The Digestive System
Lab 11 rev 4-11
• Digestion is a process of breaking down large
molecules contained in food into basic building
blocks which our body can then use as nutrients.
• Digestion process accomplished in 2 ways:
– mechanical digestion--breaking down of large
food particles into smaller pieces
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The Digestive System
Lab 11
• chemical digestion--takes these smaller pieces,
extracts the proteins, starches, or fats and then
processes these into their building blocks:
amino acids, sugars, fatty acids and glycerol.
– Enzymes and other chemicals help with
chemical digestion
– see table 15.1 on page 142 of the manual for a list
of major digestive enzymes and chemical reactions
• the digestive system also stores the waste byproducts from the digestive process until it can be
eliminated from the body.
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The Digestive System - Lab 11
• The digestive system includes:
– mouth
--small intestine
– pharynx
--large intestine
– esophagus
--rectum
– stomach
--anus
• These organs are collectively called the Gastrointestinal
System or Tract. It is actually a hollow tube extending
from the mouth to the anus.
– The space within the tube is called the lumen.
Structure of the walls of the digestive tract
– consists of 4 layers of tissue
– serosa, the outer layer; is made up of connective tissue
covered with an epithelial membrane.
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The Digestive System
Lab 11
– muscularis-the thickest part of the wall; is
composed of 2 layers of smooth muscle. Each
layer runs in a different direction
• this layer is responsible for peristalsis (the
wavelike propulsion of material through the
digestive tract) and segmentation (the back
and forth mixing of food which occurs
primarily in the small intestine).
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The Digestive System
Lab 11
– submucosa-made of connective tissue which
contains blood, lymphatic vessels, and nerves.
• This layer also has a lot of elastic fibers.
This enable the stomach to stretch with
meals and regain its usual shape after meals.
• Lymphatic capillaries in the digestive tract
are called lacteals. They play a major role
in absorbing digested fat from the intestine.
– mucosa-the innermost layer which is composed
of simple columnar epithelium
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The Digestive System
Lab 11
• The mouth (or oral cavity)
– mechanical and chemical digestion occur here
• the teeth and tongue break food into smaller
pieces (mechanical digestion)
• the salivary glands secrete water, mucus
and an enzyme, amylase, to begin the
process of chemically digestion
• The pharynx (throat) is where swallowing starts.
• The esophagus is a muscular tube. As we
swallow, we push food along in this tube until the
food reaches our stomach.
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The Digestive System
Lab 11
• The stomach performs both chemical and
mechanical digestion.
– Mechanical is the crushing and churning of
food performed by the smooth muscle in the
wall of the stomach
– Chemically, the stomach produces pepsin and
hydrochloric acid (HCl) which continue to
break down food
– Food is liquefied here before continuing further
down the intestinal tract
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The Digestive System
Lab 11
• The small intestine is the major site of chemical
digestion
– finishes the job of breaking down food
– named small intestine because of the diameter of the
tube
– is divided into sections to help identify how
different areas of the small intestine function
• the first section is the duodenum
(approximately 10 inches long)
• the second section is the jejunum(10 ft long)
• the last section is the ileum (10 ft long)
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The Digestive System
Lab 11
• The structure of the wall of the small intestine
helps in absorption
– the mucosa (name of the tissue of the walls)
contains many large folds covered with small
fingerlike projections called villi
– each epithelial cell of the villi contain
microvilli which are smaller fingerlike
projections
– the villi and the microvilli enlarge the surface
area of the small intestine thus increasing its
ability to absorb nutrients
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The Digestive System Lab 11
• The duodenum (first section or region)
– most digestion actually occurs here
– the pancreas contributes enzymes and sodium
bicarbonate (NaHCO3) into the duodenum to
help with digestion
– the liver and gallbladder deliver bile
• bile is a surfactant which breaks large fat
globules into smaller globules; this is
actually a mechanical (vs. chemical) change
• the jejunum and the ileum
• are where most nutrient and water absorption occurs
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The Digestive System
Lab 11
• The large intestine
– mainly involved in water absorption, solidification and
storage of digestive wastes
– named large intestine because of its diameter
(approximately 2-1/2 inches vs. 1 inch)
– has several sections:
– Cecum (a blind pouch)
– colon (this is further broken down into the
ascending, transverse, descending and sigmoid
colon)
– rectum
– anus
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The Digestive System
Lab 11
• The large intestine begins at the cecum. A small
fingerlike pouch, called the appendix, extends out
of the cecum. It has no known digestive function.
• The colon begins at the end of the cecum.
– The position in the abdomen of the ascending,
transverse, and descending colon are
reflected by the names of each of these
sections.
– The sigmoid colon joins the end of the
descending colon and ends in the rectum.
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The Digestive System
Lab 11
– The anal canal is the name of the passageway
from the rectum to the anus through which the
fecal matter or feces (the technical name of the
solid waste material) passes in order to exit the
body.
• Microorganisms that live in the large intestine
produce vitamin K which is important for blood
clotting.
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The Digestive System
Lab 11
• Metabolism
– a calorie is a measure of heat energy as well as a way to
quantify the amount of energy stored in food.
– Nutritionists are actually using the term kilocalorie
when they describe calories. So, when you see the term
“Calorie” used with a capital “C”, the lab manual is
referring to kilocalories.
– The Peanut Test activity on page 147 demonstrates the
connection between calories and heat energy and
demonstrates how much more efficient the human body
is at extracting energy from food than fire is.
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The Digestive System
REMINDER, page 1:
1. Learn the digestive system structures on the
models. Use the figure on page 143 as a guide.
You don't need to know the specific names of
each of the salivary glands.
2. Use the model of the digestive tract wall to learn
the four tissue layers and key structures (serosa,
muscularis, submucosa, mucosa, villi, capillary
and lacteals).
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The Digestive System
REMINDER, page 2:
3. On the fetal pig, learn the bulleted, bold print
structures on pages 145-146.
– The pig figures in the lab book are hard to follow, so
use the color photos on your tables to make this easier.
– Also note that a pig doesn't have an ascending or
transverse colon.
4. Do the Peanut Test activity on page 147 and the
Enzyme Function activity on pages 148-9. Use 1
peanut without the shell and the large test tubes.
– DON'T EAT THE PEANUTS; they are very old
(anywhere from 3 months to 3 years).
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