DIGESTION
SYSTEM
April 20-21, 2015
Functions
1. Ingestion (intake of food)
2. Digestion (physical and chemical break down of food)
3. Absorption (passage of chemicals into blood or lymph)
4. Defecation (elimination of indigestible substances as feces)
Structures
Divided into:
• Alimentary canal /
gastrointestinal (GI)
Fun fact: The
tract
• Mouth
• Pharynx
• Esophagus
• Stomach
• Small intestine
• Large intestine
• Rectum
• Accessory organs
• Teeth
• Tongue
• Gallbladder
• Salivary glands
• Pancreas
• liver
lumen of the
alimentary canal –
where the food
travels - is
considered to be
external to the
body.
We are essentially
an elongated
donut!
Digestive Organ Functions
1. Mouth
• Teeth mechanically digest
food
• Saliva
• cleans mouth (contains
many antimicrobial
chemicals)
• chemically digests food
(the enzyme amylase
breaks down starch into
sugar)
• Tongue repositions food
and helps form a bolus
that can be swallowed
Digestive Organ Functions
1. Mouth
• Teeth mechanically digest
food
• Saliva
• cleans mouth (contains
many antimicrobial
chemicals)
• chemically digests food
(the enzyme amylase
breaks down starch into
sugar)
• Tongue repositions food
and helps form a bolus
that can be swallowed
Fun Fact:
Mumps is a viral disease of the salivary
glands. Painful, but usually not fatal, it
can lead to sterility in males. Several
college campuses have had outbreaks in
recent years.
Digestive Organ Functions
2. Pharynx
• Passage for food, water,
and air
3. Esophagus
• Passage to stomach for
food and water only
• Gastroesophageal
sphincter is composed of
muscles at the lower end
of espophagus that
prevent stomach contents
and acids from traveling
back up the esophagus.
Food is moved through the GI tract
by peristalsis – wavelike contraction
& relaxation of muscles in the walls
of the GI tract
click!
Fun Fact:
Heart burn occurs when stomach acids go
up the esophagus, usually due to
• Over-eating
• Pregnancy
• Running (runner’s reflux)
• Hiated hernia
Long-term, untreated heartburn can cause
esophageal ulcers or cancer.
Digestive Organ Functions
4. Stomach
• Mechanically digests food
by churning and mixing it,
to form chyme.
• Chemically digests food
by releasing extremely
acidic gastric juice which
contains HCl and
proteases, such as
pepsin, that break down
proteins into amino acids
• LIMITED absorption
(alcohol, aspirin, other
drugs)
Fun Fact:
Vomiting is regulated by the brain, and is
triggered by excessive stomach stretching
(as from a very large meal) or by stomach
irritants, such as bacterial toxins and
some drugs (including excessive alcohol).
During vomiting, the brain signals the
diaphragm and other abdominal muscles
to contract forcefully, and it signals the
gastroesophageal sphincter to relax. The
contents of the stomach, and sometimes
the upper part of the small intestine, are
expelled.
Digestive Organ Functions
5. Small Intestine
• Digestion is completed
here
• Sm. intestine produces
intestinal juice, which is
alkaline and contains
some digestive enzymes
• Bile is produced by the
liver, stored by the gall
bladder, and is dumped
into the small intestine. It
digests fats.
• Pancreas releases
pancreatic juice into the
small intestine. Include
proteases, lipases,
amylase, and nucleases.
Fun Fact:
Most digestive enzymes only become
activated after entering the alimentary
canal, which prevents them from self
digestion.
For example,
• The stomach produces
pepsinogen which is converted to
active form – pepsin – by the low
pH of the stomach acids
• Most pancreatic enzymes are
converted to active form by other
chemicals within small intestine.
Digestive Organ Functions
5. Small Intestine
• Major site of absorption
• Digested carbohydrates,
fats, proteins, nucleic
acids, vitamins,
electrolytes, and some
water absorbed
-- more on this in a bit –
6. Large Intestine (colon)
• Absorption of water,
electrolytes, and some
vitamins
• Everything not absorbed is
expelled by rectum as feces
Fun Fact:
Diarrhea and constipation occur when
food travels either too quickly (diarrhea) or
too slowly (constipation) through the
colon.
Absorption
Absorption occurs when nutrients pass out of the alimentary
canal and into the blood capillaries (water-soluble nutrients) or
lymph lacteal (fat-soluble nutrients).
Some nutrients are absorbed through diffusion, but many require
active transport.
Absorption
The small intestine has many adaptations for absorption:
• Enormous surface area due to: long length (20 ft), folds, and
numerous villi & microvilli
• SLOOOW movement of chyme (3-6 hours)
Fun fact:
The surface area of the small
intestine is about the same as a 2
story house!
Watch me!
Review
What is digestion, and in which structures does it occur?
How does the process of digestion differ for different foods?
What is absorption, and in which structures does it occur?
Closure
1. Which questions did we answer? Which did we not?
2. What was our learner profile trait and how did we
demonstrate it?
3. How did what we do today relate to our unit question –
how do body systems work together?