Homeostasis
- Created by: sarah1234567
- Created on: 09-03-16 13:14
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- Homeostasis
- Negative Feedback
- Definition: A control system for stability. A change is detected and initiates a corrective mechanism to reverse the change
- An example is body temperature. When the body becomes too hot, negative feedback works to bring it back to the normal. Similarly, when the body is too cold, negative feedback works to warm it up and bring it back to the normal.
- Regulation of body temperature
- Ectotherms
- Endotherms gain most of their heat from the environment so their core temperature fluctuates with atmospheric temperature.
- They may warm themselves up by basking in the sun, pressing their bodies against warm surfaces such as the ground, generating metabolic heat and turning themselves a darker colour
- They may cool themselves down by going into the shade or turning themselves a lighter colour.
- Endotherms
- Any changes in core body temperature are detected by the hypothalamus - this is the body's thermoregulatory centre.
- Endotherms control their core temperature from within their body. Their temperature is a compromise which will allow their enzymes to work at their optimum temperature but does not take too much energy to maintain.
- When they are too hot: sweating, hairs lie flat, vasodilation
- When they are too cold: hairs stand on end, shivering, decrease sweating, increased metabolic rate
- Ectotherms
- Regulation of blood glucose levels
- When there is too much sugar in the blood, for example after a meal, the beta cells in the islets of Langerhans in the pancreas will release insulin which polymerises glucose into glycogen so that it can be stored and there is less of it in the blood. This is Glycogenesis.
- When there is too little sugar in the blood, the alpha cells in the islets of Langerhans in the pancreas will release glucagon which breaks down glycogen into glucose. This is glycogenolysis.
- Adrenaline is released when a short burst of energy is needed. It works by a second messenger system (similarly to glucagon). The adrenaline is the first messenger but it is too big to fit into the target cell so instead it binds to receptors on the cell surface membrane. This activates an enzyme which converts ATP into cyclic AMP which is the second messenger. This then activates enzymes which will convert glycogen into glucose.
- Gluconeogenesis is making new glucose from sources other than food, for example by combining glycerol with amino acids.
- Diabtetes
- Type 1 diabetes is due to the body being unable to produce insulin, so sufferers have to use insulin injections in order to control this.
- Type 2 diabetes is usually due to faulty glycoprotein receptors on body cells losing their responsiveness to insulin. It tends to be caused by obesity and can be controlled by diet and exercise.
- Negative Feedback
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