51
Nutrition, Digestion,
and Absorption
http://www.nigeldennis.com/stock/images/mammals/species/giraffe/25955.jpg
Animals are heterotrophs
 derive nutrition by eating
other organisms
Autotrophs
 can synthesize their necessary
nutrients
 heterotrophs depend on this
synthesis and have adapted to
take advantage of it
Energy needs can be measured
Measures of heat energy:
 calorie is amount of heat needed to
raise 1 gram of water 1°C
 Very small amount
 A kilocalorie (kcal) = 1,000 calories
 Kilocalories are used by
nutritionists and scientists but refer
to them as calories
Calorimeter
used to measure
energy content
www.parrinst.com/dynamic_images
Animals must store food
between meals
 Carbohydrates stored
in liver and muscle cells
as glycogen — enough
for about one day’s
energy needs
 Fat stores more energy
per gram and with little
water, making it more
compact
www.pathology.vcu.edu/WirSelfInst/image
Muscle fibers with
glycogen storage vacuoles
Adipose tissue – cells
almost completely filled
with fat vacuole
www.bluegrass.kctcs.edu/LCC/BSN/BIO/BiologyLabs/BIO137/137Tissues
Undernourished
 too little food taken in and
metabolism of body’s own
molecules begins
 Protein is lost rapidly to
protein synthesis
 Glycogen and fat are
broken down
 Decreased protein can lead
to edema in abdomen
Overnourished
 more food taken in than needed
 excess stored as increased body mass
 Glycogen reserves are built up
 Extra carbohydrates, fats, and proteins are converted
to body fat
“Fat cat”
www.mypkhome.com/fatcat/
Amino acids are building blocks
of proteins
 Each species has essential
amino acids that they cannot
synthesize
 Complementary diets can
supply all eight essential
amino acids for adult humans
 Other amino acids are
conditionally essential
www.mitavite.com.au/graphs
Macronutrients – elements required in large
amounts, like calcium
Micronutrients – elements required in tiny
amounts, like iron
Vitamins – carbon compounds that cannot be
synthesized
 Species-specific
 Water-soluble or fat-soluble
How organisms acquire
nutrition:
www.geog.ouc.bc.ca/physgeog/contents/images
 Saprobes absorb
nutrients from dead
organic matter -mushrooms
 Detritivores actively feed
on dead organic matter
– pillbug
 Predators feed on living
organisms
Pillbug
http://animaldiversity.ummz.umich.edu/site/resources/phil_myers/ADW_misc_inverts
Predators can be:
 Herbivores — consume plants
 Carnivores — prey on animals
 Omnivores — prey on both
www.gpnc.org/images/jpegs/animals
Bos bison
Canis lupes
Sus scrofa
www.hedweb.com/animimag
www.spiritwolf52.com/Wallpapers/Wolf/
 Filter feeders filter small
www.cs.brown.edu/people/twd/fish/Curacao
organisms from an
aquatic environment,
including baleen whales,
clams
 Fluid feeders include
mosquitoes, vampire
bats, nectivorous birds
Spirobranchus giganteus
Diaemus youngi
www.utexas.edu/research/rsc/images
Mammalian teeth have
similar structure
 Enamel composed of
calcium phosphate covers
crown
 Dentine is in crown and
root
 Pulp cavity contains blood
vessels, nerves and dentineproducing cells
Mammalian teeth have shapes
adapted to specific diets:
 Incisors: used for cutting,
chopping, or gnawing
 Canines: for stabbing,
gripping, or ripping
 Molars and premolars:
shearing, crushing, or grinding
http://animaldiversity.ummz.umich.edu/site/resource
s/anatomical_images/rodent_jaws/zygoplate.jpg
Digestion in animals is
extracellular and usually begins
in a body cavity
 Gastrovascular cavities connect
to outside through single
opening
 Tubular (complete) guts
 Opening at each end
 Mouth takes in food and
wastes eliminated via anus
www.cbu.edu/~seisen
http://ltreadwell.ifas.ufl.edu/insects
Food is broken up
mechanically in mouth
cavity by teeth, radula
(snails), or mandibles
(arthropods)
 Birds grind food with
small stones in gizzards
 Stomachs and crops are
storage chambers that
allow for gradual
digestion
http://www.biologycorner.com/resources/bird_anatomy.jpg
Small food particles are
delivered into midgut or
intestines
 Nutrients are absorbed in
midgut
 Hindgut recovers ions
and water and stores feces
 Muscular rectum expels
feces
http://eregimens.com/images/regimens/digestion.jpg
http://missinglink.ucsf.edu/lm/IDS_106_LowerGI/Lower%20GI/ASSETS/smallintestanat.jpg
In bony fishes, and
tetrapods, the gut wall
has folds with
projections called villi
 Surface cells of villi
have smaller
projections called
microvilli
http://www.jpp.krakow.pl/journal/archive/0605_s3/gfx/rys0513_16.jpg
Macromolecules are broken down
by digestive enzymes, known by
substances they hydrolyze
 Protease – breaks bonds of




amino acids
Carbohydrase – breaksdown
carbohydrates
Peptidase – peptides
Lipase – fats
Nuclease – nucleic acids
http://library.thinkquest.org/2935/Natures_Best/Nat_Best_High_Level/
Digestive_Net_Pages/Digestive_Graphics/Digetive_diagram.gif
Digestive enzymes are
produced in an inactive
form – a zymogen
 Cannot act on cells that
produce it
 In gut, zymogen is activated
by another enzyme
 Cells lining gut are
protected from enzymes by
mucus
http://www.joplink.net/prev/200103/2_fig2.gif
Vertebrate gut has layered plan
 Lumen – gut cavity
 Mucosa
 Layer of epithelial cells (mucosal
epithelium) that secretes mucus,
digestive enzymes or hormones
 some absorb nutrients via
microvilli
 Submucosa has blood and
lymph vessels, and nerves
 Circular muscle layer
 innermost cells oriented
around gut
 constricts gut
 Longitudinal muscle layer
 outermost cells oriented
along gut
 shortens gut
Mechanical activity in digestion:
 Tongue pushes food bolus to soft palate, and
initiates swallowing
 Food passes into esophagus
 Food kept out of trachea by closed larynx and the
epiglottis
Peristalsis
 Waves of muscle contractions
that move food toward
stomach
 Parts of esophagus are either
skeletal muscle or smooth
muscle
 As food reaches smooth
muscle, esophagus contracts
and pushes food toward the
stomach
Chief cells
 Secrete pepsinogen – inactive form of proteolytic
enzyme, pepsin
 Low pH of stomach converts it to active form
 Newly active pepsin activates other pepsinogen
molecules — process called autocatalysis
Stomach releases contents to the small intestine
 Chyme is mixture of gastric juice and partly
digested food
 Stomach walls contract and move chyme to
bottom of stomach
 Pyloric sphincter allows small amounts to enter
small intestine
Most chemical digestion occurs
in the small intestine
Small intestine has three
sections
 Duodenum – initial section
and site of most digestion
 Jejunum and ileum – carry
out most of nutrient
absorption
http://digestion0.tripod.com/images
Liver
 synthesizes bile salts and secretes
them as bile
 flows through hepatic duct to
duodenum
  through branch to gallbladder
 Fat entering duodenum signals
gallbladder to contract
 Bile released and flows via
common bile duct to duodenum
Contents of small intestine
pass into large intestine, or
colon
 Absorbs water and ions,
and produces feces
 Too much water
absorption leads to
constipation…
 Too little leads to
diarrhea
www.cdc.gov/colorectalcancer/basic_info/
 Large populations of bacteria live in the
colon
 includes Escherichia coli 
 synthesizes vitamin K and biotin that
are absorbed across colon wall
 Prolonged intake of antibiotics can
kill normal intestinal bacteria and
upset floral balance 
 digestive problems
 vitamin deficiency
www.microbeworld.org/img/aboutmicro/gallery
Herbivores cannot produce cellulases — enzymes
that break down cellulose
 Rely on symbiotic microorganisms living within
digestive tracts to digest cellulose
The protozoa Trichonympha
lives in each termite's gut and
breaks down cellulose so
termite can obtain nutrition
from its food.
www.durable-wood.com/termites/
www.termarid.com/images/
Ruminants (cud chewers)
 Have four-chambered stomachs: rumen, reticulum,
omasum and abomasum
 Rumen and reticulum contain microorganisms that
metabolize cellulose into nutrients for host
Dusty the llama
www.bar-q-diamond.com/llamas/Pictures
http://simulium.bio.uottawa.ca/bio2525/images/
www.palaeos.com/Vertebrates/Lists/Glossary/Images
Cecum
 Fermentation chamber in
some species
 Nutrient absorption is
incomplete from undigested
food
 In humans, the appendix is just
off the cecum
 Long thought to have no
function (vestigial)
 May function as refuge for
bacterial flora or in
immunity
http://www.toilet-related-ailments.com/images/CecumColorNew.jpg
Lipoproteins produced in liver are classified by density
(more fat  lower density)
 High-density lipoproteins (HDLs) remove cholesterol
from tissue and carry it to liver – “good”
 Low-density lipoproteins (LDLs) transport cholesterol
in body – “bad”
 Very-low-density lipoproteins (VLDLs) transport
triglycerides to fat cells.
http://distance.stcc.edu/AandP/AP/imagesAP2/blood/
Insulin
 released by pancreas
during absorptive
period, when blood
glucose rises
 Insulin promotes
uptake and
utilization or storage
of glucose
 Acts in skeletal
muscle, adipose
tissue, and liver