diffusion of gases

Question 1

what is Dalton’s law?

Answer 1

• the pressure of a gas is equal to the sum of the pressures of the indivual gases

Question 2

what is the atmospheric pressure?

Answer 2

• 760mmHg

Question 3

what is the percentage and partial pressure of nitrogen?

Answer 3

• 78.1%
• 594mmHg

Question 4

what is the percentage and partial pressure of oxygen?

Answer 4

• 20.9 %
• 159mmHg

Question 5

what is the percentage and partial pressure of carbon dioxide?

Answer 5

• 0.037%
• 0.25mmHg

Question 6

does percentage or partial pressure remain the same?

Answer 6

• percentage always remains the same whereas partial pressure can change

Question 7

describe air in the lungs in relation to water vapour

Answer 7

• fully saturated with water vapour (100% humidity)
• partial pressure of 46mmHg

Question 8

describe the thickness of the diffusion barrier

Answer 8

• 2 cell thick
• 0.1-1.5 um
• alveolar wall and vascular wall

Question 9

describe passage of oxygen once it enters the alveoli

Answer 9

• enters alveoli> dissolves in surfactant> crosses alveoli epithelium> fused basement membranes> vascular endothelium> attach to haemoglobin

Question 10

what is fick’s law of diffusion?

Answer 10

rate of diffusion proportional to (area/ thickness) x (P1-P2) x solubility

Question 11

how does pressure difference and solubility affect the speed of diffusion?

Answer 11

• greater pressure difference, the faster
• greater the solubility, the faster

Question 12

does 02 or C02 diffuse quicker?

Answer 12

• C02 diffuses quicker as it is more soluble

Question 13

what is the gas partial pressure in solution?

Answer 13

• gas and liquid molecules move between air and liquid to achieve equilibrium of PP

Question 14

what does movement of molecules depend on? (three things)

Answer 14

• temperature
• pressure difference
• solubility

Question 15

why is the rate of diffusion important- why does it need to be fast enough?

Answer 15

• fast enough so that gases in alveoli and blood equilibrate during passage of blood across an alveolus

Question 16

when is equilibrium at rest complete? compared to exercise?

Answer 16

• complete at 1/3 of the time blood spends near alveolar air
• less time during exercise

Question 17

what can diffusion rate affect and limit?

Answer 17

• affects arterial 02 content
• limits functional capacity

Question 18

what is emphysema?

Answer 18

• limited surface area and poor elastic recoil

Question 19

what is fibrotic lung disease?

Answer 19

• thick barrier and less lung compliance (expandability)

Question 20

what is pulmonary oedema caused by?

Answer 20

• pressure changes in capillaries

Question 21

what is asthma?

Answer 21

• poor ventilation due to constricted airways

Question 22

what is the law of mass action?

Answer 22

• when a reaction is at equilibrium, the ratio of substrates and products will remain constant

Question 23

what is the rate of forward and backward reaction at equilibrium?

Answer 23

• reactions are the same

Question 24

what happens if equilibrium is disturbed?

Answer 24

• rate changes

Question 25

why is dissolved oxygen not enough? compare this to resting rate of 02 consumption

Answer 25

- around 3ml/l so could only supply tissues with 15ml/ min at a cardiac output of 5l/min - 02 consumption is 250ml/ min

Question 26

what is oxygen carried by?

Answer 26

- haemoglobin; forms oxyhaemoglobin - contains 4 globin's and 4 haem groups

Question 27

what is haemoglobin?

Answer 27

- oxygen binding protein contained within red blood cells

Question 28

what do the haem groups contain?

Answer 28

- ferrous atom in centre of each haem (02 binds to Fe2+ )

Question 29

how does haemoglobin establish pp02 difference between blood and alveoli?

Answer 29

- acts to steal oxygen from blood to create a gradient - only stops when fully saturated

Question 30

does 02 bound to haemoglobin influence partial pressure?

Answer 30

- it doesn't contribute to the PP as it maintains a pressure difference causing more oxygen to diffuse across

Question 31

how much oxygen is carried around?

Answer 31

- 200ml02l/ blood

Question 32

what is anaemia- how much oxygen would be carried around?

Answer 32

- lack of red blood cells - would only carry 121ml 02l/min

Question 33

what are the two factors that determine how much oxygen is carried?

Answer 33

- partial pressure of 02 driving 02 into the blood - amount of haemoglobin in the blood

Question 34

what is the oxyhaemoglobin dissociation curve?

Answer 34

- describes relationship between partial pressure of oxygen and saturation of haemoglobin

Question 35

what is the shape of the dissociation curve- explain

Answer 35

- sigmoid shape - flat part at high partial pressure and steep part at low partial pressure - saturation drops at higher altitude

Question 36

what happens to the release of oxygen in tissues at different pp02?

Answer 36

- sensitive at low pp02 (off-loading) - 02 not affected at high pp02(loading)

Question 37

what does a shift to the left mean?

Answer 37

- increased saturation for given pp02 - improved loading but prevents unloading

Question 38

what does a shift to the right mean?

Answer 38

- less saturation for given pp02 - known as bohr shift - unloads easily but hard to load

Question 39

what three factors affect 02 binding to haemoglobin?

Answer 39

- activity - effect of DPG - temperature - volume of C02/ pH

Question 40

how does activity affect 02 binding to haemoglobin?

Answer 40

- low pH causes a right shift - high pH causes a left shift

Question 41

how does diphosphoglycerate affect 02 binding to haemoglobin?

Answer 41

- added DPG causes a right shift - no DPG causes a left shift

Question 42

how does temperature affect 02 binding to Hb?

Answer 42

- high temperature causes right shift - low temperature causes left shift

Question 43

how much C02 is dissolved in plasma and why?

Answer 43

- around 27ml/L (7 %) - as more soluble so more dissolved

Question 44

how else is C02 carried in blood?

Answer 44

- 70% of C02 carried in form of bicarbonate ions

Question 45

what is the equation for bicarbonate ions?

Answer 45

C02 + H20 > H2C03 > H+ + HC03-

Question 46

what enzyme works to convert carbon dioxide and water into carbonic acid?

Answer 46

- carbonic anhydrase

Question 47

how much C02 is bound to Hb?

Answer 47

- 23% bound - Hb + C02 = carbaminohaemoglobin

Question 48

what is the relationship between H+ ions and haemoglobin?

Answer 48

- haemoglobin binds the H+ ions that are released from reaction of C02 + H20

Question 49

what does Hb binding the H+ ions prevent?

Answer 49

- acidosis = to much acid in bodily fluids

Question 50

what does more carbon dioxide result in?

Answer 50

- more hydrogen ions - more acidic