blood supply, gas exchange, ventilation and perfusion

Question 1

where is the largest change in volume of the lungs when intrapleural pressure is changed?

Answer 1

the base

Question 2

what are the bronchial arteries?

Answer 2

arteries branching from the systemic circulation that provide nutritive circulation to the lungs, bronchial circulation

Question 3

what is the pulmonary system in terms of flow and pressure?

Answer 3

it is a high flow, low pressure system.
high flow as all the blood in the body must pass through the lungs at the same rate as it travels round the systemic system. Low pressure to reduce resistance to flow.

Question 4

what can the partial pressure of gases in the arterial system tell us about partial pressures elsewhere in the body?

Answer 4

it will tell us the partial pressures of gas in the alveoli

Question 5

what can the partial pressure of gases in the venous system tell us about partial pressures elsewhere in the body?

Answer 5

it will tell us the partial pressures of gas in cells

Question 6

what is the partial pressure of oxygen in the alveoli and arterial system?

Answer 6

100 mmHg

13.3 kPa

Question 7

what is the partial pressure of oxygen in the venous system and tissues?

Answer 7

40mmHg

5.3kPa

Question 8

what is the partial pressure of carbon dioxide in the alveoli and the arterial system?

Answer 8

40mmHg

5.3 kPa

Question 9

what is the partial pressure of carbon dioxide in the venous system and tissues?

Answer 9

46 mmHg

6.2 KPa

Question 10

why is the rate of exchange of oxygen and carbon dioxide roughly the same even though the partial pressure gradient of oxygen is much greater?

Answer 10

oxygen has a lower solubility in water than carbon dioxide

Question 11

what are the factors that affect diffusion rate?

Answer 11

• partial pressure gradient (directly proportional)
• gas solubility (directly proportional)
• available surface area (directly proportional)
• thickness of membrane (inversely proportional)
• most rapid over short distances

Question 12

how does the body maximise the efficiency of gas exchange?

Answer 12

-capillaries are always adjacent to type I alveolar cells
and not beside type II.
-elastic fibres are not found between capillaries and alveolar walls
-alveoli have a large surface area
-alveoli have thin membranes

Question 13

how does emphysema affect gas exchange?

Answer 13

it causes the destruction of alveoli which reduces the area for gas exchange. this means that partial pressure in alveoli is normal or low and PP in arteries is low

Question 14

how does fibrotic lung disease affect gas exchange?

Answer 14

the alveolar membrane is thickened, this slows gas exchange, loss of compliance may decrease alveolar ventilation. PP of oxygen is normal or lower in alveoli and low in arteries

Question 15

how does pulmonary oedema affect gas exchange?

Answer 15

fluid in interstitial space increases diffusion distance. Arterial PP of carbon dioxide may be normal as it is has a higher degree of solubility in water. However PP of oxygen will be normal in alveoli but lower on arteries

Question 16

how does asthma affectgas exchange?

Answer 16

increased resistance in airway ventilation mean PP of oxygen is low in alveoli and arteries.

Question 17

what is the most common cause of emphysema?

Answer 17

smoking, increased levels of elastase so elastic fibres are broken down

Question 18

what ideally should the relationship be between ventilation and perfusion? but is this possible at all points in the lung?

Answer 18

complimentary, this is not always possible because blood and alveolar pressure vary between the top and bottom of the lungs.

Question 19

how does blood flow vary between the base and apex of the long?

Answer 19

blood flow is highest at the base of the lung and lowest at the apex. This is because arterial pressure exceeds alveolar pressure and vascular resistance is therefore low at the base. At the apex the opposite is true as alveolar pressure compresses the arterioles, increasing resistance.

Question 20

what is the ventilation perfusion ratio?

Answer 20

the ratio between ventilation and perfusion, ideally it should be 1. This occurs at rib 3 but above it increases and below it decreases, biggest mismatch at apex.

Question 21

what is shunt?

Answer 21

blood the flows through a poorly ventilated area without being oxygenated.

Question 22

what is the body’s response to shunt?

Answer 22

The body diverts blood from poorly ventilated areas to well ventilated regions, it does this by constricting vessels going past poorly ventilated areas in response to hyopxia and dilating airways in these regions in response to increased carbon dioxide PP.

Question 23

what is alveolar dead space?

Answer 23

when ventilation is greater than blood flow

Question 24

what is the body’s response to alveolar dead space?

Answer 24

an increase in alveolar oxygen PP causes pulmonary vasodilation.
a decrease in alveolar carbon dioxide PP causes bronchial constriction.

Question 25

what is physiological dead space?

Answer 25

anatomical dead space + alveolar dead space

Question 26

why is the circulation in the lungs susceptible to the effects of gravity?

Answer 26

it is a low pressure circuit

Question 27

what is the pulmonary arterial pressure ?

Answer 27

systolic P~25 mmHg, diastolic P~8 mmHg