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The gastrointestinal tract (GI tract), also called the digestive tract, alimentary canal, or gut, is the system of organs within multicellular animals that takes in food, digests it to extract energy and nutrients, and expels the remaining waste. The major functions of the GI tract are digestion and excretion. The human digestive system is a series of hollow organs joined in a long, twisting tube from the mouth to the anus. Inside this tube is a lining called the mucosa. In the mouth, stomach, and small intestine, the mucosa contains tiny glands that produce juices to help digest food. Two solid organs, the liver and the pancreas, produce digestive juices that reach the intestine through small tubes. In addition, parts of other organ systems (for instance, nerves and blood) play a major role in the digestive system. The gastrointestinal tract (GI tract), also called the digestive tract, alimentary canal, or gut, is the system of organs within multicellular animals that takes in food, digests it to extract energy and nutrients, and expels the remaining waste. The major functions of the GI tract are digestion and excretion. The human digestive system is a series of hollow organs joined in a long, twisting tube from the mouth to the anus. Inside this tube is a lining called the mucosa. In the mouth, stomach, and small intestine, the mucosa contains tiny glands that produce juices to help digest food. Two solid organs, the liver and the pancreas, produce digestive juices that reach the intestine through small tubes. In addition, parts of other organ systems (for instance, nerves and blood) play a major role in the digestive system. Digestive system is the series of organs that process and convert food into simpler substances that the body uses for nourishment. Starch and complex sugars are digested to simple sugars; fats to fatty acids and glycerin; and proteins to amino acids. These simpler substances consist of small molecules that can then pass through the intestinal wall and into the bloodstream for distribution to all parts of the body. The digestive system consists of the alimentary canal - mouth, pharynx, esophagus, stomach, and small and large intestines - aided by secretions from the liver and pancreas. The teeth break up food by chopping end grinding it into fine particles. Glands in the mouth lubricate and moisten food with saliva, which also contains a digestive enzyme. The tongue conveys food to the throat, and the pharynx muscles push it down the esophagus, a muscular tube about 25cm long that leads to the stomach. The stomach both stores and helps to digest food. The stomach of an average adult can hold about one quart (0.9l). The muscular stomach churns food around and mixes it with gastric juice, which includes hydrochloric acid to provide the acid medium needed for the enzyme pepsin to break down protein. The partly digested food (chyme) passes from the stomach to the small intestine, usually after two to five hours. The digestive process is completed in the small intestine, a narrow muscular tube about 6m long. Enzymes from the pancreas mix with enzymes from the duodenum. Bile, made by the liver and stored in the gall bladder, also enters the small intestine. Bile helps in the digestion of fats. The digested food particles are then absorbed by lymph or blood vessels in the intestinal wall. Tiny finger-like projections (villi) on the walls of the small intestine increase the surface area that can absorb the food. The digested particles are then carried by the bloodstream to the liver, which converts them into substances needed by the body. Eaten material that can not be digested as food, such as plant fiber, passes into the large intestine, which is about 1.5m long. There, water is removed from the liquid waste, and bacteria convert it to its final form, feces. The waste material is excreted from the body through the end of the large intestine (rectum). Food is propelled along by wave-like contractions of muscles in the stomach and intestines. This is called peristalsis. The food moves in one direction only. Sphincters, circular muscles that close tightly, prevent the food from moving backward. There are sphincters at the lower end of the esophagus, at the exit from the stomach, at the lower end of the small intestine, and at the exit from the rectum.

Перечень вопросов для самоподготовки по теме практического занятия.

1. What are the organs of the abdominal cavity? 2. What organ separates the abdomen from the cavity of the thorax? 3. What is the largest organ in the abdominal cavity? 4. What does the stomach serve for? 5. Where does the food pass from the stomach? 6. Where does the liver lie? 7. What does the liver serve for? 8. What organ occupies chiefly the central portions of the abdominal cavity? 9. Describe the role of the gall-bladder. 10. How do we distinguish “small” and “large” intestines?