Lecture 11 Flashcards
What are the 4 key functions of fat in the body?
- Major energy store and fuel source
- Required for transporting fat soluble vitamins
- Provide essential fatty acids
- Important for insulating and protecting the body
Give examples of two essential fatty acids. What is their function?
Linoleic and alpha-linoleic acid
Important for cell membrane and nervous system
What is the most common type of lipid found in the body and in food?
Triglycerides
Where are long-chain fatty acids primarily found?
Meat, fish, vegetable oils
Where are medium and short chain fatty acids found?
Dairy products
What aspect of fatty acids influences the characteristics of foods and the health of the body?
Short or long
Saturated or unsaturated
Location of double bond
What is the state of different fat types at room temperature?
Saturated fats: solid and more resistant to oxidation
Polyunsaturated fats: liquid
Shorter fatty acid chains: softer than long chains
Compare the likelihood of spoilage of monounsaturated and polyunsaturated fat.
Monounsaturated: Slightly less susceptible to spoilage
Polyunsaturated: Spoils most readily
What are the effects of hydrogenation of unsaturated fats?
- Protects against oxidation, therefore prolonging shelf life
- Alters texture
- Acts more like saturated fat
What is the structure of sterols?
Multiple rings
Give an example of a well-known sterol
Cholesterol
What kind of food are sterols found in?
Both animal and plant foods
In what kind of food is cholesterol found in?
Animal foods only - meat, eggs, fish, poultry, dairy
What can plant sterols interfere with?
Cholesterol absorption
Give examples of plant-based sterols
Logicol and Flora Proactiv
What percentage of cholesterol is made in the liver? What is the rest obtained from?
We make about 80% of cholesterol in our liver and 20% is obtained by diet.
What is cholesterol material for?
Bile acids and hormones
What is endogenous and exogenous cholesterol?
Endogenous: made in liver
Exogenous: obtained by diet
What are the roles of sterols?
- Starting material for bile acids, sex hormones, adrenal hormones and vitamin D.
- Structural component of cell membranes.
How much cholesterol does the liver produce a day?
800-1500 mg
What is a disease associated with cholesterol?
Atherosclerosis is a disease that causes heart attacks. It occurs when cholesterol forms deposits in the artery wall.
How does the mouth contribute to lipid digestion?
In the mouth, salivary glands release lingual lipase. The acid-stable lingual lipase initiates lipid digestion.
How does the stomach contribute to lipid digestion?
Muscle contractions disperse fat into smaller droplets. Fat is exposed to gastric lipase.
What signals the gallbladder to release bile?
Cholecystokinin
What happens to fat in the small intestine?
Emulsified by bile. Prevents them from being attracted to each other.
Emulsified fat is broken down into monoglycerides, glycerol, and fatty acids by pancreatic and intestinal lipase.
Pancreatic cholesterolesterase sterifies some of the esters in cholesterol
Describe the recycling of bile.
In the gallbladder, bile is stored. In the small intestine, bile emulsifies fats. Bile reabsorbed into the blood. In the liver, bile is made from cholesterol. In the colon, bile that has been trapped by soluble fibers is lost in faeces. Don’t tend to lose much through this route.
What are the effects of plant sterols on bile recycling?
Plant sterols block the reabsorption of bile into blood from the small intestine, so the liver must manufacture its own cholesterol to make bile. They also increase the loss of bile in faeces.
How do statins affect cholesterol?
They reduce the production of LDL cholesterol by the liver.
What are statins prescribed for?
CV disease
What do fatty acids control in the stomach?
Gastric emptying
What are the major emulsifying agents?
Bile salts, lecithin, 2-monoacylglycerol
What is lecithin?
Phospholipid present in bile and food membranes
What is 2-MAG
Breakdown product from TAG
What are the three enzymes that catalyse adult lipid digestion?
- Pancreatic lipase digests triglycerides to glycerol and free FA’s. Requires an additional protein colipase from the pancreas (activated from procolipase) to become active.
- Pancreatic non-specific esterase (cholesterolesterase) removes FA’s from cholesterol esters, 2-MAGS, TAGS containing short and medium chain fatty acids, and fat soluble vitamin esters
- Phospholipase A2 removes an FA from the 2 position of phospholipids
What additional enzymes is there in human milk that aids with lipid digestion?
Human milk lipase. It is stable during passage through the acidic conditions of a baby’s stomach and it only becomes active in the small intestine, as this activity is bile salt-dependent.
Via what circulation are bile salts reused?
Enterohepatic circulation
What are the 4 roles that bile has during fat digestion?
1) Emulsification of fat droplets
2) Removal of products from lipid digestion from emulsified fat droplets, forming mixed micelles in the aqeuous phase
3) Cofactors required by lipases for activity
4) Mixed micelles increase the rate of delivery of the products of fat digestion across the unstirred layer at the enterocyte membrane
How are short chain fatty acids absorbed?
Absorbed straight through enterocyte into the blood supply of villi in the liver.
How are larger fatty acids (monoglycerides and long-chain fatty acids) absorbed?
Combine with bile to form a micelle that is sufficiently water soluble to penetrate the watery solution bathing the absorptive cells. There the lipid contents of the micelles diffuse into the cells. A chylomicron is formed, which passes into lacteal.
What happens to cholymicron as it circulates the body?
Chylomicron components are removed during circulation, mainly as a result of TG hydrolysis by lipases released from peripheral tissues. Chylomicrons become smaller and denser, and chylomicron remnants are endocytosed by the liver. Their remaining lipid is liberated and utilised, or re- packaged in lipoprotein complexes for export from the liver.
What is the largest lipoprotein?
Chylomicron
What is lipid transport made possible by?
A group of vehicles known as lipoproteins
What is the structure of a lipoprotein?
Triglycerides and cholesterol found on the inside. Surrounded by phospholipids and proteins.
What are chylomicrons, VLDL’s, LDL’s, and HDL’s composed primarily of?
Chylomicrons: triglycerides
VLDL’s: triglycerides
LDL’s: cholesterol
HDL’s: protein
What foods are high in fat?
Oils, butter, mayonnaise, avocado, nuts, bacon, fatty meat, chocolate, doughnuts
What are the recommendations for fat intake?
- Fat intake 20-35% total energy intake
- No more than 10% from saturated fat
- n-6 fatty acids 4-10%
- n-3 fatty acids 0.4-1%
How does following a cardio-protective diet protect our arteries?
- Improving lipids
- Lowering blood pressure
- Reducing risk of thrombosis
- Reducing inflammation
- Controlling blood glucose
- Managing weight
