DIGESTIVE SYSTEM
& ENZYME NOTES
DIGESTIVE SYSTEM
 Includes
mouth, pharynx,
esophagus, stomach, small
intestine and large intestine;
several major glands and their
secretions, including the salivary
glands, the pancreas and the liver
 Digestion
is the breakdown of
food into simpler molecules that
can be absorbed and used by the
cells of the body
THE PROCESS OF DIGESTION:
 1.
Mouth - teeth break up food in a
process called mechanical digestion;
also salivary glands secrete the first
digestive enzymes (amylase and
mucous)
 2. Pharynx - the top part of the
throat; no digestion takes place here
 Esophagus
- the muscles of the
esophagus begin to contract in
waves, pushing food toward the
stomach; this is called peristalsis
 4.
Stomach - three secretions combine
to form the gastric fluid:
Mucous - keeps food lubricated and
protects walls of the stomach
Hydrochloric acid - helps break down
food
Pepsin - mixes with hydrochloric acid to
begin digesting proteins
 Food is churned for hours becoming a
pasty mixture known as chyme
 5.
Small Intestine - the chyme is
flooded with enzymes from three
sources:
(1st part of small intestine)
- releases enzymes that continue
digesting
 Pancreas - releases pancreatic fluid
that digests carbohydrates, proteins
and fats
 Liver - secretes bile, which is stored
in the gallbladder, which breaks down
fats further
 Duodenum
 5.
Small Intestine - the now
mostly digested food passes
through the rest of the small
intestine where nutrients are
absorbed into the bloodstream;
when it LEAVES the SMALL
INTESTINE, the food is
NUTRIENT FREE
Absorption in the Small Intestine
 The
small intestine increases
SURFACE AREA to increase
absorption
 The folded surfaces are fingerlike
projections called villi
 6.
Large Intestine (Colon) - main
job is to remove water from
undigested materials passing
through it
 7. Rectum – store feces (solid
waste)
Salivary
Glands
Pharynx
Esophagus
Liver
Liver
Stomach
Mouth
Tongue
Stomach
Pancreas
Large
Intestine
Small Intestine
Gallbladder
Pancreas
Appendix
Rectum
Anus
Enzymes Used in Digestion
Enzyme
Site of Action
Site of Production
Nutrient Digested
Amylase
Mouth
Salivary Glands
Carbohydrate
Pepsin
Stomach
Lining of Stomach
Protein
Lipase
Small Intestine
Pancreas
Fat
Amylase
Small Intestine
Pancreas
Carbohydrate
Trypsin
Small Intestine
Pancreas
Protein
Lactase
Small Intestine
Lining of Small Intestine
Carbohydrate
Maltase
Small Intestine
Lining of Small
Intestine
Carbohydrate
Sucrase
Small Intestine
Lining of Small
Intestine
Carbohydrate
Peptidase
Small Intestine
Lining of Small Intestine
Protein
Chemical Reactions
Chemical Reaction – process that changes
one set of chemicals into another set of
chemicals
 Reactants – elements or compounds that
enter into a chemical reaction
 Products – elements or compounds
produced by a chemical reaction
 Example: 2H2 + O2 
2 H2O

Reactants
Product

Chemical Reactions
 Chemical
reactions always
involve the breaking of bonds in
reactants and the formation of
new bonds in products
 Energy is released or absorbed
whenever chemical bonds form or
are broken
Enzymes
Catalyst – substance that speeds up the
rate of a chemical reaction
 Enzymes – proteins that act as biological
catalysts (speed up chemical reactions
that take place in cells)
 Enzymes help lower the activation
energy of a chemical reaction (the
energy needed to get a reaction started)

Enzymes
 The
reactants of enzymecatalyzed reactions are known
as substrates
 Substrates bind to a site on
the enzyme called the active
site
Substrate
___________
______________
Active
Site
___________
Enzyme
___________
Products
 The
fit between the active site and
substrates is so precise that it is often
compared to a lock and key
 This is the old model
New Model - Induced fit
 The induced-fit theory assumes
that the substrate plays a role in
determining the FINAL SHAPE of
the enzyme and that the enzyme
is partially FLEXIBLE. Only the
proper substrate is capable of
inducing the proper alignment of
the active site.
Notice the difference in shape
Before and during binding and after