Chapyer 15

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Questions and Answers

What primary role do bile salts play in the small intestine during lipid digestion?

Converting cholesteryl esters into cholesterol

Stimulating the pancreas to release digestive enzymes

Directly breaking down triacylglycerols

Emulsifying fats to increase their surface area (correct)

Which enzyme is primarily responsible for breaking down triacylglycerol into 2-monoacylglycerol and free fatty acids?

Cholesteryl ester hydrolase

Phospholipase

Lipase

Pancreatic lipase (correct)

Which of the following is NOT an end product of lipid digestion?

Chylomicrons (correct)

Monoacylglycerol

Free fatty acids

Cholesterol

What condition can lead to a lack of pancreatic lipase, affecting the absorption of fats?

Cystic Fibrosis Signup and view all the answers

Which mutation is most commonly associated with Cystic Fibrosis?

Mutation in the CFTR gene affecting chloride regulation Signup and view all the answers

What is one of the primary dietary recommendations for patients suffering from Cystic Fibrosis?

Fat-soluble vitamin supplementation Signup and view all the answers

Which of the following enzymes breaks down cholesteryl ester into cholesterol and free fatty acids?

Cholesteryl ester hydrolase Signup and view all the answers

Why are CF patients at increased risk of lung infections?

Defective chloride transport leading to thick mucus in the lungs Signup and view all the answers

Where does the emulsification of dietary lipids primarily occur?

Duodenum Signup and view all the answers

What two complementary mechanisms accomplish emulsification?

Detergent properties of bile salts and mechanical mixing due to peristalsis Signup and view all the answers

What are bile salts derivatives of?

Cholesterol Signup and view all the answers

Which enzyme preferentially removes fatty acids from carbons 1 and 3 of TAG molecules?

Pancreatic lipase Signup and view all the answers

What is the main product of TAG hydrolysis besides free fatty acids?

2-monoacylglycerol Signup and view all the answers

What hormone activates pro-colipase to colipase in the intestine?

Trypsin Signup and view all the answers

What percentage of dietary cholesterol is in the esterified form?

10-15% Signup and view all the answers

Which enzyme hydrolyzes cholesteryl esters?

Cholesteryl ester hydrolase Signup and view all the answers

Which of the following enzymes requires bile salts for optimal activity?

Phospholipase A2 Signup and view all the answers

What does phospholipase A2 remove from carbon 2 of a phospholipid?

Fatty acid Signup and view all the answers

Which one of the following is the primary site of lipid absorption in the intestine?

Brush border membrane Signup and view all the answers

What is the role of mixed micelles in lipid absorption?

They transport hydrophobic lipids through the unstirred water layer. Signup and view all the answers

Which enzyme is responsible for the conversion of fatty acids to their activated form?

Fatty acyl-CoA synthetase Signup and view all the answers

Where are bile salts primarily absorbed during lipid metabolism?

Ileum Signup and view all the answers

Which hormone decreases gastric motility in response to the presence of lipids in the small intestine?

Cholecystokinin (CCK) Signup and view all the answers

Which cells release bicarbonate in response to secretin?

Liver and pancreatic cells Signup and view all the answers

Which enzyme complex synthesizes TAGs in the enterocytes?

TAG synthetase Signup and view all the answers

What is the primary product of lipid digestion in the jejunum?

Free fatty acids Signup and view all the answers

Which enzyme is responsible for the initial digestion of triacylglycerols in the stomach?

Lingual and gastric lipases Signup and view all the answers

Which hormone stimulates the secretion of bicarbonate from the pancreas?

Secretin Signup and view all the answers

What is the primary role of mixed micelles in the digestion of dietary lipids?

Aiding in the absorption of dietary lipids by intestinal mucosal cells Signup and view all the answers

What characteristic protein is associated with the assembly of lipids in intestinal mucosal cells?

Apo B-48 Signup and view all the answers

Which of the following is NOT a hydrophobic substrate involved in lipid metabolism?

Glucose Signup and view all the answers

Where are chylomicrons primarily secreted after their formation in intestinal mucosal cells?

Lymphatic system Signup and view all the answers

Which enzyme catalyzes the initial digestion of dietary lipids in the stomach?

Lingual lipase Signup and view all the answers

Which type of fatty acids are the primary target of lingual lipase?

Short- or medium-chain fatty acids Signup and view all the answers

What percentage of daily lipid intake by U.S. adults is normally triacylglycerol (TAG)?

90% Signup and view all the answers

To what class of biological molecules do prostaglandins and steroid hormones belong?

Lipids Signup and view all the answers

Which of the following is NOT a form in which body lipids are found?

Fatty acid droplets in red adipocytes Signup and view all the answers

Which one of the following lipids is NOT a primary component of the remainder of dietary lipids besides triacylglycerol?

Glycolipids Signup and view all the answers

Which enzyme is primarily responsible for the esterification of cholesterol to a fatty acid?

Acyl CoA:cholesterol acyltransferase Signup and view all the answers

What is the primary role of lipids in the body besides serving as a major energy source?

Forming the hydrophobic barrier in cells and subcellular structures Signup and view all the answers

Which of the following is a clinical problem associated with deficiencies or imbalances in lipid metabolism?

Atherosclerosis Signup and view all the answers

What happens to short- and medium-chain length fatty acids after they enter the enterocytes?

They are released into the portal circulation and carried to the liver by serum albumin Signup and view all the answers

Which types of fatty acids can be taken up by enterocytes without the aid of mixed micelles?

Short- and medium-chain length fatty acids Signup and view all the answers

What is one of the roles of acyltransferases in lipid metabolism?

They reacylate lysophospholipids to form phospholipids Signup and view all the answers

What does lipid malabsorption typically result in?

Steatorrhea Signup and view all the answers

What characteristic molecule is a part of the thin layer surrounding lipid droplets during secretion from enterocytes?

Apolipoprotein B-48 Signup and view all the answers

What is the primary function of the outer layer surrounding newly resynthesized triacylglycerols and cholesteryl esters in enterocytes?

To prevent the aggregation of multiple lipid particles Signup and view all the answers

Which process is depicted in Figure 15.6 of the described text?

Assembly and secretion of chylomicrons by intestinal mucosal cells Signup and view all the answers

What is the primary role of the microsomal TAG transfer protein?

Assembly of TAG-rich apolipoprotein B-containing lipoprotein particles Signup and view all the answers

What is the name of the lymph that appears milky after a lipid-rich meal?

Chyle Signup and view all the answers

Which enzyme is responsible for breaking down triacylglycerol in chylomicrons?

Lipoprotein lipase Signup and view all the answers

In what location does the hydrolysis of TAG primarily occur?

Capillaries of skeletal muscle and adipose tissues Signup and view all the answers

What rare disorder is caused by a deficiency of lipoprotein lipase or its coenzyme apolipoprotein C-II?

Type I hyperlipoproteinemia Signup and view all the answers

What happens to the free fatty acids after hydrolysis of TAG?

They are transported in blood by serum albumin Signup and view all the answers

What is the fate of glycerol released from TAG?

It is used exclusively by the liver to produce glycerol 3-phosphate Signup and view all the answers

After the majority of TAG is removed from chylomicrons, what do the chylomicron remnants contain?

Cholesteryl esters, phospholipids, apolipoproteins, and fat-soluble vitamins Signup and view all the answers

What can happen if the removal of chylomicron remnants by the liver is decreased?

Accumulation in the plasma Signup and view all the answers

What condition is associated with impaired binding of chylomicron remnants to their receptors in the liver?

Type III hyperlipoproteinemia Signup and view all the answers

Which enzyme is responsible for the degradation of cholesteryl esters in the small intestine?

Cholesteryl esterase Signup and view all the answers

What compound is NOT a primary product resulting from the enzymatic degradation of dietary lipid?

Apolipoprotein B-48 Signup and view all the answers

Which statement about emulsification of dietary lipids is correct?

Bile salts act as a detergent in the small intestine. Signup and view all the answers

Which of the following enzymes is not secreted by the pancreas?

Gastric lipase Signup and view all the answers

What is the role of mixed micelles in lipid digestion?

Facilitate absorption by enterocytes Signup and view all the answers

In cases of steatorrhea, what is observed?

Malabsorption of dietary fat Signup and view all the answers

What happens to short- and medium-chain fatty acids after absorption?

They are absorbed directly into the blood. Signup and view all the answers

Which hormone stimulates the release of bile from the gallbladder?

Cholecystokinin (CCK) Signup and view all the answers

A deficiency in which protein component can impact the formation of chylomicrons?

Apolipoprotein B-48 Signup and view all the answers

What is the consequence of a deficiency in the ability to degrade chylomicron components?

Accumulation of chylomicron remnants in blood Signup and view all the answers

Study Notes

Lipid Metabolism Overview

Lipids are a heterogeneous group of water-insoluble, hydrophobic organic molecules that are essential for energy storage and cell membrane structure.
Lipids are found in the body as membrane-associated lipids, triacylglycerol droplets in white adipocytes, lipoprotein particles in plasma, and bound to albumin.

Digestion and Absorption of Dietary Lipids

The average daily intake of lipids by U.S. adults is approximately 81g, with more than 90% being triacylglycerol (TAG).
Lipid digestion begins in the stomach with acid-stable lipases, and continues in the small intestine with pancreatic enzymes, such as pancreatic lipase, phospholipase A2, and cholesteryl ester hydrolase.
Emulsification of dietary lipids occurs in the small intestine, facilitated by bile salts and peristalsis, allowing for the formation of mixed micelles.
Mixed micelles contain lipids, bile salts, and fat-soluble vitamins, and facilitate the absorption of dietary lipids by intestinal mucosal cells (enterocytes).

Processing and Utilization of Dietary Lipids

The primary products of lipid digestion are free fatty acids, 2-monoacylglycerol, and unesterified cholesterol.
Short- and medium-chain length fatty acids are absorbed directly into the portal circulation and transported to the liver.
Long-chain fatty acids are re-esterified into TAG, phospholipids, and cholesteryl esters in the enterocytes, then packaged into chylomicrons and secreted into the lymphatic system.
Chylomicrons are transported to peripheral tissues, where TAG is broken down by lipoprotein lipase, releasing free fatty acids and glycerol.

Fate of Chylomicron Components

Free fatty acids are either oxidized for energy or re-esterified into TAG for storage.
Glycerol is used by the liver to produce glycerol 3-phosphate, which can enter glycolysis or gluconeogenesis.
Chylomicron remnants, containing cholesteryl esters, phospholipids, and apolipoproteins, are taken up by the liver and recycled.

Clinical Relevance

Deficiencies or imbalances in lipid metabolism can lead to clinical problems such as atherosclerosis and obesity.
Cystic fibrosis, an autosomal recessive disorder, can lead to pancreatic insufficiency, fat malabsorption, and difficulty in digesting fats.
Orlistat, an antiobesity drug, inhibits gastric and pancreatic lipases, decreasing fat absorption.### Lipid Digestion and Absorption
Lipid digestion involves resynthesis of TAG, CE, and PL, and synthesis of apolipoprotein B-48, which are assembled into chylomicrons.
Chylomicrons are released into the lymph and carried to the blood, transporting dietary lipids to peripheral tissues.
Short- and medium-chain fatty acids enter the blood directly.

Problems with Fat Absorption

Impaired fat absorption leads to steatorrhea.
Deficiency in degrading chylomicron components or removing their remnants leads to accumulation of chylomicrons in the blood.

Correct Statement about Lipid Digestion

Patients with cystic fibrosis have difficulties with digestion because their thickened pancreatic secretions are less able to reach the small intestine, the primary site of lipid digestion.

Important Facts

Acid-stable lipases (lingual and gastric lipase) use TAG with short to medium-chain fatty acids as substrates.
Emulsification occurs through peristalsis and bile salts that function as detergents.
Colipase restores activity to pancreatic lipase in the presence of inhibitory bile acids.
CCK (cholecystokinin) is the hormone that causes contraction of the gallbladder and release of stored bile.
Secretin causes release of bicarbonate.
Chylomicron formation requires synthesis of the protein apolipoprotein B-48.

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