The Digestive System

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.
2
Lesson Objectives
In this lesson, you will learn to

• Describe the structures and functions of the
  digestive system
• Show the pathway of food through the digestive
  system

3
Functions of the Digestive System
What Does Your Digestive System Do?

• The functions of the digestive system can be
  divided into three
• main processes
• Digestion
• Absorption
• Elimination

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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.

5
Functions of the Digestive System
The Digestive System
6
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

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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.

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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.

9
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.

10
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.

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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

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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.

13
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.

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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.

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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.

16
Quick Review
Choose the appropriate option.
Q. The process by which a series of involuntary
muscle contractions move food through the
digestive tract is called _______.

• peristalsis
• mastication
• digestion
• 4. absorption

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Quick Review - Answer
A. 1. peristalsis The process by which a series
of involuntary muscle contractions move food
through the digestive tract is called
peristalsis.
Click Next to attempt another question.
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Quick Review
Choose the appropriate option.
Q. Which of the following is NOT a part of the
pathway that food and undigested wastes follow
through the digestive system?

1. Mouth
2. Esophagus
3. Nose
4. Stomach

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Quick Review - Answer
A. 3. nose The pathway that is followed by food
and undigested wastes through the digestive
system does NOT include nose.
Click Next to attempt another question.
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Quick Review
Choose the appropriate option.
Q. The colonic system mechanically and chemically
breaks down food, absorbs nutrients, and
eliminates wastes.
True
False
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Quick Review - Answer
A. False. The digestive system mechanically and
chemically breaks down food, absorbs nutrients,
and eliminates wastes.
Click Next to attempt another question.
22
Quick Review
Choose the appropriate option.
Q. The digestive system interacts with the
cardiovascular system.
True
False
23
Quick Review - Answer
A. True. The digestive system interacts with the
cardiovascular system.
Click Next to attempt another question.
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End of Lesson 1
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