2. Composition different lipids in diet
• Triglycerides (> 90%)
• Cholesterol
• Cholesteryl esters
• Phospholipids, and
• Unesterified fatty
All of the above varieties of lipids are also
synthesized in body
6. Lipid digestion in mouth
• Digestion in Mouth
• Hydrolysis of triacylglycerols is initiated by lingual which
attack the sn-3 ester bond forming 1,2-diacylglycerols and
free fatty acids, aiding emulsification.
• Lingual lipase:
• Secreted by Ebner’s gland present on dorsal surface of
tongue
• Active at low pH (pH 2.0 – 7.5)
• optimum pH 4.0-4.5
• Ideal substrate-Short chain TGS.
• Milk fat contains short chain fatty acids which are esterified at
-3 position, thus it is the best substrate for lingual lipase
• Enzymatic action continues in stomach
• Short chain fatty acids, released are absorbed directly from
the stomach wall and enter the portal vein.
7. Lipid digestion in stomach
• Gastric Lipase- secreted by chief cells and secretion is
stimulated by gastrin.
• Hydrolysis of triacylglycerols by gastric lipase attack the
sn-3 ester bond forming 1,2-diacylglycerols and free
fatty acids
• Optimum pH is 5.5 and therefore it is more significant in
neonates
• Up to 30% TGs is digested in stomach
• Ideal substrates: Short and medium chain fatty acid
containing TGs
8. Significance of lingual lipase
• Play important role in lipid digestion in neonates
since milk is the main source of energy and pH of
neonatal stomach also favors the optimal activity of
enzymes
• Important digestive enzymes in pancreatic
insufficiency such as Cystic fibrosis or other
pancreatic disorders
9. Role of emulsification in digestion
• Emulsification is the process of breaking down of
large fat globules into uniform tiny droplets.
• It is accomplished by bile salts and peristalsis
emulsification
• it occurs in duodenum
• Emulsification decreases the surface tension and
increases the surface area of fat globules and
thereby lipolytic enzymes can hydrolyze lipids
11. Lipid digestion in small intestine
• Major site of fat digestion
• Effective digestion due to the presence of Pancreatic
enzymes and bile salts.
• Bile salts act as effective emulsifying agents for fats
Secretion of pancreatic juice is stimulated by-
• Passage of acid gastric contents in to the duodenum
• By secretion of Secretin, Cholecystokinin
Pancreozymin (CCK-PZ), the gastro intestinal
hormones
15. Absorption of lipid
• Lipolytic theory put forth by Verzar:
According to this, fats are completely hydrolysed to
glycerol & FFA
These are absorbed either as soaps or in association with
bile salts
• Partition theory proposed by Frazer:
digestion of TAGs is partial & not complete
partially digested TAGs in association with bile salts,
form emulsion droplets
Lipids are taken up by the intestinal mucosal cells
16. Absorption of Lipids
• Bergstrom theory:
Long chain fatty acids (>14 carbons) are
absorbed to the
lymph & not directly to the blood
• Mixed Micelle Formation:
The products of digestion are 2-
monoglycerides, long chain
fatty acids, cholesterol, phospholipids
and lysophospholipids
are incorporated into molecular
aggregates to form mixed
Micelle
Micelles are spherical particles with a
hydrophilic exterior &
hydrophobic interior core
17. Absorption of Lipid
• micelle formation is important of absorption of lipid
contents in intestine
• MAGs, free fatty acids , phospholipids, cholesterol are
absorbed passively and to some extent actively in
enterocytes of duodenum and jejunum
• Medium and short chain fatty acids are directly enter
portal circulation and are transported to liver
• Long chain fatty acids are activated and esterified with
MAGs ,cholesterol and phospholipids and are packed in
chylomicrons.
21. Clinical conditions
• Defective synthesis- Due to deficiency of apo-B 48 protein.
The triglyceride may accumulate in intestinal cells.
• Defective digestion: In steatorrhea, daily excretion of fat in feces is more
than 6 g per day. (Greek word, "stear", means fat).
• Defective absorption: Celiac disease, surgical removal of intestine and
obstruction in bile duct
Chyluria- Due to an abnormal connection between urinary tract& lymphatic
drainage system of the intestines, Characterized by passage of Milky
urine.
Chylothorax -can result from an abnormal connection between the pleural
cavity and thoracic duct. It is characterized by accumulation of lymph in
pleural cavity