Digestion: First, the food is roughly digested by the stomach, then further digested by the small intestine, and the food is decomposed into small molecular substances that can be absorbed by the small intestinal epithelial cells, and then absorbed into the veins by the small intestinal epithelial cells to complete the absorption process.
Second, the heart composition: right atrium, right ventricle, left atrium and left ventricle.
Blood flows back to the right atrium through the vein, then enters the pulmonary artery through the right ventricle, enters the left atrium through the pulmonary circulation, is pumped out through the left ventricle to the aorta, then enters the right atrium through all levels of arteries and capillaries, and then returns to the vein.