1 • A major func-on of the colon is to recover water that has entered the alimentary canal • Feces – Wastes of the diges-ve tract – Become more solid as they move through the colon – Pass through the rectum and exit via the anus Large Intes-ne • The colon houses strains of the bacterium Escherichia coli, some of which produce vitamins – Vitamin K • Rectum – Feces are stored in the un-l they can be eliminated • Two sphincters between the rectum and anus control bowel movements – Internal/external anal sphincter Colon
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1
• Amajorfunc-onofthecolonistorecoverwaterthathasenteredthealimentarycanal
• Feces
– Wastesofthediges-vetract
– Becomemoresolidastheymovethroughthecolon
– Passthroughtherectumandexitviatheanus
LargeIntes-ne
• ThecolonhousesstrainsofthebacteriumEscherichiacoli,someofwhichproducevitamins
– VitaminK
• Rectum
– Fecesarestoredintheun-ltheycanbeeliminated
• Twosphinctersbetweentherectumandanuscontrolbowelmovements
– Internal/externalanalsphincter
Colon
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Evolu-onaryadapta-ons
• Diges-vesystemsofvertebratesarevaria-onsonacommonplan
• However,thereareintriguingadapta-ons,oHenrelatedtodiet
– Sizeandtypeofteeth
– Lengthofintes-nes
– Numberofstomachs
SomeDentalAdapta-ons
• Den--on
– Animal’sassortmentofteeth
– Mammalshavevaryingden--onthatisadaptedtotheirusualdiet
• Theteethofpoisonoussnakesaremodifiedasfangsforinjec-ngvenom
• Allsnakescanunhingetheirjawstoswallowpreywhole
Fig. 41-18
Incisors
(c) Omnivore
Molars
(b) Herbivore
(a) Carnivore
Canines Premolars
3
StomachandIntes-nalAdapta-ons
• Herbivores
– Generallyhavelongeralimentarycanalsthancarnivores
• Indica-veofthelonger-meneededtodigestvegeta-on
Cecum
Small intestine
HerbivoreCarnivore
Colon(largeintestine)
StomachSmall intestine
Mutualis-cAdapta-ons
• Manyherbivoreshavefermenta-onchambers
– Wheresymbio-cmicroorganismsdigestcellulose
• Crop,cecum,rumen
– Coprophagy?!
• Ruminants
– Themostelaborateadapta-onsforanherbivorousdiet
– Deer,sheep,caUle
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Esophagus
OmasumAbomasum
Intestine
Rumen Reticulum1 2
4 3
EnergySourcesandStores
• Nearlyallofananimal’sATPgenera-onisbasedonoxida-onofenergy‐richmolecules:carbohydrates,proteins,andfats
• Animalsstoreexcesscaloriesprimarilyasglycogenintheliverandmuscles
• Energyissecondarilystoredasadipose,orfat,cells
• Whenfewercaloriesaretakeninthanareexpended,fuelistakenfromstorageandoxidized
Homeostasis:90 mg glucose/100 mL blood
Stimulus:Blood glucose
level risesafter eating.
Stimulus:Blood glucose
level dropsbelow set point.
5
OvernourishmentandObesity
• Overnourishment
– Causesobesity
– Resultsfromexcessiveintakeoffoodenergywiththeexcessstoredasfat
• Obesity
– Contributestodiabetes(type2)
– Cancerofthecolonandbreasts
– HeartaUacks,andstrokes
100 µm
• Researchershavediscoveredseveralofthemechanismsthathelpregulatebodyweight
• Homeosta-cmechanismsarefeedbackcircuitsthatcontrolthebody’sstorageandmetabolismoffatoverthelong‐term
• Hormonesregulatelong‐termandshort‐termappe-tebyaffec-nga“sa-etycenter”inthebrain
OvernourishmentandObesity
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LeptinPYY
Insulin
Ghrelin
• Lep-n
– Producedbyfatcells
– Appe-tesuppresant
• Micethatinheritadefectinthegeneforlep-nbecomeveryobese
OvernourishmentandObesity
Obese mouse with mutantob gene (left) next to wild-typemouse.
EXPERIMENT
RESULTS
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ObesityandEvolu-on
• Theproblemofmaintainingweight
– partlystemsfromourevolu-onarypast
• fathoardingwasameansofsurvival
• Petrelsbecomeobeseaschicks
– Inordertoconsumeenoughproteinfromhigh‐fatfood,chicksneedtoconsumemorecaloriesthantheyburn
Youshouldnowbeableto:
1. Namethethreenutri-onalneedsthatmustbemetbyananimal’sdiet
2. Describethefourclassesofessen-alnutrients
3. Dis-nguishamongundernourishment,overnourishment,andmalnourishment
4. Describethefourmainstagesoffoodprocessing
5. Dis-nguishbetweenacompletediges-vetractandagastrovascularcavity
6. Followamealthroughthemammaliandiges-vesystem:
– Listimportantenzymesanddescribetheirroles
– Comparewhereandhowthemajortypesofmacromoleculesaredigestedandabsorbed
7. Relatevaria-onsinden--onwithdifferentdiets
8. Explainwhereandinwhatformenergy‐richmoleculesmaybestoredinthehumanbody
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