Digestion

The breakdown of large molecules into smaller molecules for absorption.
Large molecules are usually insoluble and too large to pass across cell membranes.

Physical digestion

Mastication: using jaws and specialised teeth (incisors, canines, premolars and molars)

Peristalsis: circular and longitudinal smooth muscles of the gut wall producing waves of contraction

Mechanical digestion reduces the food to small particles increasing the surface area exposed to the enzymes.

As well as moving the food along the gut, peristalsis mixes the foods with digestive juices. Soluble compounds dissolve and large molecules are exposed to digestive enzymes.

Chemical digestion

Using a range of specialised enzymes that work in different conditions of the different compartments of the organ-system.

Absorption

The uptake of nutrients from the gut into the blood stream.

Most takes place in the small intestine, which is adapted for this, water is absorbed by the colon and alcohol and some minerals are absorbed by the stomach lining.

Assimilation