Intro to: The Digestive System
• The digestive system’s role is to break down
food into a form that can be absorbed by the
body, as well as to eliminate solid waste.
• The digestive system can be divided into two
parts:
• The digestive tract
• The digestive glands
Digestive Tract
• The digestive tract is defined as “The
passageway of food that begins at the mouth
down to the throat, esophagus, stomach,
intestines, and finally to the anus.”
• It is the path that food takes in and then out
of our bodies.
• The digestive tract includes the mouth,
pharynx, esophagus, stomach, small intestine,
and large intestine (which terminates with the
rectum and anus)
Digestive glands
• The digestive glands secrete chemicals that
are needed to digest food as it travels along
the digestive tract.
• The glands include salivary glands, gastric
glands (stomach), the liver, the pancreas and
intestinal glands.
Function of digestion
• Intake and propulsion of food down the
digestive tract
• Breaking food down into nutrients (digestion)
• Absorption of nutrients
• Elimination of waste (fecal) matter
Ingestion and propulsion of food
• How does food enter and move along the
digestive tract? It does so in two different
ways:
• Food is swallowed to enter the digestive tract.
This is called deglutition.
• Smooth muscle contractions in the esophagus,
stomach, and intestines move food along the
digestive tract. This is called peristalsis.
How does deglutition work?
P. 168 in textbook
Peristalsis
Digestion
• Once food enters the mouth, the process of
digestion begins.
(Yes, you have already written the definition of
digestion.. Quick review: what is it?)
• Food undergoes two types of transformation
in the digestive process:
• Mechanical transformation: physically
breaking food down into smaller pieces so
chemical transformation can happen.
• Mechanical transformation happens in two
processes:
• Chewing (crushing and grinding food in the
mouth)
• Churning of food in the stomach (muscle
contractions that mix food and digestive
juices).
• Chemical transformation: changes that occur
to break down complex molecules of food into
simpler molecules. These changes are aided
by the secretions of the digestive glands.
• Remember: Water, vitamins and minerals are
micronutrients… the body can absorb them
without changes.
• Carbohydrates, fats and proteins are
macronutrients and need to be broken down
by chemical transformation
• See page 170 in your textbook for the
complete breakdown.
Digestion breakdown
Absorption of nutrients
• Definition: Absorption is the passage of
nutrients from the digestive tract into the
blood or lymph.
• Food absorption happens within the folds of
the small intestine. The folds are called villi
(plural). Each villus (singular) has blood and
lymphatic vessels that supply nutrients to the
body.
Elimination of fecal matter
• After the absorption of nutrients, the leftover
material travels to the large intestine in a
liquid form.
• Here, the water is absorbed, and as it travels
towards the anus the material becomes more
solid.
• It travels down the rectum to the anus, where
it exits the body
The End!