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Oxygen content on leaving the tissue capillaries is still 24 volumes per cent (point B in the figure). At this point, the Po2 is approximately 1200 mm Hg, which means that oxygen is delivered to the tissues at this extremely high pressure instead of at the normal value of 40 mm Hg. Thus, once the alveolar Po2 rises above a critical level, the hemoglobin-oxygen buffer mechanism (discussed in Chapter 40) is no longer capable of keeping the tissue Po2 in the normal, safe range between 20 and 60 mm...

Weightlessness in Space

A person in an orbiting satellite or a nonpropelled spacecraft experiences weightlessness, or a state of near-zero G force, which is sometimes called micro-gravity. That is, the person is not drawn toward the bottom, sides, or top of the spacecraft but simply floats inside its chambers. The cause of this is not failure of gravity to pull on the body, because gravity from any nearby heavenly body is still active. However, the gravity acts on both the spacecraft and the person at the same time,...

Starling Equilibrium for Capillary Exchange

Starling pointed out over a century ago that under normal conditions, a state of near-equilibrium exists at the capillary membrane. That is, the amount of fluid filtering outward from the arterial ends of capillaries equals almost exactly the fluid returned to the circulation by absorption. The slight disequilibrium that does occur accounts for the small amount of fluid that is eventually returned by way of the lymphatics. The following chart shows the principles of the Starling...