BC 33 Dietary Lipids

Question 1

Major Dietary Lipids

Answer 1

TAG 90% (triglycerides)

cholesterol and cholesterol esters

phospholipids

free FA unesterified
-sat, unsat, monounsat, polysat

20-35% of calories should be from fat (lipids)

• 25% of that should be essential FA (w3 w6)
• limit consumption of saturated and trans FAs

Question 2

Digestion seven steps

Answer 2

most complex

1. ingestion
2. minimal digestion by lingual and gastric lipase in stomach
3. emulsification
4. digestion in SI using pan enzymes
5. absorbtion into intestinal enterocytes
6. resunthesis of lipids in enterocytes
7. transport from enterocyte in CM

Question 3

Acid Lipases

Answer 3

2 and both in stomach

lingual: glands in back of tongue
gastric lipase: gastric mucosa

both acid stable pH4-6
both digest TAGs with short chain FA <12

• neonates need milk for fat, human breastmilk contains acid stable lipase
• panc insufficiency such as CF??

Question 4

Emulsification of Fats

Answer 4

use of detergent properties of Bile Salts
-mechanical mixing by peristalsis

bile salts with lipase and colipase

Enteropathic circle of biosalts
liver-> GB->intestines->enterocytes-> liver

cholic acid and taurine and glycine are hydrophilic ends out

Question 5

colipase and lipase

Answer 5

colipase (procolipase when inactive)

• secreted by panc
• cleaved in intestine by trypsin
• non polar domain (tail) embedded in droplet

-polar domain (head) binds to c-terminal, anchors and activates lipase

REQUIRED FOR LIPASE

panc lipase: hydrolizes more than 80% of dietary fat. requires colipase
-overcome inhibitory effect of bile salts

Question 6

TAG degradation and Associated Clinical Corr.

Answer 6

90% too large for uptake in mucosal cell of int villi

Panc lipase: esterase that removes FA from 1 and 3 with high efficiency

• high concentrations
• binds to colipase
• deficiency causes severe malabsorbtion dietary fat

ORLISTATL antiobesity inhibits panc lipase

Question 7

phospholipid degradation and venom

Answer 7

pancreatic juices contain enzymes for phospholipid digestion

Phospholipase A2: first a proenzyme but activated by tripsin
-one FA removes from C2 position removed

Lysophospholipase: removes from C1 position

remaining glycerol and last FA and head group excreted in feces or degraded further and absorbed

snake venom: phospholipase A2, Degredatino of erythrocytes

Question 8

Cholesterol Ester Degredation

Answer 8

Dietary chol is mix of free chol (85-90) and cholesteryl ester (10-15)

humans cannot metabolize the bring structure of cholesterol (some gut bacteria can)

• cholesterol esterase produces chol + free FA
• -requires bile salts for optimal activity

Question 9

Hormone Regulation of lipid digestion

Answer 9

Cholecytokinin (CSK) produced by all cells of lower duodenum and jejunum
-in response to presence of lipids and partially degested protiens entering upper small Intestine

+bile from gall bladder
+pancreatic lipase secretion
-decreases gastric mobility

secretion causes pacrease and liver to release bicarbonates which neutralize stomach acid and restore pH

Question 10

Components of a mixed Micelle

Answer 10

• fat soluble vitamins (ADEK)
• bile salts
• monacylglycerol
• free FA
• Free Chol

-

Question 11

Absorbtion of Digested Lipids

Answer 11

Brush border of Small intestine

• cholesterol is poorly absorbed
• bile salts absorbed in ileum

short and medium chain FA do not need micelle, directly absorbed.

Question 12

Resyntehsis of Lipids

Answer 12

Absorbed fats reassembled into TAG, chol ester, and phospholipids in ER of intestinal cells

• packaged into CHYLOMICRONS
• apolipoprotien B48 and phospholipids on surface
• TAG, fat soluble vitamins and Chol Esters on inside

chylomicrons: carriers for dietary fats and vits in the lymph and blood

Question 13

CM secretion and Transport

Answer 13

released into interstitial fluid by exocytosis’-enter lymphatic system at lacteal by diffusion
-flow of lymph carris CM to the thoracic duct

CM in blood 1-2 hours after meal

can deliver fat to adipose and muscle tissue

CM remnants to liver

DRAW ASSIMILATION: (review chart for fat stages)

Question 14

Steatorrhea

Answer 14

excess lipids in feces
from:
insufficient bile salt: cholestasis
insufficient panc enz: cystic fibrosis
poor absorption
-LEADS to deficiency of essential FA and vitamins

Cystic Fibrosis: CFTR gene- chloride channel

• decrease in chloride, increase reabsorbtion of NA + H2O
• -> in pancreas decreased hydration, thickend panc enz, enz do not reach intestine

treatment: replace these enzymes and supplements with fat soluble vitamins

Question 15

lipid assimilation defects

Answer 15

lipoprotein lipase deficiency: RARE AR disorder

• deficiency of lipase
• chylomicroanemia

????