1-10. MOVEMENT OF BLOOD
a. The veins of the systemic blood circulatory system bring oxygen-poor blood
from all parts of the body to the right atrium of the heart. From the right atrium, the
blood flows into the right ventricle of the heart. Upon contraction of the right ventricle,
blood is forced into the pulmonary arch. The pulmonary arch divides into the right and
left pulmonary arteries that delivers the oxygen-poor blood to their respective lungs.
Paralleling the branching of the respiratory tree, the arteries divide and subdivide within
the lungs. These arteries lead to capillaries that surround the alveoli. The walls of
these capillaries are thin enough to accommodate the passage of gases to and from the
alveolus. The oxygen-poor blood gives up the carbon dioxide which it has been
carrying and absorbs oxygen from the alveolus. Just as oxygen travels from the
alveolus to the capillary, carbon dioxide travels from the capillary to the alveolus.
b. The blood, now saturated with oxygen, is collected by the pulmonary venous
system. The blood flows through the pulmonary veins into the left atrium of the heart.
From the left atrium, it flows into the left ventricle. When the left ventricle contracts, the
oxygen-rich blood is forced into the aorta of the systemic blood circulatory system.
Other arteries branch off of this large artery and carry the oxygen-rich blood to all living
cells within the body. As the arteries continue to subdivide and get smaller, they
eventually reach the capillary stage. At this stage, oxygen moves from the blood into
the surrounding body cells and carbon dioxide, a waste material, travels from the body
cells to the blood. The blood then flows from the capillaries into veins and eventually
returns to the right atrium of the heart.
1-11. TRANSPORTATION OF GASES
Oxygen and carbon dioxide are the primary gases involved in respiration. Under
special circumstances, nitrogen may also be of concern. Some of the gases are
dissolved directly in the plasma of the blood. Most of the gasses, however, are carried
within the erythrocytes (red blood cells, commonly called RBCs). The RBCs, found in
great numbers in the blood, are specially constructed for transporting the gases.
Hemoglobin, a substance found within RBCs, has a great affinity for oxygen. Yet, the
hemoglobin can readily give up the oxygen wherever it is needed.