AQA BIOL5 Homeostasis
- Created by: MollyPayne
- Created on: 04-05-16 17:25
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- Homeostasis
- Maintaining a constant internal environment
- Ensures cells are in environment that meets their needs and allows them to function normally
- Maintains pH and temperate so not to reduce efficiency or denature enzymes
- Maintains constant blood glucose level to ensure constant water potential to prevent cell shrinkage or bursting
- Ensures a constant, reliable source of glucose for respiration by cells
- Endotherms who maintain a constant internal environment are more independent, have greater chance of finding food and are found in most habitats
- Control Mechanisms
- Set point/ norm at which system operates
- Receptor that detects deviation from set point
- Controller (hypothalamus) coordinates the information and creates instructions
- Effector which brings about the change
- Feedback loop which informs receptors of changes from effector
- Effector which brings about the change
- Controller (hypothalamus) coordinates the information and creates instructions
- Receptor that detects deviation from set point
- Receiving information from a number of sources allows better degree of control
- Mechanisms of heat loss
- Evaporation of water - sweating or panting
- Loss of heat to environment - conduction, convection, radiation
- Conduction = transfer of energy through particles vibrating and gaining kinetic energy
- Convection = gases and fluids, heat causes fluid to expand and move carrying heat with it
- Radiation = energy transferred by electro magnetic waves
- Mechanisms of heat gain
- Production of heat through metabolism of food during respiration
- Gain of heat from the environment - conduction, convection and radiation
- Ectotherms
- Gain heat from environment, cannot internally regulate
- Expose maximum surface area to the sun
- Take shelter to prevent over heating and reduce heat loss
- Warmth from laying flat on ground
- Metabolic heat from respiration
- Varying body colours - darker skin absorbs more heat
- Endotherms
- Gain most heat through internal metabolic activities
- Shelter from cold
- Set point/ norm at which system operates
- Conserving and gaining heat in a cold environment
- Small surface area to volume ratio
- Vaso constriction- shunt vessel dialated, aterioles near skin surface constricated to reduce heat loss
- Shivering - involuntary contractions causing metabolic heat
- Hair erector contract trapping layer of still air next to the skin
- Increased metabolic rate (respiration)
- Decrease in sweating
- Behavioural mechanisms eg. sheltering
- Losing heat in a warm environment
- Vasodilation- shunt vessel constricted and arteriole dilated allowing warm blood to pass close to skin surface and heat to radiate from blood away from the body
- Increased sweating and panting in animals allows water to evaporate taking heat energy with it
- Relaxed erector muscles in skin causes hairs to lay flat so no still air gathers
- Behavioural mechanisms eg. sheltering
- Control of body temperature
- Stimulus (change in temperature) detected by receptors (thermo receptors) pass info to coordinator (hypothalamus causes effector (skin) to porudce response
- Heat gain centre activated by fall in blood temperature, increases body temperature
- Heat loss centre, activated by a rise in blood temperature, decreases body temperature
- Hormones and the regulation of blood glucose
- Produced by glands and carried in blood plasma to target cells, have a long lasting effect
- Pancreas produces insulin and glucagon
- Islets of Langerhans
- Alpha Cells - Produce glucagon
- Beta Cells - produce insulin
- Islets of Langerhans
- Second messenger model
- Hormone (adrenaline) is first messenger and binds to receptor on cell-surface membrane to produce hormone-receptor complex
- Hormone-receptor complex activates an enzyme in the cell
- Enzyme converts ATP to cyclic AMP (second messenger) which activates other enzymes
- These other enzymes convert glycogen to glucose
- Enzyme converts ATP to cyclic AMP (second messenger) which activates other enzymes
- Hormone-receptor complex activates an enzyme in the cell
- Hormone (adrenaline) is first messenger and binds to receptor on cell-surface membrane to produce hormone-receptor complex
- If the level of blood glucose raises rises too high it lowers water potential of blood and can cause dehydration
- Glucose from from 3 sources - Directly from diet, glycogenolysis (break down of glycogen) or gluconeogenesis (forming from other sources eg amino acids)
- Insulin and beta cells of the pancreas
- Beta cells detect rise in blood glucose level and secrete insulin
- Insulin binds with receptors causing - change in tertiary structure of glucose transport molecule allowing more glucose into cells
- An increrase in number of carrier molecules on cell surface membrane
- Activation of enzymes that that convert glucose to glycogen and fat
- Blood glucose level lowered by - increased rate of cell glucose absorption and cell respiratory rate
- Increase in glycogenesis and rate of conversion of glucose to fat
- Glucagon and the alpha cells of the pancreas
- Alpha cells detect fall in blood glucose and secrete glucagon
- Glucagon receptors only found on the liver cells
- Glucagon increases blood glucose by activating enzyme that converts glycogen to glucose or increasing gluconeogenesis of amino acids and glycerol
- Adrenaline
- Adrenaline raises blood glucose by activating an enzyme causing the breakdown of glycogen
- inactivates an enzyme that synthesises glycogen from glucose
- Diabetes
- Type 1
- Body unable to produce insulin
- Controlled by insulin injections
- Body unable to produce insulin
- Type 2
- Glycoprotein receptors losing responsiveness to insulin
- Controlled by regulating carbohydrate intake and exercising
- Glycoprotein receptors losing responsiveness to insulin
- Type 1
- Maintaining a constant internal environment
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