gas exchange and transport Flashcards
Once air enters lungs how does O2 enter bloodstream & CO2 leave?
Gas exchange at the respiratory membrane
describe the respiratory membrane layers
= 6 thin layers between alveolus & capillary
name the 6 diff layers of the respiratory membrane
- fluid and surfactant layer
- alveolar epithelium
- epithelial basement membrane
- interstitial space
- capillary basement membrane
- capillary endothelium
Respiratory Membrane is efficient because of:
- Substantial differences in partial pressures across respiratory membrane
- which leads to fast rate of gas diffusion - . Small distances involved in gas exchange
- Gases are lipid soluble
- Total surface area large
what is Partial pressure (Px)
pressure exerted by each gasx type in a mixture
explain daltons law
Px = % gasx times total pressure
So, gas moves from high Px to low Px
explain the movement of gasses due to Px
Usually PO2 alveolar > blood
Whereas PCO2 blood > alveolar
this indicates that gas is moving from one tissue to another.
Why feel lightheaded at high altitude?
Less O2 in alveoli, so ….
Slower diffusion into blood.
explain the effect of high altitude (in terms of a water bottle filled w air)
LHS bottle filled at high altitude (so low pressure of air inside bottle)
Taken to sea level, bottle flattens as higher pressure outside bottle than inside (RHS).
explain the process of internal and external respiration
external = pulmonary gas exchange
internal = systemic gas exchange
external:
on inhale oxygen is taken into alveoli then along pulmonary capillaries to left atrium. then….
internal:
….. oxygen goes along systemic capillaries to systemic tissue cells. carbon dioxide then exits the systemic tissue cells and transports along systemic capillaries to the right atrium and then to the lung and out via the alveoli into the atmosphere
explain how Respiratory Membrane is efficient because of: Small distances involved in gas exchange
Thickness of Respiratory Membrane?
= 0.5mm
Decreased efficiency
if fluid builds up, as in
tuberculosis or
pneumonia
(RBC diameter = 6-8um)
explain how Respiratory Membrane is efficient because of: Gases being lipid soluble
O2 & CO2 readily diffuse through surfactant layer & alveolar & endothelial cell membrane
explain how Respiratory Membrane is efficient because of: Total surface area being large
Respiratory membrane s.a. ~70m2
= half singles tennis court.
How are O2 & CO2 transported in the blood?
O2 & CO2 have limited solubilities in blood plasma
Problem solved by red blood cells (RBC) as :
- bind O2
- use CO2 to manufacture soluble compounds
(these are both temporary effects and completely reversible)
explain the gas diffusion into blood (such as why it happens)
Because these reactions in RBC remove dissolved gas from the plasma, gas will continue to diffuse into blood but never reach equilbrium
explain oxygen transport
O2 bound to iron ions in centre of each haem unit in a Hb molecule
4 haem units per Hb so 4x O2 per Hb molecule
~280 million Hb in each RBC
Each RBC potentially carry >billion O2 molecules
in tissue spaces, oxygen diffuses what direction from Hb and what happens to it
away from Hb and enters tissues
name 4 factors that influence the degree to which oxygen binds to Hb
P02
- oxygen-haemoglobin dissociation/saturation curve describes %Hb saturated at any PO2
blood PH
- Bohr effect
temperature
ongoing metabolic activity within RBC
explain how Po2 influence the degree to which O2 binds to Hb
Curve (cf. straight line) as once bound, easier to bind 2nd molecule
- Easier to bind 2nd molecule of O2 due to shape change after 1st O2 bound. If CO is just 0.1% of air, enough Hb affected to die if not receive medical assistance; treat with pure O2 or transfuse with compatible RBC.
Carbon monoxide poisoning occurs as CO binds to Hb 200x stronger than O2
Lethal % CO level in air = 0.1%
explain the O2-Haemoglobin Dissociation curve
If curve shifts to right, O2 released to tissues
in the dissociation curve O2 released to tissues with…
Increasing temperature
Decreasing pH (more acidic)
when do tight binding structure occur and what do they do
DPG = (di/biphosphoglycerate)
When 2,3-DPG binds to the Hb, the O2 is released
what does a left shift curve mean and why
increased uptake of O2 in lungs
As Hb has increased ability to pick up O2
explain Blood pH, Bohr effect
factors at influencing the degree to which oxygen binds to Hb
H+ binds to protein part of Hb
which affects shape of Hb
which affects amount of O2 carried
(Active tissue generates acid therefore decrease in pH therefore O2 released to tissues, where needed. Bohr effect (named after Danish physiologist Christian Bohr), is that Hb 2 binding affinity inversely proportional to acidity & CO2 concentration)
explain how temperature influences the degree to which oxygen binds to Hb
As temperature rises, Hb releases more O2
So, as active muscles generate heat, the warmed blood releases more O2
To be used by the active muscle cells
explain how ongoing metabolic activity within RBC influences the degree to which oxygen binds to Hb
2,3-biphosphoglycerate (BPG) produced during glycolysis (breakdown of glucose to produce ATP) increases release of O2
name some Physiological adaptations to high altitude:
Increased respiratory rate
Increased heart rate
Elevated haematocrit
- % blood volume occupied by RBC
Can use centrifuge tubes to collect blood, or microcapillary tubes; both are spun in a centrifuge (adapted if using capillary tubes) where RBC sediment to base of tube.
explain Haematocrit performed in microcapillary tubes
Can use centrifuge tubes to collect blood, or microcapillary tubes; both are spun in a centrifuge (adapted if using capillary tubes) where RBC sediment to base of tube.
name the 3 main forms for co2 transport
Dissolved CO2 in plasma
Bound to protein portion of Hb (carbamino compounds)
Bicarbonate ions (HCO3-) [most H+ bind to Hb, acting as buffers, before affect plasma pH]
explain CO2 transport in blood
Dissolved CO2 in plasma
Carbamino compounds (bound to protein of Hb)
Bicarbonate ions (HCO3-) in plasma (after CO2 + H2O with carbonic anhydrase forms carbonic acid [H2CO3], dissociating to HCO3-, leaving RBC as Cl- enters.
explain the % of oxygen and CO2 thats physically dissolved in blood
1.5% oxygen
10% co2
explain the % of oxygen and CO2 thats bound to Hb in blood
98.5% oxygen
30% co2
explain the % of oxygen and CO2 thats bound by carbonate (HC03) in blood
none oxygen
60% CO2
whats the main form of transport for oxygen
bound to Hb in blood
whats the main form of transport for co2
as bicarbonate (HCO3)
