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THE DIGESTIVE SYSTEM II
D. C. Mikulecky
Professor of Physiology
Virginia 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
DUCT
ACINUS
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
SECRETIN
CHOLECYSTOKININ
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
DETOXIFICATION2
SYNTHESIS OF PLASMA PROTEINS
STORAGE OF GLYCOGEN AND FAT, ETC.
REMOVAL OF BACTERIA AND WORN-OUT RBC
EXCRETION OF CHOLESTEROL AND BILIRUBIN
STORAGE, AND
CIRCULATION
SECRETED BY THE LIVER
RECYCLED THROUGH ENTEROHEPATIC
CIRCULATION
STORED IN GALL BLADDER
LIVER BLOOD FLOW
INFERIOR
VENA CAVA
AORTA
HEART
HEPATIC
VEIN
LIVER
HEPATIC
PORTAL
VEIN
HEPATIC
ARTERY
ARTERIES TO
DIGESTIVE TRACT
STOMACH
AND
SMALL
INTESTINE
BILE SALT CIRCULATION
LIVER
GALL BLADDER
SPHINCTER
OF ODDI
DUODENUM
S.I. MOTILITY
SEGMENTATION CONTRACTIONS
PACEMAKER CELLS
MIXING AND PROPULSION
SEGMENTATION
CONTRACTIONS
INITIATED BY PACEMAKER CELLS
MIXING ACTION
MOVES CHYME DOWNWARD
ILEOCECAL 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 SELFDIGESTION
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 DIPEPTIDASES
TRANSPORT SYSTEMS ARE NEARLESSENS THE OSMOTIC EFFECT?
ABSORPTION: THE SMALL INTESTINE
IS THE ABSORBING ORGAN
LARGE SURFACE AREA
ACTIVE SODIUM TRANSPORT
FLUID AND ELECTROLYTES
SUGARS AND AA BY SECONDARY
ACTIVE TRANSPORT
FAT
VITAMINS 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
LUMEN
AM
CL
PL
TJ
BL
CELL
BM
BLOOD
CB
PB
Sodium Reabsorption
PUMP: Na/K ATPase
Sodium
Lumen
Cells
Potassium
Plasma
Chloride
Water
Sodium Reabsorption
PUMP: Na/K ATPase
Sodium
Lumen
Cells
Potassium
Plasma
Chloride
Water
Potassium Secretion
PUMP: Na/K ATPase
Sodium
Lumen
Cells
Potassium
Plasma
Chloride
Water
THE CURRAN-MACINTOSH
MODEL
HYPERTONIC FLUID
INJECTED
FLUID MOVES
R ---> L
A
B
MEMBRANES: TIGHT
C
LOOSE
SOURCES OF WATER AND ELECTROLYTES IN
GUT(ML/DAY), EXCLUDING INTESTINAL
SECRETIONS
IMBIBED:
2,000
SECRETIONS:
SALIVA
1,500
GASTRIC JUICE
2,000
PANCREATIC JUICE
1,500
BILE
500
INTESTINAL
1,500
----------------------------------------------------------TOTAL: SECRETED + IMBIBED
9,000
SITES OF ABSORPTION
SMALL INTESTINE
8,500
COLON
400
-------------------------------------------------------------TOTAL ABSORBED
8,900
(IN FECES
100)