geh bio ii

8/13/2019 GEH bio II

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D E P . O F B I O C H E M I S T R Y

F A C U L T Y O F M E D I C I N E H A S A N U D D I N U N I V E R S I T Y

R O S D I A N A N A T Z I R

BIOMEDIC II

SYSTEMGASTROENTEROHEPATHOLOGY


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BIOCHEMICAL IMPORTANCE

UndernutritionUlcer ----> gastric acidsGallstones----> cholesterol

Lactose intolerance ------> lactase enzymeEtc.


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DIET

FATPROTEINCARBOHYDRATENUCLEIC ACIDS

VITAMINMINERALS

WATER.


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DIGESTION

BSORPTION


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Digestion, Absorption, Transport

DigestionBreakdown of food molecules for absorption intocirculation

Mechanical: breaks large food particles to smallChemical: breaking of covalent bonds by digestiveenzymes

Absorption and transportMolecules are moved out of digestive tract andinto circulation for distribution throughout body


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Carbohydrate - polysaccharide

Polysaccharide -----> oligosaccharide ------->Disaccharide------> monosaccharide.

Monosaccharide :

GlucoseGalactoseMaltose

IsomaltoseTrehalose.


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LACTOSE INTOLERANCE


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LIPIDS :

FatsOilsPhospholipids

Sterols


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FUNCTIONS OF LIPIDS :

Major components of cell membranes.Required to solubilise fat soluble vitaminsBiosynthetic precursors (e.g. steroidhormones from cholesterol)

Protection (e.g. kidneys are shielded with fat in fed state)Insulation


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LIPIDS :

1) Stomach - lingual lipase and gastric lipase attacktriacylglycerols and hydrolyse a limited number ofFA.

2) Small Intestine - acid chyme (stomach contents)stimulates mucosa cells to release choleocystokinin which stimulates gall bladder and pancreas to release

bile.


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. (bile acids help emulsify fatdroplets thus increasing their surfacearea) and digestive enzymes

respectively.

Other mucosa cells release

secretin which causes pancreas torelease bicarbonate rich fluid toneutralise chyme.


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ACTION OF BILE SALTS


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Transport of lipid


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P i S i


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Aqueous. ;Produced by columnar epitheliumlining smaller ducts.;Na +, K+, HCO3-, water. ;Bicarbonate ;lowers pH inhibiting pepsin and

providing proper pH for enzymes.

Pancreatic Secretions:Pancreatic Juice


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Enzymatic portion:

TrypsinogenChymotrypsinogen

ProcarboxypeptidasePancreatic amylasePancreatic lipasesDeoxyribonucleasesribonucleases


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Interaction of duodenal and pancreatic enzymes.

Enterokinase from the duodenalmucosa and attached to the brush border activates trypsinogen to trypsin .

Trypsin activates chymotrypsinogen tochymotrypsin.

Trypsin activates procarboxypeptidase to carboxypeptidase.


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Trypsin, chymotrypsin and carboxypeptidasedigest proteins: proteolytic.

Pancreatic amylase continues digestion ofstarch.Pancreatic lipase digests lipids

Deoxyribonucleases and ribonucleases digestDNA and ribonucleic acid, respectively


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All lipids carried in the blood are done so incombination with protein to make them soluble inplasma. :

Cholesterol: 15% ingested; 85% manufactured inliver and intestinal mucosaLipids are lower density than water; proteins arehigher density than waterChylomicrons: 99% lipid and 1% protein (extremely

low density); enter lymph


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Cont..

VLDL: 92% lipid, 8% proteinForm in which lipids leave the liverTriglycerides removed from VLDL and stored in adiposecells.

LDL: 75% lipid, 25% protein

Transports cholesterol to cellsCells have LDL receptors.HDL: 55% lipid, 45% protein

Transports excess cholesterol from cells to liver.

Amino Acid Transport


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Amino Acid Transport


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Chemical Digestion: Nucleic Acids

Absorption: active transport via membranecarriers

Absorbed in villi and transported to liver viahepatic portal veinEnzymes used: pancreatic ribonucleases anddeoxyribonuclease in the small intestines

El l Ab i


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Electrolyte AbsorptionMost ions are actively absorbed along the

length of small intestineNa + is coupled with absorption of glucose andamino acidsIonic iron is transported into mucosal cells whereit binds to ferritin

Anions passively follow the electricalpotential established by Na +

K + diffuses across the intestinal mucosa inresponse to osmotic gradientsCa 2+ absorption:

Is related to blood levels of ionic calciumIs regulated by vitamin D and parathyroidhormone (PTH)


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Water and

Ions


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