MELLSS yr1 biochemistry lipid

LIPID082012100063082012100067082012100071082012100075

INTRODUCTION

• Molecules that contain hydrocarbon • Make up the building blocks of the structure

and function of living cell• Hydrophobic

CHEMISTRY

• Triacyl Glycerol• Cholesterol• Phospholipid

DIGESTION

• StomachLingual lipase(2.5-5)

Active in stomach, from mouthActs on short chain triglycerides(SCT) eg milk,ghee and

butterMore significant in newborn infants

Gastric lipase(5.4)Acid stableSecreted by chief cellStimulated by gastrin

30% digestion

• IntestinesBile(7.7) neutralize acid chymeEmulsification by bile salt

Lipids disperse into smaller dropletsReduce surface tensionSurface area increasedFavoured by bile salt, peristalsis and phospholipid

Pancreatic lipaseHydrolyse fatty acid (1st and 3rd )Isomerase shift ester bond (2nd to 1st), then hydrolyse2-Monoacycl glycerol(78%), 1-Monoacyl glycerol

(6%),glycerol and fatty acids(14%)Partial ( incomplete)

Cholesterol EsteraseCholesterol ester hydrolysed to free cholesterol and

fatty acidsPhospholipase A2

Produces lysophospholipid and a fatty acidC0- lipase

Secreted by pancreas as inactive zymogenActivated by trypsinNeeded for lipase reaction

ABSORPTION

• Short Chain Fatty Acid and Medium Chain Fatty AcidNot need re-esterificationDirectly enter blood vessel, through portal vein

to liverRapid absorption

• Long Chain Fatty Acid

Absorb by mixed micelle formation from intestinal lumen to the mucosal cell of intestine.

What is micelle?Physical aggregates of bile salt and phospholipid that carry digested lipids and fat soluble vitamins to mucosal cell of intestine.

Where it is located?microvillous surface of jejunal mucosa

LCFA re-esterified to form triglyceride inside interstinal mucosal cell

Free glycerol absorbed from the intestinal lumen directly enters into bloodstream.

The bile salts are reabsorb from the large intestine and returned to liver via enterohepatic circulation.

The chylomicrons are used for transport of lipid from the intestinal mucosal cells trough lacteal into thoracic duct and empties lymph circulation. cylomicrons

Lipid partTAG

phospholipid

Cholesterol ester

Protein partApo-B-48Apo-A (intestinal cell)

Apo-EApo-CII (from HDL)

DISORDER

AbnormalitiesDefective digestion

(unsplit fat) chronic

pancreatic disease

steatorrhea

Defective absorption (split fat)

Celiac disease,

sprueCrohn’s

disease

Surgical removal of intestine

Obstruction of bile

duct

Chyluria

chlylothorax

CONCLUSIONLipid digestion involve 3 enzyme at 3 different location: Ligual lipase-stomach Gastric lipase-stomach Pancreatic lipase-small intestine

Lipid absorption: Minor digestion Major digestion Bile acid facilitated formation of micelle Passive absorption Reesterification Chylomicron formation

REFERENCE

Vasudevan,textbook of Biochemistry for medical student,DM Vasudevan,sixth edition.