Nutritionand Digestion
Objectives
Introduction
Describethe natureof humpbackwhalefeeding.
Food
Obtainingand Processing
herbivores,omnivores,suspensionfeeders,
Define and distinguishbetweencarnivores,
fluid feeders.and bulk feeders.
21.2 Describethe four stagesof food processing.
21.3 Comparethe structureand function of a gastrovascularcavity and an alimentary canal.
and bird.
Describethe specializeddigestivesystemsof an earthworm,grasshopPer,
2l.l
HumanDigestiveSystem
digesof thehumanalimentarycanaland the associated
21.4 Describethe main components
glands.
tive
21.5 Describethe functions of the moleculesin saliva and the roles of the tongue and teeth in
digestion.
21.6 Explain how swallowing occursand how food is directedaway from the trachea.
functions to propel food.
21.7 Explain how the structureof the esophagus
21.8 Relatethe structureof the stomachto its functions.Describethe functionsof the secretions of the stomach.Finatly, explainthe causesof heartburnand why the stomachdoes
not digestitself.
21.9 Describethe most commoncauseof stomachulcers and the primary forms of treatment.
21.10 Describethe different typesof chemicaldigestionthat occur in the small intestine.
Explain how the structureof the small intestinepromotesnutrient absorption.
Describethe structureand functionsof the large intestineand rectum. Note the causesof
2l.ll
constipationand diarrhea.
Dietsand DigestiveAdaptations
21.12 Comparethe digestivetractsof carnivoresand herbivores.Describethe cellulosedigesting specializationsof the digestiveftacts of a koala and a cow.
Nutrition
21.13 Describethe three contmonnutritionalneedsof all animals.
21.14 Define "basal metabolicrate," explainhow it is measured,and note how energyis
obtainedand storedin the bodY.
21.15 Explain why exerciseand a balanceddiet of 1200kcal or more is the best way to lose
weight.
21.16 Define essentialamino acidsand explainthe complexitiesassociatedwith a vegetarian
diet.
21.17 Define a vitamin and distinguishbetweenwater-solubleand fat-solublevitamins.
zl..lE Define dietary mineralsand explain why they are important in the diet.
21.19 Describethe types of informationfound on food labels.
diseaseand cancer.
21.20 Explain how diet can influencethe risksof cardiovascular
20s
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Instructor's Guide to Textand Media
KeyTerms
omnivore
herbivore
carnivore
feeder
suspension
substratefeeder
fluidfeeder
bulkfeeder
ingestion
digestion
absorption
elimination
gastrovascular
cavity
mouth
alimentarycanal
pharynx
esophagus
crop
stomach
gizzard
intestine
anus
peristalsis
pyloric sphincter
trachea
gastricgland
gastrin
acid chyme
gastriculcer
small intestine
pancreas
liver
bile
gallbladder
duodenum
villus
microvillus
large intestine
cecum
aPPendix
feces
rectum
ruminant mammal
kilocalorie(kcal)
basalmetabolicrate(BMR)
essentialfatty acid
Dietary
Recommended
Allowances(RDA)
essentialaminoacid
vitamin
mineral
low-density lipoprotein
(LDL)
high-densitylipoprotein
(HDL)
colon
LectureOutline
Intnoduction GettingTheir Fill of Krill
A. Review:Feeding(ingestingfood) is a distinctivecharacteristicof the animalkingdom.
B. The humpbackwhale, from an unusual habitat, shows how an animal's structureand
behaviorare directly tied to feeding and food processing.
from
1. Humpbackwhalesare suspensionfeedersthat strain small fish and crustaceans
day.
of
food
a
2
tons
processes
as
much
as
whale
A
72-ton
the ocean.
"bubble nets" to help concentratetheir food at the surface.The
2. Thesewhalesuse
mouth has a ftemendousvolume when expandedand usesthe comblike baleento
sift the food from the water.The stomachcan hold up to half a ton of food at a
time.
3. For four monthsin the summer,thesewhalesfeed in the rich, cold oceansof polar
regionsand store up vast fat reserves.In the winter, they migrate to warm, southern
oceansto breed.They eat little for eight months until they return to the polar
regions.
I. Obtaining and ProcessingFood
Module 21.1 Animalsingesttheir food in a varietyof ways.
A. Feedingcan be by absorption(as in a few parasiticworms) or by ingestion.
B. lngestivefeeding can be categorizedby type of food. Omnivores (such as humansand
crows)eat both plantsand animals.Herbivores (such as deeror seaurchins)eat plants
or algae.Carnivores (suchas lions and spiders)eat only other animals(Figure2I.lA).
Chapter2l Nutrition and Digestion
207
C. Ingestivefeedingcan be categorizedby the size and locationof the food.
1. Suspensionfeedersingest small animals such as microscopicprotists,plants,and
animals(clamsand other bivalves,Figure zl.LB).
2. Substratefeedersingestby burrowing into their food (earthwormsand caterpillars,
Figurezl.lc).
3. Fluid feedersobtainnutrientsfrom plant sap (aphids)or animalfluids (mosquitoes,
Figure21.1D).
4. Bulk feedersare thosethat consumelarger prey whole or in pieces(mostanimals,
Figure2l.lE).
Module 21.2 Overview:Food processingoccursin four stages.
A. Foodprocessingcan be divided into four stages(Figure21.2):
1. Ingestion is the act of eating.
2. Digestionis the breakdownof food into small enoughmoleculesto absorb.Digestion occursin two steps:mechanicaland chemicalbreakdown.The productsof
(Modules6.16
digestionare then usedfor eithercellular respirationor biosynthesis
and6.17).
3. Absorption is the taking up of thesesmall nutrientmolecules.
NOTE: Food doesnot actually enter the body until it is absorbed.Prior to absorption, food is in a tube (in the caseof animals with an alimentarycanal)that runs
through the body.
4. Elimination is the releaseof undigestedmaterial.
B. Food consistsof largepolymericfats, carbohydrates,proteins,andnucleicacidsthat
animalscannotabsorbdirectly. All animals need the samemonomericcomponents:fatty
acids,simplesugars,amino acids,and nucleotides.
C. During digestion,largerpolymersare chemically digestedinto smallercomponents
by hydrolysis(Module 3.3; Figure 3.3A, B). Specificenzymescatalyzeeachstepof
digestion.
Module 213 Digestionoccursin specializedcompartments.
A. Thesecompartmentsprovide environmentsthat favor the action of the specificdigestive
enzymesand ensurethat the enzymeswill not attackan animal'sown macromolecules.
B. Even a single-celledorganism,such as an amoeba,has specializedcompartmentsfor
digestion.Sponges,like thesesingle-celledorganisms,carry out all of their digestive
functionswithin their cells (Module 18.3).
C. Simple animals,such as cnidariansand flatworms, have a single digestivecompartment,
a gastrovascular cavity in which digestion and absorptionoccur,with a single opening
for ingestionand elimination(Figure2l-34)D. Other animalshavea seriesof compartments(organs)arrangedalong a tube (alimen'
tary canal) that extendsbetweenthe mouth and anus (Figure21.38).
E. Ingestedfood passesto the first cavity via a muscularpharynx and esophagus.
F. The first cavity may be a cnop (a pouchlike organ for temporarystorageand food softening),a $zzard (a muscularpouchthat containsteethor gnQ, or a stomach(a muscular pouchwithout grinding structures).
G. Chemicaldigestionand nutrientabsorptionoccur mainly in the intestine.Intestines
typically have modificationsthat increasetheir inner surfaceareaand thus increasethe
absorptivesurface.
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Instructor'sGuide to Textand Media
H. Undigestedmaterialsare expelledthroughthe anus.
I.
The exact nature of an animal's alimentarycanalreflectsits diet. An earthworm is an
omnivorous substratefeederwith an intestinethat has an inner. dorsal fold to increase
its absorptive area.A grasshopperis an herbivorewith a numberof adaptationsfor the
efficient processingof plant material.Differentbirds eatdifferentfoods, but most store
food in a crop and use a gravel-containinggizzardto grind food swallowed whole.
II. Human Digestive System
Module 21.4 T}re humandigestivesystemconsistsof an alimentarycanaland accessoryglands.
A. The main parts of the alimentarycanal are the mouth,oral cavity, tongue, pharynx,
esophagus,stomach,small intestine,largeintestine,rectum,and anus(Figure 21.4).
B . Digestive glands-the salivaryglands,pancreas,
and liver-secrete digestiveenzymes
into the cavities with which they are associated.
NOTE: These glandssecreteinto a duct; this makesthemexocrineglands.In contrast,
endocrineglandssecreteinto the blood (Module20.9).
c.
Food is propelled through the alimentarycanalby wavelikecontractions(peristalsis) of
smoothmuscle.
D. Sphincter musclescontrol the passageof food from one cavity to the next. The pyloric
sphincter regulatesmovementof food from the stomachto the small intestine.
The total digestiveprocesstakesabout5-6 hours.
NOTE: Lipids take longer and require lessenergyto digestthan carbohydratesand
proteins.
Module 21.5 Digestion beginsin the oral cavity.
Salivary juices contain lubricants,buffers, antibacterialagents,and a digestive enzyme
(salivary amylase)that hydrolyzesstarch.The releaseof salivaryjuices is riggered by
meal time and the sight or smell of food.
NOTE: Oral stimulation and the thought of food also trigger the secretionof saliva.
Other functions of saliva include helping keepteethclean,dissolving food so that it can
be tasted,and aiding in the formationof the bolus.
B . Mechanical and chemical digestionbeginsin the oral cavity as food is chewed
(Figure 21.5).
c.
Humans have four kinds of teeth (arrangedin four sets,right and left in the upper and
lower jaw): two bladelike incisors for biting, one pointedcaninefor tearing, two premolars, and three molars for grinding and crushingfood.
NOTE: Only animalswith a palateand cheekschewtheir food; the palate preventsfood
from entering the nasal cavity while chewing,and the cheeksprevent food from falling
out of the mouth. Comparehow a crocodilegulps its food with how a human chewsits
food. Vertebratesvary greatly in their complementof teeth.A pattern of dentition is
related to an animal's diet. For example,horseshaveincisorsto shearoff, and molars
to grind, the grassthey eat, but they haveno canines.Rodentshave strong, continually
growing incisors for gnawing on cellulose-richplant materials.Lions and other carnivores have prominent canineswith which they tear largehunks of flesh from their prey.
D. The tongue tastesthe food, manipulatesthe food, and shapesthe food into a bolus,
which it then pushesto the back of the oral cavity and into the pharynx (where it is
swallowed).
NOTE: The tongue also secreteslingual lipase,an enzymethat acts in the stomachand
plays a minor role in lipid digestion.
Chapter 2l Nutrition and Digestion
209
food and breathing passagesboth open into the pharynx.
Modute 21.6 T1r,ie
A. Most of the time, when not eating, the human pharynx opens into the windpipe
(trachea) for breathing and speaking(as air vibrates vocal cords in the voice box,
or larynx).
B. When a bolus of food passesinto the pharynx, the swallowing reflex is triggered. The
esophagealsphincter muscle relaxes,the tracheal opening closes off by the epiglottis,
and the food passesinto the esophagus(Figure 21.6).
Module 21.7 The esophagussqueezesfood along to the stomach.
A. Esophageal muscles are arrangedin two layers of smooth muscle, one circular and the
other longitudinal.
B. Peristalsis moves the bolus down the esophagustoward the stomach (Figure 21.7).
NOTE: The esophagusitself has no digestive function. However, salivary amylase continues to act on the food during its passagethrough the esophagus.Carbohydrate digestion stops upon entering the stomach,which is very acidic. Digestion then continues in
the small intestine.
Module 21.8 The stomach stores food and breaks it down with acid and enzymes.
A. The stomach can store up to 2 liters of food. It empties its contents slowly (after 24
hours) by opening the pyloric sphincter.
B. The inner surface of the stomach is highly folded and has pits that terminate in gastric
glands (Figure 21.8).
C. Chemical digestion continues in the stomachand is aided by contractions of smooth
muscle in the stomachwall. The digestion of proteins into smaller polypeptides occurs
by the action of the enzyme pepsin.
D. Gastric juice also includes mucus, which protects the stomach lining and also lubricates,
and hydrochloric acid, which convertspepsinogento pepsin and provides the proper pH
for the action of pepsin.
NOTE: The HCI secretedby the stomachhas a pH of =1. HCI is also important in
denaturing proteins that allow greater exposure of peptide bonds to pepsin, deactivating
hormones present in food, and killing bacteria. Further, HCI is important for the absorption of nutrients such as vitamin 812 and iron.
E. Gastric activity is initiated by a nervous signal from the brain (after seeing, tasting, or
smelling the food) and is continued by the secretion of gastrin, a gastric gland
hormone, when food is actually presentin the stomach.
F. The release of gastric juice by the gastric glands, under the control of gastrin, is a negative-feedback mechanism.
G. Occasional backflow of the stomachcontents (acid chyme) into the esophaguscauses
heartburn (what the commercials like to call acid reflux). During vomiting, the stomach
contents are eliminated by reverseperistalsisback up the esophagusand out of the oral
cavity.
NOTE: Chronic exposure of the esophagusto the acid contents of the stomach can
cause several problems. The acid can back up the esophagusand cause hoarseness,or
get to the lungs and affect respiration.The buildup of scar tissue at the base of the
esophagus can decreasethe diameter of this region of the esophagus (peptic stricture).
Ironically, the discomfort of chronic heartburn is relieved with the development of Barrett's esophagus(the growth of abnormal tissue in the esophagus),which increasesthe
risk of esophagealcancer.
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Instructor'sGuideto Textand Media
H. The pyloric sphincterregulatesthe passageof chymefrom the stomachto the small
intestine,allowingthe passageof only a small amountat a time.
Module 21.9 Connection:Bacterialinfectionscan causeulcers.
A. A gastric ulcer is an open sore on the stomachlining. The major symptomis pain in
the upperabdomenassociatedwith eating.
B . At one time ulcerswere thoughtto be due to the overproductionof pepsinand/oracid.
However,evidencenow indicatesthat a major causeof ulcers is the bacteritm Helicobacterpylori.
NOTE:This appliesto the small intestineas well as to the stomach.In addition to 1L
pylori, the othermajor causeof ulcersis the (over)useof nonsteroidalanti-inflammatory drugs(NSAID) suchas aspirinand ibuprofen.NSAID reduceinflammationby
inhibitingprostaglandinsynthesis.hostaglandinsplay a major role in cytoprotection
(protectingthe cells lining the stomachfrom damageby HCI).
c.
The body'sresponseto a H. pylori infectionresultsin stomachinflammation(gastritis).
Gastritismay progressto an ulcer.
D. H. pylori infectionis also associatedwith an increasedcancerrisk.
E. Gastriculcersusuallyrespondto an antibioticregimein combinationwith drugs such
as bismuth(the activeingredientin PeptoBismol).
NOTE: Not only is this treatrnentregime more effectivethan the older regime; it is also
lessexpensive.
Duodenalulcersoccur in the first portion of the small intestine.
Module 21.10 The small intestine is the major organ of chemical digestion and nutrient
absorption.
A. All remainingchemical digestion and most absorptionof nutrients occur in the small
intestine.This organis about6 meterslong and 2.5 cm in diameter.Peristalsismoves
the mixture.
NOTE: The chymethat entersthe small intestinefrom the stomachhas a pH of =2-3,
B . Digestioncontinuesin the first 25 cm (the duodenum).
c.
Glandularsecretionsare releasedinto the duodenum from the liver, the gallbladder
(the liver producesbile that containssalts to make fats more soluble; bile is storedin
the gallbladderuntil it is neededin the small intestine),the duodenumwall, and the
pancneas(which producesenzymesand bicarbonateions to neutralize the acid chyme
andraiseits pH) (Figure21.104).
Previan:The role of the liver in homeostasis
is discussedin more detail in Module
25.13.
NOTE: Folic acid (a B vitamin that is of great importanceduring pregnancy;Thble
21.17)is secretedalong with bile and is reabsorbed
in the small intestine.Anything
that inhibitsthis reabsorptioncan resultin a folate deficiency.
D. Eachtype of macromolecule(carbohydrates,
proteins,fats, and nucleic acids)is
digestedsequentiallyby specificenzymes.The digestionof carbohydratesand proteins
continueson fragmentsproducedby previouschemicalbreakdown.The digestion of
fats and nucleicacidsstartshere (Table21.10).
E. The surfaceareaof the lower part of the small intestineis huge, with severallevels of
folding.The wall is folded into circularpleats.Thesepleatscontainprojections(villi)
of cells, and the cells have further projections(microvilli). The total surfaceareais
about300 m2 lFigure21.108).
Chapter2l Nutition and Digestion
2ll
The core of eachvillus containscapillariesand lymph ducts.Nutrientsdiffusefrom
by an
intestinechamberto blood,or they are movedacrossmicrovillousmembranes
ATP-requiringtransportmechanism.
NOTE:Water-solublenutrientspassinto the capillaries,lipid-solublenufients into the
lacteals.
G. Nutrient-ladenblood from the small intestinepassesto the liver, which getsthe first
chanceto processor storethe nutrients,particularlystoring excessglucoseas animal
starch(glycogen).
Module 21.11 The large intestinereclaimswater.
A. The large intestine (colon) is about 1.5 m long and 5 cm in diameter(Figure2l.ll).
B. About 7 liters of digestivecontentspassinto the large intestineeachday.About 9OVoof
the water is absorbedback into the blood.
c.
Prokaryotesthat normallylive in the colon,including E. coli,live in the undigested
material.They produceandreleaseimportantvitamins (biotin, folic acid, B vitamins,
and vitamin K) that humanscannotmakethemselves.
NOTE: The amount of a vitamin synthesizedby the intestinal fauna that is availablefor
absorptionis not the samefor each vitamin. For example, intestinal bacteriacan meet
=50Voof an adult's needfor vitamin K, whereasit is not yet known how much of the
biotin synthesizedby intestinalprokaryotesis absorbed.
D . The remaining,undigestedmaterial(fiber) is compactedby peristalsisand storedin the
rectum until it is defecatedas feces.
E. The appendix is a gland at the top of the large intestine (abovethe cecum) that has a
minor immunesystemfunction.Appendicitisoccursif the appendixbecomesinfected
following irritation, or whenits openingis jammedby undigestedfood.
NOTE: A lack of fiber in the diet can also causeoutpouchings(diverticula) in the wall
of the colon. If the diverticulabecomeinflamedthe result is diveniculitis.
Itr. Diets and DigestiveAdaptations
Module 21.12 Adaptationsof vertebratedigestivesystemsreflect diet.
A. Herbivoresand omnivoreshave longer alimentarycanals than carnivores,to allow more
time and surfaceareafor digestingplant material(Figure 2I.l2A).
B . Dietary needschangefrom the larval stageto the adult stagein amphibians.The alimentarycanal of the larva is proportionally longer relative to body size than that of the
adult.
enzymesof prokaryotesand protists.
c. Most herbivoresrely on the cellulose-digesting
Populationsof theseorganismsare housedin parts of the animals'alimentarycanals.
D. Rabbits,and some rodents,produce soft fecal pellets fust, which include microorganisms that havedigestedthe cellulosein the cecum(a pouchlikeregion wheresmall and
largeintestinemeet).Theyreingestthesepelletsand absorbthe digestedcellulose(glucosemolecules)throughtheir small intestines,and then defecatehard fecal pellets.
Ruminant mammals, suchas cattle, sheep,and deer, have an elaborate,four-chamberedstomach,part of which housesthe microorganisms.Ingestedgrassentersthe
rumen and reticulum, whereprokaryotesand protists begin to digest the cellulose.Periodically, a cow regurgitatessome of this material and helps mechanicallydigest it by
"chewingthe cud." It is then swallowedinto the omasum,wherewateris absorbed,
wherethe cow's own enzymescompletethe digestionprocess
passingto the abomasum,
(Figure2l.l2B).
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Instructor'sGuideto Tbxtand Media
rv.Nutrition
Module 21.13 Overview:A healthful diet satisfiesthreeneeds.
A. Fuel to power all body activities
B. Raw materialsneededto make an animal'sown molecules
the animalcannotmakeitself)
C. Essentialnutrients(substances
Module 21.14 Chemicalenergypowersthe body.
Review:Cellular respirationin Chapter6.
NOTE: Ongoing studiesof nonhumananimalsare showingthat undernutrition,without
malnutrition,has healthbenefitsand can increasemaximumlifespans.
fats, and, when thesearein short supply,
A. The energycontent of food (carbohydrates,
proteins)is measuredin kilocalories (kcal), the accurateform of the popularword
"calorigs."
NOTE: A kilocalorie is the amount of energyrequired.to raiseonekilogram of water
onedegreeCelsius.
B. The basal metabolic rate (BMR) is the amountof energyrequiredto maintaincellular
metabolismin a resting animal.The averageBMR for adult humansis 1300-1800kcal
per day.
andvariousfoods supC. Variouslevels of activity add to a human'scaloric requirements,
ply theserequirements(Table 21.14).
D. Metabolicrates are determinedby measuringthe rate of oxygenconsumption.Each
liter of O2 consurnedliberates4.83 kcal from food (Figure21.14).
E. Liver and muscle store energyin the form of glycogen,a complexcarbohydrate.
F. Excessenergy is also storedas fat. The liver can make fat from carbohydratesand proteins even if there is little fat in the diet.
Module 21.15 Connection:Body fat and fad diets.
A. Review:Lipids (Modules3.8-3.10).
B. Fat is an essentialcomponentof the humanbody. It insulatesthe body againstcold, and
a moderateamount is correlatedwith a healthy immune system.Below-normalamounts
of fat interfere with vitamin A formation and may make peoplesusceptibleto some
cancers.
C. Thosefatty acids that our body cannot make for itself and that arerequiredin the diet
arecalledessentialfattY acids.
NOTE: The essential fatty acids are polyunsaturatedfatty acids(PUFAs).
fatty acids
Overconsumptionof PUFAs increasesthe risk of cancer.Monounsaturated
havecardiovascular
(suchas are found in olive oil and canolaoil) can, in moderation,
benefits.Saturatedfatty acids and trans fatty acids (formed whenfatty acids are hydrodiseaseandotherillnesses.
genated)increasethe risk of developingcardiovascular
D. Ideally,fat should be 20-25Voand l5-19vo of the body weightsof womenand men,
respectively."Overfat" levels should be regardedas those about20Vohigher than ideal
levels.
suchas heart
E. Too much body fat increasesthe chanceof developingcertaindiseases,
disease,and decreaseslife span.
(or proteins)increases,
therate at which it is
F. Whenthe consumptionof carbohydrates
metabolizedincreases.The body tendsto readily convertdietaryfat into body fat. Thus,
Chapter2l Nutrition and Digestion
213
dietary fat hasa more direct affect on weight (fat) gain than the consumptionof carbohydrates(or proteins).
NOTE: Even the energycost of processingfats is lessthanthe energycostsof processor proteins.This is not to say that fat storescannotincreaseon a
ing carbohydrates
(or high-protein)diet. Caloriesconsumed
do matter,but the sourceof
high-carbohydrate
the caloriesis also important.
G. However,evenwith this tendencyto storebody fat, manypeople,evenobeseones,tend
to maintain a relatively stablebody weight.
H. Fad diets not only are usuallyineffectivebut alsomay be harmful (Table21.15).A
diet, may in fact increasethe risk of
popular diet, the high-proteinlow-carbohydrate
heart disease.
L Following the guidelinesfor the RecommendedDietary Allowances (RDAs) for nutrients, and gettingregularaerobicexercise,can keepbodyfat at normallevels.
NOTE: Maintaining body fat at an appropriatelevel getsmore diffrcult with age.With
by
age, metabolicrate declinesand unlessthereis somemeasureof compensation
body
fat
the
level
of
exercise,
adjustingthe amountof food consumedand increasing
will tend to accumulate.
must be sureto obtainall eight essentialaminoacids.
Modute 21.16 Connection:Vegetarians
A. The human body can make a great variety of organicmolecules(including 11 amino
acids) from basicsourcesof organiccarbonand nitrogenprovidedin digestedfood.
(essentialnutrients)cannotbe madeandmustbe obtaineddirectly
B. Some substances
from food.
C. Meat and egg productsprovide all eight essentialamino acids.
D. A combination of plant proteins can also provide all nine essentialamino acids
(Figure 21.16).
Module 21.17 Connection:A healthfuldiet includes13 vitamins.
A. A vitamin is an organic nutrient that is essentialbut requiredin much smallerquantities than the essentialamino acids.
B. Most vitamins serveas coenzymesor parts thereof,that are reusedin metabolicreactions or in a variety of roles in maintainingcellular health.
Revia,v:Enzymefunction is discussedin Modules5.5-5.9.
C. Vitamins are groupedinto thosethat are water-solubleand thosethat are fat-soluble
(Thble 21.17).Unlike water-solublevitamins,excessfat-solublevitaminsare not easily
eliminated from the body and build up in body fat, wherethey may havetoxic effects.
D. RDAs have beenestablishedfor all vitamins, but manynutritionistsrecommendhigher
levels of certain vitamins.
NOTE: Folic acid is one suchvitamin.
E. Extreme deficienciesof eachvitamin causespecificsetsof symptoms.
Module 21.18 Connection:Essentialmineralsare requiredfor manybody functions.
A. Minerals are chemical nuftients other than carbon,hydrogen,oxygen,and nitrogen.
B. All mineralsare essential.Dependingon their rolesin structureand function,essential
minerals are requiredin various amounts(Table 21.18).
C. Too much of somemineralscan causeabnormalfunction;for example,too much
sodium in salt promoteshigh blood pressurein humans.
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Instructor'sGuideto TextandMedia
NOTE: Recentstudiesare showingthat only a subsetof the populationis sodium sensitive and that thoseindividualswho are not sodiumsensitivehaveless need to be concernedabouttheir sodiumintake (but shouldn'toverdoit).
Module 21.19 Connection:What do food labelstell us?
A. Food labelsprovidetwo piecesof informationfor the consumer(Figure 2I.19):
1. A list of ingredientsarrangedaccordingto weight, from the greatestamountto the
least amount.
(total and dietary fiber and sugars),pro2. The numberof kilocalories,carbohydrates
teins, fats (totaland saturatedfats and cholesterol),and selectedvitamins and minerals suppliedin one servingappearon the label and are expressedas percentages
of a daily value.
B. Somelabels will also list the amountof PUFA and monounsaturatedfat. If theseare
listed and their amountsare addedto the amountof saturatedfat, the sum may not be
equal to the total amountof fat listed; the differencewill be the amount of trans fat in
a serving of that food item.
diseaseand cancer.
Module 21.20 Connection:Diet can influencecardiovascular
A. Linked to cardiovasculardiseaseare diets low in fruits and vegetablesand rich in saturated fats, which in turn correlateswith high levels of blood cholesterol. Cardiovascular
diseaseis linked to high levels of low-density lipoproteins (LDLs), while increased
concentrationsof high-density Iipoproteins (HDLs) are correlatedwith lower risk of
disease.
Exercisetendsto i11s1gffs-andsmokingto decrease-HDl
cardiovascular
levels (Figure 2L20).
is discussedin Modules 5.20 and9.9.
NOTE: Inherited(famital) hypercholesterolemia
(lack
of
exercise,
a high-fat diet) will also result in
here,lifestyle
However,as discussed
hypercholesterolemia.
B. Linked to someforms of cancerare high levels of dietary fat and low levels of dietary
fiber (Thble 21.20).
for a discussion
of the cellularbasisof cancerand
Review:SeeModules11.15-11.19
lifestyle and cancerrisk.
NOTE: The benefitsof fiber include slowing glucoseabsorptionand lowering blood
cholesterollevels.In addition, foods high in fiber tend to be lower in fats. Until the
body adaps to a high-fiberdiet, the resultcanbe diarrheaor constipation,gas,and
abdominaldiscomfort.A diet can also be too high in fiber; the result can be insufficient
consumptionof energyor nutrients,inhibition of nutrient absorption,and formation of
phytobezoars(fiber balls that can obstructthe GI tracQ.
ClassActivities
l.
Haveyour studentscreatea modelof thehumandigestivesystemillustratingthe major functionsof
eachcomponentof the system.
2.
Have your studentschoosetwo differentvertebratespeciesand explore how differencesin their diet
are reflectedin differencesin the structureof their digestivesystems.
3.
concerningnutrition in the popular press.
Thereis a greatdeal of misinformation/misrepresentation
Have studentsbring in articlesto critique.
Have studentsanalyzeandcritiquethe dietsthey consume(thereare many good diet analysisprogramsavailable)and discusswaysto improvetheir diet.
4.
Chapter 2l Nutrition and Digestion
215
Acetates
Transparency
Figure 21.2
Figure 21.3A
Figure 21.38
Figure 21.4
Figure21.5
Figure21.6
Figure21.6
Figure 21.6
Figure 21.7
Figure 21.8
Figure2I.1.0A
Figure21.10B
Thble21.10
Figure21.11
Figure2l.I2A
Figure2l.L2B
Table2t.14
Table21.15
Figure21.16
Table?I.l7
Table2I.IT
Thble21.18
Figure21.19
Figure21.20
Table 21.20
Thefourmain stagesof food processing
cavityof a hydra
Digestionin the gastrovascular
and a bird
Alimentarycanalsof an earthwonn,a grasshopper,
Thehumandigestivetract
Thehumanoral cavity
The swallowingreflex(Layer 1)
The swallowingreflex(Layer2\
The swallowingreflex(Layer3)
andtheir roles in peristalsis
Musclelayersof the esophagus
Thecellsof the gasric glandsin the stomach
The smallintestineandrelateddigestiveorgans
Structure
of the smallintestine
Enzymaticdigestionin the smallintestine
Therelationshipof the smallandlargeintestine
Thealimentarycanalin a carnivore(coyote)and an herbivore(koala)
Thedigestivesystemof a ruminantmammal
energyequivalents
Food-exercise
Diet typesandtheir healtheffectsandpotentialproblems
Essentialaminoacids
Vitamins(Layer l)
Vitamins(Layer2)
Minerals
Wheatbreadlabel
with cardiovascular
disease
Risk factorsassociated
Dietaryguidelinesfor reducingcancerrisk
Media
Seethe beginningof this book for a completedescriptionof all media available for instructorsand students.Animations and videosare availablein the CampbellImage PresentationLibrary. Media Activities
and Thinking as a Scientistinvestigationsare availableon the studentCD-ROM and web site.
Animations andVideos
File Name
WhaleEatinga SealVideo
WhaleEatinga SealVideo
21-01E-WhaleEatSealVideo-B.mov
2l-0lE-WhaleEatSealVideo-S.mov
ActivitiesandThinkingasa Scientist
ModuleNumber
Function
Web/CDActivity 2IA: DigestiveSystern
Web/CDThinking asa Scientist:WhatRoleDoesAmylase
Play in Digestion?
21.10
2I.I0