Download Digestion - Mrs. Blevins` Science

Digestive System
Digestive System Learning Goals
Understand the structure and function of
the digestive system.
 Identify techniques that keep the digestive
system healthy.

Lets get a quick visual of the system
and how it works!

Animation of the Digestive System
3 Main Functions

a. Digestion –the breaking down of food
into smaller nutrient molecules the body
can use.
◦ There are two types of digestion:
 Mechanical digestion- foods are physically broken
down into smaller pieces (chewing)
 Teeth work in mechanical digestion
 Chemical digestion- chemicals produced by the
body break foods into their smaller chemical
building blocks.
 Saliva contains enzymes that break down food

b. Absorption – the process by which
nutrient molecules pass through the wall
of your digestive system into your blood.

c. Elimination – Materials that are not
absorbed, such as fiber, are eliminated
from the body as wastes.
A Tour of the Digestive System
The Digestive Process - Mouth

a. The entrance- inside the mouth
◦ When your body gets ready to eat, it
will increase the production of saliva, or
spit.
 Saliva plays an important role in both types
of digestion
 It moistens the food to help chew it and to make it
slippery so that it goes down easier.
 It contains enzymes, which are a protein that speeds
up chemical reactions to begin breaking down food
chemically.
◦ Your teeth carry out the first step of
mechanical digestion.
 Mastication- chewing
Your cent teeth, incisors, cut the food
into smaller pieces.
Your sharp point teeth, canines, tear
the food into smaller pieces.
Your back teeth, molars, crush and
grind the food.
The Journey Downward

a. When food leaves the mouth it travels
down the esophagus, a muscular tube that
connects the mouth to the stomach.
◦ It is lined with mucus, a thick slippery substance
that makes it easy to swallow.
◦ Food passes the trachea (windpipe) which is
blocked by a little flap called the epiglottis.
◦ Food is moved down the esophagus by waves of
muscle contractions called peristalsis.
 Strong enough to push food up if you swallowed food
while standing on your head (similar to squeezing a tube
of toothpaste from the bottom up)
Peristalsis

3D Animation of Peristalsis in the Large
Intestine

Endoscopy of Gastric Antrum
First Stop- The Stomach
a. The stomach is a J shaped pouch.
 b. It can expand 50 times its normal size
to hold the food we eat.
 c. Most mechanical and chemical digestion
take place here.

◦ Mechanical- 3 strong layers of smooth muscle
contract to produce a churning motion. This
mixes food and fluids much like a washing
machine does clothes and soapy water.
◦ Chemical- The lining of the stomach produces
gastric juices, which have two primary
ingredients.
 Pepsin- an enzyme that breaks proteins down into
smaller building blocks called amino acids- Pepsin
works best in an acidic environment.
 Hydrochloric Acid- helps break food down as well
as killing many bacteria that you swallow with your
food. The stomach is lined with mucus to protect it
form the acid- the cells in the stomach produce a
thick mucus and are replaced very quickly
 Food remains in the stomach until all of the solid
material has been broken down into a thick liquid
form called chyme. This is then released into the
lower part of the digestive system, starting with the
small intestine.
Second Stop- The Small Intestine

Why is it called the small intestine?
◦ The small intestine is about 6 meters long
making up about 2/3 of the length of the
whole digestive system.
◦ So why is it called the small intestine?
Because with a diameter of only 2-3
centimeters wide, it is about half the diameter
of the large intestine.

Almost all chemical digestion and
absorption of nutrients takes place in the
small intestine.
◦ Starches and proteins have been partially
broken down by now, but fats have not been
digested at all.
◦ Enzymes and secretions from the liver and
pancreas mix with those of the small intestine
to break down the food even further.
 The liver is the largest organ in the body and is like an
extremely busy factory aiding in chemical digestion and
plays a role in many body processes. (Ex. Breaking down
medicines)
 For digestion the liver produces bile, a substance that
breaks down fat particles. Bile is stored in the
gallbladder- travels to the small intestine after you eat.
 Bile doesn’t chemically digest fat, it physically breaks the
fat into smaller particles much like dishwashing liquid
does in the sink.
 The pancreas produces enzymes that then break down
the fat chemically- also breaks down proteins and
starches.
◦ After the food is broken down further, the
small intestine absorbs nutrient molecules.
 The inner surface of the small intestine is covered
with villi, millions of tiny finger shaped structures
filled with tiny blood vessels. These greatly increase
the surface are of the intestine, making it about the
size of a tennis court.
 The nutrients pass through the cells of the villi into
the bloodstream to be delivered to the rest of the
body.
 AT THIS POINT MOST NUTRIENTS HAVE NOW BEEN
ABSORBED!
Third Stop- Large Intestine
This is the last section of the digestive
system.
 About 1.5 meters long- about as long as a
bathtub
 Contains bacteria that feed on the
material passing through. These bacteria
are also helpful because they produce
Vitamin K

As the remaining material moves through
the large intestine, water is absorbed into
the blood stream.
 The large intestine ends in a short tube
called the rectum where the remaining
waste material, feces is compressed into a
solid form.
 It is then eliminated from the body
through the anus, a muscular opening at
the end of the rectum.

Digestive System Care

1. Eat foods high in fiber!
◦ Fiber helps food and waste pass through the
digestive tract
◦ Reduces risk of colon cancer
◦ Beans, Prunes, Pears, and Leafy Green
Vegetables are good sources
Digestive System Care

2. Drink plenty of water
◦ 8 glasses a day!
◦ Helps keep things moving regularly
Digestive System Care

3. Eat slowly and don’t hurry through
your meals
◦ Eating too fast can cause gas or indigestion