diffusion of gases Flashcards
what is Dalton’s law?
- the pressure of a gas is equal to the sum of the pressures of the indivual gases
what is the atmospheric pressure?
- 760mmHg
what is the percentage and partial pressure of nitrogen?
- 78.1%
- 594mmHg
what is the percentage and partial pressure of oxygen?
- 20.9 %
- 159mmHg
what is the percentage and partial pressure of carbon dioxide?
- 0.037%
- 0.25mmHg
does percentage or partial pressure remain the same?
- percentage always remains the same whereas partial pressure can change
describe air in the lungs in relation to water vapour
- fully saturated with water vapour (100% humidity)
- partial pressure of 46mmHg
describe the thickness of the diffusion barrier
- 2 cell thick
- 0.1-1.5 um
- alveolar wall and vascular wall
describe passage of oxygen once it enters the alveoli
- enters alveoli> dissolves in surfactant> crosses alveoli epithelium> fused basement membranes> vascular endothelium> attach to haemoglobin
what is fick’s law of diffusion?
rate of diffusion proportional to (area/ thickness) x (P1-P2) x solubility
how does pressure difference and solubility affect the speed of diffusion?
- greater pressure difference, the faster
- greater the solubility, the faster
does 02 or C02 diffuse quicker?
- C02 diffuses quicker as it is more soluble
what is the gas partial pressure in solution?
- gas and liquid molecules move between air and liquid to achieve equilibrium of PP
what does movement of molecules depend on? (three things)
- temperature
- pressure difference
- solubility
why is the rate of diffusion important- why does it need to be fast enough?
- fast enough so that gases in alveoli and blood equilibrate during passage of blood across an alveolus
when is equilibrium at rest complete? compared to exercise?
- complete at 1/3 of the time blood spends near alveolar air
- less time during exercise
what can diffusion rate affect and limit?
- affects arterial 02 content
- limits functional capacity
what is emphysema?
- limited surface area and poor elastic recoil
what is fibrotic lung disease?
- thick barrier and less lung compliance (expandability)
what is pulmonary oedema caused by?
- pressure changes in capillaries
what is asthma?
- poor ventilation due to constricted airways
what is the law of mass action?
- when a reaction is at equilibrium, the ratio of substrates and products will remain constant
what is the rate of forward and backward reaction at equilibrium?
- reactions are the same
what happens if equilibrium is disturbed?
- rate changes
why is dissolved oxygen not enough? compare this to resting rate of 02 consumption
- around 3ml/l so could only supply tissues with 15ml/ min at a cardiac output of 5l/min
- 02 consumption is 250ml/ min
what is oxygen carried by?
- haemoglobin; forms oxyhaemoglobin
- contains 4 globin’s and 4 haem groups
what is haemoglobin?
- oxygen binding protein contained within red blood cells
what do the haem groups contain?
- ferrous atom in centre of each haem (02 binds to Fe2+ )
how does haemoglobin establish pp02 difference between blood and alveoli?
- acts to steal oxygen from blood to create a gradient
- only stops when fully saturated
does 02 bound to haemoglobin influence partial pressure?
- it doesn’t contribute to the PP as it maintains a pressure difference causing more oxygen to diffuse across
how much oxygen is carried around?
- 200ml02l/ blood
what is anaemia- how much oxygen would be carried around?
- lack of red blood cells
- would only carry 121ml 02l/min
what are the two factors that determine how much oxygen is carried?
- partial pressure of 02 driving 02 into the blood
- amount of haemoglobin in the blood
what is the oxyhaemoglobin dissociation curve?
- describes relationship between partial pressure of oxygen and saturation of haemoglobin
what is the shape of the dissociation curve- explain
- sigmoid shape
- flat part at high partial pressure and steep part at low partial pressure
- saturation drops at higher altitude
what happens to the release of oxygen in tissues at different pp02?
- sensitive at low pp02 (off-loading)
- 02 not affected at high pp02(loading)
what does a shift to the left mean?
- increased saturation for given pp02
- improved loading but prevents unloading
what does a shift to the right mean?
- less saturation for given pp02
- known as bohr shift
- unloads easily but hard to load
what three factors affect 02 binding to haemoglobin?
- activity
- effect of DPG
- temperature
- volume of C02/ pH
how does activity affect 02 binding to haemoglobin?
- low pH causes a right shift
- high pH causes a left shift
how does diphosphoglycerate affect 02 binding to haemoglobin?
- added DPG causes a right shift
- no DPG causes a left shift
how does temperature affect 02 binding to Hb?
- high temperature causes right shift
- low temperature causes left shift
how much C02 is dissolved in plasma and why?
- around 27ml/L (7 %)
- as more soluble so more dissolved
how else is C02 carried in blood?
- 70% of C02 carried in form of bicarbonate ions
what is the equation for bicarbonate ions?
C02 + H20 > H2C03 > H+ + HC03-
what enzyme works to convert carbon dioxide and water into carbonic acid?
- carbonic anhydrase
how much C02 is bound to Hb?
- 23% bound
- Hb + C02 = carbaminohaemoglobin
what is the relationship between H+ ions and haemoglobin?
- haemoglobin binds the H+ ions that are released from reaction of C02 + H20
what does Hb binding the H+ ions prevent?
- acidosis = to much acid in bodily fluids
what does more carbon dioxide result in?
- more hydrogen ions
- more acidic
