Gas exchange

Question 1

Why is pressure used to measure amount of gas present?

Answer 1

Gasses act more in accordance with their pressure than with their conc

Question 2

Perecentages of gasses in air?

Answer 2

78% nitrogen
21% oxygen
1% other gasses

Question 3

How can the partial pressure for gas phases be calculated?

Answer 3

Substraction of water vapour pressure from total pressure
Then multiplication by gas individual mole fraction

Pgas= (Pbarometric - P H20 ) x mole fraction

Question 4

Equation linking partial pressure and solubility?

Answer 4

Concentration = Partial pressure x Solubility

Question 5

What are the layers between the alveoli and the capillaries that air has to travel through?

Answer 5

Alveolar lining fluid
Alveolar epithelial layer
Basement membrane
Capillary endothelial layer

Question 6

Describe the process of O2 reaching Hb from alveolar airspace

Answer 6

O2 dissolves in ALF
Diffuses through alveolar epithelium, basement membrane and capillary endothelial cells
O2 dissolves in blood plasma
O2 binds to Hb molecule

Question 7

Rate of difussion is directly proportional tooooo?

Answer 7

Surface area/distance^2 X (Pa-Pc)

Question 8

What is the dead space effect?

Question 9

What is the v/q ratio?

Answer 9

Ventilation/perfusion ratio

Question 10

What will happen if perfusion is reduced relative to ventilation?

Answer 10

V/Q ratio will increase (V/Q >1)

inspired oxygen will in effect be ‘wasted’ and not participate in gas exchange.

Question 11

List some causes for decreased perfusion with the same ventilation rate

Answer 11

pulmonary embolism, damage/blockade of blood vessels

Question 12

Why might a pulmonary embolism not affect perfusion rate

Answer 12

blood is simply diverted through other pulmonary arteries/capillaries. In theory, increased ventilation of these areas of the lungs may compensate for the reduction in gas exchange in others. Otherwise, hypoxaemia and hypercapnia5 (increased PaCO2) will occur.

Question 13

What is hypoxic vasoconstriction?

Answer 13

occurs when ventilation to an alveoli is reduced; the decreased ventilation results in rising CO2and falling O2levels, which cause contraction of the vascular smooth muscle within nearby capillaries. The constriction of these blood vessels diverts blood to other capillaries that innervate better-ventilated alveoli.

Question 14

What is a pulmonary shunt

Answer 14

Reduced ventilation of alveoli
decrease in V/Q ratio
deoxygenated blood returns to the left side of the heart from the right, without taking part in gas exchange.