During this lesson students adventure through the
digestive system via the Internet. They then use their knowledge of the
digestive system to create an original story about their favorite food's
adventure down the digestive track.
Content Standard(s):
Identify
major body systems and their functions, including the circulatory system,
respiratory system, excretory system, and reproductive system.
Compose expository texts using an introductory
paragraph that includes a main idea; supporting paragraphs with a minimum
of three reasons, explanations, or steps in a process; and a conclusion.
Apply
mechanics in writing, including capitalization of first word in a direct
quotation and use of punctuation, including quotation marks and comma with
direct quotations, colon to introduce a list, and commas after introductory
words, with a noun of direct address, and in a compound sentence.
Demonstrate knowledge of grammar and usage
concepts, including subject-verb agreement with a compound subject;
present, past, and future verb tenses; forms of adjectives; forms of nouns;
and subject, object, and possessive pronouns.
Collect information from a variety of digital
sources.
Write informative or explanatory texts to
examine a topic and convey ideas and information clearly.
Demonstrate command of the conventions of
Standard English grammar and usage when writing or speaking.
Demonstrate command of the conventions of
Standard English capitalization, punctuation, and spelling when writing.
Primary Learning Objective(s):
Students will demonstrate their knowledge of the
digestive system by writing a short story from the viewpoint of a favorite
food traveling through the digestive system.
Approximate Duration
61 to 90 Minutes
Technology Resources Needed:
Computer with Internet access
Background/Preparation:
Students should have studied the digestive
system, be able to use the writing process to create a short story, and be
able to navigate the Internet.
Procedures/Activities:
1.)Begin the lesson by reviewing what students
have learned about the digestive system:
Digestion is the process that breaks down food into small molecules so that
they can be absorbed and moved into the blood. From the blood, food molecules
are transported across the cell membrane to be used by the cell. Unused
molecules pass out of your body as wastes. Food passes through the mouth
where saliva begins to break it down. Food then is pushed down the esophagus
by a muscle contraction called peristalsis. Food is emptied into the stomach
where more chemical digestion takes place by hydrochloric acid and enzymes
break down food for the body to use it. The food is passed into the small
intestines where it is absorbed by the body. The large intestine is its last
stop where all of the water is absorbed.
2.)Allow students to continue the review by
visiting the following websites:
(Human Digestive System) This site has many details about digestion and a diagram of the different
body parts.
3.)Website:
(http://digestivelessonplan1.blogspot.com/) This blog contains videos even movie that gives many facts about the
digestive system. Students will enjoy learning how our digestive system
compares to other animals.
4.)Website:
(MEDtropolis) This site allows students to take a guided tour of the digestive system.
It also allows students to practice putting the digestive track in order.
5.)To conclude this lesson, ask students to write
a short story about the digestive track. Instruct students to write about
their favorite food's journey down the digestive track. Instruct them to
include all the parts of the digestive track and their functions in their
story.
What is Digestive system? The digestive system is a group of organs
working together to convert food into energy and basic nutrients to
feed the entire body. Food passes through a long tube inside the body
known as the alimentary canal or the gastrointestinal tract (GI tract).
The alimentary canal is made up of the oral cavity, pharynx, esophagus,
stomach, small intestines, and large intestines. In addition to the
alimentary canal, there are several important accessory organs that help
your body to digest food but do not have food pass through them. Accessory organs of the
digestive system include the teeth, tongue, salivary glands, liver,
gallbladder, and pancreas. To achieve the goal of providing energy and
nutrients to the body, six major functions take place in the digestive
system:
Ingestion
Secretion
Mixing and movement
Digestion
Absorption
Excretion
Digestive System Anatomy
Mouth
Food begins its journey through the digestive system in the mouth, also known as the oral cavity.
Inside the mouth are many accessory organs that aid in the digestion of
food—the tongue, teeth, and salivary glands. Teeth chop food into small
pieces, which are moistened by saliva before the tongue and other
muscles push the food into the pharynx.
Teeth. The teeth
are 32 small, hard organs found along the anterior and lateral edges of
the mouth. Each tooth is made of a bone-like substance called dentin
and covered in a layer of enamel—the hardest substance in the body.
Teeth are living organs and contain blood vessels and nerves under the
dentin in a soft region known as the pulp. The teeth are designed for
cutting and grinding food into smaller pieces.
Tongue. The tongue
is located on the inferior portion of the mouth just posterior and
medial to the teeth. It is a small organ made up of several pairs of muscles
covered in a thin, bumpy, skin-like layer. The outside of the tongue
contains many rough papillae for gripping food as it is moved by the
tongue’s muscles. The taste buds on the surface of the tongue detect
taste molecules in food and connect to nerves in the tongue to send
taste information to the brain. The tongue also helps to push food
toward the posterior part of the mouth for swallowing.
Salivary Glands. Surrounding the mouth are 3 sets of
salivary glands. The salivary glands are accessory organs that produce a
watery secretion known as saliva. Saliva helps to moisten food and
begins the digestion of carbohydrates. The body also uses saliva to
lubricate food as it passes through the mouth, pharynx, and esophagus.
Pharynx
The pharynx, or throat, is a
funnel-shaped tube connected to the posterior end of the mouth. The
pharynx is responsible for the passing of masses of chewed food from the
mouth to the esophagus. The pharynx also plays an important role in the
respiratory system, as air from the nasal cavity passes through the
pharynx on its way to the larynx and eventually the lungs. Because the pharynx serves two different functions, it contains a flap of tissue known as the epiglottis that acts as a switch to route food to the esophagus and air to the larynx.
Esophagus
The esophagus is a muscular tube connecting the pharynx to the stomach that is part of the upper gastrointestinal tract.
It carries swallowed masses of chewed food along its length. At the
inferior end of the esophagus is a muscular ring called the lower esophageal
sphincter or cardiac sphincter. The function of this sphincter is to
close of the end of the esophagus and trap food in the stomach.
Stomach
The stomach is a muscular sac that is located on the left side of the abdominal cavity, just inferior to the diaphragm.
In an average person, the stomach is about the size of their two fists
placed next to each other. This major organ acts as a storage tank for
food so that the body has time to digest large meals properly. The
stomach also contains hydrochloric acid and digestive enzymes that
continue the digestion of food that began in the mouth.
Small Intestine
The small intestine is a long, thin tube about 1 inch in diameter and about 10 feet long that is part of the lower gastrointestinal tract.
It is located just inferior to the stomach and takes up most of the
space in the abdominal cavity. The entire small intestine is coiled like
a hose and the inside surface is full of many ridges and folds. These
folds are used to maximize the digestion of food and absorption of
nutrients. By the time food leaves the small intestine, around 90% of
all nutrients have been extracted from the food that entered it. Liver and Gallbladder
The liver
is a roughly triangular accessory organ of the digestive system located
to the right of the stomach, just inferior to the diaphragm and
superior to the small intestine. The liver weighs about 3 pounds and is
the second largest organ in the body. The liver has many different
functions in the body, but the main function of the liver in digestion
is the production of bile and its secretion into the small intestine.
The gallbladder
is a small, pear-shaped organ located just posterior to the liver. The
gallbladder is used to store and recycle excess bile from the small
intestine so that it can be reused for the digestion of subsequent
meals.
Pancreas
The pancreas
is a large gland located just inferior and posterior to the stomach. It
is about 6 inches long and shaped like short, lumpy snake with its
“head” connected to the duodenum and its “tail” pointing to the left
wall of the abdominal cavity. The pancreas secretes digestive enzymes
into the small intestine to complete the chemical digestion of foods.
Large Intestine The large intestine
is a long, thick tube about 2 ½ inches in diameter and about 5 feet
long. It is located just inferior to the stomach and wraps around the
superior and lateral border of the small intestine. The large intestine
absorbs water and contains many symbiotic bacteria that aid in the
breaking down of wastes to extract some small amounts of nutrients.
Feces in the large intestine exit the body through the anal canal.
Digestive System Physiology
The digestive system is responsible for taking whole foods and
turning them into energy and nutrients to allow the body to function,
grow, and repair itself. The six primary processes of the digestive
system include:
Ingestion of food
Secretion of fluids and digestive enzymes
Mixing and movement of food and wastes through the body
Digestion of food into smaller pieces
Absorption of nutrients
Excretion of wastes
Ingestion
The first function of the
digestive system is ingestion, or the intake of food. The mouth is
responsible for this function, as it is the orifice through which all
food enters the body. The mouth and stomach are also responsible for the
storage of food as it is waiting to be digested. This storage capacity
allows the body to eat only a few times each day and to ingest more food
than it can process at one time.
Secretion
In
the course of a day, the digestive system secretes around 7 liters of
fluids. These fluids include saliva, mucus, hydrochloric acid, enzymes,
and bile. Saliva moistens dry food and contains salivary amylase, a
digestive enzyme that begins the digestion of carbohydrates. Mucus
serves as a protective barrier and lubricant inside of the GI tract.
Hydrochloric acid helps to digest food chemically and protects the body
by killing bacteria present in our food. Enzymes are like tiny
biochemical machines that disassemble large macromolecules like proteins, carbohydrates, and lipids into their smaller components. Finally, bile is used to emulsify large masses of lipids into tiny globules for easy digestion.
Mixing and Movement
The digestive system uses 3 main processes to move and mix food:
Swallowing. Swallowing is the process of using smooth and
skeletal muscles in the mouth, tongue, and pharynx to push food out of
the mouth, through the pharynx, and into the esophagus.
Peristalsis. Peristalsis is a muscular wave that travels
the length of the GI tract, moving partially digested food a short
distance down the tract. It takes many waves of peristalsis for food to
travel from the esophagus, through the stomach and intestines, and reach the end of the GI tract.
Segmentation. Segmentation occurs only in the small
intestine as short segments of intestine contract like hands squeezing a
toothpaste tube. Segmentation helps to increase the absorption of
nutrients by mixing food and increasing its contact with the walls of
the intestine.
Digestion
Digestion is the process of
turning large pieces of food into its component chemicals. Mechanical
digestion is the physical breakdown of large pieces of food into smaller
pieces. This mode of digestion begins with the chewing of food by the
teeth and is continued through the muscular mixing of food by the
stomach and intestines. Bile produced by the liver is also used to
mechanically break fats into smaller globules. While food is being
mechanically digested it is also being chemically digested as larger and
more complex molecules are being broken down into smaller molecules
that are easier to absorb. Chemical digestion begins in the mouth with
salivary amylase in saliva splitting complex carbohydrates into simple
carbohydrates. The enzymes and acid in the stomach continue chemical
digestion, but the bulk of chemical digestion takes place in the small
intestine thanks to the action of the pancreas. The pancreas secretes an
incredibly strong digestive cocktail known as pancreatic juice, which
is capable of digesting lipids, carbohydrates, proteins and nucleic
acids. By the time food has left the duodenum, it has been reduced to its chemical building blocks—fatty acids, amino acids, monosaccharides, and nucleotides.
Absorption
Once
food has been reduced to its building blocks, it is ready for the body
to absorb. Absorption begins in the stomach with simple molecules like
water and alcohol being absorbed directly into the bloodstream. Most
absorption takes place in the walls of the small intestine, which are
densely folded to maximize the surface area in contact with digested
food. Small blood and lymphatic vessels in the intestinal wall pick up
the molecules and carry them to the rest of the body. The large
intestine is also involved in the absorption of water and vitamins B and K before feces leave the body.
Excretion
The
final function of the digestive system is the excretion of waste in a
process known as defecation. Defecation removes indigestible substances
from the body so that they do not accumulate inside the gut. The timing
of defecation is controlled voluntarily by the conscious part of the
brain, but must be accomplished on a regular basis to prevent a backup
of indigestible materials
esophageal
sphincter or cardiac sphincter. The function of this sphincter is to
close of the end of the esophagus and trap food in the stomach.