RESP- Gas Exchange in the Lung

Question 1

give a basic outline of how oxygen goes from the atmosphere into the blood stream

Answer 1

oxygen enters alveolar airspace from the atmosphere

oxygen dissolves in the alveolar lining fluid

oxygen diffuses through alveolar epithelium basement membrane and capillary endothelial cells

oxygen dissolves in blood plasma

oxygen binds to haemoglobin

Question 2

what is gas exchange

Answer 2

diffusion of gases between air and blood

Question 3

what factors achieve maximum diffusion at gas exchange surfaces

Answer 3

increased partial pressure gradient, increased surface area, decreased barrier thickness

Question 4

name some defects in diffusion at gas exchange surfaces

Answer 4

hypoventilation (type II respiratory failure)
emphysema - decrease in surface area
fibrosis = increase in basement barrier thickness

Question 5

what are the adaptations of the alveoli which allow them to maximise the rate of gas exchange

Answer 5

large surface area (high surface area to volume ratio)
wall = 1 cell thick
basement membrane is fused to blood vessels
richly innervated by capillaries (adequate blood supply)

Question 6

what is v/q coupling

Answer 6

efficient gas exchange requires matching of ventilation (v) to perfusion (q)

Question 7

what is the ideal VQ ratio

Answer 7

<1 = hypoperfusion (Dead space effect)
=1 = normal
<1 = hypoventilation (shunt)

Question 8

what homeostatic mechanism exists to reduce ventilation-perfusion mismatching?

Answer 8

hypoxic vasoconstriction of capillaries

diverts blood flow from poor to well ventilated alveoli

Question 9

how is the hypoxic constriction of blood vessels activated

Answer 9

if ventilation of specific alveoli decreases
partial pressure of carbon dioxide will rise and partial pressure of oxygen will fall

a decrease in the oxygenation of blood flowing through capillaries = a decrease in pp of oxygen

this induces vasoconstriction

Question 10

why does V/Q mismatch not seem to affect pp of co2

Answer 10

V/Q mismatch affects both oxygen and carbon dioxide exchange however in most cases increased pp of CO2 will induce reflex hyperventilation which will clear the excess CO2 but does not increase the pp of oxygen

Question 11

how does a pulmonary embolism affect ventilation-perfusion

Answer 11

an embolism occludes a pulmonary artery supplying a region of the lung

after the blockage, this has created un-perfused alveoli

perfusion increases to the alveoli before the blockage as cardiac output is diverted

unless ventilation of these alveoli can increase to keep up with perfusion, hypoxaemia and hypercapnia will occur

Question 12

what V/Q inequality is physiological dead space

Answer 12

ventilation without perfusion
reduced perfusion of lung regions due to

heart failure, blocked vessels, loss / damage to capillaries

Question 13

what V/Q inequality is shunt

Answer 13

perfusion without ventilation

cardiac shunt - blood from the right side of the heart is transported to the left without taking part in gas exchange

pneumonia, acute lung injury, respiratory distress syndrome, atelectasis

Question 14

what would be the result of pneumothorax of the left lung

Answer 14

there would be increased ventilation of the functional alveoli of the right lung which would take a higher proportion of the blood supply in an attempt to increase perfusion (due to hypoxia induced vasoconstriction of the blood vessels in the left lung)