Digestive System—Physiology of the Mouth,
Esophagus, and Stomach
Lecture 15
Today we’re going to pick up where we left off in anatomy and now
follow food as it goes from the mouth to the antrum of the stomach and
see the physiology and the chemical processes that are at work, just
before we move the food into the duodenum and the next portion of the
intestinal tract.
H
aving studied the anatomy of the mouth, esophagus, and stomach,
we turn now to the processes of digestion, absorption of nutrients,
and excretion of waste products. This lecture examines, rst,
mechanical digestion (the stomach’s mixing of the food, now called chyme),
then chemical digestion (the action of various acids, hormones, and enzymes
on the chyme). Next, we examine the three phases of gastric secretion and
the process of gastric emptying, as the chyme passes from the stomach to the
duodenum. Finally, we consider various stomach and digestive disorders and
their treatments.
We have already reviewed the mouth and esophagus. Breakdown of
carbohydrates and some triglycerides begins in the mouth but is not
completed there. The esophagus is merely an active passageway to the
stomach (designed not to take up too much room in the chest). We proceed
now with a bolus of food arriving in the cardia of the stomach.
The processes
Digestion is the physical and chemical breakdown of nutrients into
particles suitable for absorption.
Absorption is the movement of these broken-down nutrients from the
digestive tract into the bloodstream for use by the cells of the body.
Excretion is the expulsion of the unused products of digestion and
absorption from the body.
85
, During detoxi cation, ingested material that might otherwise be
toxic is rendered harmless.
Summary of the process to this point:
The mouth begins digestion but has no role in absorption
or excretion.
Lecture 15: Digestive System—Physiology of the Mouth, Esophagus, and Stomach
The esophagus is a conduit and has no role in absorption
or excretion.
The stomach is an organ of digestion and limited absorption
but not of excretion.
None of these is involved in detoxi cation; the primary
detoxi er is the liver.
Two primary digestion processes in the stomach
Mechanical digestion
Waves of peristalsis (muscle contractions) grind and mix the food.
The bolus is mixed with stomach juices and is now called chyme.
Very little mixing takes place in the fundus.
Salivary enzymes continue to work in the fundus, because they
have not yet mixed with acid gastric juices.
In the body of the stomach, the bolus of chyme is exposed to and
mixes with gastric acid, and salivary enzymes are inactivated.
More grinding and mixing occur in the body of the stomach.
At the antrum, there is a purposeful holdup. Only a small amount of
chyme can get into the duodenum at a time; the rest remains in the
antrum for additional mixing and grinding.
86
Esophagus, and Stomach
Lecture 15
Today we’re going to pick up where we left off in anatomy and now
follow food as it goes from the mouth to the antrum of the stomach and
see the physiology and the chemical processes that are at work, just
before we move the food into the duodenum and the next portion of the
intestinal tract.
H
aving studied the anatomy of the mouth, esophagus, and stomach,
we turn now to the processes of digestion, absorption of nutrients,
and excretion of waste products. This lecture examines, rst,
mechanical digestion (the stomach’s mixing of the food, now called chyme),
then chemical digestion (the action of various acids, hormones, and enzymes
on the chyme). Next, we examine the three phases of gastric secretion and
the process of gastric emptying, as the chyme passes from the stomach to the
duodenum. Finally, we consider various stomach and digestive disorders and
their treatments.
We have already reviewed the mouth and esophagus. Breakdown of
carbohydrates and some triglycerides begins in the mouth but is not
completed there. The esophagus is merely an active passageway to the
stomach (designed not to take up too much room in the chest). We proceed
now with a bolus of food arriving in the cardia of the stomach.
The processes
Digestion is the physical and chemical breakdown of nutrients into
particles suitable for absorption.
Absorption is the movement of these broken-down nutrients from the
digestive tract into the bloodstream for use by the cells of the body.
Excretion is the expulsion of the unused products of digestion and
absorption from the body.
85
, During detoxi cation, ingested material that might otherwise be
toxic is rendered harmless.
Summary of the process to this point:
The mouth begins digestion but has no role in absorption
or excretion.
Lecture 15: Digestive System—Physiology of the Mouth, Esophagus, and Stomach
The esophagus is a conduit and has no role in absorption
or excretion.
The stomach is an organ of digestion and limited absorption
but not of excretion.
None of these is involved in detoxi cation; the primary
detoxi er is the liver.
Two primary digestion processes in the stomach
Mechanical digestion
Waves of peristalsis (muscle contractions) grind and mix the food.
The bolus is mixed with stomach juices and is now called chyme.
Very little mixing takes place in the fundus.
Salivary enzymes continue to work in the fundus, because they
have not yet mixed with acid gastric juices.
In the body of the stomach, the bolus of chyme is exposed to and
mixes with gastric acid, and salivary enzymes are inactivated.
More grinding and mixing occur in the body of the stomach.
At the antrum, there is a purposeful holdup. Only a small amount of
chyme can get into the duodenum at a time; the rest remains in the
antrum for additional mixing and grinding.
86
