The digestive system consists of the digestive tract (also called the alimentary canal) and associated glands and organs. The alimentary canal is the passage leading from the mouth to the anus and includes the oral cavity, pharynx, oesophagus, stomach, small and large intestine and the anus. The associated glands (also called the accessory organs) only help in digestion by secreting enzymes important for the digestion process and include the liver, gallbladder and pancreas.

The digestive system is responsible for digesting food, absorbing nutrients and eliminating solid waste.

The process of digestion starts in the oral cavity. The teeth cut and chew the food into small pieces. These are mixed with saliva produced by the salivary glands. Saliva contains enzymes that break down starches. Saliva also lubricates the food, so it is easier to swallow it.

Next, the food travels down the pharynx. There is a structure called epiglottis that closes off the larynx when we swallow, so the food does not go down the wrong tube.

The food passes from the pharynx into the oesophagus. This is a muscular tube about 25 cm long behind the trachea connecting the pharynx and the stomach. Its walls can contract and relax. This movement, called peristalsis, pushes the food into the stomach.

The stomach is a pouch that can get bigger and smaller. It depends on how much food is inside. Its walls are very strong and can squeeze and mix the food. The mucous membrane in the stomach walls secretes gastric juices that contain enzymes. These enzymes break down the food into the semifluid mixture called chyme.

The chyme leaves the stomach and enters the small intestine. The small intestine is divided into the duodenum, jejunum and ileum. The most important part is the duodenum which is responsible for breaking down the food into constituent nutrients. The rest of the small intestine is the place where these nutrients are absorbed into the bloodstream. On the inner wall of the small intestine there are finger-like projections called villi that are rich in blood vessels. They increase the absorptive area of the intestine, so more constituent nutrients can pass through the bloodstream to the body cells.

Water and food that cannot be digested move into the large intestine. It consists of the caecum, colon, rectum and anus. The appendix is a part of the ceacum. The large intestine is the place where water and some substances are reabsorbed. The undigested food is processed into the stool (also called faeces). It is stored in the rectum and eliminated through the anus.

The liver has many functions. It stores glycogen and iron, it decomposes red blood cells, it detoxifies the body, it stores vitamins A, D, E, K, B12 and it produces bile. Bile is a yellowish brown fluid. It is stored in the gallbladder and secreted into the duodenum, where it helps in breaking down lipids.

The pancreas secretes pancreatic juices containing enzymes that break down carbohydrates, proteins and lipids. It also empties its juices into the duodenum.