Digestion is the process of breaking down food into smaller components that can be absorbed into the bloodstream. This process, also known as catabolism, is divided into two types: mechanical digestion, which occurs in the mouth when food is physically broken down into smaller pieces, and chemical digestion, which occurs in the gastrointestinal tract when digestive enzymes break down food into small molecules. The digestive system includes the digestive tract and its accessory organs, which process food into molecules that can be absorbed and used by the body's cells. Mechanical digestion greatly increases the surface area of food particles so that digestive enzymes can act on them more effectively.
The end products of digestion are absorbed in the digestive tract, mainly in the small intestine. For example, sucrose, or table sugar, is a disaccharide that the enzyme sucrase breaks down to form glucose and fructose, which are easily absorbed by the small intestine. The sugar lactose, found in milk, requires the enzyme lactase to break it down into glucose and galactose, which are then absorbed by the small intestine. Less than half of adults produce enough lactase to digest lactose; those who cannot are said to be lactose intolerant.In addition to digestion in humans and other animals, external digestion is used by some fungi.
In this process, food is digested from the outside by secreting enzymes that degrade the food material and are then absorbed by diffusion.The mouth is the beginning of the digestive system and digestion begins here before you even take the first bite of a meal. Chewing and secretions are part of this process, as well as absorption of nutrients mainly in the small intestine. Defecation and urination are also part of digestion as they remove waste products through the rectum and bladder.