The Pulmonary Circulation
The pulmonary circulation resembles the systemic circulation in many ways. It has arteries, capillaries, and veins. The right ventricle pumps deoxygenated blood containing carbon dioxide into the pulmonary artery. The pulmonary artery divides into smaller and smaller branches which end in the pulmonary capillaries. The pulmonary capillaries lie in the wall of the air sacs (alveoli) in the lungs. Here carbon dioxide is given up into the air and oxygen enters the blood. The oxygen rich blood returns to the heart by the pulmonary veins. The oxygenated blood is then pumped out by the heart into the systemic circulation.
Pulmonary Congestion and Edema
1. When the heart fails, blood accumulates in the left ventricle and thereafter in left auricle.
2. The pulmonary veins and then the pulmonary capillaries get distended with and the pressure of blood in the pulmonary capillaries rises.
3. Blood and plasma ooze out from the pulmonary capillaries into the air spaces.
4. With the reduction of air spaces. the patient develops dyspnoea (difficüity in breathing) and ultimately dies.
5. The collection of fluid in the air spaces is called pulmonary edema. The patient virtually drowns in the fluid in his lungs.