Lesson 1
The Digestive System
When does digestion begin?
Digestion begins when you take your
first bite of food.
Food and drink must be changed into
smaller nutrients before they can be
absorbed into the blood and carried
to cells in the body.
Lesson 1
Lesson Objectives
In this lesson, you’ll learn to:
Identify the structures and functions of the digestive
system.
Describe the pathway of food through the digestive system.
Demonstrate knowledge about personal health concerns
related to the digestive system.
Lesson 1
Functions of the Digestive System
What Does Your Digestive System Do?
The functions of the digestive system can be divided into three
main processes:
1. Digestion
2. Absorption
3. Elimination
Lesson 1
Functions of the Digestive System
The Digestive Processes
The nervous system triggers the digestive process.
Digestion includes a mechanical process involving chewing,
mashing, and breaking food into smaller pieces.
It also includes a chemical process involving digestive juices
that change food into simpler substances.
After the food has been broken down, nutrients are absorbed
into the blood and delivered to all cells of the body by the
cardiovascular system.
Lesson 1
Functions of the Digestive System
The Digestive System
Lesson 1
Structures of the Digestive System
Structures Involved in Ingestion
The digestive process begins in the mouth. Ingestion, the first
stage of the digestive process, is the taking of food into the
body.
Structures involved in ingestion include:
Teeth
Salivary glands
Tongue
Lesson 1
Structures of the Digestive System
Teeth
The primary function of
the teeth is to break the
food you eat into smaller
pieces.
Mastication prepares food
to be swallowed.
Lesson 1
Structures of the Digestive System
Salivary Glands
The salivary glands in the mouth
produce the first digestive juices
used in the digestive process.
Saliva produced by these glands
contains an enzyme that begins
to break down the starches and
sugars in food into smaller
particles.
Saliva also lubricates food,
making it easier to swallow.
Lesson 1
Structures of the Digestive System
Tongue
The tongue forms chewed food into a size and shape that can be
swallowed.
As you swallow, muscular
contractions force food into the
pharynx, or throat.
The uvula closes the opening to the
nasal passages.
The epiglottis closes the opening to
the trachea to prevent food from
entering the respiratory system.
Lesson 1
Structures of the Digestive System
The Esophagus
When food is swallowed, it
enters the esophagus.
Food is moved through the
esophagus, stomach, and
intestines by a process called
peristalsis.
A sphincter muscle at the
entrance to the stomach
allows food to move from the
esophagus into the stomach.
Lesson 1
Structures of the Digestive System
The Stomach
The stomach has three tasks in digestion:
1. Mixing foods with gastric juices
2. Storing swallowed food and liquid
3. Moving chyme into the small
intestine
Lesson 1
Structures of the Digestive System
The Pancreas, Liver, and Gall Bladder
In the small intestine, juices
of two other digestive organs
mix with the food to continue
the process of digestion.
The pancreas produces
enzymes that break down the
carbohydrates, fats, and
proteins in food.
The liver produces bile, which
is stored in the gall bladder.
Lesson 1
Structures of the Digestive System
The Small Intestine
The small intestine consists of three parts, the duodenum, the
jejunum, and the ileum.
As chyme enters the duodenum from the stomach, it is further
dissolved by digestive juices secreted from glands in the lining
of the small intestine, liver, and pancreas.
Nutrients entering the capillaries that line the villi are absorbed
and carried throughout the body by the cardiovascular system.
Unabsorbed material leaves the small intestine in the form of
liquid and fiber and moves by peristalsis into the large intestine.
Lesson 1
Structures of the Digestive System
The Large Intestine
The undigested parts of food pass into the colon, or large
intestine.
The main functions of the large intestine are to absorb water,
vitamins, and salts, and to eliminate wastes.
Lesson 1
Structures of the Digestive System
Removing Wastes from the Body
Solid wastes are eliminated
through the large intestine.
Some waste is excreted through
the pores by perspiration.
Carbon dioxide is expelled
through the lungs when you
exhale.
Liquid wastes are filtered
through the urinary system.