LIPID DIGESTION

Group 2 DAADe Vera, Antonio Jr.Paule, Michelle NoreenRañola, Anna Patricia JoVillafranca, Anna Kareninna

Lipid digestion

Lipid digestion is the breakdown of dietary

fats into smaller molecules of nutrients

for the absorption of the body

BILEProduced by the liverStored and release by the gallbladder

Laboratory Experiment

Materials

Litmus paper

To determine whether any acids are formed on hydrolysis

Pancreatin

A mixture of digestive enzymes. It contains protease, lipase, and amylase.

Disodium carbonate

Provides an alkaline medium for the pancreatin

PROCEDURE1. Add 4ml thin Dari cream to each of 3 labeled test

tubes.2. To the first tube, add 0.5 of pancreatin and 2ml of

Na2CO3 solution.3. To the second tube add 0.5g of pancreatin.4. On the third tube add 2cc of the Na2CO3

solution.5. Keep the contents of the test tubes warm of the

body temperature for about 1 hour, shaking them at intervals.

6. Place a piece of litmus paper in each tube to determine whether any acids are formed on hydrolysis. Observe and record the results.

IDEAL RESULTSTEST TUBE CONTAINS: Litmus

Paper Color Result

pH

1 4ml thin Dari cream0.5g of pancreatin2ml Na2CO3 sol’n

Red Litmus – REDBlue Litmus – RED

Acidic

2 4ml thin Dari cream0.5g of pancreatin

Red Litmus – BLUEBlue Litmus – BLUE

Basic

3 4ml thin Dari cream2cc Na2CO3 sol’n

Red Litmus – BLUEBlue Litmus – BLUE

Basic

V. TESTS FOR LIPID DIGESTION

TEST DESCRIPTION

POSITIVE RESULT

NEGATIVE RESULT

GREASE SPOT TEST

Some oil and some water are smeared onto a piece of paper. Some time later, the water smear would become not translucent. But the smear of oil would keep translucent for a long time.

formation of translucent spot on the paper.

No Color Change

SUDAN IV TEST Sudan red is a fat-soluble dye that stains lipids red. Using Sudan red can show the amount and the location of lipids.

Red No Color Change

VI. POST LABORATORY ANSWERS

POST LAB (cont.)

1.) What are the enzymes used in Lipid Digestion?

Lipasesa. Pancreatic Lipaseb. Lipoprotein Lipasec. Hepatic-triglyceride lipase

(LIPC)

POST LAB (cont.)

2.) What are the similarities and differences of these enzymes?

Name Gene Location Description

pancreatic lipase PNLIP digestive juice

In order to exhibit optimal enzyme activity in the gut lumen, HPL requires another protein, colipase, which is also secreted by the pancreas.

lingual lipase ? digestive juice -

hepatic lipase LIPC endothelium

Hepatic lipase acts on remaining lipids carried on lipoproteins in the blood to regenerate LDL (low density lipoprotein).

lipoprotein lipase LPL or "LIPD" endothelium

Lipoprotein lipase functions in the blood to act on triacylglyceridescarried on VLDL (very low density lipoprotein) so that cells can take up the freed fatty acids.

gastric lipase LIPF digestive juice

Functions in the infant at a near-neutral pH to aid in the digestion of lipids

POST LAB (cont.)3.) What are the factors that would bring

about Lipid Digestion?

• Bile plays a key role in the digestion of lipids (fats). It takes part in the emulsification of fats, making it possible for them to be digested. Bile helps to emulsify fats (increases its solubility in water), and aid in their absorption in the small intestine.

• Lipase converts triglycerides into monoglycerides (individual fatty acids) and gycerol.

POST LAB (cont.)4.) Trace the pathway of Lipid Digestion.

Fat Digestion Overview• Mouth and salivary glands

Melting Fat; Lingual lipase

 • Stomach

Lingual Lipase active in low pHHydrolysis low; Milk fat betterGastric Lipase – low activity

 • Small Intestine

Emulsification – bilePancreatic and Intestinal LipasesFatty acidsMono and Diglycerides

 • Large Intestine

Reabsorption of bile and some fatty acidsLosses in feces

POST LAB (cont.)

5.) What tests are used to detect the completeness of Lipid Digestion?

•Grease spot test/Brown paper testAs we all know from experience, lipids leave translucent spots (grease spots) on unglazed brown paper bags.

•Sudan Red testSudan red is a fat-soluble dye that stains lipids red. Using Sudan red can show the amount and the location of lipids.

POST LAB (cont.)

6.) What are the factors affecting Lipid Digestion?

Enzyme Activity Digestive Hormone pH Weak acidic – Mouth, Pharynx,

esophagus Alkaline – Small intestine

LIPID DIGESTION and TRANSPORT

In order for the triglyceride to be absorbed, two processes must

occur:

1.EMULSIFICATIONLarge aggregates of dietary

triglyceride, which are virtually insoluble, must be broken down physically and

held in suspension.

2. ENZYMATIC DIGESTION Triglyceride molecules must be enzymatically

digested to yield:

a.Monoglycerideb. fatty acids-both of which can efficiently

diffuse or be transported into the enterocyte

I. Emulsification

• Bile acids- play their first critical role in lipid

assimilation by promoting emulsification- both hydrophilic and

hydrophobic domains• On exposure to a large aggregate of

triglycerideHYDROPHOBIC PORTION

HYDROPHILIC PORTION

Intercalate into the lipid

Remains at the surface

II.Hydrolysis

•Pancreatic lipase▫predominantly hydrolyzes triglyceride into

monoglyceride and free fatty acids▫A protein colipase is required to aid

binding of the pancreatic lipase at the lipid-water interface

Cont…• The activity of this enzyme is to clip the fatty acids at positions 1 and 3 of the triglyceride, leaving two free fatty acids and a 2-monoglyceride.

III. Micelle Formation–As monoglycerides and fatty acids are liberated

through the action of lipase, they retain their association with bile acids and complex with other lipids to form structures called micelles

• Micelles are essentially small aggregates of mixed lipids and bile acids suspended within the ingesta.

• As the ingesta is mixed, micelles bump into the brush border of small intestinal enterocytes, and the lipids, including monoglyceride and fatty acids, are taken up into the epithelial cells.

Cont…

•Monoacylglycerols, fatty acids, and cholesterol are absorbed by intestinal epithelial cells.▫Within intestinal epithelial cells,

triacylglycerols are resynthesized from fatty acids and monoacylglycerols.

Absorption and Transport into Blood

• The major products of lipid digestion:– fatty acids and 2-monoglycerides• enter the enterocyte by simple diffusion

across the plasma membrane.• Once inside the enterocyte, fatty acids and monoglyceride are transported into the endoplasmic reticulum

–where they are used to synthesize triglyceride

Cont…

•Beginning in the endoplasmic reticulum and continuing in the Golgi, triglyceride is packaged with cholesterol, lipoproteins and other lipids into particles called chylomicrons.

Pathways of Lipid Transport

The Pathways of Lipid Transport•Three main pathways responsible for the

generation and transport of lipids within the body:▫Exogenous (Dietary) Lipid Pathway▫Endogenous Pathway▫Reverse Cholesterol Transport

Exogenous (Dietary) Lipid Pathway• Following digestion and absorption of

dietary fat, Triglycerides(TG) and cholesterol are packaged to form chylomicrons in the epithelial cells of the intestines.

- Chylomicrons circulate through the intestinal lymphatic system.

- In the blood, circulating chylomicrons interact at the capillaries of adipose tissue and muscle cells releasing TG to the adipose tissue to be stored and available for the body's energy needs.

Cont…

•Enzyme: Lipoprotein lipase (LPL)•Cofactor: Apo-CII •Action: hydrolyzes the TG in lipoproteins

- such as those found in chylomicrons and Very Low-Density Lipoproteins (VLDL)

Products:2 free fatty acids and 1 monoacylglycerol

Endogenous Pathway

•involves the liver synthesizing lipoproteins.

•TG and cholesterol ester are generated by the liver and packaged into Very low-density lipoprotein (VLDL) particles and then released into the circulation.

•VLDL is then processed by LPL in tissues to release fatty acids and glycerol.

Cont…

•The fatty acids are taken up by: muscle cells - for energy adipose cells - for storage.

Very-Low Density lipoprotein

•Once processed by LPL, the VLDL becomes a VLDL remnant.

•The majority of the VLDL remnants are taken up by the liver via the Low-Density lipoprotein receptor

• the remaining remnant particles become Intermediate-Density lipoprotein(IDL), a smaller, denser lipoprotein than VLDL.

Intermediate-Density Lipoprotein•The fate of some of the IDL particles

requires them to be reabsorbed by the liver ▫Again, by the Low-density lipoprotein receptor

▫however, other IDL particles are hydrolyzed in the liver by hepatic-triglyceride lipase to form Low-Density Lipoprotein (LDL), a smaller, denser particle than IDL.

Low-Density Lipoprotein

•the main carrier of circulating cholesterol within the body

•is used by extra-hepatic cells for cell membrane and steroid hormone synthesis

•Much of the LDL particles are taken up by LDL receptors in the liver;

•the remaining LDL is removed by way of scavenger pathways at the cellular level.

Cont…

•As LDL is taken up by receptors, free cholesterol is released and accumulates within the cells▫acyl-CoA cholesterol acyltransferase, which esterifies free cholesterol into cholesterol ester, storing cholesterol in the cell.

Reverse Cholesterol Transport

•the process by which cholesterol is removed from the tissues and returned to the liver

•High-Density Lipoprotein (HDL) is the key lipoprotein involved

•for the transfer of cholesteryl esters between lipoproteins

Cont…

•HDL is formed through a maturation process of a series of conversions (known as the "HDL cycle") ▫to attract cholesterol from cell membranes

and free cholesterol to the core of the HDL particle

Cont…• The exact mechanism by which the HDL delivers cholesterol

esters to the liver is not well understood BUT; several mechanisms have been suggested. This Include:

• The action of cholesteryl ester transfer protein–which transforms HDL into a TG-rich particle that

interacts with hepatic-triglyceride lipase• Cholesterol ester-rich HDL may also be taken

up directly by the receptors in the liver• Another mechanism may be that cholesterol

esters are delivered directly to the liver for uptake without catabolism of the HDL cholesterol particle