Homeostasis and negative feedback

Keeping the internal environment constant despite external changes
1. Body temperature
2. Blood glucose concentration
3. Blood salt concentration
4. Water potential of the blood
5. Blood pressure
6. Carbon dioxide concentration
Negative feedback
1. In order to maintain a constant internal environment a number of processes must occur
  1. Any change of the internal environment must be detected
    1. The change must be signalled to other cells
      1. There must be a response that reverses the change
2. For negative feedback to work effectively there must be a complex arrangement of structures that are all coordinated through cell signalling
  1. Sensory receptors
    1. These are internal and monitor change in the body
    2. If they detect change then they are stimulated to send a message
    3. E.g. temperature receptors or glucose concentration receptors
  2. A communication system
    1. Acts by signalling between cells
    2. Used to transmit a message from the receptor cells to effector cells
    3. The message may or may not pass through a coordination centre such as the brain
    4. E.g. the nervous system or hormonal system
  3. Effector cells
    1. These cells will bring about a response that reverses the change detected by receptor cells
    2. E.g. liver cells or muscle cells
Positive feedback
1. Less common than negative feedback
2. The response is to increase the original change
3. Destabilises the system and is usually dangerous
  1. E.g. when the body gets too cold, the enzymes become less active, and reactions slow causing less heat to be released - cooling the body further
4. The end of pregnancy is an example of beneficial positive feedback
  1. As the cervix begins to stretch the change is signalled to anterior pituitary gland
    1. Stimulates it to secrete the hormone oxytocin
      1. Oxytocin increases uterine contractions, which stretch the cervix even more
        Once the cervix is fully dilated the baby can be born
The meaning of constant
1. The conditions will never remain perfectly constant
2. There will be some variation about the mean or optimum condition
3. As long as the variation is not too great then the conditions will remain acceptable

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Homeostasis and negative feedback

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	Creado por hannahdrane hace alrededor de 10 años