• Blood glucose concentration

• Blood water potential

Why is maintaining a stable core temperature in the body important?

• If temperature is too high, hydrogen bonds in the tertiary structures of enzymes break

• Active sites denature, so enzyme-substrate complexes cannot be formed

• If temperature is too low, there is insufficient kinetic energy

• So infrequent collisions, so fewer enzyme-substrate complexes formed

Why is maintaining a stable body pH important?

• Above/below optimal pH, ionic and hydrogen bonds in the tertiary structure will break

• Active sites denature, so enzyme-substrate complexes cannot be formed

Why is maintaining a stable blood glucose concentration important?

• If blood glucose concentration is too low, there is not enough glucose for respiration

• So less ATP produced

• So active transport cannot take place

• If blood glucose concentration is too high, water potential of blood decreases

• Water is lost from tissue to blood via osmosis

• Kidneys cannot reabsorb all glucose, so more water is lost in urine causing dehydration

What is negative feedback?

A system in which any change is restored to original levels

How does a negative feedback system work?

• Receptors detect changing conditions inside or outside the body

• Effectors respond to counteract change

• Returning conditions to their original optimum levels

Why is it important that conditions in the body are controlled using separate negative feedback mechanisms?

• Allows changes to environment in both directions to be reversed

• Increases control so the body can make precise and small adjustments to keep conditions at optimum

What is positive feedback?

A response that causes the factor to deviate even more from the normal range to enhance the effect of the original stimulus

How does a positive feedback system work?

• Receptors detect changing conditions

• Effectors respond to amplify change

• Producing a greater deviation from normal

What are some examples of positive feedback mechanisms?

• Contractions in childbirth

• Blood clotting