The picture is a schematic diagram of the structure of the human small intestine. As the main place for digestion and absorption, the small intestine has a structure suitable for this function. Please answer the following questions based on the diagram.

(1) The small intestine is about 5 to 6 meters long. There are annular folds on the inner wall of the small intestine. There are many villi protrusions on the surface, called small intestinal villi, which increase the area for digesting food and absorbing nutrients; There are various digestive juices such as intestinal juice secreted by glands, pancreatic juice secreted by pancreas and bile secreted by liver; these digestive juices contain a variety of enzymes for digesting food; there are capillaries in the villi of the small intestine, and the villus wall and capillary wall are all composed of a layer of It is composed of epithelial cells. These characteristics are conducive to the absorption of nutrients, so the small intestine is the main organ of the human body for digestion and absorption of nutrients.

(2) Food is eventually broken down into nutrients that can be absorbed by the human body through the action of digestive enzymes in the digestive juice in the small intestine of the digestive tract, such as starch into glucose, protein into amino acids, and fat into nutrients. Into

Glycerol, fatty acids.

(3) The small intestine is the longest section of the digestive tract. It contains folds and small intestinal villi, which increases the area for digesting food and absorbing nutrients. The small intestine contains a variety of digestive juices, which is conducive to the digestion of food. ; The villus walls, capillary walls and lymphatic capillary walls of the small intestine are very thin, which is conducive to the absorption of nutrients. There are abundant blood vessels on the wall of the small intestine. According to the direction of blood flow, the blood entering the wall of the small intestine has a higher oxygen content than the blood flowing out of the wall of the small intestine. It is arterial blood and has a low content of nutrients.

(4) Excretion is the physiological process in which the end products produced during the metabolism of the body are excreted from the body. The excretion of the human body refers to breathing, perspiration and urination. The discharge of food residue from the anus is not excretion, it can only be called excretion.

So the answer is: (1) Expanded area for absorbing nutrients?

(2) Glucose (or amino acids, glycerol, fatty acids)?

( 3) Decrease? Increase?

(4) It does not participate in the metabolic process of the human body and is classified as elimination