The digestive system ii
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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

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THE DIGESTIVE SYSTEM II

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The digestive system ii

THE DIGESTIVE SYSTEM II

D. C. Mikulecky

Professor of Physiology

Virginia Commonwealth University


Pancreatic secretions

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

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

A FUNCTIONAL UNIT OF THE EXOCRINE PANCREAS

DUCT

ACINUS


Aqueous component of pancreatic secretion

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

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

HORMONES SECRETED IN DUODENUM SIGNAL THE COMPOSITION OF THE INCOMING CHYME

  • SECRETIN

  • CHOLECYSTOKININ


Secretin

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

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

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


Bile secretion storage and circulation

BILE SECRETION, STORAGE, AND CIRCULATION

  • SECRETED BY THE LIVER

  • RECYCLED THROUGH ENTEROHEPATIC CIRCULATION

  • STORED IN GALL BLADDER


Liver blood flow

LIVER BLOOD FLOW

INFERIOR

VENA CAVA

AORTA

HEART

HEPATIC

VEIN

HEPATIC

ARTERY

LIVER

HEPATIC

PORTAL

VEIN

ARTERIES TO

DIGESTIVE TRACT

STOMACH

AND

SMALL

INTESTINE


Bile salt circulation

BILE SALT CIRCULATION

LIVER

GALL BLADDER

SPHINCTER

OF ODDI

DUODENUM


S i motility

S.I. MOTILITY

  • SEGMENTATION CONTRACTIONS

  • PACEMAKER CELLS

  • MIXING AND PROPULSION


Segmentation contractions

SEGMENTATION CONTRACTIONS

  • INITIATED BY PACEMAKER CELLS

  • MIXING ACTION

  • MOVES CHYME DOWNWARD

  • ILEOCECAL VALVE


S i secretions

S.I. SECRETIONS

  • MANLY MUCOUS

  • NO DIGESTIVE ENZYMES


Digestion

DIGESTION

  • MAINLY IN THE SMALL INTESTINE

  • PANCREATIC ENZYMES

  • BRUSH BORDER ENZYMES


Mainly in the small intestine

MAINLY IN THE SMALL INTESTINE

  • SALIVARY AMYLASE

  • ACID AND PEPSIN IN THE STOMACH

  • ENZYMES COME FROM PANCREAS


Pancreatic enzymes

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

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

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

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

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

An Epithelial Membrane in Cartoon Form:


A network model of coupled salt and volume flow through an epithelium

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

CL

PL

LUMEN

AM

TJ

BL

CELL

BM

BLOOD

PB

CB


Sodium reabsorption

Sodium Reabsorption

PUMP: Na/K ATPase

Plasma

Sodium

Lumen

Cells

Potassium

Chloride

Water


Sodium reabsorption1

Sodium Reabsorption

PUMP: Na/K ATPase

Plasma

Sodium

Lumen

Cells

Potassium

Chloride

Water


Potassium secretion

Potassium Secretion

PUMP: Na/K ATPase

Plasma

Sodium

Lumen

Cells

Potassium

Chloride

Water


The curran macintosh model

THE CURRAN-MACINTOSH MODEL

HYPERTONIC FLUID

INJECTED

FLUID MOVES

R ---> L

B

A

C

MEMBRANES: TIGHT LOOSE


Sources of water and electrolytes in gut ml day excluding intestinal secretions

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

  • IMBIBED:2,000

  • SECRETIONS:

  • SALIVA1,500

  • GASTRIC JUICE2,000

  • PANCREATIC JUICE1,500

  • BILE 500

  • INTESTINAL1,500

  • -----------------------------------------------------------TOTAL: SECRETED + IMBIBED9,000


Sites of absorption

SITES OF ABSORPTION

SMALL INTESTINE8,500

COLON 400

--------------------------------------------------------------TOTAL ABSORBED8,900

(IN FECES 100)


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