Biology > The Digestive System
The digestive system enables the food we eat to be used by the millions of cells in our bodies. Each of the digestive processes has a role to play in physically and chemically changing what we eat and disposing of waste products.
The diagram below shows the processes involved in the digestive system and how long each process takes to complete its unique role.
Food enters the mouth and is chewed (masticated). This mechanical process breaks down the food which at the same time is mixed with saliva containing the enzyme ptyalin.
Time: 1 minute.
Swallowing (Gullet) (B)
A lump of chewed food (a bolus) is moved to the back of the throat using the tongue. A reflex action takes place where the soft palate closes off the nose and the larynx rises so that the epiglottis closes off the trachea. The bolus travels down the gullet (oesophagus) and into the stomach
Time: 10-15 seconds.
The stomach secretes both acid and mucus (for self protection). It serves as a temporary store for food which is also churned by muscular layers. It is here food and the digestive juices are mixed.
Time: 1-6 hours.
Small Intestine (D)
Here fully digested food is absorbed into the blood stream. The surface area of the inside of the small intestine is increased with circular folds. More juices are added and further mixing occurs.
Time: 5-6 hours.
Large Intestine (E)
The large intestine has three longitudinal muscle bands with bulges in the wall between them. The anus has voluntary and involuntary sphincter and ability to distinguish whether contents are gas or solid. Undigested material only reaches the large intestine. Excess water is absorbed into the body, producing more solid waste.
Time: 12-24 hours.
The diagram below shows the order of process:
Fig 1: The Digestive System