gas exchange in the lung

Question 1

how do you calculate partial pressure of an individual gas ?

Answer 1

Question 2

how does oxygen get from the alveolar air to the blood ?

Answer 2

Question 3

what determines the rate of diffusion ?

Answer 3

Question 4

what are some examples of defects in factors that determine rate of diffusion ?

Answer 4

Question 5

why do the levels of ventilation and perfusion(Q) need to be closely matched ?

Answer 5

• During gas exchange, oxygen diffuses into the plasma of blood flowing through capillaries before binding to haemoglobin.
• To ensure gas exchange takes place in an efficient manner, there must be sufficient blood (specifically haemoglobin binding sites) to absorb the quantity of oxygen arriving at the alveoli.
• Therefore the level of ventilation (supply of oxygen) and perfusion (supply of blood) need to be closely matched.

Question 6

how is ventilation perfusion coupling maintained ?

Answer 6

maintained via hypoxic pulmonary vasoconstriction

Question 7

what is a pulmonary embolism ?

Answer 7

• example of V/Q inequality

Question 8

what is physiological dead space ?

Answer 8

• If perfusion is reduced relative to ventilation, V/Q ratio will increase (V/Q >1) and the inspired oxygen will in effect be ‘wasted’ and not participate in gas exchange.
• This can occur due to reduced blood supply to specific regions of the lung (e.g. pulmonary embolism, damage/blockade of blood vessels).
• The affected regions of the lung are referred to as ‘physiologic dead-space’ as they are effectively not participating in gas exchange, despite the presence of O2, similar to the anatomic dead-space consisting of the airways).

Question 9

what is a pulmonary shunt ?

Answer 9

• another type of V/Q inequality
• occurs when blood bypasses the alveoli in the lungs without participating in gas exchange, leading to low oxygen levels in the blood (hypoxemia). This means deoxygenated blood returns to the systemic circulation without picking up oxygen from the lungs.
• it is resistant to supplemental oxygen therapy as in shunt there will always be a volume of relatively deoxygenated blood returning to the systemic circulation, for which additional ventilation of more functional parts of the lung cannot compensate