FAQ on Gastric Digestion

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1. Describe the composition of saliva and the differences in composition between the different salivary glands.

Saliva is 99% water and 0.5% solutes. The solutes comprise of Na, K, Cl, HCO3-, etc. The parotid glands secrete a watery (serous) liquid containing salivary amylase. The submandibular glands also secrete salivary amylase, but also secrete mucus. The sublingual glands secrete thick mucous that only contains a small trace of amylase.

2. List the functions of the saliva.

There are many. To name a few: digestion, cleansing, moistening and lubricating, and excretory.

3. Describe the process of digestion that occurs in mouth. Which enzymes are found in the Saliva? What is the function of each? Where else in the gastrointestinal tract is each of these found?

Digestion begins with chewing (mastication) that takes place in the mouth. When food enters the mouth, secretion of saliva also increases. Most saliva is secreted by the major salivary glands: parotid gland, submandibular gland, and sublingual gland. Major enzymes found in the saliva are IgA (bacterial antibody: also found in gastrointestinal secretions), salivary amylase (digests starch: also found in pancreas), and lingual lipase (digestion of fats: also found in stomach and pancreatic juices).

4. Describe the digestion of proteins in the stomach. Why are proteins that are part of the stomach itself not affected by the digestion process?

In the stomach, the only proteolytic (protein-digesting) enzyme is pepsin which works in the presence of HCl and breaks down proteins into large polypeptides. Pepsin is secreted by chief cells.

5. Describe the role of gastric inhibitory protein (GIP), secretin and cholecystokinin. Where are they produced?

GIP: Inhibits gastric gland secretions and gastric motility during gastric phase: secreted from K cells in the intestinal epithelium.

Secretin: Inhibits gastric gland secretions and gastric motility during gastric phase of secretion; Increases output of pancreatic juice rich in bicarbonate ions; potentiates CCK's action: released by enteroendocrine cells in the small intestinal mucosa.

CCK: Potentiates secretin's actions; Increases output of enzyme-rich pancreatic juice; stimulates organ to contract and expel stored bile: released by enteroendocrine cells in the small intestinal mucosa.

6. List some of the substances that can be absorbed by the stomach.

Only a small amount of absorption occurs in the stomach because its epithelial cells are impermeable to most materials. Some materials absorbed are water, ions, alcohol, and short-chain fatty acids, as well as some drugs.

7. Describe the secretion and function of hydrochloric acid in the stomach.

An enzyme called pepsin only works in the presence of HCl in the stomach.

Additional Reading:

Basic Gastroenterology

1. Basic Gastrointestinal Physiology
2. Digestion FAQ, Defecation reflex, etc.
3. Digestion
4. Notes on Functions of the Liver
5. Notes on Jaundice
6. Types of Jaundice
7. Diagram of Gastric Blood Supply
8. FAQ on Gastric Digestion
9. Usage of the D-xylose Absorption Test

Gastroenterology Videos

1. Video of Abdominal Examination in a Clinical Setting

Related Topics

1. Gastrointestinal Disorders
2. Hepatobiliary and Pancreatic Disorders
3. Histology of the Digestive Tract I: Oral Cavity
4. Histology of the Digestive Tract II: Esophagus through Intestines
5. Histology of the Liver, Pancreas, and Gall Bladder
6. Abdominal Examination for Internal Medicine

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