Topic 6.4 - Homeostasis Flashcards
(15 cards)
What is homeostasis
The maintenance of an internal environment within restricted limits in organisms. It causes constant fluctuations brought about by variations in internal and external conditions. They occur around an optimum point and homeostasis is the ability to return to that optimum point
What is the importance of homeostasis in relation to biochemical reactions within cells
The enzymes that control these reactions are sensitive to changes in pH and temperature. Any change to these factors reduces the rate of reaction of enzymes or may even prevent them working altogether, for example, by denaturing them. Maintaining a constant internal environment means these reactions can take place at a suitable rate
What is the importance of homeostasis in relation to water potential and tissue fluids
May cause cells to shrink or expand (or burst) as a result of water entering or leaving by osmosis, meaning the cells cannot operate normally. A constant blood glucose concentration is essential in ensuring a constant water potential, and ensures a reliable source of glucose for respiration by cells
What is the importance of homeostasis in relation to maintaining a constant internal environment and staying independent of changes in the external environment
They may have a wider geographical range and therefore have a greater chance of finding food and shelter
What are the control mechanisms
-Optimum point
-Receptor
-Coordinator
-Effector
-Feedback mechanism
What is negative feedback
Most systems, including biological ones, use negative feedback which is when the change produced by the control system leads to a change in the stimulus detected by the receptor and turn the system off
What is positive feedback
Occurs when a deviation from an optimum causes changes that result in an even greater deviation from the normal
What is the benefit of control systems having many receptors and effectors
-They have separate mechanisms that each produce a positive movement towards an optimum, allowing a greater degree of control of the particular factor being regulated.
-It is importantly to ensure that the information provided by receptors is analysed by the coordinator before action is taken so the brain can decide the best course of action
-The control centre must coordinate the action of the effectors so they operate harmoniously
When does negative feedback occur
When the stimulus causes the corrective measures to be turned off. In doing so this tends to return the system to its original level
How does negative feedback work if there is a fall in the concentration of glucose in the blood.
-Detected by receptors on the cell-surface membrane of alpha cells (coordinator) in the pancreas which secrete the hormone glucagon
-Glucagon causes liver cells to convert glycogen to glucose which is released into the blood raising the BG conc.
-As this raised conc. blood circulates back to pancreas there is reduced simulation of A-cells which therefore secrete less glucagon. So secretion of glucagon leads to a reduction in its own secretion.
How does negative feedback work if there is a rise in the concentration of glucose in the blood.
Insulin will be produced from the B-cells in the pancreas. Insulin increases the uptake of glucose by cells and its conversion to glycogen and fat. The fall in blood glucose concentrations that results reduces insulin production once blood glucose concentrations return to their optimum.
What is the benefit of having separate negative feedback mechanisms + example
Gives greater degree of homeostatic control as there are positive actions in both directions.
-e.g. If glucagon raised the blood sugar concentration above the optimum, it would take some time for it to fall again if the only method was metabolic activity. By having a second hormone, insulin its secretion brings about a return to optimum blood sugar concentrations far more rapidly.
Outline hormones
-Produced in glands, which secrete the hormone directly into the blood
-Carried in the blood plasma to the cells on which they act- target cells- which have specific receptors on their cell-surface membranes that are complementary to a specific hormone
-Are effective in very low concentrations but often have widespread and long-lasting effects
Outline the second messenger model
-Adrenaline binds to a transmembrane protein receptor within the cell surface membrane of a liver cell
-The binding of adrenaline causes the protein to change shape on the inside of the membrane
-This change of protein shape leads to the activation of an enzyme called adenyl cyclase. This activated coverts ATP to cyclic AMP
-the cAMP acts as a second messenger that binds to protein kinase enzyme, changing its shape and activating it
-The active protein kinase enzyme catalyses the conversion of glycogen to glucose which moves out of the liver cell by facilitated diffusion and into the blood, through channel proteins
Outline the pancreas
A large pale-coloured gland that is situated in the upper abdomen, behind the stomach. It produces enzymes for digestion and hominem for regulating blood glucose concentration
