What are the two types of feedback?
- Negative feedback
- Positive feedback
When does negative feedback occur?
- When stimulus causes the corrective measures to be turned off
- Return the system to its original (opitmum) level and prevents any overshoot
Why are there separate negative feedback mechanisms?
This regulates departures from the norm in each direction
Greater degree of homeostatici control
Because of positive actions in both directions
What happens if there is a fall of blood glucose concentration?
- Stimulus detected by receptors on cell surface membrane of alpha cells (coordinator) in pancreas
- These alpha cells secrete the hormone glucagon
- Glucagon causes the liver cells (effectors) to convert glycogen into glucose which is released into the blood raising blood glucose concentration
- As blood with high glucose concentration circulates back to the pancreas , reduced stimulation of alpha cells so secrete glucagon less
- Secretion of glucagon leads to reduction in its own secretion (=negative feedback)
What happens if blood glucose concentration rises?
- Insulin will be produced from the beta cells in the pancreas
- Insulin increases the uptake of glucose by cells and its conversion to glycogen and fat
- The fall of blood glucose concentration that results reduces the insulin production once the blood glucose concentration return to their optimum (=negative feedback)
Why is it important we have the second hormone of insulin?
- Glucagon raised the blood sugar concentration aove the optimum , it would take some time to fall again if only way of lowering it through metabolic activity
- By having the second hormone of insulin , lowers blood sugar concentration its secretion brings about a return to optimum blood sugar concentration more rapidly
When does positive feedback occur?
- Feedback causes corrective measures to remain turned on
- Causes the system to deviate even more from the normal level
What is an example of positive feedback?
- Neurones cause a small influx of sodium ions
- Influx increases the permability of the neurone to sodium ions so more ions enter
- Causes further permability and even more rapid entry of ions
- It causes a build up of action potential that allows an equally rapid response to stimulus
When does positive feedback occur more often?
- Breakdown of control systems
What is an example of positve feedback when there is a break down of control systems?
- In certain diseases e.g tyhoid fever
- There is a breakdown of temperature regulation resulting in a rise of body temperature leading to hyperthermia
- In a same way when the body gets too cold , hypothermia , temperature control systems break down , leading to positive feedback resulting in body temperature to lower even more
What happens if temperature of blood increases above normal?
- Thermoreceptors in region of brain called hypothalamus sends more nerve impulses to the heat loss centre (in hypothalamus)
- This in turn sends impulses to the skin (effector organ)
- Vasodilation - sweating and lowering the body hairs lead to reduction of blood temperature
- Cooler blood temperature
What happens if the blood temperature returned to normal not fed back to hypothalamus?
It will continue to stimulate the skin to lose body heat
Blood temperature will then fall below the normal and may cause hypothermia and death of an organism
What happens when the cooler blood is returning from skin passes through hypothalamus?
Thermoreceptor send fewever impulses to the heat loss centre
This in turn stops sending impulses to the skin and vasodiliation sweating , etc, cease and blood temperature remains at the normal level than falling
The blood , have been cooled to its normal temperature and resulted in turning off the effector (skin) that correcting the rise in temperature
NEGATIVE FEEDBACK OF TEMP CONTROL