Dietary Lipids: Digestion and Absorption

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Questions and Answers

What is the primary function of Lipoprotein Lipase (LPL)?

To transport cholesterol to peripheral tissues

To release fatty acids and glycerol from triglycerides (correct)

To store excess glucose as glycogen

To synthesize new fatty acids from glucose

What can cause steatorrhea?

Blockages in pancreatic or bile ducts (correct)

High-protein diet

Increased absorption of carbohydrates

Excessive fat intake without digestive enzymes

Which fatty acid is known as the precursor to all other fatty acids?

Stearic acid

Palmitic acid (correct)

Linoleic acid

Oleic acid

Which condition is associated with a decrease in fat-soluble vitamin absorption?

Chronic pancreatitis Signup and view all the answers

Where does the synthesis of fatty acids primarily take place?

Cytoplasm of liver and lactating mammary glands Signup and view all the answers

What is required for the activation of Lipoprotein Lipase (LPL)?

ApoCII Signup and view all the answers

What occurs to the turbidity of blood after consuming a high-fat meal?

It increases due to chylomicrons Signup and view all the answers

What type of fatty acids are more common in biological systems, cis or trans double bonds?

Cis double bonds Signup and view all the answers

What is the primary function of bile salts in the emulsification process?

To increase the surface area of lipid aggregates for enzyme action Signup and view all the answers

Which lipases primarily hydrolyze triacylglycerols with short and medium chain fatty acids?

Lingual and gastric lipases Signup and view all the answers

What role does colipase play in the digestive process?

It binds to lipase and fat, facilitating lipase activity Signup and view all the answers

Which hormonal substance is responsible for inducing the secretion of bicarbonate in the pancreas?

Secretin Signup and view all the answers

What are the primary products of dietary lipid degradation found in the jejunum?

Free fatty acids, free cholesterol, and 2-monoacylglycerol Signup and view all the answers

How does pancreatic lipase contribute to lipid digestion?

By hydrolyzing triglycerides into fatty acids and glycerol Signup and view all the answers

What is the role of peristalsis in the emulsification process of lipids?

To mix bile salts with dietary lipids Signup and view all the answers

Which of the following statements regarding short- and medium-chain fatty acids is correct?

They can be absorbed directly by mucosal cells without micelles Signup and view all the answers

What is the primary function of the citrate-malate shuttle?

It transports acetyl CoA to the cytoplasm for fatty acid synthesis. Signup and view all the answers

Which of the following compounds inhibits the activity of the fatty acid synthase enzyme?

Palmitoyl CoA Signup and view all the answers

How does malonyl CoA play a role in fatty acid metabolism?

It prevents the oxidation of newly synthesized fatty acids. Signup and view all the answers

What is the end product of the fatty acid synthase reaction?

Palmitate (16:0) Signup and view all the answers

What effect does high insulin and low glucagon have on lipogenesis?

It promotes the synthesis of glucose 6-phosphate dehydrogenase. Signup and view all the answers

Which molecule is NOT involved in the synthesis of triacylglycerols?

Acetyl CoA Signup and view all the answers

In which cellular compartment can fatty acids be elongated in humans?

In both mitochondria and endoplasmic reticulum. Signup and view all the answers

What prevents humans from synthesizing double bonds between the w carbon and the seventh carbon from the w end?

Lack of desaturase enzymes. Signup and view all the answers

Study Notes

Dietary Lipids: Digestion, Absorption, and Transport

Triacylglycerols, phospholipids, and cholesteryl esters are primary dietary lipids.
Digestion: Lipases play a crucial role in breaking down these lipids.
- Lingual and Gastric Lipases: Begin digestion with short and medium chain fatty acids (12 carbons or fewer).
- Pancreatic Lipase: Key enzyme for triacylglycerol breakdown in the small intestine (duodenum).
Emulsification: Bile salts from the liver and gallbladder increase the surface area of lipid droplets, promoting digestion.
Micelles: These structures, formed by bile salts, contain triacylglycerols, free fatty acids, cholesterol, and monoglycerides, facilitating absorption.
Absorption in Jejunum: The primary products of lipid degradation (free fatty acids, cholesterol, monoglycerides) are absorbed into mucosal cells.
Packaging: Short and medium chain fatty acids enter the portal circulation, while long chain fatty acids are re-esterified into triacylglycerols and packaged into chylomicrons.
Chylomicron Function: Chylomicrons transport dietary lipids from the intestines to tissues.
Lipoprotein Lipase (LPL): Located on capillary walls, LPL hydrolyzes triacylglycerols in chylomicrons, releasing free fatty acids for tissue use.

Fatty Acid Synthesis

Palmitate (16:0): Key precursor for most fatty acids.
Synthesis Process: Occurs primarily in the cytoplasm of liver and mammary glands, and to a lesser extent, adipose tissue.
Citrate-Malate Shuttle: Translocates acetyl CoA from the mitochondria to the cytoplasm for fatty acid synthesis.
Rate-Limiting Step: Acetyl-CoA carboxylase converts acetyl CoA to malonyl CoA, regulated by insulin, glucagon, citrate, and palmitoyl CoA.
Malonyl CoA Inhibition: Prevents fatty acid degradation while simultaneously promoting synthesis.
Elongation: Palmitate can be elongated in the ER or mitochondria, producing longer chain fatty acids.
Desaturases: These enzymes introduce double bonds into fatty acid chains. Humans cannot introduce double bonds beyond the 9th carbon from the methyl end, requiring dietary essential fatty acids.

Triacylglycerol Synthesis

Glycerol Phosphate: Obtained from dihydroxyacetone phosphate (DHAP) in liver and adipose tissue, or glycerol in the liver.
Integration of Lipid and Carbohydrate Metabolism: High insulin levels promote lipogenesis by stimulating pyruvate dehydrogenase and inducing enzymes involved in fatty acid synthesis.

Steatorrhea

Frothy, Foul-Smelling Stools: Resulting from undigested fat.
Causes: Pancreatic lipase deficiency, bile duct obstruction, or cystic fibrosis.
Consequences: Impaired absorption of fat-soluble vitamins (A, D, E, and K) and essential fatty acids.

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Description

Explore the complex process of dietary lipid digestion, absorption, and transport in this informative quiz. Learn about the roles of lipases, emulsification by bile salts, and the formation of micelles in the small intestine. Test your knowledge on how different fatty acids are processed and absorbed in the body.