Chapter 18Chapter 18

The Digestive The Digestive

SystemSystem

General info:General info: Basic “tube-within-a-tube”Basic “tube-within-a-tube” Digestion by mechanical & Digestion by mechanical &

chemical meanschemical means Mechanical DigestionMechanical Digestion from from

cutting, grinding, chewing in cutting, grinding, chewing in mouth. From churning by mouth. From churning by peristalsis in stomachperistalsis in stomach

Chemical DigestionChemical Digestion beginning in mouth through beginning in mouth through stomach & small intestines. stomach & small intestines.

Acidic pHAcidic pH in mouth & in mouth & stomachstomach

Switches to Switches to basic pHbasic pH in in small intestinesmall intestine

Accessory OrgansAccessory Organs – food – food doesn’t pass thru them. doesn’t pass thru them. They supply digestive They supply digestive “juices”.“juices”.

Salivary glands, Liver, gall Salivary glands, Liver, gall bladder & pancreasbladder & pancreas

The Digestive SystemThe Digestive SystemMouthpharynxesophagusstomachduodenumjejunumileumcecum ascending colontransverse colondescending colonsigmoid colonrectumanus

Upper Digestive TractUpper Digestive Tract Mouth & PharynxMouth & Pharynx

Teeth Teeth IncisorsIncisors- slice- slice CaninesCanines – tear – tear PremolarsPremolars – grind – grind Molars Molars - grind- grind

Tooth StructureTooth Structure Crown, neck & rootCrown, neck & root EnamelEnamel – hard for protection – hard for protection Dentine Dentine – softer, alive bone-– softer, alive bone-

likelike Pulp Pulp – soft blood & nerve – soft blood & nerve

tissuetissue Cementum & PeriodontalCementum & Periodontal

membrane “glue” tooth to membrane “glue” tooth to the bony socket the bony socket

Chewed Food (smaller Chewed Food (smaller pieces w/ higher surface pieces w/ higher surface area) mixes w/ saliva area) mixes w/ saliva becomes becomes bolusbolus. Enzyme . Enzyme AmylaseAmylase begins begins Carbohydrate chemical Carbohydrate chemical digestion.digestion.

Swallowed food passes thru Swallowed food passes thru pharynx, past pharynx, past epiglottisepiglottis & & into esophagusinto esophagus

The EsophagusThe Esophagus Involuntary contractions Involuntary contractions

and relaxation of smooth and relaxation of smooth muscle surrounding muscle surrounding esophagus moves food esophagus moves food down esophagus: down esophagus: PeristalsisPeristalsis

Cardiac SphincterCardiac Sphincter: Ring : Ring shaped muscle shaped muscle separating the esophagus separating the esophagus from the stomachfrom the stomach

sphincters sphincters are muscles that squeeze the digestive tube closed and help move material in only one direction.

The StomachThe Stomach Mechnical & Chemical Mechnical & Chemical

digestion digestion Stomach secretes Stomach secretes HCl HCl – very – very

acidicacidic Mucus secretions protect Mucus secretions protect

lining from self-digestionlining from self-digestion Stomach lining w/ folds to Stomach lining w/ folds to

increase surface areaincrease surface area Bolus is mixed w/ acids for Bolus is mixed w/ acids for

several hours – now called several hours – now called chyme.chyme.

Carbohydrate and protein Carbohydrate and protein digestion takes place. digestion takes place.

Enzyme Enzyme PepsinPepsin used in used in protein digestionprotein digestion

Leaves thru Leaves thru Pyloric SphyncterPyloric Sphyncter to the duodenum.to the duodenum.

Cardiac Sphincter

Small IntestineSmall Intestine About 20 ft long, 1”-2” in diameterAbout 20 ft long, 1”-2” in diameter Most chemical digestion takes Most chemical digestion takes

place hereplace here 3 regions – duodenum, jejunum 3 regions – duodenum, jejunum

and ileumand ileum Chemical pH 8 – protein, fats & Chemical pH 8 – protein, fats &

carbohydrates are digestedcarbohydrates are digested Increased surface area by millions Increased surface area by millions

of villi and microvilliof villi and microvilli Absorption into blood stream by Absorption into blood stream by

highly vascular integration highly vascular integration surrounding digestive tract.surrounding digestive tract.

Large Intestine (aka Colon)Large Intestine (aka Colon) 5-6 feet in length, 3”-4” in 5-6 feet in length, 3”-4” in

diameterdiameter Main FunctionsMain Functions

Reabsorption of waterReabsorption of water Reabsorption of vitaminsReabsorption of vitamins Waste elininationWaste elinination Very little digestion (most is Very little digestion (most is

done in the stomach & done in the stomach & small intestine)small intestine)

Divided into Divided into Cecum,Cecum, Ascending, Transverse, Ascending, Transverse, Descending, and Sigmoid Descending, and Sigmoid ColonColon

Undigested food & Wastes Undigested food & Wastes stored in the stored in the rectumrectum before before being eliminated thru the being eliminated thru the anusanus..

Accessory Digestive OrgansAccessory Digestive Organs Salivary GlandsSalivary Glands – –

secretes saliva and secretes saliva and enzyme enzyme amylaseamylase. Mixes . Mixes w/ food forms w/ food forms BolusBolus. .

Liver-Liver- filters blood & filters blood & secretes secretes BileBile used to used to emulsify & digest Fatsemulsify & digest Fats

Gall BladderGall Bladder – stores – stores bile until neededbile until needed

PancreasPancreas- 3 functions- 3 functions Release & control of Release & control of

insulin in the insulin in the Islets of Islets of LangerhansLangerhans. Controls . Controls sugar blood levelssugar blood levels

Release Release digestive digestive enzymesenzymes

Produce Produce sodium sodium bicarbonatebicarbonate to convert to convert stomach acid to a basic stomach acid to a basic solution in the solution in the duodenumduodenum

Chapter 17Chapter 17

Muscle Muscle

& Digestive & Digestive SystemsSystems

That’s all folks!!That’s all folks!!