LIFESCI 2N03 Chapter 2: Life Sci 2N03: Chapter 2
4 May 2018
School
Department
Course
Professor
Digestion
Gastrointestinal+tract+(GI+tract) -a+flexible+muscular+tube+that+extends+from+the+mouth,+through+the+
esophagus,+stomach,+small+intestine,+large+intestine,+and+rectum+to+the+anus+
Only+when+a+nutrient+or+other+substances+enter+penetrate+the+GI+tract's+wall+does+it+enter+the+body,+
many+materials+pass+through+the+GI+tract+without+being+digested+or+absorbed+
Pathway+of+Digestion:+
Mouth
Teeth+crush+larger+ food+pieces+to+smaller+ones+via+chewing+
•
Fluids+from+food,+beverages+and+salivary+glands+help+ease+swallowing+
•
Fluid+helps+dissolve+food+so+the+taste+buds+can+react+with+the+solution+
•
Taste+buds+can+detect+sweet,+sour,+bitter,+salty+and+umami+
•
Other+factors+such+as+the+temperature,+aroma,+texture+etc.+also+influence+taste+(our+sense+of+
smell+is+more+sensitive+than+our+taste+buds+are)
•
When+a+mouthful+of+food+is+swallowed+it+passes+through+the+pharynx+
•
Since+the+pharynx+is+shared+with+the+digestive+and+respiratory+systems+the+epiglottis+closes+off+
the+airway+so+that+choking+doesn't+occur+when+swallowing
•
When+a+mouthful+of+food+has+been+chewed+and+swallowed+it+is+referred+to+as+"bolus"
•
Esophagus
The+esophagus+has+a+sphincter+muscle+at+each+end+
•
Sphincter -a+circular+ muscle+surrounding+and+able+to+close+a+body+opening
During+a+swallow+the+upper+esophageal+sphincter+opens,+the+bolus+slides+down+the+esophagus,+
passes+through+a+hole+in+the+diaphragm+to+the+stomach+
•
The+lower+esophagus+sphincter+closes+so+there+is+no+back+tracking+of+the+bolus+
•
Stomach
The+bolus+is+transferred+from+the+upper+to+lower+portion+of+the+stomach+while+receiving+juices+
•
It+is+grinded+by+the+stomach+into+a+semiliquid+mass+called+"chyme"+
•
Bit+by+bit+the+stomach+releases+the+chyme+to+through+the+pyloric+sphincter+(which+opens+into+the+
small+intestine)+and+then+closes+behind+the+chyme+
•
Small3intestine
The+bladder+and+pancreas+provide+fluids+to+the+small+intestine+
•
The+small+intestine+is+split+into+3+segments:+the+duodenum,+the+jejunum+and+the+ileum+
•
The+small+intestine+is+almost+3+meters+of+tubing+coiled+within+the+abdomen+•
Large3Intestine3(Colon)
The+contents+passes+through+the+ileocecal+ sphincter+located+at+the+beginning+(cecum)+of+the+
large+intestine+in+the+lower+right+side+of+the+abdomen+
•
The+contents+pass+through+another+opening,+and+if+any+intestinal+contents+slip+into+this+opening+
it+would+end+up+in+the+appendix+
•
Normally+they+bypass+this+opening+and+travel+to+the+rectum+•
The+colon+withdraws+water+leaving+semisolid+waste+•
The+strong+muscles+of+the+rectum+and+anal+canal+hold+back+the+waste+until+the+two+sphincters+of+
the+anus+open+to+allow+excretion+
•
Muscular+Action+of+Digestions:+
Peristalsis33
Peristalsis -wavelike+muscular+contractions+of+the+GI+tract+that+propel+its+contents+along+
The+entire+inside+wall+of+the+GI+tract+is+ringed+with+circular+muscles+that+are+surrounded+by+
longitudinal+muscles+
•
When+the+rings+tighten+and+the+long+muscles+relax+the+tube+is+constricted,+when+the+rings+relax+
and+the+long+muscles+tighten+the+tube+bulges;+and+that’s+how+the+intestinal+contents+are+
propelled+
•
The+waves+of+contraction+normally+ripple+along+the+GI+tract+at+varying+rates+and+intensities+
depending+on+the+part+of+the+GI+tract+and+on+whether+food+is+present+
•
Factors+such+as+stress,+medicines+and+medical+conditions+may+interfere+with+normal+GI+tract+
contractions+
•
Stomach3Action3
The+GI+tract+has+a+third+layer+of+diagonal+muscles+that+also+alternately+contracts+and+relaxes+•
These+3+layers+work+together+to+break+apart+the+bolus+and+force+the+chyme+downward•
The+Pyloric+sphincter+stays+closed+when+the+chyme+is+forced+down,+allowing+gastric+juices+to+
completely+liquefy+the+chyme+before+sending+it+to+the+small+intestine+
•
Segmentation3
Segmentation -a+periodic+squeezing+or+partitioning+of+the+intestine+at+intervals+along+its+length+by+its+
circular+muscles+
It+further+breaks+apart+food+particles+to+mix+the+chyme+and+promote+close+contact+with+the+
digestive+juices+and+the+absorbing+cells+of+the+intestine+walls+
•
Sphincter3Contractions3
Sphincter+muscles+periodically+open+and+close+allowing+the+contents+of+the+GI+tract+to+move+
along+at+a+controlled+pace+
•
The+upper+esophageal+sphincter+opens+in+response+to+swallowing+•
The+lower+esophageal+sphincter/cardiac+sphincter+prevents+reflux+of+stomach+contents+•
The+pyloric+sphincter,+which+stays+closed+most+of+the+time,+holds+the+chyme+in+the+stomach+long+
enough+for+it+to+be+thoroughly+mixed+with+the+gastric+juice+and+liquefied
•
The+pyloric+sphincter+also+prevents+intestinal+contents+from+backing+into+the+stomach+•
The+ileocecal+ sphincter+performs+a+similar+function+allowing+the+contents+of+the+small+intestine+to+
empty+into+the+large+intestine
•
The+tightness+of+the+rectal+muscle+together+with+the+two+sphincters+of+the+anus+act+as+a+safety+
device+to+prevent+continuous+elimination+of+waste+
•
Secretions+of+Digestion+
Saliva3
The+salivary+glands+squirt+just+enough+saliva+to+moisten+each+mouthful+of+food+so+that+it+can+pass+
easily+down+the+esophagus+
•
Saliva+contains+water,+salts,+mucus,+and+enzymes+that+initiate+the+digestion+of+carbohydrates+•
Saliva+also+protects+the+teeth+and+the+lining+of+the+mouth,+esophagus+and+stomach+from+
substances+that+might+cause+damage+
•
Gastric3Juice3
Gastric+glands+secrete+gastric+juice+which+is+a+mixture+of+water,+enzymes+and+hydrochloric+acid+•
The+cells+ of+the+stomach+wall+secrete+ mucus+to+protect+themselves+from+the+gastric+juices•
The+acidity+of+the+gastric+juice+registers+below+2+on+the+pH+scale+•
Once+in+the+stomach+salivary+enzymes+just+become+other+proteins+to+be+digested+•
Pancreatic3Juice3and3Intestinal3Enzymes3
The+pancreas+contributes+digestive+juices+by+way+of+ducts+leading+into+the+duodenum•
The+pancreatic+juice+contains+sodium+bicarbonate+(which+is+basic)+to+neutralize+the+acidic+ chyme+
arriving+in+the+small+intestine+
•
The+pH+of+the+pancreatic+juice+is+8•
From+this+point+on+the+chyme+remains+slightly+basic+•
Bile3
The+liver+ continuously+produces+bile+which+is+then+concentrated+and+stored+in+the+gallbladder+•
The+gallbladder+squirts+bile+into+the+duodenum+when+the+dietary+fat+arrives+•
Bile+is+an+emulsifier+that+brings+fats+into+suspension+in+water+so+that+enzymes+can+break+them+
down+into+their+component+parts+
•
Absorption
Anatomy+of+the+Absorptive+System+
The+small+intestine+is+wrinkled+into+hundreds+of+folds,+each+fold+is+contoured+into+thousands+of+
fingerlike+projections++known+as+villi+
•
A+single+villi+is+contains+thousands+of+its+own+microscopic+hairs+called+microvilli+•
The+crypt+glands+lie+between+the+villi+in+the+cervices+•
Crypt+glands -tubular+glands+that+lie+ between+the+intestinal+villi+and+secrete+intestinal+juices+into+the+
small+intestine
Nearby+Goblet+cells+secrete+mucus+•
The+villi+ are+in+constant+motion,+because+they+are+lined+by+a+thin+sheet+of+muscle+and+can+wave,+
squirm+and+wriggle
•
Some+partially+digested+nutrients+are+caught+in+the+microvilli,+digested+further+by+enzymes+there+
and+then+absorbed+into+the+cells+++
•
The+microvilli+ contain+hundreds+of+different+kinds+of+enzymes+and+pumps+which+recognize+and+
act+on+different+nutrients+
•
Specialization3of3the3GI3tract3
Nutrients+that+are+ready+for+absorption+early+are+absorbed+near+the+top+of+the+GI+tract+•
Nutrients+that+take+longer+to+be+digested+are+absorbed+farther+down+•
Medical+professionals+who+treat+digestive+disorders+learn+the+specialized+absorptive+functions+of+
different+parts+of+the+GI+tract+so+that+if+one+part+is+dysfunctional+the+diet+can+be+adjusted+
accordingly+
•
Food3Combining3Myth3
The+idea+that+people+should+not+eat+certain+food+combinations+at+the+same+meal+because+the+
digestive+system+cannot+handle+more+than+one+task+at+a+time+is+false+
•
The+opposite+is+true,+foods+eaten+together+can+enhance+the+each+other's+use+by+the+body+•
Ex.+Vitamin+C+in+a+pineapple+can+enhance+the+absorption+of+iron+from+a+meal+of+beans+and+rice+or+
other+iron-containing+foods+
Preparing3Nutrients3for3Transport3
When+a+nutrient+molecule+has+crossed+the+absorptive+cell+of+a+villus+it+enters+either+the+
bloodstream+or+the+lymphatic+system+
•
Both+transport+systems+supply+vessels+to+each+villus+•
The+water-soluble+nutrients+including+smaller+products+of+fat+digestion+are+released+directly+into+
the+bloodstream+and+guided+directly+to+the+liver+when+their+fate+and+destination+will+be+
determined+
•
The+larger+ fats+and+the+fat-soluble+vitamins+are+insoluble+in+water,+therefore+insoluble+in+blood+•
Intestinal+cells+assemble+many+products+of+fat+digestion+into+larger+molecules,+these+larger+
molecules+cluster+together+with+special+proteins+forming+chylomicrons
•
These+chylomicrons+are+released+into+the+lymphatic+system,+they+move+through+the+lymph+and+
then+later+enter+the+bloodstream+at+a+point+near+the+heart+bypassing+the+liver+
•
Chapter(2
Tuesday,+ September+ 19,+2017
11:38+PM
Digestion
Gastrointestinal+tract+(GI+tract) -a+flexible+muscular+tube+that+extends+from+the+mouth,+through+the+
esophagus,+stomach,+small+intestine,+large+intestine,+and+rectum+to+the+anus+
Only+when+a+nutrient+or+other+substances+enter+penetrate+the+GI+tract's+wall+does+it+enter+the+body,+
many+materials+pass+through+the+GI+tract+without+being+digested+or+absorbed+
Pathway+of+Digestion:+
Mouth
Teeth+crush+larger+ food+pieces+to+smaller+ones+via+chewing+•
Fluids+from+food,+beverages+and+salivary+glands+help+ease+swallowing+•
Fluid+helps+dissolve+food+so+the+taste+buds+can+react+with+the+solution+•
Taste+buds+can+detect+sweet,+sour,+bitter,+salty+and+umami+•
Other+factors+such+as+the+temperature,+aroma,+texture+etc.+also+influence+taste+(our+sense+of+
smell+is+more+sensitive+than+our+taste+buds+are)
•
When+a+mouthful+of+food+is+swallowed+it+passes+through+the+pharynx+•
Since+the+pharynx+is+shared+with+the+digestive+and+respiratory+systems+the+epiglottis+closes+off+
the+airway+so+that+choking+doesn't+occur+when+swallowing
•
When+a+mouthful+of+food+has+been+chewed+and+swallowed+it+is+referred+to+as+"bolus"
•
Esophagus
The+esophagus+has+a+sphincter+muscle+at+each+end+•
Sphincter -a+circular+ muscle+surrounding+and+able+to+close+a+body+opening
During+a+swallow+the+upper+esophageal+sphincter+opens,+the+bolus+slides+down+the+esophagus,+
passes+through+a+hole+in+the+diaphragm+to+the+stomach+
•
The+lower+esophagus+sphincter+closes+so+there+is+no+back+tracking+of+the+bolus+•
Stomach
The+bolus+is+transferred+from+the+upper+to+lower+portion+of+the+stomach+while+receiving+juices+
•
It+is+grinded+by+the+stomach+into+a+semiliquid+mass+called+"chyme"+•
Bit+by+bit+the+stomach+releases+the+chyme+to+through+the+pyloric+sphincter+(which+opens+into+the+
small+intestine)+and+then+closes+behind+the+chyme+
•
Small3intestine
The+bladder+and+pancreas+provide+fluids+to+the+small+intestine+•
The+small+intestine+is+split+into+3+segments:+the+duodenum,+the+jejunum+and+the+ileum+
•
The+small+intestine+is+almost+3+meters+of+tubing+coiled+within+the+abdomen+•
Large3Intestine3(Colon)
The+contents+passes+through+the+ileocecal+ sphincter+located+at+the+beginning+(cecum)+of+the+
large+intestine+in+the+lower+right+side+of+the+abdomen+
•
The+contents+pass+through+another+opening,+and+if+any+intestinal+contents+slip+into+this+opening+
it+would+end+up+in+the+appendix+
•
Normally+they+bypass+this+opening+and+travel+to+the+rectum+•
The+colon+withdraws+water+leaving+semisolid+waste+•
The+strong+muscles+of+the+rectum+and+anal+canal+hold+back+the+waste+until+the+two+sphincters+of+
the+anus+open+to+allow+excretion+
•
Muscular+Action+of+Digestions:+
Peristalsis33
Peristalsis -wavelike+muscular+contractions+of+the+GI+tract+that+propel+its+contents+along+
The+entire+inside+wall+of+the+GI+tract+is+ringed+with+circular+muscles+that+are+surrounded+by+
longitudinal+muscles+
•
When+the+rings+tighten+and+the+long+muscles+relax+the+tube+is+constricted,+when+the+rings+relax+
and+the+long+muscles+tighten+the+tube+bulges;+and+that’s+how+the+intestinal+contents+are+
propelled+
•
The+waves+of+contraction+normally+ripple+along+the+GI+tract+at+varying+rates+and+intensities+
depending+on+the+part+of+the+GI+tract+and+on+whether+food+is+present+
•
Factors+such+as+stress,+medicines+and+medical+conditions+may+interfere+with+normal+GI+tract+
contractions+
•
Stomach3Action3
The+GI+tract+has+a+third+layer+of+diagonal+muscles+that+also+alternately+contracts+and+relaxes+•
These+3+layers+work+together+to+break+apart+the+bolus+and+force+the+chyme+downward•
The+Pyloric+sphincter+stays+closed+when+the+chyme+is+forced+down,+allowing+gastric+juices+to+
completely+liquefy+the+chyme+before+sending+it+to+the+small+intestine+
•
Segmentation3
Segmentation -a+periodic+squeezing+or+partitioning+of+the+intestine+at+intervals+along+its+length+by+its+
circular+muscles+
It+further+breaks+apart+food+particles+to+mix+the+chyme+and+promote+close+contact+with+the+
digestive+juices+and+the+absorbing+cells+of+the+intestine+walls+
•
Sphincter3Contractions3
Sphincter+muscles+periodically+open+and+close+allowing+the+contents+of+the+GI+tract+to+move+
along+at+a+controlled+pace+
•
The+upper+esophageal+sphincter+opens+in+response+to+swallowing+•
The+lower+esophageal+sphincter/cardiac+sphincter+prevents+reflux+of+stomach+contents+•
The+pyloric+sphincter,+which+stays+closed+most+of+the+time,+holds+the+chyme+in+the+stomach+long+
enough+for+it+to+be+thoroughly+mixed+with+the+gastric+juice+and+liquefied
•
The+pyloric+sphincter+also+prevents+intestinal+contents+from+backing+into+the+stomach+•
The+ileocecal+ sphincter+performs+a+similar+function+allowing+the+contents+of+the+small+intestine+to+
empty+into+the+large+intestine
•
The+tightness+of+the+rectal+muscle+together+with+the+two+sphincters+of+the+anus+act+as+a+safety+
device+to+prevent+continuous+elimination+of+waste+
•
Secretions+of+Digestion+
Saliva3
The+salivary+glands+squirt+just+enough+saliva+to+moisten+each+mouthful+of+food+so+that+it+can+pass+
easily+down+the+esophagus+
•
Saliva+contains+water,+salts,+mucus,+and+enzymes+that+initiate+the+digestion+of+carbohydrates+•
Saliva+also+protects+the+teeth+and+the+lining+of+the+mouth,+esophagus+and+stomach+from+
substances+that+might+cause+damage+
•
Gastric3Juice3
Gastric+glands+secrete+gastric+juice+which+is+a+mixture+of+water,+enzymes+and+hydrochloric+acid+•
The+cells+ of+the+stomach+wall+secrete+ mucus+to+protect+themselves+from+the+gastric+juices•
The+acidity+of+the+gastric+juice+registers+below+2+on+the+pH+scale+•
Once+in+the+stomach+salivary+enzymes+just+become+other+proteins+to+be+digested+•
Pancreatic3Juice3and3Intestinal3Enzymes3
The+pancreas+contributes+digestive+juices+by+way+of+ducts+leading+into+the+duodenum•
The+pancreatic+juice+contains+sodium+bicarbonate+(which+is+basic)+to+neutralize+the+acidic+ chyme+
arriving+in+the+small+intestine+
•
The+pH+of+the+pancreatic+juice+is+8•
From+this+point+on+the+chyme+remains+slightly+basic+•
Bile3
The+liver+ continuously+produces+bile+which+is+then+concentrated+and+stored+in+the+gallbladder+•
The+gallbladder+squirts+bile+into+the+duodenum+when+the+dietary+fat+arrives+•
Bile+is+an+emulsifier+that+brings+fats+into+suspension+in+water+so+that+enzymes+can+break+them+
down+into+their+component+parts+
•
Absorption
Anatomy+of+the+Absorptive+System+
The+small+intestine+is+wrinkled+into+hundreds+of+folds,+each+fold+is+contoured+into+thousands+of+
fingerlike+projections++known+as+villi+
•
A+single+villi+is+contains+thousands+of+its+own+microscopic+hairs+called+microvilli+•
The+crypt+glands+lie+between+the+villi+in+the+cervices+•
Crypt+glands -tubular+glands+that+lie+ between+the+intestinal+villi+and+secrete+intestinal+juices+into+the+
small+intestine
Nearby+Goblet+cells+secrete+mucus+•
The+villi+ are+in+constant+motion,+because+they+are+lined+by+a+thin+sheet+of+muscle+and+can+wave,+
squirm+and+wriggle
•
Some+partially+digested+nutrients+are+caught+in+the+microvilli,+digested+further+by+enzymes+there+
and+then+absorbed+into+the+cells+++
•
The+microvilli+ contain+hundreds+of+different+kinds+of+enzymes+and+pumps+which+recognize+and+
act+on+different+nutrients+
•
Specialization3of3the3GI3tract3
Nutrients+that+are+ready+for+absorption+early+are+absorbed+near+the+top+of+the+GI+tract+•
Nutrients+that+take+longer+to+be+digested+are+absorbed+farther+down+•
Medical+professionals+who+treat+digestive+disorders+learn+the+specialized+absorptive+functions+of+
different+parts+of+the+GI+tract+so+that+if+one+part+is+dysfunctional+the+diet+can+be+adjusted+
accordingly+
•
Food3Combining3Myth3
The+idea+that+people+should+not+eat+certain+food+combinations+at+the+same+meal+because+the+
digestive+system+cannot+handle+more+than+one+task+at+a+time+is+false+
•
The+opposite+is+true,+foods+eaten+together+can+enhance+the+each+other's+use+by+the+body+•
Ex.+Vitamin+C+in+a+pineapple+can+enhance+the+absorption+of+iron+from+a+meal+of+beans+and+rice+or+
other+iron-containing+foods+
Preparing3Nutrients3for3Transport3
When+a+nutrient+molecule+has+crossed+the+absorptive+cell+of+a+villus+it+enters+either+the+
bloodstream+or+the+lymphatic+system+
•
Both+transport+systems+supply+vessels+to+each+villus+•
The+water-soluble+nutrients+including+smaller+products+of+fat+digestion+are+released+directly+into+
the+bloodstream+and+guided+directly+to+the+liver+when+their+fate+and+destination+will+be+
determined+
•
The+larger+ fats+and+the+fat-soluble+vitamins+are+insoluble+in+water,+therefore+insoluble+in+blood+•
Intestinal+cells+assemble+many+products+of+fat+digestion+into+larger+molecules,+these+larger+
molecules+cluster+together+with+special+proteins+forming+chylomicrons
•
These+chylomicrons+are+released+into+the+lymphatic+system,+they+move+through+the+lymph+and+
then+later+enter+the+bloodstream+at+a+point+near+the+heart+bypassing+the+liver+
•
Chapter(2
Tuesday,+ September+ 19,+2017 11:38+PM
Digestion
Gastrointestinal+tract+(GI+tract) -a+flexible+muscular+tube+that+extends+from+the+mouth,+through+the+
esophagus,+stomach,+small+intestine,+large+intestine,+and+rectum+to+the+anus+
Only+when+a+nutrient+or+other+substances+enter+penetrate+the+GI+tract's+wall+does+it+enter+the+body,+
many+materials+pass+through+the+GI+tract+without+being+digested+or+absorbed+
Pathway+of+Digestion:+
Mouth
Teeth+crush+larger+ food+pieces+to+smaller+ones+via+chewing+•
Fluids+from+food,+beverages+and+salivary+glands+help+ease+swallowing+•
Fluid+helps+dissolve+food+so+the+taste+buds+can+react+with+the+solution+•
Taste+buds+can+detect+sweet,+sour,+bitter,+salty+and+umami+•
Other+factors+such+as+the+temperature,+aroma,+texture+etc.+also+influence+taste+(our+sense+of+
smell+is+more+sensitive+than+our+taste+buds+are)
•
When+a+mouthful+of+food+is+swallowed+it+passes+through+the+pharynx+•
Since+the+pharynx+is+shared+with+the+digestive+and+respiratory+systems+the+epiglottis+closes+off+
the+airway+so+that+choking+doesn't+occur+when+swallowing
•
When+a+mouthful+of+food+has+been+chewed+and+swallowed+it+is+referred+to+as+"bolus"•
Esophagus
The+esophagus+has+a+sphincter+muscle+at+each+end+•
Sphincter -a+circular+ muscle+surrounding+and+able+to+close+a+body+opening
During+a+swallow+the+upper+esophageal+sphincter+opens,+the+bolus+slides+down+the+esophagus,+
passes+through+a+hole+in+the+diaphragm+to+the+stomach+
•
The+lower+esophagus+sphincter+closes+so+there+is+no+back+tracking+of+the+bolus+•
Stomach
The+bolus+is+transferred+from+the+upper+to+lower+portion+of+the+stomach+while+receiving+juices+•
It+is+grinded+by+the+stomach+into+a+semiliquid+mass+called+"chyme"+•
Bit+by+bit+the+stomach+releases+the+chyme+to+through+the+pyloric+sphincter+(which+opens+into+the+
small+intestine)+and+then+closes+behind+the+chyme+
•
Small3intestine
The+bladder+and+pancreas+provide+fluids+to+the+small+intestine+•
The+small+intestine+is+split+into+3+segments:+the+duodenum,+the+jejunum+and+the+ileum+
•
The+small+intestine+is+almost+3+meters+of+tubing+coiled+within+the+abdomen+
•
Large3Intestine3(Colon)
The+contents+passes+through+the+ileocecal+ sphincter+located+at+the+beginning+(cecum)+of+the+
large+intestine+in+the+lower+right+side+of+the+abdomen+
•
The+contents+pass+through+another+opening,+and+if+any+intestinal+contents+slip+into+this+opening+
it+would+end+up+in+the+appendix+
•
Normally+they+bypass+this+opening+and+travel+to+the+rectum+
•
The+colon+withdraws+water+leaving+semisolid+waste+
•
The+strong+muscles+of+the+rectum+and+anal+canal+hold+back+the+waste+until+the+two+sphincters+of+
the+anus+open+to+allow+excretion+
•
Muscular+Action+of+Digestions:+
Peristalsis33
Peristalsis -wavelike+muscular+contractions+of+the+GI+tract+that+propel+its+contents+along+
The+entire+inside+wall+of+the+GI+tract+is+ringed+with+circular+muscles+that+are+surrounded+by+
longitudinal+muscles+
•
When+the+rings+tighten+and+the+long+muscles+relax+the+tube+is+constricted,+when+the+rings+relax+
and+the+long+muscles+tighten+the+tube+bulges;+and+that’s+how+the+intestinal+contents+are+
propelled+
•
The+waves+of+contraction+normally+ripple+along+the+GI+tract+at+varying+rates+and+intensities+
depending+on+the+part+of+the+GI+tract+and+on+whether+food+is+present+
•
Factors+such+as+stress,+medicines+and+medical+conditions+may+interfere+with+normal+GI+tract+
contractions+
•
Stomach3Action3
The+GI+tract+has+a+third+layer+of+diagonal+muscles+that+also+alternately+contracts+and+relaxes+•
These+3+layers+work+together+to+break+apart+the+bolus+and+force+the+chyme+downward•
The+Pyloric+sphincter+stays+closed+when+the+chyme+is+forced+down,+allowing+gastric+juices+to+
completely+liquefy+the+chyme+before+sending+it+to+the+small+intestine+
•
Segmentation3
Segmentation -a+periodic+squeezing+or+partitioning+of+the+intestine+at+intervals+along+its+length+by+its+
circular+muscles+
It+further+breaks+apart+food+particles+to+mix+the+chyme+and+promote+close+contact+with+the+
digestive+juices+and+the+absorbing+cells+of+the+intestine+walls+
•
Sphincter3Contractions3
Sphincter+muscles+periodically+open+and+close+allowing+the+contents+of+the+GI+tract+to+move+
along+at+a+controlled+pace+
•
The+upper+esophageal+sphincter+opens+in+response+to+swallowing+•
The+lower+esophageal+sphincter/cardiac+sphincter+prevents+reflux+of+stomach+contents+•
The+pyloric+sphincter,+which+stays+closed+most+of+the+time,+holds+the+chyme+in+the+stomach+long+
enough+for+it+to+be+thoroughly+mixed+with+the+gastric+juice+and+liquefied
•
The+pyloric+sphincter+also+prevents+intestinal+contents+from+backing+into+the+stomach+•
The+ileocecal+ sphincter+performs+a+similar+function+allowing+the+contents+of+the+small+intestine+to+
empty+into+the+large+intestine
•
The+tightness+of+the+rectal+muscle+together+with+the+two+sphincters+of+the+anus+act+as+a+safety+
device+to+prevent+continuous+elimination+of+waste+
•
Secretions+of+Digestion+
Saliva3
The+salivary+glands+squirt+just+enough+saliva+to+moisten+each+mouthful+of+food+so+that+it+can+pass+
easily+down+the+esophagus+
•
Saliva+contains+water,+salts,+mucus,+and+enzymes+that+initiate+the+digestion+of+carbohydrates+•
Saliva+also+protects+the+teeth+and+the+lining+of+the+mouth,+esophagus+and+stomach+from+
substances+that+might+cause+damage+
•
Gastric3Juice3
Gastric+glands+secrete+gastric+juice+which+is+a+mixture+of+water,+enzymes+and+hydrochloric+acid+•
The+cells+ of+the+stomach+wall+secrete+ mucus+to+protect+themselves+from+the+gastric+juices•
The+acidity+of+the+gastric+juice+registers+below+2+on+the+pH+scale+•
Once+in+the+stomach+salivary+enzymes+just+become+other+proteins+to+be+digested+•
Pancreatic3Juice3and3Intestinal3Enzymes3
The+pancreas+contributes+digestive+juices+by+way+of+ducts+leading+into+the+duodenum•
The+pancreatic+juice+contains+sodium+bicarbonate+(which+is+basic)+to+neutralize+the+acidic+ chyme+
arriving+in+the+small+intestine+
•
The+pH+of+the+pancreatic+juice+is+8•
From+this+point+on+the+chyme+remains+slightly+basic+•
Bile3
The+liver+ continuously+produces+bile+which+is+then+concentrated+and+stored+in+the+gallbladder+•
The+gallbladder+squirts+bile+into+the+duodenum+when+the+dietary+fat+arrives+•
Bile+is+an+emulsifier+that+brings+fats+into+suspension+in+water+so+that+enzymes+can+break+them+
down+into+their+component+parts+
•
Absorption
Anatomy+of+the+Absorptive+System+
The+small+intestine+is+wrinkled+into+hundreds+of+folds,+each+fold+is+contoured+into+thousands+of+
fingerlike+projections++known+as+villi+
•
A+single+villi+is+contains+thousands+of+its+own+microscopic+hairs+called+microvilli+•
The+crypt+glands+lie+between+the+villi+in+the+cervices+•
Crypt+glands -tubular+glands+that+lie+ between+the+intestinal+villi+and+secrete+intestinal+juices+into+the+
small+intestine
Nearby+Goblet+cells+secrete+mucus+•
The+villi+ are+in+constant+motion,+because+they+are+lined+by+a+thin+sheet+of+muscle+and+can+wave,+
squirm+and+wriggle
•
Some+partially+digested+nutrients+are+caught+in+the+microvilli,+digested+further+by+enzymes+there+
and+then+absorbed+into+the+cells+++
•
The+microvilli+ contain+hundreds+of+different+kinds+of+enzymes+and+pumps+which+recognize+and+
act+on+different+nutrients+
•
Specialization3of3the3GI3tract3
Nutrients+that+are+ready+for+absorption+early+are+absorbed+near+the+top+of+the+GI+tract+•
Nutrients+that+take+longer+to+be+digested+are+absorbed+farther+down+•
Medical+professionals+who+treat+digestive+disorders+learn+the+specialized+absorptive+functions+of+
different+parts+of+the+GI+tract+so+that+if+one+part+is+dysfunctional+the+diet+can+be+adjusted+
accordingly+
•
Food3Combining3Myth3
The+idea+that+people+should+not+eat+certain+food+combinations+at+the+same+meal+because+the+
digestive+system+cannot+handle+more+than+one+task+at+a+time+is+false+
•
The+opposite+is+true,+foods+eaten+together+can+enhance+the+each+other's+use+by+the+body+•
Ex.+Vitamin+C+in+a+pineapple+can+enhance+the+absorption+of+iron+from+a+meal+of+beans+and+rice+or+
other+iron-containing+foods+
Preparing3Nutrients3for3Transport3
When+a+nutrient+molecule+has+crossed+the+absorptive+cell+of+a+villus+it+enters+either+the+
bloodstream+or+the+lymphatic+system+
•
Both+transport+systems+supply+vessels+to+each+villus+•
The+water-soluble+nutrients+including+smaller+products+of+fat+digestion+are+released+directly+into+
the+bloodstream+and+guided+directly+to+the+liver+when+their+fate+and+destination+will+be+
determined+
•
The+larger+ fats+and+the+fat-soluble+vitamins+are+insoluble+in+water,+therefore+insoluble+in+blood+•
Intestinal+cells+assemble+many+products+of+fat+digestion+into+larger+molecules,+these+larger+
molecules+cluster+together+with+special+proteins+forming+chylomicrons
•
These+chylomicrons+are+released+into+the+lymphatic+system,+they+move+through+the+lymph+and+
then+later+enter+the+bloodstream+at+a+point+near+the+heart+bypassing+the+liver+
•
Chapter(2
Tuesday,+ September+ 19,+2017 11:38+PM
Document Summary
Gastrointestinal tract (gi tract) - a flexible muscular tube that extends from the mouth, through esophagus, stomach, small intestine, large intestine, and rectum to the anus. Only when a nutrient or other substances enter penetrate the gi tract"s wall does it enter the bo many materials pass through the gi tract without being digested or absorbed. Teeth crush larger food pieces to smaller ones via chewing. Fluids from food, beverages and salivary glands help ease swallowing. Fluid helps dissolve food so the taste buds can react with the solution. Taste buds can detect sweet, sour, bitter, salty and umami. Other factors such as the temperature, aroma, texture etc. also influence taste (our sense smell is more sensitive than our taste buds are) When a mouthful of food is swallowed it passes through the pharynx. Since the pharynx is shared with the digestive and respiratory systems the epiglottis closes the airway so that choking doesn"t occur when swallowing.
