Flashcards in Feedback mechanisms Deck (10):
What are the stages of homeostasis control?
-the optimum point
-a feedback mechanism
What is the optimum point?
-the optimum point, or desired level, at which the system operates
What is a receptor?
-a receptors, which sects the stimulus of any deviation from the set point (norm)
What is a coordinator?
-a coordinator, which coordinates information from various sources
What is an effector?
-an effector, which brings about the corrective measures needs to return the system to the optimum point (norm)
What is a feedback mechanism?
-a feedback mechanism, by which a receptor detects a stimulus created by the change to the system and the effect or brings about the appropriate response
What is the relation between feedback and effectors?
-let us now look in more detail at the last stage in the lit - the feedback mechanism
-when an effect or has correlated any deviation and returned the system to the optimum point, it is important that this information is fed back to the receptor
-if the information is not red back, the receptor will continue to stimulate the effector leading to an over-correction and causing a deviation in the opposite direction
-there are two types of feedback -negative feedback and positive feedback
What is negative feedback?
-negative feedback occurs when the stimulus causes the corrective measures to be turned off
-in doing so this tends to return the system to its original optimum level and prevents any overshoot
-there are separate negative feedback mechanisms to regulate departures from the norm in each direction
-an example is in the control of blood glucose
-if there is a fall in the concentration of glucose in the blood this stimulates is detected by receptors on the cell-surface membrane of the alpha cells coordinator in the pancreas
-these alpha cells secrete the hormone glucagon
-glucagon causes liver cells (effectors) to convert glycogen to glucose which is released into blood raising the blood glucose concentration
-as this blood with a raised glucose concentration circulates back to the pancreas there is reduced stimulation of alpha cells which therefore secrete less glucagon
-so the secretion of glucagon leads to a reduction in its own secretion (=negative feedback)
-in the same way if the blood glucose concentration rises, rather than falls, 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 in blood glucose concentration that results reduced insulin production once blood glucose concentrations return to their optimum (=negative)
What is positive feedback?
-positive feedback occurs when the feedback causes the corrective measures to remain turned on
-in doing so it causes the system to deviate even more from the original (normal) level
-examples are less common, but one occurs in neurones when a stimulus causes a small influx of sodium ions
-this influx increases the permeability of the neurone to sodium ions so more items enter, causing a further increase in permeability and even more rapid entry causing a further increase in permeability and even more rapid entry of ions
-this results in a very rapid build-up of an action potential that allows an equally rapid response to a stimulus
-positive feedback occurs more often when there is a breakdown of control systems
-in certain diseases, for example typhoid fever, there is a breakdown of temperature regulation resulting in a rise in body temperature leading to hyperthermia
-in the same way when the body gets too cold (hypothermia) the temperature control systems ten dot breakdown, leading to positive feedback resulting in the body temperature dropping even lower