AQA BIOL5 Homeostasis

HideShow resource information
View mindmap
  • 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
      • 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
    • 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
      • 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
      • 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
      • Type 2
        • Glycoprotein receptors losing responsiveness to insulin
          • Controlled by regulating carbohydrate intake and exercising

Comments

No comments have yet been made

Similar Biology resources:

See all Biology resources »See all Homeostasis resources »