Wednesday, May 2, 2012

Digestive Tract #1

The digestive tract (also called the alimentary canal or the gastrointestineal tract) consists of: mouth→ pharynx→ epiglottis→ esophagus→ stomach→ small intestine→ large intestine→ anus

This entire post will be used to describe each part of the digestive tract, as well as other organs in the digestive system, such as livers and gallbladders.

The mouth (oral cavity) is where the food enters our body, and in it, both physical and chemical digestion take place.

The teeth physically break down the food, with different types of teeth breaking the food down different ways:

The saliva contains mucus and enzymes, such as amylase (breaks down polysaccharides) and maltase. Saliva is produced by the salivary glands, which are the parotid gland, the sublingual gland, and the submandibular gland:

The tongue moves the food when the person is chewing. In addition, it has taste buds, which are receptors that send messages to our brain: 

In the mouth, with the chewing and the mixing with the saliva, the food becomes a food bolus, and it now travels to the pharynx.

The food bolus then goes through the pharynx and into the esophagus, and long muscular tube made up circular and longitudinal muscles. In the esophagus, food is moved along with peristalsis.

At the end of the esophagus, there's the cardiac sphincter, which controls the movement of the food from the esophagus to the stomach. The stomach is a J-shaped organ with a volume of 1.5L, and it has thick layers of smooth muscle (rugae) that allows it to stretch. The stomach uses its longitudinal, circular, and oblique muscles to churn the food, and it also secretes gastric juices to chemically digest the food.

With both physical and chemical digestion, the food bolus is turned into a thick liquid called chyme.

Some components of the gastric juice:
  • Hydrochloric acid: destroys invading microbes, breaks down food bolus, and turns pepsinogen into pepsin
  • Pepsinogen: In acidic environments, it turns into pepsin, which breaks polypeptides into dipeptides
  • Lipases: enzymes that break down lipids
  • Mucus: secreted by the rugae, it forms a protective coating for the stomach that prevents the hydrochloric acid from burning through