16 Homeostasis Flashcards
Purpose of homoeostasis
Internal environment is made up of tissue fluid that bathe each cell, supply nutrients and removing wastes, maintaining the features of this fluid at optimum levels protects the cells from changes in external environment Organisms maintained in balanced equilibrium
Importance of homoeostasis
Enzymes that control biochemical reactions are sensitive to changes in pH and temperature, any changes to these factors reduces the rate of reaction of enzymes or may even prevent them working Changes to the water potential of the blood and tissue fluid may cause cells to shrink and expand as a result of osmosis, maintenance of constant blood conc essential in ensuring a constant water potential Organisms with ability to maintain a constant internal environment are more independent of changes in the external environment, wider geographical range and therefore have a greater chance of finding food shelter etc.
Control of any self regulated system involves which steps
Optimum point, monitored by a Receptor which detects any deviation from optimum point and informs the Coordinator, coordinates info from receptors and sends instructions to Effector, brings about changes, this return to normality creates a Feedback mechanism by which a receptor responds to a stimulus created by the change the system brought about by the effector
Negative feedback
When the change produced by the control system leads to a change in the stimulus detected by the receptor and turns the system off
Positive feedback
Occurs when a deviation from an optimum causes changes that result in an even greater deviation from the normal Example occurs in neurons where a stimulus leads to a small influx of sodium ions increasing permeability to sodium ions causing further increase
What is benefit of control system having many receptors and affecters
Allows them to have separate mechanisms that each produce a positive movement towards an optimum, this allows a greater degree of control of a particular factor being regulated By analysing the info from all detectors the brain can decide the best course of action
What happens when there is a fall in the concentration of glucose in the blood
Stimulus is detected by receptors on the cell surface membrane of alpha cells (coordinator) in the pancreas Alpha cells secrete hormones glucagon Glucagon causes liver cells (effectors) to convert glycogen to glucose, released into blood raising blood glucose conc As this blood circulates back to pancreas there is reduced stimulation of alpha cells which therefore secrete less glucagon Negative feedback
What happens if blood glucose concentration rises
Insulin will be produced from the beta cells in the pancreas Insulin increases uptake of glucose by cells and its conversion to glycogen and fat Fall in blood glucose conc reduces insulin production once blood glucose conc returns to their optimum Negative feedback
Benefits of having separate negative feedback mechanisms
Gives greater degree of homoeostatic control
When does positive feedback occur most often
When there is a breakdown of a control system When body gets too cold, hypothermia, the temperature control system tends to break down leading to positive feedback resulting in body temperature dropping even lower
Negative feedback in temperature control
If temperature of blood increases Thermo receptors in the region of the brain called hypothalamus send more nerve impulses to heat loss centre, also in hypothalamus This sends impulses to the skin (effector organ) Vasodilation, sweating and lowering of body hairs lead to reduction in body temp
Endocrine glands
Secrete the hormone directly into the blood
Target cells
Have specific receptors on their cell surface membranes that are complementary to a specific hormone
One mechanism of hormone action is known as
Second messenger model Mechanism is used by 2 hormones: adrenaline and glucagon Hormone has it’s effect inside a cell even though it never enters the cell
How does cAMP acts as a 2nd messenger
Binds to protein kinase enzyme, changing its shape and therefore activating it Then when glycogen converted to glucose it moves out of the liver cell by facilitated diffusion and into the blood thru channel proteins
Diagram of second messenger model
SEE TEXTBOOK PG 387
