(1) There are capillaries and lymphatic capillaries in the villi of small intestine. The villus wall, capillary wall and lymphatic capillary wall are all composed of a layer of epithelial cells, which is beneficial for nutrients to be absorbed into the capillaries and lymphatic capillaries on the inner wall of small intestine.

(2) There are intestinal glands in the wall of small intestine, which open between two adjacent villi of small intestine and can secrete intestinal juice, and the intestinal juice contains enzymes for digesting sugar, protein and fat.

(3) Blood vessel ⑤ is venous blood flowing from villi of small intestine, and nutrients in small intestine enter the blood through villi wall and capillary wall, so the blood in ⑤ is rich in nutrition.

So, the answer is: (1) one; Absorb nutrition?

(2) internal; Between two adjacent small intestinal villi; Intestinal fluid?

(3) nutrients