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  Digestion

Digestion:

The digestive system:

The digestive system comprises the gastro-intestinal tract (mouth to anus) and the glandular organs. Such system serves to transfer organic molecules, salts and water from the exterior atmosphere to the body’s internal atmosphere. Most of the food taken into the mouth is large particles having macromolecules like polysaccharides and proteins. As such they can’t be absorbed by the intestinal wall. They should be dissolved and broken down into much smaller molecules. This procedure is termed as digestion. Digestion is proficient by substances known as enzymes generated from the digestive glands. The enzymes are biocatalysts in the food breakdown procedure.

The process of digestion:

Mouth:

In mouth, digestion begins with chewing. It breaks up large pieces of food into smaller particles which can be swallowed without choking. It is accomplished by teeth, jaws, tongue, and saliva.

Chewing is controlled by the somatic nerves to the skeletal muscles of the jaw and mouth. Rhythmic chewing motions are reflexly started by the pressure of food against the gums, hard palate at roof of the mouth and tongue.

Saliva:

The saliva is concealed by three pairs of exocrine glands, viz.: The parotid, the sub-mandibular and the sublingual. The everyday secretion of saliva ranges from 1000-1500ml. It has the organic substances mucin and amylase. The salivary amylase or ptyalin can act on starch. It transforms cooked starch into disaccharide, maltose. Mucin is a glycoprotein. It aids in the lubrication of food. The lubricated, swallowable form of food is termed as bolus. Salivary secretion is controlled by the reflex activities.

Swallowing:

It is a complicated reflex activity. It is controlled by the swallowing center in the medulla oblongata. Throughout swallowing the soft palate is eminent, the larynx acquires raised. The tongue forces the food back into the pharynx, the epiglottis closes the glottis and the food gradually passes into the oesophagus.

The oesophageal stage starts with relaxation of the upper oesophageal sphincter. In the oesophagus the food is moved to the stomach by a progressive wave of muscle contractions which proceed downward to the stomach. These waves of contraction in the muscle layer surrounding a tube is termed as peristaltic waves. In the oesophagus one peristaltic wave takes around 9 seconds to arrive at the stomach. Due to peristaltic waves, swallowing can take place even while a person is upside down.

 

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