Gas Exchange In The Lung

Question 1

How is partial pressure calculated?

Answer 1

Multiplying total pressure by mole fraction

Question 2

What is concentration of a gas dissolved within a liquid determined by?

Answer 2

Partial pressure and solubility of a gas

Question 3

What does partial pressure of a gas dissolved in a liquid mean?

Answer 3

The amount of gas that would dissolve at equilibrium if the liquid was placed in contact with a gas phase of equivalent partial pressure

Question 4

What are the 5 steps in gas exchange?

Answer 4

1- o2 enters the alveolar airspace from the atmosphere
2- o2 dissolves in the alveolar lining fluid
3- o2 diffuses rough alveolar epithelium, basement membrane and capillary endothelial cells
4- o2 dissolves in blood plasma
5- o2 binds to Hb molecule

Question 5

What is gas exchange?

Answer 5

Diffusion of gases between air and blood

Question 6

What determines rate of diffusion in the lungs?

Answer 6

Alveolar surface area
Partial pressure gradient between alveolar air and capillary blood
Epithelial and and endothelial cell thickness and basement membrane thickness and fluid layer depth

Question 7

What features do you want for maximum diffusion?

Answer 7

Inc partial pressure gradient
Inc surface area
Dec distance

Question 8

What happens if you have a low partial pressure gradient in the lungs?

Answer 8

Hypoventilation (type 2 respiratory failure)

Question 9

What happens if you have a decreased surface area in the alveoli?

Answer 9

Emphysema

Question 10

What is an increased basement membrane thickness called?

Answer 10

Fibrosis

Question 11

What is VQ coupling?

Answer 11

Matching of ventilation to perfusion

Question 12

What is the ideal VQ ratio?

Answer 12

1

Question 13

What happens if the VQ ratio is more than 1?

Answer 13

Hypoperfusion (dead space effect)

Question 14

What happens if the VQ ratio is less than 1?

Answer 14

Hypoventilation (shunt)

Question 15

What is VQ coupling maintained by?

Answer 15

Hypoxic vasoconstriction

Question 16

What is hypoxic vasoconstriction?

Answer 16

Homeostatic mechanisms exist to reduce ventilation so there isn’t perfusion mismatching

Hypoxic vasoconstriction of capillary diverts blood flow from poor to well ventilated alveoli

Question 17

What happens if the ventilation of specific alveoli decreases?

Answer 17

Partial pressure of CO2 will rise and O2 will fall

Leads to decreased oxygenation of blood flowing through innervating capillaries

Question 18

What happens when ventilation and perfusion to alveolar units are not matched?

Answer 18

Gas exchange is reduced

Question 19

What happens in most cases when CO2 partial pressure increases?

Answer 19

Reflex hyperventilation that clears the excess CO2 but doesnt increase o2 partial pressures

Question 20

What happens when an embolism blocks the pulmonary artery supplying a region of the lung?

Answer 20

Perfusion to the other alveoli increases as cardiac output is diverted

Unless ventilation of alveoli is increased, hypoxia and hypercapnia will occur

Question 21

What causes reduced perfusion to the lungs?

Answer 21

Heart failure
Blocked vessels
Loss/damage to capillaries

Question 22

What is physiologic dead space?

Answer 22

Ventilates alveoli that aren’t perfused

Question 23

Does oxygen help with the dead space effect?

Answer 23

Yes

Question 24

What is a shunt in the lungs?

Answer 24

Perfusion without ventilation

Question 25

What causes a shunt In the lungs?

Answer 25

Cardiac shunts

Pneumonia, acute lung injury, RDS, atelactasis

Question 26

What does reduced ventilation do to the VQ ratio?

Answer 26

Decrease it

Question 27

Does O2 therapy help when there’s a lung shunt?

Answer 27

Not really