(1) Arteries are blood vessels that transport blood from the heart to all parts of the body, while veins are blood vessels that transport blood from all parts of the body back to the heart. Capillary is the blood vessel connecting the smallest artery and vein. There are many capillaries, which are widely distributed, and the inner diameter of blood vessels is small, only 8- 10 micron. Only red blood cells are allowed to pass in a single row. The tube wall is very thin and consists of only one layer of epithelial cells. The blood flow rate in the tube is the slowest. The blood flow velocity in venous blood vessels is slower than that in arterial blood vessels. There are venous valves in venous vessels of limbs to prevent blood from flowing backwards. After the blood from the inferior vena cava reaches the heart, it first flows into the right atrium.

(2) When blood flows through the glomerulus, uric acid, urea, water, inorganic salts and glucose in the blood enter the renal capsule through the filtration of the glomerulus, forming protourine. At this time, due to the large reduction of water, the concentration of macromolecules in blood entering glomerular arterioles is significantly higher than that in blood entering glomerular arterioles [4]. When the original urine flows through the renal tubule, all glucose, most water and some inorganic salts are reabsorbed by the renal tubule, and these reabsorbed substances enter the capillaries wrapped around the renal tubule and are sent back to the blood, and the remaining water, inorganic salts and urea form urine, so [7] the blood composition of renal vein is obviously lower than that of renal artery [6].

(3) 1 ventilation of lung means that the gas exchange between alveoli and blood is completed by gas diffusion. When blood flows through pulmonary capillaries, the oxygen concentration in alveoli is the highest, and the carbon dioxide concentration in blood is low, so it diffuses. Carbon dioxide in blood diffuses to alveoli, and oxygen in alveoli diffuses to blood. In this way, blood changes from venous blood with little oxygen content to arterial blood with rich oxygen content.

(4) After oxygen enters the blood, it combines with hemoglobin and is transported to all tissues and cells of the whole body to decompose organic matter and provide energy for its life activities.

(5) Before entering tissue cells, glucose absorbed by small intestine flows through small intestine capillaries → veins at all levels → inferior vena cava → right atrium → right ventricle → pulmonary artery → pulmonary vein → left atrium → left ventricle → aorta → arteries at all levels → capillaries in tissues, so the sequence of glucose flowing through heart cavity is: right atrium → right ventricle → left atrium → left ventricle.

(6) When someone suffers from appendicitis, the number of white blood cells in his blood will greatly increase due to inflammation. In his routine blood test list, the item with a large increase is white blood cells.

So the answer is: (1) venous valve; Right atrium (2) glomerular filtration; ? Urea (3) gas diffusion; ? Venous blood becomes arterial blood (4) Hemoglobin? (5) Right atrium → Right ventricle → Left atrium → Left ventricle (6) White blood cells