Under normal conditions, hemoglobin is 100% saturated with oxygen when the blood leaves the pulmonary capillaries, and the end-capillary Po2 equals alveolar Po2. However, the blood that leaves the lungs (via the pulmonary veins) and returns to the left side of the heart has a lower Po2 than pulmonary end-capillary blood. As a result, the systemic arterial blood has an average oxygen tension (Pao2) of about 95 mm Hg and is only 98% saturated.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.