chapter 7 - mass transport

• what is haemoglobin?

  a protein with a quarternary structure
• what are sources of transport of oxygen?

  haemoglobin & red blood cells
• what do each of the 4 polypeptide chains contain?

  haem group which has iron within them & is where oxygen would bind
• what does affinity of haemoglobin for oxygen mean?

  ability of haemoglobin to attract, or bind, oxygen
• what does saturation of haemoglobin with oxygen mean?

  when haemoglobin is holding the maximum amount of oxygen it can bind to
• what does loading/association of haemoglobin mean?

  binding of oxygen to haemoglobin
• what does unloading/dissociation of haemoglobin mean?

  when oxygen detaches/unbinds from haemoglobin
• oxyhaemoglobin dissociation curve

  • oxygen is loaded in regions with high partial pressure of oxygen ( e.g. alveoli) & is unloaded in regions of low partial pressure of oxygen (e.g. respiring tissues)
  • cooperative binding - this is where the first oxygen binds to haemoglobin and this changes the shape of haemoglobin & this makes it easier for further oxygens to bind
• what is an advantage of low affinity at low partial pressure?

  haemoglobin is unloading oxygen at regions where it is needed
• The Bohr Effect:

  • it is the effect of carbon dioxide
  • when a high carbon dioxide concentration causes the oxyhaemoglobin curve to shift to the right & the affinity for oxygen decreases because the acidic carbon dioxide changes shape of the haemoglobin slightly
  • when lots of CO2 is present, it'll form carbonic acid when dissolved in water in blood - so if there is a lot of respiration occuring, lots of CO2 dissolves in the blood, the blood becomes acidic therefore curve shifts to right, haemoglobin affinity for oxygen decreases so unloads more oxygen
• what is a double circulatory system?

  blood passes through the heart twice in each circuit
• why do mammals require a double circulatory system?

  to manage the pressure of blood flow
• coronary arteries

  • supply the cardiac muscle with oxygenated blood
  • branch off the aorta
  • if become blocked, cardiac muscle won't receive oxygen so cells cannot respire
• 4 chambers of the heart

  2 atria: thinner muscular walls, elastic walls to stretch when blood enters

  • left atrium
  • right atrium

  2 ventricles: thicker muscular walls to enable bigger contraction & this creates higher blood pressure to enable blood flow

  • left ventricle - thicker muscular wall to enable larger contraction to create higher pressure, pumps blood to the body at high pressure to ensure blood reaches all cells
  • right ventricle - thinner muscular wall than left ventricle , pumps blood to the lungs, low pressure to prevent damage to capillaries in alveoli & so blood flows slowly to allow gas exchange
• blood vessels connected to the heart

  2 veins: carries blood to the heart

  • vena cava - carries deoxygenated blood from the body to the right atrium
  • pulmonary vein - carries oxygenated blood from the lungs to left atrium

  2 arteries: carries blood away from heart

  • pulmonary artery - carries deoxygenated blood from right ventricle to the lungs to become oxygenated
  • aorta - carries oxygenated blood from left ventricle to rest of the body

  valves: prevent backflow of blood

  • semi-lunar valves - aorta & pulmonary artery
  • atrioventricular valves - between atria & ventricles
• what are 3 stages of cardiac cycle?

  1. diastole
  2. atriasystole
  3. ventricular systole
• 1st stage of the cardiac cycle - diastole

  • heart is relaxed, atria starts to fill with blood via the vena cava & pulmonary vein (increases pressure within the atria)
  • atrioventricular valves are originally closed but start to open due to increased pressure
  • semi-lunar valves closed
• 2nd stage of the cardiac cycle - atriasystole

  • atria muscular walls contract, increasing pressure & causes atrioventricular valves to open & blood to flow into ventricles
  • ventricular muscular walls are relaxed
  • pressure decreases in atria due to small volume of blood
  • pressure in ventricles increases due to increasing volume of blood
  • semi-lunar valves closed
• 3rd stage of the cardiac cycle - ventricular systole

  • ventricular muscular contracts, increasing pressure beyond atria & causes atrioventricular valves to close & semi-lunar valves open
  • blood is pushed into arteries
• how to calculate cardiac ouput

  heart rate x stroke volume
• what do arteries, arterioles & veins all have?

  • tough outer layer
  • muscle layer
  • elastic layer
  • narrow lumen (except veins which have the widest lumen)
  • no valves ( except veins)
• comparison of structure between arteries, arterioles & veins

  arteries

  • thick muscular layer
  • thickest elastic layer
  • no valves
  • narrow lumen
  • thickest tough outer layer

  arterioles

  • thickest muscular layer
  • thinner elastic layer
  • thick tough outer layer
  • no valves
  • narrow lumen

  veins

  • thin muscle
  • thin elastic layer
  • thin outer layer
  • valves
• arteries :

  • thick muscular layer - to constrict and dilate in order to control volume of blood
  • elastic tissues - maintains the pressure to ensure blood reaches extremities
  • no valves - blood is under high pressure from heart contractions
  • thickest outer layer - prevents vessel bursting
• arterioles:

  • thickest muscle layer - restrict blood flow into capillaries
  • thinner elastic layer - blood is at a lower pressure
  • no valves - blood is under high pressure from heart contractions
  • thick tough outer layer - prevents vessel from bursting
• veins:

  • thin muscle layer - no need to control blood flow to tissues
  • thin elastic layer & thin outer layer - low pressure
  • valves - prevent backflow of blood due to low pressure
• structure of capillaries:

  • lining layer - provides short diffusion pathway
  • narrow diameter - permeate all tissues
  • narrowest lumen - red blood cells touch the side of the lumen, decreasing diffusion distance
  • highly branched - provides large surface area
• what is tissue fluid?

  fluid containing glucose, water, oxygen, amino acids, ions & fatty acids which bathes the tissues
• formation of tissue fluid

  • capillaries have fermentations in the walls so that liquid & small molecules can be forced out
  • as blood enters capillaries from the arterioles, the small diameter results in a high hydrostatic pressure so water, glucose, amino acids, fatty acids, ions and oxygen are forced out & red blood cells, large proteins & platelets remains in the capillaries
• how is it reabsorbed?

  • large molecules remain in the capillaries & therefore creates a lowered water potential
  • towards the venule end of the capillaries, the hydrostatic pressure is lowered due to loss of liquid but water potential is still low
  • water then re-enters the capillaries via osmosis
• what role does the lymphatic vessel play in reabsorbing tissue fluid to the bloodstream?

  • not all liquid will be reabsorbed by osmosis, as equilibrium will be absorbed
  • the rest of the tissue fluid is absorbed into the lymphatic system & eventually drains back into the bloodstream near the heart
• what is transpiration?

  loss of water vapour from the stomata by evaporation
• 4 factors that affect rate of transpiration

  1. light intensity
  2. temperature
  3. humidity
  4. wind
• how does light intensity affect the rate of transpiration?

  • positive correlation - higher light intensity, faster rate of transpiration
  • more light causes more stomata to open = larger surface area for evaporation
• how does temperature affect the rate of transpiration?

  • positive correlation - higher the temperature, faster the rate of transpiration
  • more heat means more kinetic energy, faster moving molecules & so more evaporation
• how does humidity affect the rate of transpiration?

  • negative correlation - more humid the air surrounding the leaf, lower rate of transpiration
  • more water vapour in the air will make the water potential more positive outside the leaf, reducing water potential gradient
• how does wind affect the rate of transpiration?

  • positive correlation
  • more wind will blow away humid air containing water vapour, maintaining water potential gradient
• what is the cohesion-tension theory?

  • cohesion - water is dipolar molecule and this enables hydrogen bonds to form between slightly negative oxygen & slightly positive hydrogens of different water molecules - this creates cohesion between water molecules as they stick together to form a continous column of water in the xylem
  • capillarity adhesion - water sticks to the xylem walls - the narrower the xylem, the bigger the impact
  • root pressure - as water moves into the roots by osmosis, it increases the volume of liquid inside the root therefore the pressure inside the root increases & forces water above it upwards
• how does water move up the xylem?

  1. water vapour evaporates out of the stomata on leaves & this creates a lower pressure
  2. when water is lost by transpiration more water is pulled up the xylem to replace it
  3. due to the hydrogen bonds between water molecules, they are cohesive & creates a column of water within the xylem
  4. water molecules also adhere to the walls of the xylem & this helps to pull the water column upwards
  5. as this column of water is pulled up the xylem it creates tension, pulling xylem in to become narrower
• what does the phloem transport in plants?

  sugars
• what does the phloem tissue contain?

  1. sieve tube elements
  2. companion cells