Homeostasis
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What is homeostasis
the maintenance of an internal environment within restricted limits in organisms
What factors are controlled by homeostasis
-Body temperature -pH -water potential -blood glucose concentration
what is the internal environment made up of
tissue fluid
What does homeostasis ensure
The cells of the body are in an environment that meets their requirements and allows them to function normally despite external changes
Why is homeostasis important
-Enzymes are sensitive to changes in pH and temperature -changes to the water potential of the blood and tissue fluid may cause cells to shrink or burst -Organisms with the ability to maintain a constant internal environment are more independent of changes in the external environment
What is a control mechanism
self regulating system that involves a series of stages to control it
What are the stages of a control mechanism
-optimum point- point the system works best -receptor-detects any deviation from optimum -coordinator- coordinates information from receptor -effector- often a muscle or gland, brings about change -feedback mechanism-receptor responds to a stimulus created by the change by the effector
What is an example of a control mechanism
-(change)room temperature drops from 20 to 18 -(receptor)room thermostat signals that the temperature is below optimum -(coordinator)Programmer checks that heating should be on at his time -(Effector)Boiler fires up, pump circulates water and radiators become hot -Room is raised to 20 -(feedback loop)circulation of air in room takes air at 20 from radiator to thermostat
How are control systems co-ordinated
Mostly by negative feedback
What is negative feeback
The change produced by the control system leads to a change in the stimulus detected by the receptor and turns the system off
What is positive feedback
When a deviation from an optimum causes changes that result in an even greater deviation from the normal
What is an example of positive feedback
Neurones where a stimulus leads to a small influx of Na+ ions -This influx increases the permeability of the neurone membrane to Na+ ions, more enter, causing a further increase in permeability
Why do control systems have many receptors and effectors
Allows them to have separate mechanisms that each produce positive movement towards an optimum
What is an example of negative feedback
control of blood glucose
What does having separate negative control mechanisms in either directions
A greater degree of homeostatic control
Why is negative feedback important in maintaining a system at a set point
If the information is not fed back once an effector has corrected any deviation and returned the system to the set point, the receptor will continue to stimulate the effector and an over-correction will lead to deviation in the opposite direction
What are hormones
chemical messengers that are produced in glands and carried in blood plasma directly to target cells
Second messenger model
-Adrenaline binds to protein receptor in membrane of liver cell -The binding of adrenaline changes the shape of the receptor -This activates adenyl cyclase by changing its shape -Adenyl cyclase then synthesises cAMP from ATP -cAMP is called a second messenger -The production of cAMP activates a-kinase -a-kinase hydrolyses glycogen to release glucose -glucose moves out of the liver cell into the blood by facilitated diffusion
What is the pancreas
A gland that produces enzymes for digestion and hormones for regulating blood glucose concentration
What do alpha cells produce
Glucagon
What do alpha cells detect
A fall in blood glucose concentration
What do beta cells produce
Insulin
What do beta cells detect
An increase in blood glucose concentration
Where are alpha and beta cells loctaed
Islets of Langerhans