Question

A) Explain the digestion that occurs in the oral cavity.

B) What is the function of the liver in digestion?

C) What role does the gallbladder play in digestion?

D)Why is the orientation of muscle in the stomach wall important? How does this contribute to its function?

Answer 1

1. The digestive tract begins from the oral cavity and ends at the anus. The major function performed by the oral cavity is mastication that allows proper mixing of food. The food then is called bolus. Apart from this, the action of salivary amylase breaks down the carbohydrates to a simpler form, starch which is then broken down to maltose by the action of the same enzyme. Another enzyme called lysozyme which has antibacterial action is also present in saliva. The bolus passes from the pharynx to the esophagus from where it goes to the stomach by peristalsis.
2. Liver forms bile. Bile is released into the duodenum and is responsible for emulsification of fats. Emulsification is the breaking down of fat into smaller droplets which reduces their surface tension and help in their absorption. Bile also activates lipase which helps in the further digestion of fat.
3. Gall bladder essentially stores bile and releases it when required. It is small sac like structure located beneath the liver and releases bile as soon as fatty meal reaches the duodenum. This happens under hormonal stimulation.
4. The stomach has 3 layers of muscles. These are smooth muscles which contract in three different directions. These are:

• Inner oblique layer: It is only found in the stomach and is responsible for churning the food and breaking down the bolus. It is thickest in the antral region.
• Middle circular layer: It wraps around the pylorus and remains contracted in the normal state and thus forms the pyloric sphincter.It helps in the movement of the chyme into the duodenum.
• Outer longitudinal layer: This layer lies above the Auerbach/Myenteric plexus and regulates peristalsis.
• The contraction of these different layers allows the stomach to properly churn the bolus by mixing it in all possible directions.