355. Describe the course of the blood from the right auricle in the heart to the lungs.
Observation. If the blood is not changed in the lungs, it will not flow to the pulmonary veins. This phenomenon is seen in instances of death from drowning, strangling, carbonic acid, &c. The same is true, but in a less degree, of individuals whose apparel is tight, as well as of those who breathe impure air, or have diseased lungs.
356. The left auricle, (12,) by its contraction, forces the blood into the left ventricle, (14.) The mitral valves (15) prevent its reflowing. From the left ventricle the blood is forced into the aorta, (16,) through which, and its subdivisions, it is distributed to every part of the system. The semilunar valves (17) prevent its returning.
Observation. The parts of the circulatory organs most liable to disease are the valves of the heart, particularly the mitral. When these membranous folds become ossified or ruptured, the blood regurgitates, and causes great distress in breathing. The operations of the system are thus disturbed as the movements of the steam engine would be if its valves were injured, or did not play freely.
357. The difference between the functions of the pulmonary artery and aorta is, the former communicates with the right ventricle of the heart, and distributes only impure blood to the lungs; the other connects with the left ventricle of the heart, and distributes pure blood to the whole body, the lungs not excepted. At the extremity of the divisions of the aorta, as well as the pulmonary artery, are found capillary vessels. This curious net-work of vessels connects with the minute veins of the body, which return the blood to the heart.
Observation. The function of the veins of the systemic 167 circulation is similar to the office of the arteries in the lungs, and that the veins of the pulmonic circulation transmit to the heart the pure, or nutrient blood, and thus supply the arteries of the general system with assimilating fluid.
What is the effect when the blood is not changed in the lungs? 356. Describe the circulation of the blood from the left auricle to the general system. What part of the circulatory organs is most liable to disease? What is the effect when the valves are diseased? 357. Give the difference in the functions of the pulmonary artery and aorta. Show the relation between the functions of the arteries and veins both of the pulmonic and systemic circulation.
358. The veins that receive the blood from all parts of the body, follow nearly the same course as the arteries. The myriads of these small vessels beneath the skin, and others that accompany the arteries, at last unite and form two large trunks, called ve´na ca´va as-cend´ens, and de-scend´ens.
Observation. A peculiarity is presented in the veins which come from the stomach, spleen, pancreas, and intestines. After forming a large trunk, they enter the liver, and ramify like the arteries, and in this organ they again unite into a trunk, and enter the ascending vein, or cava, near the heart. This is called the portal circulation.