Page 33, CV Review, Essentials, Develop. Physiol., Dr. D. Penney


Cardiac Cycle (cont...)

Normal blood pressure and oxygen saturation values in the central circulation are important and should be committed to memory (Figure 1.15). In the atria, blood pressure is low, but slightly higher in the left (7 mmHg) than in the right (5 mmHg) atrium. As discussed earlier, systolic pressures are 3-4 fold higher in left (110 mmHg) than in right (25 mmHg) ventricle, and systolic and diastolic pressures are comparably higher in the aorta (110/70 mmHg) than in the pulmonary artery (25/10 mmHg).

Blood entering the right atrium and right ventricle, that is, venous blood, is approximately 75% saturated. Following passage through the pulmonary circuit where oxygen is taken up by erythrocytes containing hemoglobin, the blood becomes 95-98% saturated - it is now "arterialized". Oxygen saturation remains as such in the left atrium, left ventricle, and aorta. Small differences in saturation between the pulmonary capillary and aortic blood are due to shunting, involving some admixture of less saturated blood in the lung.

Animated cardiac cycle cartoons are also available.


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