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Ans 12. Peristalsis refers to the process by which the food is transported from the buccal cavity to the stomach with the help of the expansion and contraction of the muscles present in the oesophagus.
After the peristaltic movement in the oesophagus, food particles move down the oesophagus and reach the stomach.

Ans 13. Stomach, an important and dilated part of our gastro-intestinal tract produce and secrete many important substance to control and help in digestion.

• Mucus is secreted by mucous cell. It provides coating to the inner lining of stomach which protects the stomach from strong acidic action of hydrochloric acid .

• Hydrochloric acid- It is secreted by parietal cells present in gastric pits. It maintains the pH of stomach and by the action of this hormone pepsinogen is converted to its active form pepsin which aid in the digestion of protein by breaking it into its simpler units like amino acids and peptides. Besides, it kills the micro organism that comes into our stomach along with our food.

• Intrinsic factor- It is secreted by parietal cells. It's a glycoprotein and helps in the absorption of vitamin B12

• Pepsinogen- It is secreted by chief cells. It is the inactive form of protein digesting enzyme pepsin. By the action of hydrochloric acid it is converted to pepsin ,which aids in the digestion of protein.

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