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maintainance of a constant internal environment


Importance of homeostasis

  • consistency of temperature and pH, as it can affect enzyme activity;
  • if blood glucose too high, water moves out by osmosis leading to dehydration



Describe how thermoregulation can combat a large decrease in external temperature

  • thermoreceptors in hypothalamus detect temperature changes of blood;
  • thermorecepters in skin detect temperature changes of skin
  • Impulse is sent to the heat gain centre of hypothalamus
  • nerve impulses transmitted from hypothalamus results in:
  • vasoconstriction of arterioles, leading to less blood to skin;
  • Shivering,which  generates heat via respiration;
  • Piloerector muscles contract, causing hair to rise (insulator)
  • negative feedback occurs to regulate increase


Why is a tall,thin person more likely to lose heat than a small and stout one?

  • larger surface area to volume ratio;
  • more heat loss by radiation;


Advantages of endothermy over ectothermy

  • endotherms maintains its body at a metabolically favourable temp
  • enzymes can work at optimum temperature;
  • so metabolic reactions proceed more quickly;
  • more independent of environment so better able to survive in different environment;


Why do reptiles seek shade when the temperature increases abover 40 degrees

-body will ‘overheat’ in very hot environments;

- they have no physiological cooling mechanism

-may lead to enzyme dentaturation


Role of insulin

  • secreted when blood sugar increases
  • it binds to specific receptors on liver cells;
  • binding of insulin activates enzymes in liver which encourages glycogenesis
  • increases permeability to glucose, leading to more glucose entering cells from blood
  • so the glucose entering the cell is converted to glycogen, reducing blood glucose conc


Even with no insulin, why does the blood glucose conc still decrease

  • glucose is used in cell respiration
  • glucose enters cells and is converted to glycogen
  • glucose is excreted in urine;


Differences in nervous and hormonal systems in mammals

Nervous vs Hormones:

  • Fast vs Slow acting
  • Localised vs Broadcast
  • short lived vs long term effects 
  • electrical via nerves vs chemical delivered by blood vessels


How can diet and exercise maintain low glucose conc in type 2 diabetics?

  • feeding on polysaccharides e.g starch slower digestion therefore no surge in blood sugar level;
  • exercise - increased respiration which uses glucose


Describe the role of the hormone glucagon in the control of blood sugar concentration.

  • Binds to specific receptor;
  • On muscle and liver cell;
  • Activates adenylate cyclase, which converts ATP into cAMP 
  • This activates enzymes in liver
  • These catalyse the hydrolysis of glycogen;
  • Also leads to glyconeogenesis
  • Glycogensis inhibited 
  • Glucose facilitatedly diffused of out of liver cell cells into blood
  • This Increases blood glucose levels;



Describe the physiological responses to a fall in temp

  • Reduction in sweating;
  • Hair erection; 
  • Rapid contraction of skeletal muscles;
  • Vasoconstriction
  • Release adrenaline and thyroxine which increases resp; 


Describe three physiological responses to a rise in temp

  • More sweating 
  • Vasodialation 
  • Hair lowers


How does shivering and having raised hair help to increase heat

  • Shivering generates heat by respiration;
  • Hair has tendency to keep air trapped thereby reducing air movement;
  • This gives insulation so less heat loss 


Role of blood vessels in skin when conserving heat

  • Vasoconstriction of arterioles, which leads to less blood to surface
  •  Less heat loss by radiation


Differences between hormones and local chemical mediators


  • have widespread effect
  • affect distant organs
  • only affect cells with right receptor;
  • are transported in the blood whereas mediators spread by diffusion


How does panting reduce body temp

  • Evaporation of water from lining of mouth 
  • Heat transferred from blood;


Explain how Increased exercise  intensity leads to an increased heart rate. 

  • More resp by muscle tissue
  • More CO2 released, this lowers pH
  • Decreased pH detected by chemoreceptors in carotid arteries
  • This send impulses to the Medulla Oblangata involved;
  • MORE  impulses to SAN along sympathetic nerve
  • Leads to increased HR, so more blood flow leads to more CO2 moved to lungs 


Explain how increased cardiac output is advantageous during exercise

  • Increases glucose and O2 supply to muscles
  • Increases lactate, heat and CO2 removal from muscles
  • More aerobic respiration can therefore take place for muscles;


Why can a successful diabetic still have high glucose conc

  • Recently eaten food high in carbohydrates
  • Glucose absorbed from intestine into blood;
  • Long time after insulin injection 
  • Insulin does not convert glucose to glycogen


Why does oxygen consumption increase with temperature?

  • Increases kinetic energy
  • More respiration occurs so more oxygen used up
  • More energy in the form of ATP made


Why do diabetics have higher blood glucose

In Diabetic person:

  • Lack of insulin /reduced sensitivity of cells to insulin;
  • Reduced uptake of glucose by liver cells
  • Reduced conversion of glucose to glycogen;


How does glycogenesis in liver cells lead to a reduced blood glucose

  • Glucose concentration in cell is decreased so higher glucose conc in blood;
  • This creates a diffusion gradient;
  • Glucose enters cell from blood by facilitated diffusion through a channel protein


The body secretes a large number of different Hormones but only a few different neurotransmitters. Explain the importance of this

  • Hormones reach all cells via blood
  • Neurotransmitters secreted directly on to target cell;
  • Different hormones are specific to different target cells;


Disadvantages of injection of insulin

  • Pain of injections
  • Short lived effect, so constant reinjection
  • Need to consistently measure blood sugar 
  • Diet restriction