Test analysis: (1) Macromolecular water-insoluble organic substances such as sugar, fat and protein must be decomposed into small molecular water-soluble substances in the digestive tract before being absorbed by the human body; Protein must be completely decomposed into amino acids before it can be absorbed by human body. Nutrients are digested and absorbed by digestive tract, absorbed by villi of small intestine, then flow into right atrium and right ventricle through inferior vena cava, into lung through pulmonary artery, into arterial blood through pulmonary vein, and then into left atrium and left ventricle through pulmonary vein. Therefore, the sequence of substance flowing through blood circulation and cavity is A → B → D → C. 。
(2) Insulin is secreted by islet. Its main function is to regulate sugar metabolism. Specifically, it can promote the synthesis of glycogen in blood sugar and accelerate the decomposition of blood sugar, thus reducing the blood sugar concentration. Therefore, after normal people eat, with the increase of blood sugar, insulin secretion also increases, thus reducing blood sugar and maintaining it in the normal range.
(3) The diagram shows that ① oxygen enters the alveoli, ② carbon dioxide is discharged from the alveoli, which belongs to the process of exchanging air between the lungs and the outside world, and is realized by breathing exercise; When blood flows through the capillaries in the tissue, the oxygen in the blood is utilized by the mitochondria of the tissue cells, and the oxygen participates in the oxidative decomposition of the organic matter in the cells, releasing the energy stored in the organic matter for the needs of human life activities.
(4) The organ D formed by urine represents the kidney, and the formation of urine is filtered by glomerulus and reabsorbed by renal tubules. When blood flows through the glomerulus, other substances, such as water, inorganic salts, urea, glucose, etc., will be filtered into the renal capsule cavity except protein and macromolecules of blood cells, forming protourine. When raw urine flows through renal tubules, most water, some inorganic salts and all glucose are reabsorbed into blood, and the rest, such as urea, some inorganic salts and water, flow out of renal tubules to form urine. When blood flows through the glomerulus, other substances such as water, inorganic salts, urea and glucose will be filtered into the renal capsule except protein and macromolecules of blood cells, forming protourine. When the original urine flows through the renal tubule, most of the water, some inorganic salts and all glucose are reabsorbed into the blood, and the rest, such as urea, some inorganic salts and water, flow out of the renal tubule to form urine.
(5) Reasonable nutrition means that all kinds of nutrients ingested from food are in balance with the human body's demand for these nutrients, neither lacking nor excessive. In order to meet the human body's daily demand for energy and various nutrients, human nutrition must be reasonable, and only reasonable nutrition can meet the human body's demand for various nutrients. Pay attention to three meals a day, regular and quantitative, not partial eclipse, not picky eaters, not overeating, and reasonable collocation of meat and vegetables. Only in this way can we meet the human body's needs for various nutrients and energy for life activities, especially teenagers are in a critical period of growth and development. It is particularly important to maintain protein and energy supply every day.