Plan
► General concept of digestion in animal and human organism. Functions of digestive system. Kinds of digestion.
► Oral cavity and its role in digestion in humans.
► Digestion in stomach. Gastric juice, its composition and role of its components in digestion.
► Digestion in small intestine. Composition of intestinal juice, role of its components in digestion.
► Digestion in large intestine.
► Motility in different parts of gastrointestinal tract.
► Absorption in different parts of gastrointestinal tract.
► Methods of study of gastrointestinal tract functions.
General Concept of Digestion
For normal functioning the body requires plastic and energetic material. These substances are obtained from food, but only mineral salts, water and vitamins are assimilated in the form they enter the body. Proteins, fats and carbohydrates enter the body in the form of complex compounds and should undergo physical and chemical processing to be absorbed and assimilated. Here, food components should be deprived of their species specificity not to be recognized by the immune system as foreign matter. All the above functions are performed by the digestive system.
Digestion is a complex of physical, chemical and physiological processes, which break down foodstuffs and convert them into chemical compounds capable of being absorbed by body cells. These processes occur in a strictly defined sequence in all parts of the gastrointestinal tract (the mouth, pharynx, esophagus, stomach, duodenum, small and large intestine) with participation of the liver, gallbladder and pancreas, and are controlled by regulatory mechanisms of different levels. This chain of processes which ends in a complete breakdown of food into monomers capable of being absorbed, is called a digestive conveyor.