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Firstly, as the air enters the lungs, it is humidified by the upper airway and thus the partial pressure of water vapour (47 mmHg) reduces the oxygen partial pressure to about 150 mmHg. The rest of the difference is due to the continual uptake of oxygen by the pulmonary capillaries , and the continual diffusion of CO 2 out of the capillaries ...
Capillary action of water (polar) compared to mercury (non-polar), in each case with respect to a polar surface such as glass (≡Si–OH). Capillary action (sometimes called capillarity, capillary motion, capillary rise, capillary effect, or wicking) is the process of a liquid flowing in a narrow space without the assistance of external forces like gravity.
It can be successfully applied to air flow in lung alveoli, or the flow through a drinking straw or through a hypodermic needle. It was experimentally derived independently by Jean Léonard Marie Poiseuille in 1838 [1] and Gotthilf Heinrich Ludwig Hagen, [2] and published by Hagen in 1839 [1] and then by Poiseuille in 1840–41 and 1846. [1]
Venous blood from the bronchi inside the lungs drains into the pulmonary veins and empties into the left atrium; since this blood never went through a capillary bed it was never oxygenated and so provides a small amount of shunted deoxygenated blood into the systemic circulation. [1] Infarction of the lung due to a pulmonary embolism
A pulmonary ventilation-perfusion scan (lung V/Q scan) can be used to diagnose the V/Q mismatch. A ventilation scan is used to measure airflow spread and a perfusion scan for blood flow distribution in the lungs. A radioactive tracer is used to scan the whole lung and the ventilation and perfusion function. [21]
At first there is no flow because of obstruction at the venous end of the capillary bed. Pressure from the arterial side builds up until it exceeds alveolar pressure and flow resumes. This dissipates the capillary pressure and returns to the start of the cycle. Flow here is sometimes compared to a starling resistor or waterfall effect.
When the heart rate increases and more blood must flow through the lungs, capillaries are recruited and are also distended to make room for increased blood flow. This allows blood flow to increase while resistance decreases. [citation needed] Extreme exercise can make capillaries vulnerable, with a breaking point similar to that of collagen. [23]
The bubbles which are small enough to pass through the lung capillaries may be small enough to be dissolved due to a combination of surface tension and diffusion to a lowered concentration in the surrounding blood, though the Varying Permeability Model nucleation theory implies that most bubbles passing through the pulmonary circulation will ...