(2) Glucosamine enters the blood and reaches tissue cells: small intestinal capillaries → hepatic portal vein → liver → inferior vena cava → right atrium → right ventricle → pulmonary artery → pulmonary vein → left atrium → left ventricle → aorta → arteries at all levels → tissue capillaries → tissue cells. It participates in respiration in mitochondria and releases energy for tissue use.
(3) The formation of urine is mainly related to glomerular filtration and renal tubular reabsorption. The filtration of glomerulus makes macromolecular protein and blood cells stay in blood, and the reabsorption of renal tubules reabsorbs useful substances in urine, such as all glucose, most water and some inorganic salts containing a small amount of protein. The rest of the useless substances form urine. After blood flows through the kidney, there is no glucose in urine, which is mainly related to the reabsorption of renal tubules.
(4) A. If M is the kidney, when the blood flows through the human kidney, the carbon dioxide content increases and the urea content decreases, so the curve can indicate that the description of the change of carbon dioxide or urea content is wrong.
B If M is small intestine, when blood flows through human small intestine, the content of carbon dioxide and nutrients increases, then the curve can show that the description of the change of carbon dioxide or nutrients is correct.
C. If M is skeletal muscle, when blood flows through human skeletal muscle, carbon dioxide increases and the contents of oxygen and nutrients decrease, then the curve can indicate that the curve can indicate the narrative error of oxygen or nutrients change.
So the answer is: (6 points) (1) small intestine insulin.
(2)① Mitochondria
③ reabsorption (or reabsorption)
(4)B