Chapter 3
Digestion, Absorption, and Transport
Digestion
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Digestion breaks down foods into nutrients.
Absorption brings the nutrients into the cells of the small intestine for
transport to the body’s cells
Path of Digestion
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Food enters the mouth and travels down the esophagus
From the esophagus it goes to the stomach
It exits the stomach through the pyloric sphincter and enters the small
intestine
It enters the large intestine and travels to the rectum
Waste is then expelled through the anus
This can be reviewed in figure 3-1
Movement of Digestion
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Once food enters the mouth and is chewed and swallowed, it is called a bolus
The bolus is moved through the body by contractions, called peristalsis
Along the route of the GI Tract, secretions are added to the bolus from many
parts of the body:
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Salivary glands
Stomach
Pancreas
Liver
Small intestine
Absorption
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Absorption takes place in the small intestine
The many folds and villi of the small intestine increase its surface area,
making nutrient absorption efficient
Nutrients pass through the cells of the intestinal villi, and enter either the
blood (if they are water soluble) or the lymph (if they are fat soluble)
The Circulatory System
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Nutrients leaving the digestive system via the blood are transported to the
liver
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The liver breaks down these nutrients into useable pieces and then transports them to the
body’s cells
Nutrients leaving the digestive system via the lymphatic system skip the liver
as the first step, but eventually get there after traveling more through the body
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The liver again processes these nutrients so that the body can use them
Health and Regulation of the GI Tract
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A diverse and abundant bacteria population supports GI health
The regulation of GI processes depends on the coordinated efforts of the
hormonal system and the nervous system
Together, digestion and absorption break down foods into nutrients for the
body’s use
To function optimally, a healthy GI tract needs a balanced diet, adequate rest,
and regular physical activity