Digestive System
Obtaining nutrients
Energy
• Body cells need energy to run cell
processes.
• Animals obtain chemical energy from
food. Energy is derived from breaking
chemical bonds.
• Food energy is measured in units called
calories.
Lipids
Many lipids are made up of
fatty acids and glycerine.
• Lipids are fats, oils, and
waxes.
• Lipids are used for
storing energy, making
cell membranes, and
synthesizing steroid
hormones.
• No Monomer
Carbohydrates
• Sugars and starch are
the carbohydrates that
humans can digest.
“Fiber” is indigestible
carbohydrates, such as
cellulose and inulin.
• Glucose is needed by
all body cells as energy.
• Monomer =
monosaccharide
Starch is made up of glucose.
Proteins
• Amino acids from
digested proteins are
used by cells to build all
the proteins that our
body needs.
• Humans need a balance
of the 20 amino acids,
which can be obtained
from animal proteins, or
by blending plant
protein sources.
• Monomer = amino acids
Proteins are made up of
amino acids.
Macromolecule summary
Polymers
Complex
Carbohydrates
(i.e. starch)
Monomers
Glucose and other Broken apart to get energy to
simple sugars
make ATP.
Proteins
Amino acids
Lipids (Fats,
waxes, oils, and
steroids)
None
Nucleic Acids
Roles
Nucleotides
Used to make our own
enzymes and other body
proteins.
Used for cellular energy and
energy storage; used to
make cell membranes,
steroid hormones.
Store and transmit hereditary
information
Digestion
Two-way digestion
• Simple animals have a
single digestive pouch
with a single opening.
• Food enters through
the opening, waste
leaves through the
same opening.
• These organisms must
finish digesting before
eating again.
One-way digestion
• More complex animals
have one-way
digestion.
• Food enters one
opening and waste
leaves from another.
• Animals with one-way
systems can eat any
time, which is an
advantage.
Mechanical digestion
• In humans, mechanical
digestion takes place in the
mouth.
• Human incisors and
canines are adapted for
tearing food, while molars
are adapted for grinding
food.
• Saliva, which contains
enzymes, mixes with food.
Stomach
• Acid digestion occurs in
the stomach.
• Gastrin, a hormone,
stimulates acid release.
• Pepsin, an enzyme
that breaks up
proteins, requires an
acidic environment to
become active.
Duodenum
• Alkaline digestion takes
place in the upper small
intestine, the duodenum.
• Enzymes from the
pancreas require an
alkaline environment to
be active.
Pancreas and Liver
• Pancreas releases
pancreatic juice,
containing
bicarbonate, lipases,
proteases, and
amylase.
• The liver makes bile,
which emulsifies fats.
Bile is made from
cholesterol, which is
made in the liver.
Small intestine
• The walls of the small
intestine are lined with
millions of microvilli.
This is the site of
nutrient absorption.
• Small intestines also
produce many
digestive enzymes to
break large polymers
completely down into
monomers.
Digestion and pH
Location
pH
Enzymes
Molecules digested
Mouth
neutral
Amylase
Starch
Stomach
acidic
Pepsin (a peptidase)
Initial protein
digestion
Small intestine
Basic to neutral
Mixture of amylase,
peptidases, lipases
Digestion of
starches, final
breakdown of
proteins, digestion of
lipids.
Large intestine
• Water from digested food
is absorbed in the large
intestine.
• Bacteria present in the
large intestine feed on
unabsorbed nutrients, and
produce several vitamins.
• Fecal material is formed
from fiber and other
undigested material.
Digestion
Diagram
Digestion