Gas exchange in thelungs

Question 1

How to calculate total pressure of a mixutre of gases

Answer 1

P(Total) = P(H2O) + (sum)P(constituent gases)

where P = pressure

Question 2

How to calculate partial pressures of individual gases

Answer 2

P(gas) = (P(barometric) - P(H2O)) x n (gas)

P (Gas) = partial pressure of individual gas
P (barometric) = atmospheric pressure
P(h2o) = Water vapour pressure

Question 3

What determines the concentration of an individual gas dissolved in a liquid

Answer 3

Partial pressure and solubility of the gas

Question 4

Describe features of the alveoli

Answer 4

Large surface area
Thin outer structure (one cell thick)
Richly innervated by capillaries, which help to maximise the rate of diffusion

Question 5

What is rate of diffusion determined by

Answer 5

Partial pressure gradient between the two areas, size of the diffusion distance, and the surface area

Question 6

Conditions for maximum diffusion

Answer 6

Increased partial pressure gradient
Increased surface area
Decreased barrier thickness

Question 7

How may some diseases affect diffusion

Answer 7

Hypoventilation and hypoperfusion decrease alveolar pressure gradient and capillary pressure gradient

Emphysema decreases surface area

Fibrosis increases membrane thickness
Pulmonary oedema increases thickness of fluid layer/oedema

Question 8

How is efficient gas exchange ensured

Answer 8

Sufficient haemoglobin binding sites to absorb the quantity of oxygen arriving at the alveoli, so level of ventilation and perfusion must match

Question 9

What is the V/Q ratio

Answer 9

Ratio of ventilation to perfusion

Question 10

What happens if the V/Q ratio is reduced

Answer 10

Inspired oxygen will in effect be wasted and not participate in gas exchange

Question 11

What are the regions of the lungs being affected by reduced V/Q called

Answer 11

Physiologic dead-space

Question 12

What is a pulmonary embolism

Answer 12

Block of an artery in the lungs

Question 13

Why may a pulmonary embolism not affect perfusion in the lungs

Answer 13

Because the blood is diverted through other pulmonary arteries/capillaries

Question 14

What is hypoxaemia and hypercapnia

Answer 14

Increased PaCO2

Question 15

What is pulmonary shunt

Answer 15

Reduced ventilation of alveoli or limits to diffusion, resulting in a decrease in V/Q ratio

Deoxygenated blood returns to the left side of the heart from the right without taking part in gas exchange

Question 16

What is hypoxic vasoconstriction

Answer 16

When ventilation to an alveoli is reduced, the decreased ventilation results in rising CO2 and falling O2 levels, causing contraction of the vascular smooth muscle within nearby capillaries. Constriction diverts blood to other capillaries that innervate better-ventilated alveoli