a2 bio f214

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  • Created on: 30-09-10 19:12

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Communication CHAPTER 1:

Principles of Homeostasis:

Negative Feedback - requires a receptor and effector. Receptor monitors the factor being controlled. if value of the factor is not within suitable range the receptor communicates with the effector. The effector then causes an action that brings factor back to normal.
Positive Feedback - mechanism that carries on increasing body temperature

Change in Temperature:

Fever - chemical pyrogens release white blood cells, raise set point causing body temp to increase by 2-3C
Hibernation - some mammals release hormones that reduce set point to 5C = reduces metabolic rate and conserves food reserves
Torpor - bats and hummingbirds reduce set point everyday while they are inactive; they have large surface area: volume ratio

Temperature in Ectotherms:

Ectotherms obtain most of their heat from the outside of bodies. They need less food as they don't generate heat. They are inactive in cold as their cells are cold and metabolic reactions slow.

Temperature in Endotherms:

Heat Inputs

Heat Outputs

Generated by chemical reactions

Radiation from body

Absorption from sun/fire

Conduction to colder substances

Conduction from warmer substances

Conduction and convection in sweating

Above 37C enzymes begin to denature and lose their shape. When temperatures rise the rate of enzyme controlled reactions slow down.

Effectors:

  • smooth muscles in peripheral arterioles in skin
  • erector pili muscles in skin
  • sweat glands
  • skeletal muscles
  • glands
  • behaviour

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