. Adventures with animals and plants. Biology. Diaphragm 228 How a Complex A?ii?nal Uses Food unit iv cartilage. Their walls contain, besides the epithelial lining, rings of involuntary muscle. In an attack of asthma these muscles contract; this results in partially shutting off the air supply. The lungs — a vast membrane. A study of lamb or beef lungs, as described in Exercise 3, will help you to understand the structure of lungs. The branch from the windpipe disappears inside of the lung. Here, as you know, it divides into branches, bronchial tubes, taking on the appearance of a tree without
. Adventures with animals and plants. Biology. Diaphragm 228 How a Complex A?ii?nal Uses Food unit iv cartilage. Their walls contain, besides the epithelial lining, rings of involuntary muscle. In an attack of asthma these muscles contract; this results in partially shutting off the air supply. The lungs — a vast membrane. A study of lamb or beef lungs, as described in Exercise 3, will help you to understand the structure of lungs. The branch from the windpipe disappears inside of the lung. Here, as you know, it divides into branches, bronchial tubes, taking on the appearance of a tree without leaves. The branching is clearly diagramed in Figure 226. The bronchial tubes are not lung tissue. The lung tissue itself is found where the leaves of the tree would be. Each fine twig opens out into an air sac whose walls are made of a single layer of flat cells (epithelium) and a thin layer of elastic tissue. This is the lung tissue. Each sac can fold up into a small space or stretch to a great size. In the walls of each air sac there is a network of capil- laries (see Fig. 227). If the lungs were a simple bag the number of square inches of membrane that could be brought in contact with capillaries would be small. A large house left as an empty shell would have rela- tively httle wall surface inside. If, how- ever, this same building were divided up into apartments the interior wall surface would be increased astonishingly. The lung is built on the same principle. For this reason, the lung membrane has an enormous area. All of the area is in contact with capillaries. Gases are con- tinually diff^using into the capillaries and out of them. Thus the composition of the blood is rapidly changing as it flows through the lungs. A B Fig. 229 Figure A shows the chest cavity while you are exhaling. Figure B shows it while inhal- ing. Co7//pare the position of the diaphragm in A and B. What difference do you note? What differejice do you observe in the ribs of the two chest cavities
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Keywords: ., bookcentury1900, bookpublisherbostondcheath, booksubjectbiology
