Chapter 3
Carbohydrates
Mouth
 Digestion of carbohydrate begins in the mouth, with the
secretion of the enzyme salivary amylase from the
serous cells of the salivary gland.
 This enzyme breaks starch and glycogen into
disaccharides.
 The mucous cells of the salivary gland secrete a mucus,
which causes the food to stick together, and acts as a
lubricant to aid in swallowing.
 The salivary glands are grouped into three categories:
the parotid gland, submandibular glands, and
sublingual, all located near the mouth.
Lipids
Mouth
 Mechanical digestion occurs in the mouth by the
mixing and churning of food and the release of mucus
to lubricate the food.
 The food containing fats essentially follow the same
pathway as carbohydrate foods, with chemical
digestion primarily beginning in the stomach.
 No chemical digestion of lipids occurs in the mouth.
Protein
Mouth
 As food containing protein enters the
mouth, mucus is secreted to bind the
particles together.
 No chemical digestion of protein
occurs in the mouth.
Esophagus
 The food (bolus) is forced into the pharynx by the
tongue. As the food is swallowed, it moves into the
esophagus (a straight collapsible tube), which
essentially provides a passageway from the pharynx to
the stomach.
 The mucus glands of the esophagus secrete mucus to
aid in moistening and lubricating the bolus.
 The peristaltic reactions of the muscles push the bolus
through the esophagus.
Cardiac Sphincter
 The bolus passes through the cardiac sphincter, into
the first section of the stomach.
Regions of the Stomach
 The stomach is divided into several regions: the
cardiac region, body region, fundic region, and
pyloric region.
Carbohydrates
Stomach
 The stomach works to mix and churn the food, which
aids in further digestion of carbohydrates.
 At this point, the bolus is converted into a semifluid
paste of bolus and gastric juices called chyme.
 No chemical digestion occurs in the stomach.
Lipids
Stomach
 The surface of the inner lining of the stomach contains
openings called gastric glands, which are made up of
three types of cells: mucous cells, chief cells, and
parietal cells. A hormone called gastrin stimulates the
gastric glands to secrete their fluids.
Lipids
Stomach
 Gastric enzymes are secreted by the chief cells, while
hydrochloric acid is secreted by the parietal cells. The
combination of mucus, hydrochloric acid and enzymes
is referred to as gastric juices.
 The gastric juices contain small amounts of gastric
lipase, which begin the breaking down of specific
lipids.
 A hormone called somatostatin inhibits the release of
acid. As the stomach churns, it mixes the bolus and
converts it into a semifluid referred to as chyme.
Protein
Stomach
 The chief cells located in the stomach secrete gastric
juices containing an enzyme precursor called
pepsinogen. As it comes in contact with hydrochloric
acid, it is converted into an active form referred to as
pepsin.
Pyloric Sphincter
 The chyme then travels through the pyloric sphincter
into the first section of the small intestines.
Sections of Small Intestines
The small intestines is divided
into three sections:
duodenum,
jejunum,
ileum.
Carbohydrates
Small Intestines
 As the chyme moves into the duodenum, an enzyme
called pancreatic amylase is released through the
pancreatic duct. This enzyme splits molecules of
starch and glycogen into disaccharides.
 Enzymes released by the walls of the small intestines
sucrase, maltase, and lactase, break down the
disaccharides into monosaccharide.
Lipids
Small Intestines
 As the chyme passes into the duodenum,
cholecystokinin stimulates the gallbladder to release a
substance called bile through the common bile duct.
The function of bile is to emulsify fats, or break them
into smaller droplets. This allows the small droplets of
fat to be digested more effectively.
 Pancreatic Amylase is released by the Pancreas to
continue to work on the Lipids.
 The mucosal cells of the SI release an enzyme called
intestinal lipase, which splits fats into fatty acids and
glycerol.
Protein
Small Intestines
 When protein reaches the duodenum, the pancreas
releases three protein splitting enzymes in inactive forms
called trypsinogen, chymotrypsinogen, and
procarboxypeptidase.
 Once trypsinogen comes in contact with an enzyme
called enterokinase, which is secreted by the mucosal
cells of the small intestines, then trypsin is activated.
 The presence of trypsin then activates the inactive
procarboxypeptidase and chymotrypsinogen, and
they are converted into chymotrypsin and
carboxypeptidase.
Illeocecal Valve
 The remainder (waste, fiber and water) moves through
the Illeocecal valve into the colon.
Colon
Sections:
Cecum, Ascending Colon,
Transverse, Descending,
Sigmoid
Rectum
Anus
Waste is then removed from the
body from this passage.