Lipids in Lactation Flashcards
Define lipids
A diverse range of compounds that have nonpolar groups that make them relatively insoluble in water
What are the functions of lipids in the cell?
Structure (ex. phospholipid membranes, FA)
Signaling
Storage (of energy)
How are lipids sub-classified?
By their chemical structure
Describe triglycerides
Triglycerides are used to store energy in plants and animals
They are the most energy dense of the lipids
Characteristics:
- glycerol backbone, 3 fatty acids
- major lipid class in concentrate feeds
- main lipid store in animal tissues
- diverse because they may contain different fatty acids
- the fatty acid is the energy dense part
Describe glycolipids
Glycolipids are “complex” structural lipids that contain a carbohydrate (therefore they are less energy dense than a TAG)
Characteristics:
- glycerol backbone, 2 fatty acids, and one or two sugars
- major lipid class in forages
Describe phospholipids
Phospholipids are “complex” structural lipids that contain a phosphate group (also less energy dense than TAG)
Characterisitics:
- glycerol backbone
- 2 fatty acids
- one phosphate group
- a base
Important biological roles:
1. cell membrane structure, integrity, and transport
2. second messenger in intracellular transduction (signaling) of hormone actions
Describe steroids
Steroids are also lipids and include cholesterol, vitamin D, and steroid hormones
They have a cyclopentane ring as a shared common structure
They are important to membrane structure and endocrine functions (steroid hormones)
Describe fatty acids
Fatty acids are long carbon chains with a methyl group (CH3) at one end and a carboxyl group (COOH) at the other
Characterized by:
1. Number of carbons (chain length)
2. Number of double bonds (unsaturation)
3. Location and orientation of these bonds (position relative to methyl end is nutritionally important, ex. Omega 3 and Omega 6; cis and trans bonds are different)
The structure of a fatty acid is important to how it is metabolized, how it is used, and if it is bioactive
Describe trans fats
Trans fats are only found in industrial processed oils and ruminant fat (meat and milk too).
The industrial sources ones are bad for people, while the ruminant ones are likely more healthy.
How can we characterize fatty acids?
By number of double bonds
Describe the composition of palm oil
high in palmitic fatty acid (C16:0)
Describe the composition of flax oil
high in omega 3 (18:3)
Describe the composition of corn and soybean oil
high in omega 6 (18:2)
Describe the composition of canola oil
balance of a higher ratio of omega 9 and 3 to a lower ratio of omega 6
What type of feeds are generally high in omega-3?
forages
What types of feeds are high in omega-6?
Soy and corn
What types of feeds are high in saturated fatty acids or 18:1?
animal fats and palm oil
Why are fatty acids somewhat different today?
We have selected for different fatty acid profiles.
For instance, canola oil was selected to be low in erucic acid.
What are two simple methods to characterize an oil?
Saponification number and iodine numbers
Discuss saponification number
This is an indicator of the average chain length of a fatty acid
The longer the average chain length, the lower the number
Saponification number is not used very often because many FA are similar in length
Discuss iodine number
This is a measure of the unsaturation of fat
The more unsaturated bonds, the higher the iodine number
Discuss fatty acid profile
This determines the actual concentration of each fatty acid in the oil via gas chromatography
It is expensive and time consuming
What are the two ways oils can spoil or become rancid?
Hydrolytic rancidity and oxidative rancidity
Discuss hydrolytic rancidity
Triglycerides are broken down to free fatty acids, which may lead to odors.
The nutritional value of the fatty acid is not affected, and this is not toxic to the animal.
Discuss oxidative rancidity
Double bonds of the unsaturated fatty acids (PUFA) are attacked by oxygen. This causes off flavors and odors.
Peroxides (free radicals) are formed and perpetuate, eventually attacking gut tissue.
This may reduce performance in animals and may damage tissues, so it is potentially dangerous and can be considered an issue for health or safety.
How can oxidative rancidity be prevented?
With antioxidants like Vitamin E
They prevent formation of free radicals or dispose of them before they can attack the gut tissue.
What can increase the risk of oxidation?
exposure to air, sunlight, and high temperatures
Where are lipids absorbed and how must they be broken down?
Lipids are digested and absorbed in the small intestine (80% in jejunum)
They must be broken down into free FA and monoglycerides and emulsified into small droplets
Short-chain FA (VFAs) are absorbed in the rumen, omasum, and hindgut
The 2 main agents of breakdown are bile salts and lipase
How do bile salts and lipase help breakdown lipids?
Bile salts increase the solubility
Lipase breaks down triglycerides
Describe lipase
Lipase is the enzyme that breaks down triglycerides to monoglycerides and fatty acids
Lipase comes from saliva and gastric secretions (mammals only), pancreas, and intestinal cells
Lipase also breaks down phospholipids and cleaves FA from cholesterol in the pancreas
Describe bile salts
Bile salts are important to emulsify lipids into small droplets and micelles.
Na and K are the salts of bile acids
Bile salts are secreted through the bile duct
They are activated by pancreatic lipase
Emulsify fats to micelles (tiny droplets of mixed lipids and bile salts)
- recycled to the liver via the portal vein
Why is the breakdown of fat droplets important?
Fat droplets are broken apart into smaller droplets, which makes it easier to lipase to attach and work to breakdown the droplets to micelles
Describe the absorption of micelles
Micelles are coated in bile and free FA and monoglycerides that are absorbed by the epithelial cells. This is ultimately a futile cycle because once absorbed, the MG and free FA are reformed as triglycerides.
These triglycerides are then packaged into chylomicrons and absorbed by lymph vessels (run to heart first, then rest of body)
What is the function of chylomicron
Chylomicrons are lipoproteins coated in protein and carbs, which allow them to be absorbed in the lymph vessels and move through the body
Chylomicrons are molecules used to transport FA in plasma, and they are transported through lymph vessels
Describe micelle formation
Micelles are composed of fatty acids, bile salts, and monoglycerides
They have long-chain saturated FA solubilized in the hydrophobic interior of the micelle (micelles have a hydrophobic core and a hydrophilic exterior)
Ruminants use lysolecithin in place of monoglycerides since they don’t have monoglycerides
Describe bile salt synthesis
Bile salts are synthesized from cholesterol in the liver. They aid in digestion and are efficiently absorbed and recycled (95% reabsorbed in the portal vein)
How can plasma cholesterol be reduced?
If forced to make bile salts, plasma cholesterol will decrease. This can be forced by preventing the reabsorption of bile salts
What are required for transport of FA in the blood?
lipoproteins
Describe lipoproteins in general
Lipoproteins come from different tissues and have different compositions because of what they are doing
They differ in their density because of differences in fat to protein composition
Discuss VLDLy
VLDLy is a special lipoprotein made by birds in the liver and deposited in the egg yolk; it transports fats to the oocyte
Its synthesis is increased by giving the bird estrogen
How do cells intake triglycerides
Cells DO NOT take in triglycerides; lipoprotein lipase breaks down triglycerides into free FA and glycerol, then the FA are absorbed by the cell
What is the function of lipoprotein lipase
They break down trigylcerides into glycerol and FA in the blood so that the FA can be taken up by cells
What is the purpose of triglycerides in the body?
storage of energy and insulation
What is the purpose of phospholipids, glycolipids, and steroids in the body?
make up cell membranes and regulate cell function
What is the purpose of essential fatty acids in the cell?
comprise cell membranes and work in synthesis of eicosanoids
How do lipids act as transporters?
They can be carriers of fat soluble vitamines
What are the two essential fatty acids?
Linoleic (C18:2) and linolenic (C18:3) are essential because they cannot be synthesized by animals
They are important to cell membranes and important in the synthesis of regulatory compounds like eicosanoids
What fatty acids are “conditionally essential?”
arachidonic acid can be synthesized from C18:2
EPA and DHA can be synthesized from C18:3
What are signs of essential fatty acid deficiencies?
skin lesions, reproductive failure, edema, subcutaneous hemorrhage
What type of fat synthesis is limited in most animals?
Synthesis of very long chain n-3 polyunsaturate fats (PUFA) from linolenic acid
What are eicosanoids?
These are signaling molecules made from arachidonic acids (Omega 6) or EPA (Omega 3).
They can form prostaglandins, thrombaxones, and leukotrienes.
How does the activity of an eicosanoid differ?
They differ based on if they are made from omega 3 or omega 6.
Omega 3 are more anti-inflammatory
Omega 6 are more pro-inflammatory
Where is EPA not found?
plant sources
What are EPA and DHA and why are they important?
EPA and DHA are very long chain omega-3 fatty acids that are bioactive.
They are essential to brain and nerve development.
They reduce inflammation, benefit heart disease, arthritis, blood cholesterol, retinal degeneration, etc.
They are found only in cold water fish and algae
18:1 and 18:3 n-3 may be key to “Mediterranean diet” that has lower obesity and heart disease
How do the fatty acids consumed by a ruminant differ from the fatty acids they absorb?
Rumen microbes saturate fatty acids in a process known as biohydrogenation, so they absorb saturated FA
Describe biohydrogenation
First, esterified fatty acids are hydrolyzed by bacterial lipases in the rumen to release free FA
Then, biohydrogenation converts cis bonds to trans bonds before removing the double bond entirely
Biohydrogenation is done because unsaturated fatty acids are toxic to the rumen microbes