THE DIGESTIVE
SYSTEM
A.K.A. THE GASTROINTESTINAL (GI) TRACT
Converts foods into simpler
molecules, then absorbs
them into the blood stream
for use by cells
Mechanical verses Chemical Digestion
1. Mechanical digestion: breaks food into smaller
pieces
a. increases the surface area of food
2. Chemical digestion: changes the chemical
composition of the food
a. breaks food down into smaller polymers and
individual monomers
b. Uses digestive enzymes to break down food
MOUTH & Salivary
Glands
1. Teeth – cut & grind food
a. This is mechanical digestion
2. Salivary Glands – moisten mouth & food with
saliva, which has amylase to break down starches
a. This is chemical digestion
b. Carbohydrates are the only foods that undergo
partial chemical digestion in the mouth
ESOPHAGUS
1. Esophagus –food tube leading
to stomach
2. Peristalsis – smooth muscle
involuntary contractions to push
food into stomach (also moves
food through small intestines)
STOMACH
1. Large muscular sac which:
a. secretes mucus (to protect stomach)
b. secretes hydrochloric acid which activates
pepsin (digests protein -- chemical digestion)
c. churns food & liquid into “chyme” (mechanical
digestion – because the process coats the food
with digestive enzymes)
SMALL
INTESTINE
1. Where most of the chemical digestion & nutrient
absorption occurs
2. Villi – tiny projections that increase surface area
for absorption
3. Microvilli – tiny projections on the surface of villi –
creates even more surface area for digestion and
nutrient absorption
LARGE
INTESTINE
PERISTALSIS
1. Also called the colon
2. Water is removed from the materials leaving the small
intestine to form solid waste
3. Bacteria in large intestines produce vitamins B & K
4. Diarrhea: large intestines do not absorb enough water
5. Constipation: large intestines absorb too much water
RECTUM
1. Holds solid wastes, called feces, until they
exit the body through the anus
A. SALIVARY GLANDS
B. MOUTH
C. ESOPHAGUS
D. STOMACH
E. LARGE
INTESTINE
H. ANUS
F. SMALL
INTESTINE
G. RECTUM
PANCREAS
1.Produces digestive enzymes that break down
carbohydrates, proteins, and fats
2. The enzymes are released into the small
intestine
3. Produces insulin
LIVER & Gall
Bladder
1. Liver: Largest internal organ
a. Secretes bile which helps aids in fat
digestion; breaks fat into smaller fat particles –
mechanical digestion
b. Stores excess glucose
2. Gall Bladder: stores bile until needed by the
small intestines to digest lipids
LIVER
GALL
BLADDER
PANCREAS