The main purpose of the digestive system is to break large molecules down into smaller subunits due to the fact that:
- Large molecules are typically chemically inert and need to be broken down and reassembled into usable products
- Large molecules are typically insoluble and cannot be absorbed into cells, whereas smaller subunits are soluble
The process of digestion occurs across a number of stages, including:
- Ingestion – food is taken into the body via the act of eating
- Digestion – food is broken down both physically (e.g. mastication) and chemically (e.g. enzymatic hydrolysis)
- Absorption – digested food products are absorbed into the bloodstream and transported to cells
- Assimilation – digested food products are converted into the fluid and solid parts of a cell / tissue
- Elimination – undigested food residues are egested from the body as semi-solid faeces
Stages of Digestion
