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Human Digestion
(mammals)
Chapter 32.2 and 32.3
Comparative Physiology
(comparing digestion in a
variety of organisms)
~this information isn’t
available in your book in a
single chapter location, but
this information is test
material~
Mechanical Digestion
• Physical change –
breaking into smaller
pieces, mixing, etc.
• Ex – chewing
• Purpose – to increase
surface area available
for reactions to occur
Chemical Digestion
• Use of enzymes to break
food into smaller subunits
(monomers)
• Carbs 
monosaccharides
• Proteins  amino acids
• Lipids  glycerol & fatty
acids
• Chemical change
• Ex – protein broken into
amino acids by pepsin
Type of Digestion
Secretion or
Enzyme
Function
Chemical 
Mechanical 
Salivary
amylase
Teeth, tongue,
saliva
Breaks starch into glucose
None
To move bolus (partially
digested food) from mouth
to stomach by peristalsis
(wavelike contractions)
Organ
Mouth
http://hopkinsgi.org/multimedia/dat
abase/intro_250_Swa
llow.swf
Esophagus
Stomach
Mechanical
Mechanical  Churning
Chemical  Pepsin, HCl,
mucus
Small
Intestine
*primary
organ of
digestion*
Mechanical 
Chemical 
Peristalsis 
Trypsin 
Lipases 
Amylase 
Breaks food into smaller
pieces, moistens it
Mixes food (turns bolus into
chyme)
Digests proteins into amino
acids
Moves food from stomach to SI
Digests proteins
Digests lipids
Digests carbs (starch)
*digestion finished in first 30cm
of S.I. – called duodenum
*absorption of nutrients thru villi
Organ
Type of Digestion
Secretion or
Enzyme
Function
Liver
(accessory
organ)
None
Bile – which is
stored in the
gall bladder
Emulsifies fat – breaks fat
into smaller droplets, is
released into SI from gall
bladder
Pancreas
(accessory
organ)
None
Trypsin
Lipases
Amylase
Sodium
bicarbonate
Aids in digestion of nutrients
None
Excess water is reabsorbed
Bacteria produces vitamins
A&K
@ end – elimination of
waste
Whole process takes 24-30
hours
Large
Intestine
None
Neutralizes stomach acid in
chyme as it goes into SI
http://www.biocourse.com/mhhe/bcc/resources/concept.xsp?id=000012109&ty
pe=MOVIE (animation of whole process)
Your Digestive System
• Overview of each
organ’s function:
http://kidshealth.o
rg/kid/htbw/digesti
ve_system.html
• Digestion in
action:
http://kitses.com/a
nimation/swfs/dig
estion.swf
Digestion Across Kingdoms Sponges
• Sponges
– Sessile (attached to something, not moving)
– Filter feeders – they eat by straining particles from the water
– No true digestive system
Cnidarians (jellyfish & hydra)
• Capture prey, often by
use of stinging tentacles
• Prey is stuffed into mouth
which leads to
gastrovascular cavity
• This cavity has cells that
secrete digestive
enzymes and absorb
nutrients
• Wastes are eliminated
through the mouth
Planaria (type of flatworm)
• Mouth is on the
bottom of the
worm
• Mouth leads to gut
cavity
• Pharynx extends
out of mouth to get
food and bring it in
Tapeworms (flatworms)
• Adult worm
does not
swallow food
• Segmented
worm –
absorbs
nutrients from
digested food it
lives in
All Other Bilateral Organisms
• Have complete digestive tract
with 2 openings (mouth and
anus) at opposite ends of a
continuous tube
• Food moves one way through
the gut
• Has specialized areas for
digestion and absorption
• Complete digestive tracts
allow organisms to eat
continuously
Earthworm
Mollusk (clam)
Echinoderms (sea stars, etc.)
• Sea stars have
complete digestive
systems with a mouth,
stomach, small length of
intestine and anus.
• Uses tube feet to grab
food
• It pushes its stomach
outside of its body and
digests the food in its
stomach but outside of
the body
Sea Star
Arthropods
(crustaceans, insects and arachnids)
• Crustaceans have mandibles for crushing
and biting food before ingestion
• Insects eat by either chewing or sucking
• Arachnids either mash up food and push it
into their mouths or they inject venom into
their prey and then suck the digested
nutrients out
• All have a continuous tube that is open at
both ends
Arthropods
Fish
• Fish have a mouth,
throat, areas for
absorption and areas
for compaction of
waste.
• Differences in diet
result in small changes
in size of each of these
areas, including teeth
shape, presence of
stomach, etc.
Carnivorous fish
(have stomach)
Omnivorous fish
(do not have stomachs)
Amphibians and Reptiles
• Amphibians and reptiles have very similar
digestive systems: a mouth, esophagus,
stomach, small intestine, large intestine and a
rectum.
Birds
• The stomach has two
chambers.
• The gizzard is used to
grind up very hard
items (it relies on
ingestion of grainy
materials to help)
• Some have a crop to
store food after
eating.
stomach
Bacteria
• Bacteria don’t have a
digestive system
• They absorb the
nutrients they need for
energy and building
other compounds
• Different types of
bacteria have different
sources for energy
and carbon
Protists
• Protists take in food
through phagocytosis
(active transport process
by which the cell
membrane folds
outwards around the
object to be taken into
the cell and then
deposits the material
inside the cell).
• The materials taken in
via active transport are
then digested in vesicles
that contain digestive
enzymes
Fungus
• Fungi absorb their
food from their
environment
• As fungi grow, their
extensions (hyphae)
release digestive
enzymes into the food
sources
• As the food is broken
down, the fungi
absorb the nutrients
through their cell
walls
Plants
• Plants do not have a digestive
system
• All organisms need energy
(characteristic of life)
• Plants absorb sunlight energy
to make sugars
(photosynthesis) – they are
autotrophs
• They then break down the
sugars to convert them to
cellular energy (ATP) through
cellular respiration
• They absorb water and other
nutrients through their roots