Digestion
Grade 9
Video Demo
http://videos.howstuffworks.com/hsw/
5822-digestive-system-stomachvideo.htm
 Bill Nye

Jelly Bean Digestion

What biochemical compound makes up
this jelly bean?

Eg. lipids, carbohydrates, proteins or
nucleic acids
What happens when you put the jelly bean
into your mouth?
 Than what happens? …

Teeth

Tear, rip and chew food to physically
break it into smaller pieces.
(Mechanical Digestion).

Let’s look at the internal structure of teeth.
Teeth
The crown
is the part
of the tooth
above the
gum line
The root is
the part of
the tooth
below the
gum line
•The enamel is the white
part you can see
covering the crown.
•Enamel is the hardest
substance in the human
body
•It covers the dentine
and stops bacteria
getting inside the tooth
Teeth
The crown
is the part
of the tooth
above the
gum line
The root is
the part of
the tooth
below the
gum line
•The dentine is the
major component within
the tooth.
•It is made from softer
material than enamel so
is easier to decay.
Teeth
The crown
is the part
of the tooth
above the
gum line
The root is
the part of
the tooth
below the
gum line
•The pulp contains the
nerves and blood
vessels of the tooth.
•It is underneath the
dentine.
•This is the part that
hurts when you have a
toothache!
Teeth
The crown
is the part
of the tooth
above the
gum line
The root is
the part of
the tooth
below the
gum line
•The cementum is found
outside the dentine in
the root.
•It cements (holds) the
tooth into the jaw bone.
Bacteria

Our mouths are busy places, full of friendly
bacteria that coat our teeth

Sometimes unfriendly bacteria, including
one called Porphymonas gingivalis, will
overgrow the friendly bacteria and cause
damage to the gums and the jawbone. This
bacterium is one of the main causes of
gum disease.
Porphymonas gingivalis

To fend off the attack, the body will
send immune cells to kill the bacteria.
The bacteria are difficult to kill so the
immune cells can cause even more
damage to your gums.
Mouth: What happens
Food is crushed and ground up by teeth
 The salivary glands secrete saliva which
makes the food moist and easy to swallow
(Semi-solid lump now called Bolus).


Amylase enzyme (in saliva) breaks the
carbohydrate starch down into glucose.
Enzymes
Remember :
 Large particles cannot be absorbed
in the small intestine
INSIDE THE
BODY (BLOOD)
GUT
starch
starch
G
starch
G
G
G
Large particles
(e.g. starch) are
left in the gut and
small particles
(e.g. glucose)
pass into the
bloodstream.
G
G
starch
BUT large particles can be
broken down into small particles.
This is called DIGESTION
Enzymes
Large particles need to be broken down
chemically by ENZYMES.
 Enzymes are biological catalysts. They
speed up chemical reactions in the body.
 Digestive enzymes cleave (cut) the larger
molecules into smaller ones.

Digestive Enzymes

Mouth:
Amylase breaks starch down into glucose.

Stomach:
Protease (Pepsin) breaks protein down
into peptides.
Digestive Enzymes
Amylase
Glucose
Starch
Protease
Peptides
Protein
Enzymes and pH
Enzymes work best at one pH. This pH is
different for each different enzyme.
 If the pH goes too low (more acidic) or too
high (more alkaline), the enzyme will not
work as effectively.
 However, changes to pH will NOT denature
enzymes.

Epiglottis

Is the flap of cartilage lying behind the
tongue and in front of the entrance to the
larynx (voice box).

At rest, the epiglottis is upright, allowing
air to pass into the trachea (for breathing).
At Rest
During Swallowing
The tongue pushes the bolus toward the
pharynx (throat).
 The epiglottis folds back to cover the entrance
to the trachea, protecting the larynx.
 This allows food to enter into the esophagus.

*The epiglottis acts as a lid*
Swallowing
Esophagus

A muscular tube that leads from the throat
to the stomach.
The smooth muscle of the esophagus
pushes the bolus toward the stomach using
wave-like contractions.
 This is called Peristalsis.

Peristalsis
Entering the Stomach

From the esophagus, the bolus enters the
stomach through the Cardiac sphincter
(muscular ring).
-Sphincters help move digested material in
one direction.
Entering the Stomach
The Stomach

A hollow, sac-like organ that stores, mixes,
sterilizes and continues the digestive
process.

Storage: walls have folds called Rugae
which allow the stomach to expand.

Food spends 3-4 hours in here!
The Stomach

Mixes:


The stomach walls contain three layers of
smooth muscle arranged in longitudinal,
circular, and oblique (diagonal) rows.
These muscles allow the stomach to
squeeze and churn the food (mechanical
digestion).
Muscles and Rugae
The Stomach
Sterilizes and Chemically Digests:
 Secretes gastric juice & hydrochloric acid

The acid kills germs in the food (pH 2)
 The gastric juice contains the protease
enzyme PEPSIN to digest protein into
peptides

Protease
Peptides
Protein
Mucus

A thick mucus layer lines the stomach walls
to prevent the stomach from digesting itself.
Mucus
Mucus

What do you think may happen when
mucus is limited?
Ulcer

Peptic ulcer disease occurs when
the protective mucus layer wears
away in certain areas, allowing
damage to occur from the natural
acids of the stomach.
Ulcer- 60% to 80% of gastric
ulcers caused by bacteria
Helicobacter pylori is a spiral shaped
bacterium that lives in the stomach and
duodenum (section of intestine just below
stomach)
 The stomach is protected from its own
gastric juice by a thick layer of mucus that
covers the stomach lining. Helicobacter
pylori takes advantage of this protection by
living in the mucus lining.

Helicobacter pylori
Once H. pylori is safely ensconced in the
mucus, it is able to fight the stomach acid
that does reach it with an enzyme it
possesses called urease
 However, the immune system will respond to
an H. pylori infection
 It may not be H. pylori itself which causes
peptic ulcer, but the inflammation of the
stomach lining; i.e. the immune response to
H. pylori.

Continuation of Digestion

The chyme is slowly transported from the
stomach through the pyloric sphincter and
into the small intestine where further
digestion and nutrient absorption occurs.
DIGESTION
Definitions
 Gland:
an organ or group of cells
which secretes enzymes or
hormones
 Peristalsis:
muscle contractions
that push food through a tube
 Bolus:
chewed food
Definitions continued
 Chyme:
nutrients in semi-liquid
form
 Uvula: component that stops
food from entering nasal cavity
 Epiglottis: component that
stops food from entering the
trachea
Digestive Tract and
Functions
1)
2)
3)
4)
5)
6)
7)
8)
Mouth
Pharynx
Esophagus
Stomach
Small intestine
Large intestine
Rectum
Anus
 Decomposition
of food
Absorption of
nutrients
Elimination of
waste
Digestive Glands and
Functions

Salivary glands


In mouth
Gastric glands

In walls of
stomach
Pancreas
 Liver
 Intestinal glands


In small
intestine
Secretion of:
 saliva
Gastric
enzymes
Digestive juices
Bile
Physical/Mechanical
Breakdown

Food DOES NOT change its
molecular makeup, just its shape and
size, looks different
1.
2.
3.
4.
5.
Mouth- chewing and swallowing
Esophagus- peristalsis
Stomach- churning, grinding and
peristalsis
Small intestine- peristalsis and
churning
Large intestine- peristalsis and
Chemical Breakdown
Food changes its molecular makeup,
looks and is different
 See handout*

Absorption
Through folds called villi by diffusion
 Small intestine – amino acids,
glucose, glycerol and fatty acids
 Large intestine – vitamins, minerals
and water
