HLSC 2110U Lecture 9: Study Notes - Lecture 9
19 Feb 2019
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Lipids
- Heterogeneous group
- Hydrophobic
- Organic molecules
- Can be extracted from tissues by non-polar solvents
Major Classes of Lipids
- Fatty acids
- Triacylglycerols
- Phospholipids
- Steroids
- Glycolipids
Structure of Fatty Acids
- Consist of hydrophobic hydrocarbon chain and a terminal carboxyl group (ionized at pH 7)
Functions of Lipids
- Energy source
- Cell membrane structure
- Fat-soluble vitamins have regulatory or coenzyme functions
- Prostaglandins and steroid hormones have a role in homeostasis
- Deficiencies in lipid metabolism can lead to clinical problems (atherosclerosis and obesity)
GI Tract
- Buccal cavity (mouth) – mastication
- Oesophagus
- Stomach – storage, endocrine and paracrine communication, protein digestion
- Gall bladder – reservoir of bile
- Pancreas – secretes digestive enzymes
- Duodenum – digestion
- Jejunum – digestion and absorption
- Ileum – absorption
- Colon – reabsorption of fluid, fermentation
- Rectum – storage of feces
- Anus
Lipids
- Most of lipid from diet is triacylglycerol (TAG) → used to be known as triglyceride
- Any remainder of diet lipid is cholesterol, cholesteryl esters, phospholipids, and free
(unesterfired) fatty acids
Processing of Lipids
Stomach – two acid-stable enzymes act together
- Lingual lipase (from back of tongue)
- Gastric lipase (from gastric mucosa)
Both target TAG with fatty acids of a chain less than 12 carbons (ex. milk fat)
Emulsification of Lipids in the SI
- Critical emulsification happens in the duodenum
- Increases the surface area of hydrophobic lipid droplets, stabilizes the particles, and keeps them
in smaller sizes so that digestive enzymes can act effectively
- Carried out by bile salts detergent action and mechanical mixing from peristalsis
Bile salts are derivatives of cholesterol
Degradation of Lipids by Pancreatic Enzymes
- Happens after emulsification
- TAG, cholesteryl esters, and phospholipids are degraded by pancreatic enzymes
- Secretion of these enzymes is hormonally controlled
- TAG molecules are big and are hydrolysed by pancreatic lipase (esterase) which yields a mix of
2-monoacylglycerol and free fatty acids
- Lipase catalysis helped by pancreatic co-lipase that exposes its catalytic sites for better activity
Orlistat is an anti-obesity drug that inhibits gastric and pancreatic lipases, decreasing fat absorption, and
resulting in weight loss
Cholesteryl Esters
- Mostly free (esterified)
- Only those that are non-esterfied are hydrolyzed by pancreatic cholesteryl ester hydrolase
(cholesterol esterase)
Document Summary
Can be extracted from tissues by non-polar solvents. Consist of hydrophobic hydrocarbon chain and a terminal carboxyl group (ionized at ph 7) Prostaglandins and steroid hormones have a role in homeostasis. Deficiencies in lipid metabolism can lead to clinical problems (atherosclerosis and obesity) Stomach storage, endocrine and paracrine communication, protein digestion. Most of lipid from diet is triacylglycerol (tag) used to be known as triglyceride. Any remainder of diet lipid is cholesterol, cholesteryl esters, phospholipids, and free (unesterfired) fatty acids. Both target tag with fatty acids of a chain less than 12 carbons (ex. milk fat) Increases the surface area of hydrophobic lipid droplets, stabilizes the particles, and keeps them in smaller sizes so that digestive enzymes can act effectively. Carried out by bile salts detergent action and mechanical mixing from peristalsis. Tag, cholesteryl esters, and phospholipids are degraded by pancreatic enzymes. Tag molecules are big and are hydrolysed by pancreatic lipase (esterase) which yields a mix of.
