Digestive SystemDigestive System

Pancreas – Large Intestine

Pancreas (accessory)Pancreas (accessory)

LocationPancreatic ductIslets

PancreasPancreas

Pancreatic JuiceAcinar Cells – exocrineBicarbonatePancreatic Amylase

PancreasPancreas

Protein Enzymes – Trypsin– Chymotrypsin– Carboxypolypeptidase

Lipase

Controls of Juice ReleaseControls of Juice Release

SecretinCholecystokininNeurally – Vagus nerve stimulates release

Liver (accessory)Liver (accessory)

Hepato-4 lobes; Falciform ligament separates large

R & L lobesCells are hepatocytesCommon Bile Duct (Hepatic duct + Gall

bladder duct), which empties into duodenum

LiverLiver

Blood supply – enormousBile Production

– 600-1000 mls per day– Liver cells make bile, gall bladder STORES

bile

Bile CompositionBile Composition

WaterBilirubin (from Hb breakdown)Bile Salts function in Emulsification

Enterohepatic CirculationEnterohepatic Circulation

Bile salts secreted into duodenum, are reabsorbed in ileum and returned to liver

Bile Secretion ControlsBile Secretion Controls

Enterohepatic CirculationVagus NerveSecretinIncreased hepatic blood flowCholecystokinin

More liver functionsMore liver functions

Metabolic regulation (blood filtering, monitoring blood)

Clotting factors are made by liverBlood protein synthesisPhagocytosis of old WBC & RBCsDetoxification, storage of toxinsStores glucose (glycogen), fat, protein, Cu,

Fe, Vitamins

SUMMARY of GI SUMMARY of GI HORMONESHORMONES

GASTRIN– Made by pylorus cells– Increases gastric motility– Increases gastric secretions

SUMMARY of GI SUMMARY of GI HORMONESHORMONES

SECRETIN– Made by duodenal cells– Decreases gastric motility & secretions– Increases pancreatic juice release– Increases bile secretion

SUMMARY of GI SUMMARY of GI HORMONESHORMONES

CHOLECYSTOKININ– Made by duodenal cells– Decreases gastric motility & secretions– Increases pancreatic juice release– Increases gall bladder contraction

SUMMARY of GI SUMMARY of GI HORMONESHORMONES

GIP (Gastric Inhibitory Peptide)– Made by duodenal cells– Decreases gastric motility & secretions– Promotes insulin release

Small IntestineSmall Intestine

21 foot tubeDuodenum – 1 footJejunum – 8 ft.Ileum – 12 ft.

Small Intestine MicrostructureSmall Intestine Microstructure

VilliMicrovilliBlood vesselsLacteals

Small Intestinal SecretionsSmall Intestinal Secretions

2-3 liters of “juice” per dayDuodenal glands (Brunner’s) make

protective mucusIntestinal glands make isotonic fluid

containing some digestive enzymes

Small Intestine MotilitySmall Intestine Motility

SegmentationPeristalsis

AbsorptionAbsorption

Definition – 90% of all absorption occurs in SI

Nutrients from SI to blood or lymph vesselVilli & MicrovilliProcesses include active transport,

diffusion, facilitated diffusion, cotransport

AbsorptionAbsorption

CarbohydratesProteinsLipids

– Emulsification– Lipase– Micelles (fat + bile salt)– Chylomicrons– Lacteals

AbsorptionAbsorption

Vitamins (ADEK along with fat, B’s and C along with water)

AbsorptionAbsorption

Water & Electrolytes (ions in soln.)9 liters/day by osmosisSodiumCalcium absorption is Vit. D dependent

Large IntestineLarge Intestine

Five feet longCecum

– Ileocecal sphincter = valve– Appendix

Large IntestineLarge Intestine

Colon– Ascending– Transverse– Descending– Sigmoid

RectumAnus

Large IntestineLarge Intestine

No villiGoblet cells make mucusTaeniae coli – flat muscular bandsHaustra – pouches as taeniae coli contract

Large Intestine MotilityLarge Intestine Motility

PeristalsisHaustral churningMass peristalsis drives contents into rectumGastroileal reflex activates mass peristalsisDefecation reflexAnal sphincters – Internal and External

Large Intestine FunctionsLarge Intestine Functions

Some water absorptionLubrication of contents Form and store fecesSynthesis of Vitamin K and some B

vitamins and absorptionBacterial fermentation