How did the position of the bolus change?

What is the similarity of movement of food illustrated in the diagram and the activity performed by you?

The walls of the food pipe secrete a slippery substance called mucus. Mucus lubricates and protects the oesophageal walls from damage. This helps the food bolus to slide down easily just as the oiled potatoes that move in the tube. Besides this, the saliva in the bolus also aids in easy movement of food, which moves into the stomach.

The walls of the oseophagus is made up two kinds of smooth muscles.The inner layer consists of circular muscles and the outer layer of longitudinal muscles. Contraction of the circular muscles results in narrowing of the oesophagus just behind the bolus. So the food is squeezed downwards. Contraction of the longitudinal muscles infront of the bolus widen the tube, this results in shortening of that particular part of the oesophagus. Contraction and relaxation of these muscles bring in a wave like motion that propels the food bolus into the stomach by the action called as "peristalsis" (you have studied about this in the chapter on nutrition). This is involuntary and under the control of autonomous nervous system.

What makes the movement of the food bolus in the oesophagus easy?

Think why people are advised not to swallow food without chewing properly or do not eat in hurry

Why do you think the stomach is structured like a bag rather than a tube like oesophagus?

What sets such processes into action?

When the food is in the oral cavity, the nerves in the cheek and tongue are stimulated. These carry messages in the form of nerve impulses to the brain. Brain analyses the message. These messages are transmitted from the brain through motor nerve to the wall of the stomach, and stimulate the gastric glands to produce gastric juice.

The walls of stomach secrete juice containing hydrochloric acid (HCl) Most of us may have experienced belching and the burning sensation after vomiting. What do you think may have caused the burning sensation?