Digestion is the process of breaking
down foods into nutrients to prepare for
absorption while overcoming 7
Anatomy of the Digestive Tract –
The gastrointestinal (GI) tract is
the flexible muscular tube from
mouth to anus. The lumen is the
inner space of the tract.
The start of the process –
The digestive process begins in the
mouth. Food is partly broken down by
the process of chewing (mastication)
and by the chemical action of salivary
enzymes (amylase) These enzymes are
produces by the salivary glands and
break down starches into smaller
On the way to the stomach:
After being chewed and swallowed, the
food enters the esophagus. The
esophagus is a long tube that runs from
the mouth to the stomach. It uses
rhythmic, wave-like muscle movements
(called peristalsis) to force food from
the throat into the stomach. This
muscle movement gives us the ability to
eat or drink even when we're upside-
In the stomach -
The stomach is a large, sack-like
organ that churns the food and
bathes it in a very strong acid (gastric
Food in the stomach that is partly
digested and mixed with stomach
acids is called chyme
In the small intestine
After being in the stomach, food enters the
duodenum, the first part of the small
It then enters the jejunum and then the
ileum (the final part of the small intestine).
In the small intestine, bile (produced in the
liver and stored in the gall bladder),
pancreatic enzymes, and other digestive
enzymes produced by the inner wall of the
small intestine help in the breakdown of food.
In the large intestine
After passing through the small intestine,
food passes into the large intestine. In
the large intestine, some of the water
and electrolytes (chemicals like sodium)
are removed from the food.
Many microbes (bacteria like
Bacteroides, Lactobacillus acidophilus,
Escherichia coli, and Klebsiella) in the
large intestine help in the digestion
In the large intestine
The first part of the large intestine is
called the cecum (the appendix is
connected to the cecum).
Food then travels upward in the
ascending colon. The food travels
across the abdomen in the transverse
colon, goes back down the other side of
the body in the descending colon, and
then through the sigmoid colon.
The end of the process
Solid waste is then
stored in the rectum
until it is excreted via
The Secretions of Digestion
Includes digestive enzymes that act as
catalysts in hydrolysis reactions
Saliva from the salivary glands moistens foods
Gastric juice from the gastric glands includes
hydrochloric acid. The goblet cells of the
stomach wall secrete mucus to protect the
walls of the stomach from the high acidity
levels that are measured by pH units.
The Secretions of Digestion
Pancreatic juice contains intestinal
enzymes (carbohydrase, lipase, protease)
Bile is produced by the liver, stored in the
gall bladder, and acts as an emulsifier to
The Final Stage
Energy-yielding nutrients are disassembled
Vitamins, minerals and water can be
Undigested residues, including some fibers,
continue through the digestive tract and
Recycling of usable materials
The enormous surface area of the small
intestine facilitates nutrient absorption.
Nutrients can be absorbed through
simple diffusion, facilitated diffusion, or
Outside Carrier loads Carrier loads
cell nutrient on nutrient on
outside of cell . . . outside of cell . . .
Inside . . . and then . . . and then
cell releases it on releases it on
inside of cell. inside of cell.
SIMPLE FACILITATED ACTIVE
DIFFUSION DIFFUSION TRANSPORT
Some nutrients (such Some nutrients (such as the water- Some nutrients (such as
as water and small soluble vitamins) are absorbed by glucose and amino acids)
lipids) are absorbed by facilitated diffusion. They need a must be absorbed actively.
simple diffusion. They specific carrier to transport them These nutrients move
cross into intestinal from one side of the cell membrane against a concentration
cells freely. to the other. (Alternatively, gradient, which requires
facilitated diffusion may occur energy.
when the carrier changes the cell
membrane in such a way that the
nutrients can pass through.) Stepped Art
Fig. 3-9, p. 81
Anatomy of the Absorptive System
Villi are the fingerlike projections within the folds
of the small intestine that move in a wave-like
pattern to trap nutrients.
Microvilli are the microscopic hairlike projections
on each villi.
Crypts are the tubular glands that lie between the
Goblet cells are located between the villi and
secrete a protective thick mucus.
A Closer Look at the Intestinal Cells
Specialization of the cells to absorb different nutrients
“Food combining” which emphasizes separating food
for digestive purposes is a myth.
Preparing Nutrients for Transport
Water-soluble nutrients and small products of fat
digestion are released to the bloodstream.
Fat-soluble vitamins and larger fats form
chylomicrons and are released to the lymphatic
Common Digestive Problems
Food becomes lodged in the trachea.
The larnyx cannot make sounds.
The Heimlich maneuver may need to be used.
Don’t talk or laugh with food in the mouth.
Don’t eat when breathing hard.
Body’s adaptive mechanism
Dehydration is a concern.
May be self-induced as in eating
Frequent, loose, watery stools
Irritable bowel syndrome or colitis is
one of the common GI disorders.
Medical help is needed if it persists.
Thought of the day
Never, under any
circumstances, take a
sleeping pill and a
the same night
Defecation habits are different among people.
Many causes are possible.
Hemorrhoids may be a problem.
Diverticulosis is a condition in which the
intestinal walls weaken and bulge. The
bulging pockets are called diverticula.
Diverticulitis is a worsened condition and
Use of laxatives, enemas and mineral oil may
not be necessary with lifestyle changes.
Colonic irrigation is the internal washing of
the large intestine and can be hazardous.
Respond quickly to the urge to defecate.
Belching and Gas
Relax while eating.
Watch bothersome foods.
Hiccups are triggered by eating or
drinking too fast.
Gastroesophageal reflux is the
backward flow of stomach contents into
Antacids and acid controllers may help
Liquids between meals
Sit up while eating.
Wait 1 hour after eating before lying down.
Wait 2 hours after eating before exercising.
Refrain from tight-fitting clothing.
Avoid bothersome foods.
Refrain from tobacco use.
Lose weight if overweight.
Peptic ulcers can be gastric or
Take prescribed medicine.
Avoid caffeine- and alcohol-containing
Minimize aspirin and ibuprofen use.