THE DIGESTIVE SYSTEM II

D. C. MikuleckyProfessor of PhysiologyVirginia Commonwealth University

PANCREATIC SECRETIONS

THE PANCREAS IS BOTH ENDOCRINE AND EXOCRINE

THE EXOCRINE PANCREAS SECRETES DIGESTIVE ENZYMES AND AN AQUEOUS ALKALINE FLUID

PANCREATIC SECRETION IS HORMONALLY REGULATED

PANCREATIC SECRETIONS REACH THE SMALL INTESTINE VIA THE COMMON BILE DUCT

THE ENDOCRINE PANCREAS

INSULIN AND GLUCAGON

IMPORTANT IN THE CONTROL OF GLUCOSE, FAT AND PROTEIN METABOLISM

ACT IN OPPOSITE WAYS

A FUNCTIONAL UNIT OF THE EXOCRINE PANCREAS

ACINUSDUCT

AQUEOUS COMPONENT OF PANCREATIC SECRETION

COMPOSITION CHANGES WITH SECRETION RATE (TRANSIT TIME)

DUCTILE CELLS SECRETE BICARBONATE AND WATER

CHLORIDE AND BICARBONATE VARY RECIPROCALLY

SODIUM AND POTASSIUM ARE LIKE IN PLASMA

HORMONAL CONTROL OF PANCREATIC SECRETION

ACID IN DUODENAL LUMEN >SECRETIN: STIMULATES PANCREATIC DUCT CELLS TO PRODUCE SIGNIFICANT QUANTITES OF AQUEOUS ALKALINE SECRETION

FAT AND PROTEIN IN DUODENAL LUMEN>CHOLECYSTOKININ (CCK):STIMULATES PANCREATIC ACINAR CELLS TO SECRETE DIGESTIVE ENZYMES

HORMONES SECRETED IN DUODENUM SIGNAL THE COMPOSITION OF THE INCOMING CHYME

SECRETINCHOLECYSTOKININ

SECRETIN

ENDOCRINE CELLS IN DUODENAL MUCOSA ACID IN DUODENAL LUMEN INHIBITS GASTRIC EMPTYING INHIBITS GASTRIC SECRETION STIMULATES AQUEOUS BICARBONATE

SECRETION BY PANCREAS STIMULATES BICARBONATE RICH BILE

SECRETION BYLIVER

CHOLECYSTOKININ

ENDOCRINE CELLS IN DUODENAL MUCOSA FAT AND PROTEIN IN DUODENAL LUMEN INHIBITS GASTRIC EMPTYING INHIBITS GASTRIC SECRETION CAUSES GALL BLADDER CONTRACTION CAUSES RELAXATION OF THE SPHINCTER OF

ODDI CONTRIBUTES TO SATIETY

FUNCTIONS OF THE LIVER

METABILIC PROCESSING OF ABSORBED FOOD

DETOXIFICATION2SYNTHESIS OF PLASMA PROTEINSSTORAGE OF GLYCOGEN AND FAT, ETC.REMOVAL OF BACTERIA AND WORN-OUT

RBCEXCRETION OF CHOLESTEROL AND

BILIRUBIN

BILE SECRETION, STORAGE, AND CIRCULATION

SECRETED BY THE LIVERRECYCLED THROUGH

ENTEROHEPATIC CIRCULATIONSTORED IN GALL BLADDER

LIVER BLOOD FLOW

HEART

LIVER

STOMACHANDSMALLINTESTINE

HEPATICPORTALVEIN

HEPATICVEIN

INFERIORVENA CAVA AORTA

HEPATICARTERY

ARTERIES TODIGESTIVE TRACT

BILE SALT CIRCULATION

LIVER

GALL BLADDER

DUODENUM

SPHINCTEROF ODDI

S.I. MOTILITY

SEGMENTATION CONTRACTIONS

PACEMAKER CELLS

MIXING AND PROPULSION

SEGMENTATION CONTRACTIONS

INITIATED BY PACEMAKER CELLSMIXING ACTIONMOVES CHYME DOWNWARDILEOCECAL VALVE

S.I. SECRETIONS

MANLY MUCOUS

NO DIGESTIVE ENZYMES

DIGESTION

MAINLY IN THE SMALL INTESTINE

PANCREATIC ENZYMES

BRUSH BORDER ENZYMES

MAINLY IN THE SMALL INTESTINE

SALIVARY AMYLASE

ACID AND PEPSIN IN THE STOMACH

ENZYMES COME FROM PANCREAS

PANCREATIC ENZYMES

PROTEOLYTIC: BREAK PROTEINS DOWN TO SMALLER PEPTIDE FRAGMENTS AND/OR AMINO ACIDS

PANCREATIC AMYLASE BREAKS STARCH DOWN TO OLIGOSACHHARIDES AND DISACCHARIDES

PANCREATIC LIPASE, PHOSPHOLIPASE AND OTHERS

OTHERS

ENZYME PRECURSORS ARE A WAY OF PROTECTING THE GUT FROM SELF-DIGESTION

PEPSIN IN THE SOMACH AND PROTEOLYTIC ENZYMES IN THEM PANCREAS

SECRETED IN AN INACTIVE FORM, LONGER MOLECULE

REMOVAL OF A SEGMENT ACTIVATES THEM

BRUSH BORDER ENZYMES

CARBOHYDRATES: DISACCARIDASES IN BRUSH BORDER MEMBRANE FINISH THE JOB

PROTEINS: ALSO POLY AND DI-PEPTIDASES

TRANSPORT SYSTEMS ARE NEAR-LESSENS THE OSMOTIC EFFECT?

ABSORPTION: THE SMALL INTESTINE IS THE ABSORBING ORGAN

LARGE SURFACE AREAACTIVE SODIUM TRANSPORTFLUID AND ELECTROLYTESSUGARS AND AA BY SECONDARY

ACTIVE TRANSPORTFATVITAMINS AND MINERALS

FLUID AND ELECTROLYTE ABSORPTION IS BY A SPECIAL PROCESS: ISOTONIC TRANSPORT

THE WHOLE TISSUE (SODIUM TRANSPORTING EPITHELIUM) IS INVOLVED

SODIUM/POTASSIUM ATPASE PUMPS ONLY ON BASOLATERAL CELL MEMBRANES

TIGHT JUNCTIONS VS LOOSE SEROSAL SIDE (6-PACK ANALOGY)

An Epithelial Membrane in Cartoon Form:

A Network Model of Coupled Salt and Volume Flow Through an Epithelium

AM TJ

BM

BL

CL PL

CB PB

CELL

LUMEN

BLOOD

Sodium Reabsorption

Lumen

Plasma

Cells

PUMP: Na/K ATPase

Sodium

Potassium

Chloride

Water

Sodium Reabsorption

Lumen

Plasma

Cells

PUMP: Na/K ATPase

Sodium

Potassium

Chloride

Water

Potassium Secretion

Lumen

Plasma

Cells

PUMP: Na/K ATPase

Sodium

Potassium

Chloride

Water

THE CURRAN-MACINTOSH MODEL

A B C

FLUID MOVESR ---> L

HYPERTONIC FLUID

INJECTED

MEMBRANES: TIGHT LOOSE

SOURCES OF WATER AND ELECTROLYTES IN GUT(ML/DAY), EXCLUDING INTESTINAL

SECRETIONS

IMBIBED: 2,000 SECRETIONS:

SALIVA 1,500GASTRIC JUICE 2,000PANCREATIC JUICE 1,500BILE 500INTESTINAL 1,500

-----------------------------------------------------------TOTAL: SECRETED + IMBIBED 9,000

SITES OF ABSORPTION

SMALL INTESTINE 8,500COLON 400--------------------------------------------------------------TOTAL ABSORBED8,900

(IN FECES 100)