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Questions and Answers
What is the primary function of chylomicrons in the body?
What is the primary function of chylomicrons in the body?
Which apoprotein is essential for activating lipoprotein lipase, facilitating the breakdown of triglycerides in capillaries?
Which apoprotein is essential for activating lipoprotein lipase, facilitating the breakdown of triglycerides in capillaries?
What is the ultimate fate of chylomicron remnants after they have delivered their triglyceride cargo?
What is the ultimate fate of chylomicron remnants after they have delivered their triglyceride cargo?
Which lipoprotein primarily functions to transport triglycerides synthesized within the liver to peripheral tissues?
Which lipoprotein primarily functions to transport triglycerides synthesized within the liver to peripheral tissues?
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What is the role of HDL in reverse cholesterol transport?
What is the role of HDL in reverse cholesterol transport?
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During fasting, what enzyme within adipocytes is responsible for breaking down stored triglycerides?
During fasting, what enzyme within adipocytes is responsible for breaking down stored triglycerides?
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What is the role of ApoE in lipoprotein metabolism?
What is the role of ApoE in lipoprotein metabolism?
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What is the metabolic fate of glycerol released from triglycerides during lipolysis in adipose tissue?
What is the metabolic fate of glycerol released from triglycerides during lipolysis in adipose tissue?
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Which of the following enzymes is active in the stomach and exhibits increased activity in infants due to their lower stomach acidity?
Which of the following enzymes is active in the stomach and exhibits increased activity in infants due to their lower stomach acidity?
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What is the primary function of bile salts in lipid digestion?
What is the primary function of bile salts in lipid digestion?
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Which enzyme is responsible for breaking down cholesterol esters into cholesterol and one fatty acid?
Which enzyme is responsible for breaking down cholesterol esters into cholesterol and one fatty acid?
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What are Micelles?
What are Micelles?
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What is the role of fatty acyl CoA synthase in the context of lipid absorption within the mucosal cells?
What is the role of fatty acyl CoA synthase in the context of lipid absorption within the mucosal cells?
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Why can't triglycerides be directly absorbed in the intestine?
Why can't triglycerides be directly absorbed in the intestine?
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Which of the following is the correct sequence of events for long-chain fatty acid processing after they are absorbed into the intestinal mucosal cells?
Which of the following is the correct sequence of events for long-chain fatty acid processing after they are absorbed into the intestinal mucosal cells?
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Flashcards
Triacylglycerols
Triacylglycerols
The main type of dietary lipids, making up 90% of lipids consumed.
Lingual Lipase
Lingual Lipase
An acid-stable enzyme secreted in the mouth that starts fat digestion.
Emulsification
Emulsification
A process that increases the surface area of lipids for digestion by breaking them into smaller droplets.
Micelles
Micelles
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Bile Salts
Bile Salts
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Pancreatic Lipase
Pancreatic Lipase
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Lipid Absorption
Lipid Absorption
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Chylomicrons
Chylomicrons
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Chylomicron Structure
Chylomicron Structure
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Transport Pathway of Chylomicrons
Transport Pathway of Chylomicrons
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Primary Function of Chylomicrons
Primary Function of Chylomicrons
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Triglyceride Breakdown
Triglyceride Breakdown
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Chylomicron Remnants
Chylomicron Remnants
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Function of HDL
Function of HDL
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Liver's Role with Cholesterol
Liver's Role with Cholesterol
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Study Notes
Lipid Digestion, Absorption, and Transport
- Dietary Lipids: Primarily triglycerides (90%), with cholesterol, phospholipids, and free fatty acids also present.
Lipid Digestion
- Enzymes:
- Lingual lipase (mouth, activated in stomach).
- Gastric lipase (stomach, activated in duodenum).
- Pancreatic lipase (primary intestinal enzyme).
- Digestion Locations:
- Mouth: Minimal lipid digestion.
- Stomach: Lingual lipase action begins; infants have more stomach lipase activity due to less acidic stomach environment.
- Small Intestine (Duodenum): Major site of lipid digestion; requires emulsification for efficient enzyme action.
Lipid Emulsification
- Necessity: Lipids are hydrophobic; emulsification increases surface area for enzyme action.
- Bile Salts: Key emulsifiers;
- Structure: Hydrophobic region interacts with lipids, hydrophilic region interacts with water.
- Origin: Produced by the liver, stored in the gall bladder, and secreted into the duodenum.
- Precursors: Bile acids converted to bile salts.
Pancreatic Enzyme Action
- Triglyceride Breakdown: Pancreatic lipase converts triglycerides into 2 fatty acids and 2-monoacylglycerol.
- Cholesterol Ester Breakdown: Cholesterol esterase converts cholesterol esters to cholesterol and a fatty acid.
- Phospholipid Breakdown: Phospholipase A2 converts phospholipids to lysophospholipid and a fatty acid; further broken down by lysophospholipase.
- Trypsin: Activates phospholipase A2.
Lipid Absorption
- Micelles: Tiny complexes of lipid digestion products and bile salts.
- Function: Transport lipid products to the intestinal mucosa (jejunum) for absorption.
- Bile Salt Recycling: Bile salts are reabsorbed in the ileum and return to the liver via the hepatic portal system.
- Absorption Limitation: Triglycerides are too large for direct absorption, so they need breakdown by pancreatic lipase.
- Lipid Reconstruction:
- Fatty acids are converted to fatty acyl CoA.
- Monoacylglycerol and fatty acyl CoA are reassembled into triglycerides.
- Short-chain fatty acids enter the blood directly.
- Long-chain fatty acids are packaged into chylomicrons.
Chylomicrons
- Definition: Lipoproteins transporting dietary lipids from the intestines to tissues.
- Structure: Interior: triglycerides and cholesterol esters; exterior: phospholipids and apoproteins (apolipoprotein B-48).
- Pathway: Exocytosed from intestinal mucosal cells → lymphatic system (intestinal lacteals) → blood circulation (left subclavian vein).
- Function: Deliver triglycerides to skeletal muscle (energy) and adipose tissue (storage).
- Triglyceride Breakdown in Capillaries: Lipoprotein lipase on endothelial cells breaks down triglycerides; fatty acids enter cells or circulate bound to albumin; glycerol used by the liver for glycolysis or gluconeogenesis.
- Chylomicron Remnants: Taken up by the liver.
Lipoprotein Metabolism & Cholesterol Transport
- Lipoproteins: Transport lipids in blood.
- Types: Chylomicrons (dietary triglycerides), VLDLs (liver triglycerides), LDLs (cholesterol to tissues), HDLs (scavenge cholesterol, return to liver).
- LDL Formation: VLDLs lose triglycerides, becoming LDLs.
- HDL Functions: Reservoir of ApoCII and ApoE for chylomicron & VLDL maturation; scavenges cholesterol from cells; converts cholesterol to cholesterol esters.
- Lipoprotein Apoproteins: ApoCII (activates lipoprotein lipase); ApoE (lipoprotein recognition and clearance).
- Liver Role: Converts cholesterol from chylomicron remnants into LDL, HDL, or VLDL.
Lipid Mobilization During Fasting
- Hormone-sensitive lipase (adipocytes): Breaks down stored triglycerides when energy is needed.
- Fatty Acid Release: Free fatty acids are released into circulation, bound to albumin.
- Glycerol Utilization: Glycerol is utilized by the liver for gluconeogenesis.
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Description
This quiz covers the processes involved in lipid digestion, absorption, and transport, focusing on dietary lipids such as triglycerides, cholesterol, and phospholipids. It discusses the role of various enzymes and the importance of emulsification in the digestive system.
