Class notes
Chapter 3 - Digestion
- Course
- Nutrition
- Institution
- Charleston Southern University
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Ch 3. Digestion, Absorption, TransportThursday, August 25, 2022 7:53 AM
1. Review the parts of and organs associated with the digestive tract
a. Digestion - the process by which food is broken down into
absorbable units
b. Gastrointestinal tract - the digestive tract. The principal organs
are the stomach and intestines
c. Digestive system - all the organs and glands associated with the
ingestion and digestion of food
2. Describe the digestion that occurs in the mouth
a. Mechanical digestion - chewing and breaking of the food into
smaller pieces
b. Chemical - where starches are broken down by enzymes
i. Amylase - from the saliva
3. Define bolus
a. a portion; with respect to food, the amount swallowed at one
time
4. Describe the actions of the esophagus and stomach
a. Peristalsis - wavelike muscular contractions of the GI tract that
push its contents along
i. The stomach has pacemaker cells in the longitudinal
muscle of the greater curvature that causes the stomach
to contract once every 20 seconds
b. Hydrochloric Acid (HCl) - released to cause denaturing of the
proteins
5. Define chyme - the semiliquid mass of partly digested food expelled
by the stomach into the duodenum
6. Describe digestion in the small intestine
a. Intestinal cells contain enzymes embedded in the cell
membranes to break down food molecules
b. Zymogens - enzymes that need to be cut in order to be active
c. Bicarbonate - secreted by the pancreas to neutralize the acid
from the stomach
d. Bile - made by the liver and stored in the gallbladder
e. Emulsifier - helps fats mix with water; the breaking down of
large fat globules to medium size globules, to small fat globules
7. Define intestinal flora - normal bacteria that live inside of the
intestine
a. About 400 different kinds of bacteria
○ Microbes - microscopically small organisms including bacteria,
, c. Bicarbonate - secreted by the pancreas to neutralize the acid
from the stomach
d. Bile - made by the liver and stored in the gallbladder
e. Emulsifier - helps fats mix with water; the breaking down of
large fat globules to medium size globules, to small fat globules
7. Define intestinal flora - normal bacteria that live inside of the
intestine
a. About 400 different kinds of bacteria
○ Microbes - microscopically small organisms including bacteria,
viruses, fungi, and protozoa; also called microorganisms
○ Human microbiome - the collection of microbes found in or on
the human body
○ Prebiotics - food components (such as fibers) that are not
digested by the human body but are used as food by the GI
bacteria to promote their growth and activity
8. Define segmentation - the squeezing of intestinal muscles back and
forth to move the food
a. Segmentation - a periodic squeezing or partitioning of the
intestine at intervals along its length by its circular muscles
b. Probiotics - living microorganisms found in foods and dietary
supplements that, when consumed in sufficient quantities, are
beneficial to health
9. Describe the wall of the small intestine
a. Microvilli - small projections responsible for absorbing
nutrients; aka the brush border of the small intestine; have
enzymes, receptors, and chemicals imbedded in them for
absorbing nutrients
○ Villi - fingerlike projections from the folds of the small
intestine ; singular villus
○ Microvilli - tiny, hairlike projections on each cell of every
villus that can trap nutrient particles and transport them
into the cells; singular microvillus
○ Crypts - tubular glands that lie between the intestinal villi
and secrete intestinal juices Into the small intestine
○ Goblet cells - cells of the GI tract (and lungs) that secrete
mucus
b. Lacteals - blood and lymphatic capillaries deep inside the
microvilli
10. Discuss absorption of carbohydrates, proteins, nucleic acids,
vitamins, minerals, salts, and fats
a. Everything except fats is absorbed into the blood by the
microvilli and go directly to the liver
b. Fats are combined with proteins
i. Then they are absorbed by the lymphatic capillaries of
the villi and then go straight to the heart
c. Absorption - the uptake of nutrients by the cells of the small
intestine for transport into either the blood or the lymph
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