[Digestion] 1.What is digestion ?

When we eat such things as bread, meat, and vegetables, they are not in a form that the body can use as nutrients. Our food and drink must be changed into smaller molecules of nutrients before they can be absorbed into the blood and carried to cells throughout the body.

Digestion is the process by which food and drink are broken down into their smallest parts so that the body can use them to build and nourish cells and to provide energy.

Digestion occurs at the multicellular, cellular, and sub-cellular levels, usually in animals. This process takes place in the digestive system known as alimentary canal.

Digestion is usually divided into mechanical manipulation and chemical action. In most vertebrates, digestion is a multi-stage process in the digestive system, following ingestion of the raw materials, most often other organisms. The process of ingestion usually involves some type of mechanical manipulation.

Digestion is separated into four separate processes:
Ingestion: Placing food into the mouth,
Mechanical digestion & Chemical digestion: Mastication, the use of teeth to tear and crush food, and churning of the stomach. Addition of chemicals (acid, bile, enzymes, and water) to break down complex molecules into simple structures,
Absorption: Movement of nutrients from the digestive system to the circulatory and lymphatic capillaries through osmosis, active transport, and diffusion,
Egestion: Removal of undigested materials from the digestive tract through defecation.
Underlying the process is muscle movement throughout the system, deglutition and peristalsis.