blood supply, gas exchange, ventilation and perfusion Flashcards
where is the largest change in volume of the lungs when intrapleural pressure is changed?
the base
what are the bronchial arteries?
arteries branching from the systemic circulation that provide nutritive circulation to the lungs, bronchial circulation
what is the pulmonary system in terms of flow and pressure?
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.
what can the partial pressure of gases in the arterial system tell us about partial pressures elsewhere in the body?
it will tell us the partial pressures of gas in the alveoli
what can the partial pressure of gases in the venous system tell us about partial pressures elsewhere in the body?
it will tell us the partial pressures of gas in cells
what is the partial pressure of oxygen in the alveoli and arterial system?
100 mmHg
13.3 kPa
what is the partial pressure of oxygen in the venous system and tissues?
40mmHg
5.3kPa
what is the partial pressure of carbon dioxide in the alveoli and the arterial system?
40mmHg
5.3 kPa
what is the partial pressure of carbon dioxide in the venous system and tissues?
46 mmHg
6.2 KPa
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?
oxygen has a lower solubility in water than carbon dioxide
what are the factors that affect diffusion rate?
- partial pressure gradient (directly proportional)
- gas solubility (directly proportional)
- available surface area (directly proportional)
- thickness of membrane (inversely proportional)
- most rapid over short distances
how does the body maximise the efficiency of gas exchange?
-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
how does emphysema affect gas exchange?
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
how does fibrotic lung disease affect gas exchange?
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
how does pulmonary oedema affect gas exchange?
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
how does asthma affectgas exchange?
increased resistance in airway ventilation mean PP of oxygen is low in alveoli and arteries.
what is the most common cause of emphysema?
smoking, increased levels of elastase so elastic fibres are broken down
what ideally should the relationship be between ventilation and perfusion? but is this possible at all points in the lung?
complimentary, this is not always possible because blood and alveolar pressure vary between the top and bottom of the lungs.
how does blood flow vary between the base and apex of the long?
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.
what is the ventilation perfusion ratio?
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.
what is shunt?
blood the flows through a poorly ventilated area without being oxygenated.
what is the body’s response to shunt?
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.
what is alveolar dead space?
when ventilation is greater than blood flow
what is the body’s response to alveolar dead space?
an increase in alveolar oxygen PP causes pulmonary vasodilation.
a decrease in alveolar carbon dioxide PP causes bronchial constriction.
what is physiological dead space?
anatomical dead space + alveolar dead space
why is the circulation in the lungs susceptible to the effects of gravity?
it is a low pressure circuit
what is the pulmonary arterial pressure ?
systolic P~25 mmHg, diastolic P~8 mmHg
