Digestion of food in the human beings:

In human beings, digestion of food starts from the mouth. Mouth opens into a chamber or cavity called buccal cavity. The buccal cavity contains teeth, tongue and salivary glands. The teeth cut the food into small pieces, chew and grind it. Thus, teeth help in physical digestion. Salivary glands produce saliva which mixes with the food. Saliva is a watery fluid that makes the food slippery for swallowing. These glands help in chemical digestion of food.

The saliva contains an enzyme called salivary amylase which digests the starch into maltose sugar. Buccal cavity opens into pharynx which leads to a long tube called oesophagus. The walls of oesophagus are highly muscular. Digestion does not occur in the oesophagus. It carries the food down into the stomach. When the slightly digested food enters the oesophagus, its walls starts contraction and expansion movements called peristaltic movements. These movements push the food from the oesophagus into the stomach.

The glands present on the walls of the stomach secrete gastric juice that contains three substances: hydrochloric acid, the protein digesting-enzyme, called pepsin and mucus. Hydrochloric acid makes acidic medium inside the stomach which is necessary for pepsin enzymes to work. In acidic medium, pepsin breaks down proteins into peptones. Another function of hydrochloric acid is to kill germs that entered the stomach along with food. The mucus helps to protect the stomach wall from its own secretions of hydrochloric acid.

From the stomach, the partially digested food goes into the small intestine through sphincter muscle. In humans, small intestine is the site of complete digestion of food like carbohydrates, proteins and fats. It receives the secretions of two glands, liver and pancreas through a common duct. Liver secretes bile which is alkaline and contains bile salts and bile pigments. Bile salts helps to emulsify the fats. The bile secreted by the liver is stored in the gall bladder. Pancreas secretes pancreatic juice which contains trypsin, lipase and pancreatic amylase. Trypsin digests the proteins, lipase emulsifies the fats and pancreatic amylase breaks down the starch. The wall of small intestine contains glands which secrete intestinal juice. Intestinal juice contains a number of enzyme which complete the digestion process.

Human Digestive System