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Lipids are one of the major components of human and animal bodies
Lipids are structurally very diverse and thus problematic to define.
Usually defined as organic molecules composed principally of
Carbon and hydrogen that are predominantly nonpolar and therefore hydrophobic.
The chemical components that most lipids have in common are what?
Fatty acids, which are hydrocarbons built on a backbone consisting of a chain of carbon atoms.
One important chemical category of lipids is the what?
A triglyceride consists of what?
Three fatty acid molecules combined with a molecule of glycerol
A fatty acid is saturated if what?
All the bonds between carbon atoms are single bonds, as exemplified by palmitic acid.
A fatty acid is unsaturated if what?
One or more of the bonds between carbon atoms are double.
Polyunsaturated fatty acids are what?
The subset of unsaturated fatty acids that contain multiple (two to six) double bonds, exemplified by linoleic acid.
Functional roles of lipids...
- Phospholipids and cholesterol are principle components of cell and intracellular membranes.
- Storage compounds in both animals and plants. (Exceed proteins and carbs in every value per unit of weight).
-Lipids in or on the integument greatly reduce the permeability of the integument to water.
The high energy density of lipids means that...
The weight of material an animal must carry around to store a given amount of chemical-bond energy is far lower if lipids are the storage compounds than if other compounds are used.
Carbon chains used to synthesize lipids may be derived from
Dietary carbohydrates and proteins, as well as dietary lipids.
Biochemical flexibility is one reason that...
Lipid nutrition is less likely than protein nutrition to be fraught with problems.
Another reason is the fact that...
Animals maintain stores of lipids; contrary to the case with proteins, lipids obtained in excess of needs at one time are often held over in the body for use in the future
Many types of animals—including mammals—lack what?
The enzymes needed to create double bonds at the omega-3 and omega-6 positions.
The omega-3 and omega-6 fatty acids therefore cannot be synthesized and must be obtained from where?
From foods or other outside sources, at least during critical life stages.
The omega-3 and omega-6 fatty acids thus are...
Essential Fatty Acids
In most mammals, digestion of triglycerides begins in the oral cavity, under the action of what?
Lingual lipase from glands of the tongue.
Gastric lipase can be found in many mammals and acts similarly to what?
What percent of lipids is broken down before entering the small intestine?
A small percentage
Where does most lipid digestion occur?
Small intestine (in the jejunum)
The digestion of triglycerides in the small intestine can be divided into what two phases?
Emulsification (Phase 1) and Enzymatic Digestion (Phase 2)
Emulsification (Phase 1) ------>
Emulsified triacylglycerols, diacylglycerols, and fatty acid micelles (Bile; no lipase)
Enzymatic digestion ------>
Monoacylglycerols and fatty acids (Pancreatic lipase produced in pancreas)
First, bile salts emulsify the lipid drops into tiny emulsion droplets, thereby providing better access for pancreatic lipase.
The emulsification takes place only after the chyme has been mixed with bile in the duodenum.
Pancreatic lipase then breaks apart the triglycerides to form a mixture of
Monoglycerides and fatty acids.
As molecules of monoglycerides and fatty acids are released, they interact with bile salts in the surrounding chyme to form small lipid-bile salt complexes called...
The micellar particles are sufficiently water soluble to penetrate the unstirred water layer that bathes the
enterocytes of the small intestine.
When a micelle contacts the intestinal epithelium, the lipids diffuse across the plasma membrane and enter the cytoplasm.
The intestinal cells synthesize new triglycerides from the monoglycerides and fatty acids.
These triglycerides, together with absorbed steroids, phospholipids, and fat-soluble vitamins, are then coated with what?
The resulting complexes are known as what?
The intestinal cells then secrete the chylomicrons into interstitial fluid by what?
The protein coating keeps the chylomicrons suspended in the interstitial fluid, but they are generally what?
Too large to diffuse into capillaries
Most of the chylomicrons diffuse into the intestinal what?
Lacteals (lymphatic capillaries), which lack basement membranes and have large gaps between adjacent endothelial cells.
From the lacteals, the chylomicrons proceed along the lymphatic vessels and through the what?
They finally enter the bloodstream at the what?
Left subclavian vein
Chylomicrons transport lipids absorbed from the intestine to where?
Adipose, cardiac, and skeletal muscle tissue.
Triglyceride components are hydrolyzed by the activity of the what?
Lipoprotein lipase, releasing free fatty acids.
May release fatty acids and glycerol at times of fasting or starvation.
-Atherosclerosis (Abnormalities in Metabolism of Lipids)
•Accumulation of lipids in liver
•Increased hormone output
•Cellular liver damage
•Vitamin E-Se deficiency
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