SOME ADDITIONAL POINTS
ABOUT DIGESTION
Mouth:
Salivary
glands
 Salivary
 Starch
amylase
 glucose +
maltose
ENZYMES
Stomach:
Gastric
glands
 Mucus
 HCl
 Pepsinogen
Becomes
Protein
acids
ENZYMES
pepsin
 amino
Small Intestine:
 Pancreas
 Pancreatic juice
Trypsinogen
Becomes
trypsin
Protein  amino acids
Pancreatic amylase
Lipase
Lipids  glycerol + fatty acids
Hydrogen carbonate (neutralize stomach acid)
ENZYMES
Small
Intestine:
Pancreas
– Exocrine glands
 has
ducts which take a secretion from
the gland to a specific location
 (Endocrine
gland is ductless and
secretes into bloodstream)
ENZYMES
Small
Intestine:
Pancreas
– Exocrine glands
 Secretion
is usually a protein
 Review:
proteins are created in ribosomes 
ribosomes are attached to ER  transports to
Golgi  creates vesicles
 Steps
require ATP
 Exocrine
ENZYMES
cells have extensive ER & mitochondria
Small
Intestine:
Pancreas
– Exocrine glands
 Exocrine
gland cells arrange
around a ductile (think of
houses around a cul-de-sac)
 Arrangement
 Several
duct
ENZYMES
is called an acinus
acini join together and drain into larger
Small
Intestine:
Liver
 Bile
 Stored
in the gall bladder
 Emulsifies
lipids
Increases
Salts
side
ENZYMES
surface area for lipase
have a hydrophilic and hydrophobic
Small
Intestine:
Glandular
 Secretes
cells
are variety of enzymes
Some
are added to partially digested fluid
Some
stay attached to villi cells
ENZYMES
Small
Intestine:
Glandular
cells
Benefit
of membrane-bound
enzymes:
 These
 They
enzymes do not join the “soup”
stay in the intestine and can be reused
 Enzymes
may be linked to secondary functions (like
transport across the membrane)
ENZYMES
Draw
and label a transverse section of the
ileum as seen under a light microscope.
HOW ARE DIGESTED FOODS ABSORBED?
HOW ARE DIGESTED FOODS ABSORBED?
Microvilli
Increase
surface area and allow for
greater absorption
Membrane is embedded with enzymes
and channel proteins
Mitochondria
Provide
ATP for active transport
HOW ARE DIGESTED FOODS ABSORBED?
Pinocytotic
absorption
Tight
vesicles
of liquids and dissolved solutes
junctions
Create
an impermeable barrier
Keep
digestive fluids separate from tissue
fluids and ensure one-way flow across the
membrane
HOW ARE DIGESTED FOODS ABSORBED?
HOW ARE DIGESTED FOODS ABSORBED?
Diffusion
lipids
Facilitated
diffusion
Channel
proteins help hydrophilic foods
move across the membrane
Water-soluble
vitamins
molecules, minerals, and
HOW ARE DIGESTED FOODS ABSORBED?
Active
transport
Use
of ATP against
concentration gradient
Glucose,
amino acids, mineral ions
Endocytosis
Contains
channels and pumps to help
fluid move from vesicle to cytoplams
HOW ARE DIGESTED FOODS ABSORBED?
Sight
 Saliva
& smell start the process
& gastric juice (Pavlov)
Receptors
the brain
in cells send signals to
Distension
of stomach releases
gastrin  leads to sustained
release of gastric fluid
SECRETION … WHAT STARTS IT?
Cellulose
Mammals
don’t produce cellulose
(digests β–glucose polymers)
Grazers
have mutualistic relationship
with intestinal bacteria that produce
enzyme (humans do NOT)
WHAT DON’T WE DIGEST?
Our
digestive system (alimentary canal)
Protease
enzymes (pepsin & trypsin) are
secreted in inactive forms (zymogens)
Pepsinogen becomes active with HCl
Mucus
lining protects stomach
Trypsinogen
becomes active with
enterokinase
Mucus lining protects
small intestine
WHAT DON’T WE DIGEST?
B
: bile pigments
E : epithelial cells from the intestine
L : lignin
Cellular
binding substance in wood
C
: cellulose
H : human microflora
bacteria
WHAT DO WE POOP?