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SC 131 Unit 5
Digestive System
EMILY BRADSHAW, PH.D.
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Agenda
 Anatomy of the digestive system
 Process of digestion
 Benefits of dietary fiber
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
The Digestive System and Body
Metabolism
 Digestion
 Breakdown of ingested
food
 Absorption of nutrients
into the blood
 Metabolism
 Production of cellular
energy (ATP)
 Constructive and
degradative cellular
activities
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Processes of the Digestive System
 Ingestion
 Mechanical Digestion
 Chemical Digestion
 Enzymes break down food
 Carbohydrates are broken
to simple sugars
 Proteins are broken to
amino acids
 Fats are broken to fatty
acids and alcohols
 Absorption
 Defecation
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Mouth (Oral Cavity) Anatomy
 Mastication (chewing)
of food
 Mixing masticated food
with saliva
 Initiation of swallowing
by the tongue
 Allowing for the sense
of taste
Figure 14.2a
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Pharynx Function
 Serves as a passageway
for air and food
 Food is propelled to the
esophagus by two
muscle layers
 Longitudinal inner
layer
 Circular outer layer
 Food movement is by
alternating contractions
of the muscle layers
(peristalsis)
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Esophagus
 Runs from pharynx to
stomach through the
diaphragm
 Conducts food by
peristalsis
(slow rhythmic
squeezing)
 Passageway for food
only (respiratory
system branches off
after the pharynx)
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Stomach Functions
 Acts as a storage
tank for food
 Site of food
breakdown
 Chemical
breakdown of
protein begins
 Delivers chyme
(processed food)
to the small
intestine
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Structure of the Stomach Mucosa
 Gastric pits formed by
folded mucosa
 Presence of food or falling
pH causes the release of
gastrin
 Gastrin causes stomach
glands to produce proteindigesting enzymes
 Hydrocholoric acid makes
the stomach contents very
acidic
 Activates pepsinogen to
pepsin for protein digestion
 Provides a hostile
environment for
microorganisms
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Chemical Digestion in the Small Intestine
 Source of enzymes that are mixed with chyme
 Intestinal cells
 Pancreas
 Bile enters from the gall bladder
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Villi of the Small Intestine
 Fingerlike structures
formed by the mucosa
 Give the small intestine
more surface area
 Absorptive cells
 Blood capillaries
 Lacteals – absorb fat
Figure 14.7a
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Stimulation of the Release of Pancreatic
Juice
 Vagus nerve
 Local hormones
 Secretin
 Cholecystokinin
 Pancreatic enzymes
play the major
digestive function
 Lipase
 Nucleases
 Alkaline
Figure 14.16
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Absorption in the Small Intestine
 Water is absorbed along the length of the
small intestine
 End products of digestion
 Most substances are absorbed by active
transport through cell membranes
 Lipids are absorbed by diffusion
 Substances are transported to the liver by the
hepatic portal vein or lymph
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Large Intestine
 Larger in diameter, but
shorter than the small
intestine
 Does NOT participate in
digestion of food; ONLY
absorption of water
 Eliminates indigestible food
from the body as feces
 Goblet cells produce mucus
to act as a lubricant
 Resident bacteria digest
remaining nutrients
 Produce some vitamin K
and B
 Release gases
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Liver
 Largest gland in the body
 Consists of four lobes suspended from the
diaphragm and abdominal wall
 Connected to the gall bladder via the common
hepatic duct
 Bile - produced by cells in the liver
 Composition: bile salts, bile pigment (mostly
bilirubin from the breakdown of hemoglobin),
cholesterol, phospholipids, electrolytes
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Gall Bladder
 Sac found in hollow fossa of liver
 Stores bile from the liver by way of the cystic
duct
 Bile is introduced into the duodenum in
the presence of fatty food
 Gallstones can cause blockages
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Dietary Fiber
 Includes all parts of plant foods that your body
can't digest or absorb.
 Fiber is commonly classified into two categories:
those that don't dissolve in water (insoluble fiber)
and those that do (soluble fiber).
 Insoluble fiber: Promotes the movement of
material through your digestive system and
increases stool bulk.
 Examples: Whole-wheat flour, wheat bran,
nuts and many
 Soluble fiber: Dissolves in water to form a gel-like
material. It can help lower blood cholesterol and
glucose levels.
 Examples: Oats, peas, beans, apples, citrus
fruits, carrots, and barley
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www.pharmage.com
Benefits of Dietary Fiber
 Normalizes bowel movements. Dietary fiber increases the weight and size of your
stool and softens it. A bulky stool is easier to pass, decreasing your chance of
constipation.
 Helps maintain bowel integrity and health. A high-fiber diet may lower your risk of
developing hemorrhoids, and small pouches in your colon (diverticular disease).
 Lowers blood cholesterol levels. Soluble fiber found in beans, oats, flaxseed and oat
bran may help lower total blood cholesterol levels by lowering low-density
lipoprotein, or "bad," cholesterol levels.
 Helps control blood sugar levels. Fiber, particularly soluble fiber, can slow the
absorption of sugar, which for people with diabetes can help improve blood sugar
levels.
 Aids in weight loss. High-fiber foods generally require more chewing time, which
gives your body time to register when you're no longer hungry, so you're less likely to
overeat. Also, a high-fiber diet tends to make a meal feel larger and linger longer, so
you stay full for a greater amount of time. And high-fiber diets also tend to be less
"energy dense," which means they have fewer calories for the same volume of food.
 Uncertain effect on colorectal cancer. Evidence that dietary fiber reduces colorectal
cancer is mixed — some studies show benefit, some show nothing and some suggest
increased risk.
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Sources of dietary fiber
 Grains and whole-grain products
 Fruits
Image credit:
www.fiberchoice.com
 Vegetables
 Beans, peas and other legumes
 Nuts and seeds
 Refined or processed foods — such as canned fruits and
vegetables and pulp-free juice, white bread and pasta, and
non-whole-grain cereals — are lower in fiber content. Whole
foods rather than fiber supplements are generally better.
 Fiber supplements — such as Metamucil, Citrucel and
FiberCon — don't provide the vitamins, minerals and other
beneficial nutrients that high-fiber foods do.
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Questions????
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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings