Anatomy of Digestion and Salivation

Study Notes

The parotid gland produces serous saliva to hydrate food.
The sublingual gland produces mucus saliva to lubricate food.
The submandibular gland produces serous saliva to hydrate food.
The mouth aids in food lubrication and hydration, and contains digestive enzymes like lingual (salivary) amylase, lingual lipase, and lysozyme.

The duodenum receives chyme from the stomach.
Brunner’s glands, pancreatic secretions, and gallbladder secretions neutralize chyme.

Swallowing (deglutition) involves the epiglottis closing, the bolus being pushed back, the oropharynx relaxing, and peristalsis.

The mouth secretes saliva, enzymes, and mucus.
The stomach secretes acid, pepsinogen, lipase, and mucus.
The small intestine (duodenum) receives secretions from Brunner's glands, the pancreas, and the gallbladder.

Primary peristalsis begins at the pharynx, is regulated by the vagus nerve, involves skeletal muscle contraction, and circular muscle relaxations followed by contractions.
Secondary peristalsis is initiated by the stretching of muscles by digesta, results in muscle contractions, and can be reversed.

The lower esophageal sphincter (LOS) should remain closed.
The pylorus regulates the flow of chyme from the stomach.
Churning involves stomach muscle contractions, peristalsis, and the pylorus remaining closed.
Emptying involves peristalsis, and the pylorus opening.

Autonomic motility, called peristalsis, begins in the mouth, involves the contraction of circular and longitudinal muscles, and the relaxation of circular muscles.

Carbohydrates, proteins, and lipids are digested before entering the small intestine.
A slow, constant flow of digesta to the small intestine is achieved even after a large meal.

The duodenum is where the majority of digestion occurs.
The following enzymes aid in protein digestion in the duodenum: trypsin, chymotrypsin, elastase, carboxypeptidases, and aminopeptidases.
Brush border aminopeptidases are located on the enterocytes, while others are secreted from the pancreas.
Carbohydrate digestion in the duodenum involves the following enzymes: amylase, dextrinase, glucolyase, lactase, maltase, isomaltase, and sucrase.
These brush border enzymes break down carbohydrates into monosaccharides for absorption.
Lipid digestion in the duodenum involves the following components: lipase, bile salts, and bile acids.
These components aid in the formation of lipid droplets.

Protein digestion involves trypsin, chymotrypsin, elastase, carboxypeptidases, and aminopeptidases, which are secreted from the pancreas or the brush border of enterocytes.
Carbohydrate digestion involves amylase, dextrinase, glucolyase, lactase, maltase, isomaltase, and sucrase. These enzymes are all located on the brush border of the small intestine.
Lipid digestion involves lipase, bile salts, and bile acids, which are secreted from the pancreas and gallbladder.

Absorption occurs in the duodenum and jejunum.
Di- and tri-peptides, and amino acids are absorbed.
Active transporters mediate absorption on the apical side of the intestinal epithelium.
Passive transporters mediate absorption on the basolateral side.