Zibo human body photography

(1) The digestion of food and the absorption of nutrients are mainly carried out in the small intestine. The structural characteristics of the small intestine adapted to its function are: the small intestine is very long, about 5 ~ 6 m, and there are many digestive juices such as intestinal juice, pancreatic juice and bile in the small intestine; There are annular folds on the inner wall of the small intestine, and there are small intestinal villi on the folds, which increases the area of digestion and absorption; There are capillaries and lymphatic capillaries in the villi of small intestine, and the villi wall, capillary wall and lymphatic capillary wall are all composed of a layer of epithelial cells, which is beneficial to the absorption of nutrients into the circulatory system.

(2) The circulation of blood from the right ventricle into the pulmonary artery, through the pulmonary capillary network, and then back to the left atrium from the pulmonary vein is called pulmonary circulation. In pulmonary circulation, venous blood injected into pulmonary artery from right ventricle flows through pulmonary capillaries, carbon dioxide in blood enters alveoli, and oxygen in alveoli enters blood. Therefore, after pulmonary circulation, blood changes from venous blood to arterial blood. Therefore, when blood flows through the lungs, the change is caused by venous blood compared with the blood composition in ⑤. The kidney is the organ that forms urine. When the blood flows through the kidney, the metabolic waste such as urea in the blood will be significantly reduced, so the content of metabolic waste such as urea in ④ is significantly lower than that in ③.

So the answer is: (1) small intestine; The small intestine is very long, about 5 ~ 6 m, and there are many digestive juices such as intestinal juice, pancreatic juice and bile in the small intestine. There are annular folds on the inner wall of the small intestine, and there are small intestinal villi on the folds, which increases the area of digestion and absorption?

(2) From venous blood to arterial blood; c； Left atrium; urea