Lippincott's Biochemistry Chapter 15 - Dietary Lipid Metabolism
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Questions and Answers

What role do lipases play in infants regarding lipid digestion?

  • They are only important for the digestion of animal fats.
  • They are primarily responsible for emulsifying lipids in the stomach.
  • They assist in the digestion of lipid molecules when pancreatic lipase is absent. (correct)
  • They prevent the absorption of fatty acids from milk fat.

How does cystic fibrosis affect pancreatic function?

  • It leads to the degeneration of pancreatic tissue.
  • It results in thickened mucus that obstructs enzyme secretion. (correct)
  • It increases the production of pancreatic enzymes.
  • It enhances the secretion of chloride in the pancreas.

Which treatment is commonly employed for individuals with cystic fibrosis?

  • Replacement of pancreatic enzymes (correct)
  • Increased dietary fiber intake
  • Long-term corticosteroid therapy
  • Vitamin B12 injections

What is a significant implication of having the CFTR gene mutation in cystic fibrosis?

<p>Decreased secretion of chloride leading to dehydration of mucus. (A)</p> Signup and view all the answers

Which type of fatty acids do ungual and gastric lipases primarily degrade in individuals with pancreatic insufficiency?

<p>Short- to medium-chain fatty acids (B)</p> Signup and view all the answers

What is the primary outcome of the emulsification process during lipid digestion?

<p>Reduce the size of lipid droplets to allow enzyme action (A)</p> Signup and view all the answers

Which mechanism does NOT contribute to the emulsification of dietary lipids in the duodenum?

<p>Chemical digestion by pancreatic lipase (B)</p> Signup and view all the answers

How does cystic fibrosis impact lipid digestion?

<p>It leads to reduced bile salt efficacy (A)</p> Signup and view all the answers

What is the main role of pancreatic lipase in lipid digestion?

<p>To hydrolyze triacylglycerols into free fatty acids and monoacylglycerol (C)</p> Signup and view all the answers

What primary products result from the hydrolysis of triacylglycerols by pancreatic lipase?

<p>2-monoacylglycerol (2-MAG) and free fatty acids (FFA) (D)</p> Signup and view all the answers

What is the function of the amphipathic nature of bile salts in lipid digestion?

<p>To interact with both lipid droplets and aqueous solutions (D)</p> Signup and view all the answers

Which factor does NOT affect the secretion of pancreatic enzymes?

<p>Volume of bile released (A)</p> Signup and view all the answers

In the context of enzyme replacement therapy for individuals with cystic fibrosis, what is a primary goal?

<p>Supplement pancreatic enzyme deficiencies (B)</p> Signup and view all the answers

What role do mixed micelles play in lipid absorption?

<p>They facilitate the transport of hydrophobic lipids to the brush border membrane. (D)</p> Signup and view all the answers

What is the primary function of lipases in the digestive process?

<p>To break down triglycerides into fatty acids and monoglycerides (D)</p> Signup and view all the answers

How does cystic fibrosis affect lipid absorption?

<p>It leads to thicker pancreatic secretions, hindering lipase activity. (D)</p> Signup and view all the answers

What is a potential treatment strategy for individuals with cystic fibrosis regarding lipid digestion?

<p>Using enzyme replacement therapy to provide missing digestive enzymes (A)</p> Signup and view all the answers

What is the primary mechanism of emulsification in the digestive system?

<p>The action of bile salts which disperse fats into smaller droplets (D)</p> Signup and view all the answers

Which component of mixed micelles aids in the transport of lipids across the unstirred water layer?

<p>Hydrophilic surface properties (B)</p> Signup and view all the answers

Which of the following statements about emulsification processes is correct?

<p>Bile salts are key emulsifiers that reduce the interfacial tension of lipids. (C)</p> Signup and view all the answers

Which physiological barrier must lipids cross for absorption in the intestine?

<p>Cell membrane of enterocytes (B)</p> Signup and view all the answers

What aspect of the brush border membrane enhances lipid absorption?

<p>Microvilli-rich structure (A)</p> Signup and view all the answers

Which of the following is a critical condition for lipid solubility and absorption in the intestine?

<p>Formation of micelles (D)</p> Signup and view all the answers

What is the primary function of bile salts during lipid digestion?

<p>To emulsify dietary lipids (D)</p> Signup and view all the answers

Which enzyme is particularly important for breaking down triglycerides into free fatty acids?

<p>Pancreatic lipase (A)</p> Signup and view all the answers

What implication does cystic fibrosis have on lipid digestion?

<p>It decreases the production of pancreatic enzymes. (C)</p> Signup and view all the answers

What aspect of enzyme replacement therapy is crucial for patients with impaired pancreatic function?

<p>It provides necessary digestive enzymes. (D)</p> Signup and view all the answers

Which type of fatty acids are primarily hydrolyzed by pancreatic enzymes during digestion?

<p>Short- and medium-chain fatty acids (D)</p> Signup and view all the answers

How does emulsification contribute to lipid digestion?

<p>It increases the surface area of lipids for enzyme action. (A)</p> Signup and view all the answers

What is the primary function of pancreatic lipase in lipid digestion?

<p>Catalyzes the hydrolysis of triglycerides. (D)</p> Signup and view all the answers

Which enzyme is responsible for hydrolyzing cholesteryl esters into cholesterol and free fatty acids?

<p>Pancreatic cholesteryl ester hydrolase (A)</p> Signup and view all the answers

What is the role of 2-monoacylglycerol in lipid digestion?

<p>It is a product of triglyceride hydrolysis. (C)</p> Signup and view all the answers

Which biochemical component do pancreatic enzymes primarily break down during lipid digestion?

<p>Triglycerides (D)</p> Signup and view all the answers

What role does co/lipase play in lipid digestion?

<p>Supports pancreatic lipase by anchoring it at the lipid-aqueous interface. (C)</p> Signup and view all the answers

How does cystic fibrosis affect lipid absorption?

<p>It results in significant malabsorption of fats due to pancreatic deficiency. (A)</p> Signup and view all the answers

What does hydrolysis of triglycerides primarily yield in the context of lipid digestion?

<p>Free fatty acids and glycerol (D)</p> Signup and view all the answers

What is the primary mechanism by which Ortistat promotes weight loss?

<p>Inhibits gastric and pancreatic lipases, reducing fat absorption. (B)</p> Signup and view all the answers

What is the order of digestion for lipids in the small intestine?

<p>Emulsification, enzyme action, absorption (C)</p> Signup and view all the answers

Why are bile salts necessary for optimal activity of some enzymes during lipid digestion?

<p>They enhance the solubility and emulsification of lipids. (A)</p> Signup and view all the answers

What product results from the action of phospholipase A2 on phosphatidylcholine?

<p>Lysophosphatidylcholine (A)</p> Signup and view all the answers

What is true about the secretion of co/lipase in its inactive form?

<p>It is secreted as procolipase and activated by trypsin. (C)</p> Signup and view all the answers

What distinguishes the esterified form of dietary cholesterol from the free form?

<p>Esterified cholesterol is less common, making up 5%-10% of dietary cholesterol. (B)</p> Signup and view all the answers

What happens to the remaining fatty acid at carbon 1 of a phospholipid after the action of phospholipase A2?

<p>It is removed by lysophospholipase, yielding a glycerol backbone. (C)</p> Signup and view all the answers

What facilitates the transport of hydrophobic lipids through the unstirred water layer to the brush border membrane?

<p>Hydrophilic surface of micelles (B)</p> Signup and view all the answers

What characterizes the brush border membrane of enterocytes?

<p>It possesses a microvilli-rich structure. (C)</p> Signup and view all the answers

Which process occurs after mixed micelles approach the brush border membrane?

<p>Absorption into enterocytes (D)</p> Signup and view all the answers

Which statement correctly describes the role of bile salts in lipid absorption?

<p>Their action is crucial for emulsification and absorption. (D)</p> Signup and view all the answers

What is the relationship between the unstirred water layer and lipid absorption?

<p>It acts as a barrier to lipid absorption. (A)</p> Signup and view all the answers

What types of lipids primarily consist of triacylglycerol?

<p>Three fatty acids esterified to a glycerol (B)</p> Signup and view all the answers

Which enzyme plays a significant role in lipid digestion within the stomach?

<p>Lingual lipase (D)</p> Signup and view all the answers

What condition is necessary for the optimal activity of gastric lipase during digestion?

<p>pH between 4 and 6 (A)</p> Signup and view all the answers

The remaining dietary lipids aside from triacylglycerol include which of the following?

<p>Cholesterol and cholesteryl esters (B)</p> Signup and view all the answers

What is the primary function of lingual lipase during the process of lipid digestion?

<p>Initiating the breakdown of triglycerides (D)</p> Signup and view all the answers

During lipid digestion, what process occurs primarily in the small intestine?

<p>Absorption of fatty acids (C)</p> Signup and view all the answers

What type of lipids is predominantly involved in the dietary lipid absorption process?

<p>Triacylglycerols (C)</p> Signup and view all the answers

What happens when pancreatic lipase encounters bile salts?

<p>It requires co/lipase to restore its activity. (B)</p> Signup and view all the answers

Which enzyme is responsible for converting cholesteryl esters into cholesterol and free fatty acids?

<p>Pancreatic cholesteryl ester hydrolase (D)</p> Signup and view all the answers

What is the primary role of procolipase in lipid digestion?

<p>To restore activity to pancreatic lipase (B)</p> Signup and view all the answers

What forms the primary substrate for phospholipase A2 during lipid digestion?

<p>Phospholipids (B)</p> Signup and view all the answers

How is co/lipase secreted before it is activated for lipid digestion?

<p>As a zymogen (B)</p> Signup and view all the answers

What distinguishes free dietary cholesterol from its esterified form?

<p>Free cholesterol can be hydrolyzed directly by lipases. (C)</p> Signup and view all the answers

Which enzyme requires bile salts for optimum activity during the degradation of dietary lipids?

<p>All of the above (D)</p> Signup and view all the answers

What is the fate of the lysophospholipid generated from the action of phospholipase A2?

<p>It can be absorbed, further degraded, or excreted. (A)</p> Signup and view all the answers

What is the mechanism of action for the drug Ortistat in relation to lipid metabolism?

<p>It decreases fat absorption by inhibiting pancreatic lipase. (C)</p> Signup and view all the answers

What is the consequence of mutations to the CFTR protein in cystic fibrosis?

<p>Thickened mucus in pancreatic ducts (C)</p> Signup and view all the answers

Which type of fatty acids are more effectively degraded by ungual and gastric lipases in individuals with pancreatic insufficiency?

<p>Short- to medium-chain fatty acids (D)</p> Signup and view all the answers

How does cystic fibrosis primarily affect the secretion of digestive enzymes?

<p>By preventing enzymes from reaching the intestine (A)</p> Signup and view all the answers

What is the primary purpose of enzyme replacement therapy in cystic fibrosis patients?

<p>To facilitate fat absorption (C)</p> Signup and view all the answers

Which genetic inheritance pattern is associated with cystic fibrosis?

<p>Autosomal-recessive inheritance (A)</p> Signup and view all the answers

What is a key consequence of the CFTR protein's dysfunction in cystic fibrosis patients?

<p>Reduced secretion of digestive enzymes (D)</p> Signup and view all the answers

Which population has the highest prevalence of cystic fibrosis?

<p>Caucasians of Northern European ancestry (A)</p> Signup and view all the answers

What complication arises due to the thickened mucus in cystic fibrosis patients?

<p>Malabsorption of fat-soluble vitamins (B)</p> Signup and view all the answers

What role do ungual and gastric lipases play in lipid digestion for individuals with cystic fibrosis?

<p>They assist in degrading TAG molecules (C)</p> Signup and view all the answers

Which hormone is primarily responsible for stimulating the contraction of the gallbladder and the release of bile?

<p>Cholecystokinin (CCK) (B)</p> Signup and view all the answers

What is the primary effect of secretin on pancreatic function?

<p>Promotes the release of bicarbonate solution (A)</p> Signup and view all the answers

What is the primary product of lipid digestion taken up by enterocytes in the jejunum?

<p>2-MAG and free fatty acids (C)</p> Signup and view all the answers

What is the role of bile salts in the digestive process?

<p>They form mixed micelles to aid in lipid absorption. (D)</p> Signup and view all the answers

Which structure is primarily formed by the coalescence of hydrophobic and hydrophilic lipid groups during digestion?

<p>Micelles (D)</p> Signup and view all the answers

How does cholecystokinin (CCK) affect gastric motility?

<p>It reduces gastric motility. (B)</p> Signup and view all the answers

What type of solution does secretin cause the pancreas to release?

<p>A bicarbonate-rich solution (D)</p> Signup and view all the answers

Which components make up the mixed micelles in the jejunum?

<p>Bile salts, fat-soluble vitamins, and lipid digestion products (A)</p> Signup and view all the answers

What does the release of bile primarily facilitate during digestion?

<p>The emulsification of fats (D)</p> Signup and view all the answers

Which of the following conditions triggers the release of cholecystokinin (CCK)?

<p>Presence of lipids and partially digested proteins (A)</p> Signup and view all the answers

Match the types of lipids with their characteristics:

<p>Triacylglycerol = Major energy source and stored in adipocytes Glycerophospholipid = Key component of cellular membranes Steroid = Regulates homeostasis via hormones Fat-soluble vitamins = Essential for various biochemical functions</p> Signup and view all the answers

Match the functions of bile salts with their roles in digestion:

<p>Emulsification = Increases lipid surface area for enzyme action Micelle formation = Facilitates lipid absorption in the intestine Hydrophobic barrier = Separates aqueous and lipid components in the body Activation of lipases = Enhances the efficacy of lipid-digesting enzymes</p> Signup and view all the answers

Match the outcomes of lipid digestion with their corresponding products:

<p>Triacylglycerols = Broken down into free fatty acids and glycerol Phospholipids = Hydrolyzed into lyso-phospholipids and fatty acids Cholesteryl esters = Converted into free cholesterol and fatty acids Triglycerides = Yields 2-monoacylglycerol and free fatty acids</p> Signup and view all the answers

Match the lipid-related conditions with their implications:

<p>Atherosclerosis = Related to imbalances in lipid metabolism Diabetes = Associated with impaired lipid utilization Obesity = Result of excessive lipid storage Cystic fibrosis = Affects pancreatic function and lipid digestion</p> Signup and view all the answers

Match the enzymes with their specific roles in lipid metabolism:

<p>Pancreatic lipase = Digests dietary triacylglycerols Phospholipase A2 = Breaks down phospholipids Co/lipase = Activates pancreatic lipase for efficient digestion Cholesterol esterase = Hydrolyzes cholesteryl esters</p> Signup and view all the answers

Match the following lipid types with their primary characteristics:

<p>Triacylglycerol (TAG) = Consists of three fatty acids esterified to glycerol Cholesterol = A sterol involved in membrane structure Phospholipids = Make up the cell membrane bilayer Free Fatty Acids (FFA) = Nonesterified fatty acids in the diet</p> Signup and view all the answers

Match the following organs with their role in lipid digestion:

<p>Stomach = Initial limited digestion of lipids Small intestine = Completes digestion of dietary lipids Tongue = Source of lingual lipase Pancreas = Secretes enzymes for lipid digestion</p> Signup and view all the answers

Match the following enzymes with their action in lipid digestion:

<p>Lingual lipase = Begins lipid digestion in the stomach Gastric lipase = Secreted by gastric mucosa Pancreatic lipase = Hydrolyzes triglycerides in the small intestine Phospholipase A2 = Breaks down phosphatidylcholine</p> Signup and view all the answers

Match the following lipid digestion processes with their locations:

<p>Emulsification = Occurs in the small intestine Initial digestion = Takes place in the stomach Hydrolysis of triglycerides = Performed by pancreatic enzymes Formation of mixed micelles = Facilitates lipid absorption in the intestine</p> Signup and view all the answers

Match the following features with their respective lipids:

<p>Free Fatty Acids = Present in nonesterified form in the diet Cholesteryl esters = Formed from cholesterol and fatty acids Sphingolipids = Complex molecules containing a sphingosine backbone Phospholipids = Contain a phosphate group in addition to fatty acids</p> Signup and view all the answers

Flashcards

Lipid Emulsification

The process that increases the surface area of lipid droplets in the small intestine, allowing digestive enzymes to work more effectively.

Conjugated Bile Salts

Amphipathic molecules derived from cholesterol that act as detergents during lipid digestion.

Pancreatic Lipase

An enzyme that hydrolyzes triglycerides (TAG) into 2-monoacylglycerol (2-MAG) and fatty acids (FFA).

Dietary TAG

Triglycerides (TAG) found in food that need to be broken down for absorption.

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Emulsification Mechanism

Two ways of increasing the surface area of fat droplets: detergents (bile salts) and mechanical mixing (peristalsis).

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Hydrolysis

The chemical process of breaking down molecules by adding water.

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2-Monoacylglycerol (2-MAG)

A product of triglyceride digestion.

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Fatty Acids (FFA)

Released during the breakdown of triglycerides by enzymes.

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Small Intestine

Part of the digestive tract where most lipid digestion occurs.

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Enterocytes

Cells lining the intestinal villi, responsible for absorbing digested nutrients.

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Micelle solubility in intestinal lumen

Mixed micelles, formed with bile salts, are soluble in the watery environment of the small intestine, aiding lipid absorption.

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Brush border membrane location

The brush border membrane is the absorptive surface on the enterocytes, lined with microvilli, where lipids are primarily absorbed.

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Unstirred water layer

A thin, stationary layer of water on the surface of the intestinal lining, impeding the direct movement of hydrophobic lipids.

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Micelle's hydrophobic core

The lipid molecules within a mixed micelle aggregate to form a hydrophobic interior, carrying the fats through the aqueous environment.

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Bile salts absorption site

Bile salts are absorbed in the ileum (the lower small intestine).

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Lipid absorption mechanism

Hydrophilic micelles facilitate the transport of hydrophobic lipids through the unstirred water layer to the enterocyte brush border membrane for absorption.

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Lipid Digestion

The process where dietary fats are broken down into smaller molecules for absorption.

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Small Intestine

Part of the digestive system where most lipid digestion occurs.

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Bile Salts

Substances that emulsify fats, breaking them into smaller droplets, increasing enzyme accessibility.

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Pancreatic Enzymes

Enzymes produced by the pancreas to break down dietary lipids into their components.

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Micelles

Aggregates of fatty acids, monoglycerides, cholesterol, and other products of lipid digestion, that facilitate absorption by cells.

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Free Fatty Acids

Individual fatty acids released from triglycerides during digestion.

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2-Monoacylglycerol

A glycerol molecule with one fatty acid attached, a product of fat digestion.

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Triglycerides (TAG)

The main form of fat storage in the body, composed of glycerol attached to three fatty acids.

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Cholesterol

A type of lipid crucial for cell structure and hormone production, broken down during digestion.

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Fatty Acid Chain Length

The length of the hydrocarbon chain of a fatty acid, influencing its digestion efficiency.

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Cystic Fibrosis (CF)

A genetic disease causing thick mucus buildup in the lungs and pancreas, disrupting enzyme delivery.

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Pancreatic insufficiency

Inability of the pancreas to produce enough digestive enzymes, often linked to CF.

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CFTR protein

A chloride channel protein whose malfunction is linked to CF, impacting digestive enzyme function.

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Lipid digestion in infants

Lipid digestion heavily relies on lipases (e.g., lingual and gastric lipases) when milk is the primary energy source.

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Role of Lipases

Lipases are crucial in breaking down fats, particularly important in infants and individuals with disrupted pancreatic function.

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Autosomal Recessive Disorder

Genetic condition requiring two mutated copies of a gene to cause the disease.

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Pancreatic lipase

A digestive enzyme in pancreatic secretions that efficiently breaks down fats.

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Colipase

A pancreatic protein that binds lipase and anchors it to lipid surfaces, activating it in presence of inhibitors such as bile salts.

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Procolipase

The inactive form of colipase, activated by trypsin in the intestine.

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Cholesteryl ester hydrolase

An enzyme that breaks down cholesterol esters into cholesterol and free fatty acids (FFAs).

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Phospholipase A2

An enzyme that removes a fatty acid from a phospholipid, producing lysophospholipid.

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Lysophospholipase

An enzyme that removes another fatty acid from lysophospholipid.

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Orlistat

An anti-obesity drug that inhibits gastric and pancreatic lipases.

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Bile salts

Substrates that increase the activity of cholesteryl ester hydrolase and phospholipase A2.

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Dietary Cholesterol

Most present in free form, with a small percentage in esterified form.

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Lipid Digestion in Stomach

Limited lipid digestion occurs in the stomach. It's catalyzed by lingual lipase (from tongue) and gastric lipase (from stomach lining). These enzymes are acid-stable and function best at pH 4-6.

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Lingual Lipase

An enzyme in the mouth (tongue) that helps break down dietary fats, specifically lipids.

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Gastric Lipase

Enzyme in the stomach that aids in breaking down dietary fats.

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Dietary Lipids

Lipids consumed through foods, mainly triacylglycerols (TAGs), cholesterol, cholesteryl esters, phospholipids, and free fatty acids (FFAs).

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Triacylglycerols (TAGs)

The primary fat in our diet, composed of three fatty acids attached to a glycerol molecule.

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Lipid digestion in infants

Lipid digestion in infants relies heavily on lipases like lingual and gastric lipases, as milk fat is a primary energy source.

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Pancreatic insufficiency

The pancreas's inability to produce enough digestive enzymes, often associated with conditions like cystic fibrosis (CF).

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Cystic Fibrosis (CF)

A genetic disorder causing thick mucus buildup in organs, impeding enzyme delivery, especially to the intestine; this results in pancreatic insufficiency, thereby affecting lipid digestion.

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CFTR protein

A chloride channel protein whose malfunction is linked to cystic fibrosis (CF), leading to thickened mucus and impacting pancreatic enzyme function; this subsequently affects lipid digestion.

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Role of lipases

Lipases are crucial in breaking down fats, particularly important in infants and individuals with pancreatic dysfunction.

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Pancreatic lipase

An enzyme that plays a key role in lipid digestion and is an important constituent of pancreatic juice. It aids in the breakdown of triglycerides.

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Pancreatic Lipase Function

Efficiently breaks down fats in pancreatic secretions.

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Colipase Role

Binds pancreatic lipase, anchoring it to lipid surfaces and activating it in the presence of inhibitors.

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Procolipase

Inactive form of colipase, activated by trypsin in intestines.

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Cholesteryl Ester Hydrolase

Enzyme breaking down cholesterol esters into cholesterol and fatty acids.

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Phospholipase A2

Removes fatty acid from phospholipids, creating lysophospholipids.

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Lysophospholipase

Removes another fatty acid from lysophospholipids.

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Orlistat's Function

Inhibits gastric and pancreatic lipases, decreasing fat absorption and promoting weight loss.

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Bile Salts Lipid Digestion Role

Increase activity of enzymes that breakdown fats (cholesteryl ester hydrolase and phospholipase A2).

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Dietary Cholesterol Form

Mainly free / non-esterified, small amount esterified.

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Cholecystokinin (CCK)

A peptide hormone produced by the small intestine in response to lipids and partially digested proteins, stimulating gallbladder contraction and pancreatic enzyme release; it also slows gastric motility.

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Secretin

A peptide hormone produced by the small intestine in response to low pH chyme, triggering pancreatic bicarbonate release to neutralize intestinal contents.

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Mixed micelles

Disc-shaped clusters of lipids, including fatty acids, monoglycerides, cholesterol, and bile salts, that aid lipid absorption in the intestines.

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Lipid digestion products

Free fatty acids (FFAs), monoglycerides (2-MAG), and free cholesterol absorbed in the small intestine are the key products of dietary lipid digestion.

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Enterocytes

Cells lining the villi of the small intestine, responsible for absorbing nutrients, such as absorbed lipids.

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Mixed micelles

Aggregates of bile salts, fatty acids, monoglycerides, and cholesterol that are soluble in the aqueous environment of the small intestines.

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Intestinal lumen

The space inside the small intestine, where food and digestive juices mix.

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Brush border membrane

The surface of the intestinal cells (enterocytes) facing the intestinal lumen, covered in microvilli, facilitating absorption.

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Unstirred water layer

A thin layer of water near the brush border membrane, which slows down the movement of hydrophobic lipids.

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Lipid absorption mechanism

Mixed micelles facilitate the transport of hydrophobic fats through the unstirred water layer to the brush border membrane for absorption.

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Bile salts absorption site

Bile salts are absorbed in the terminal ileum (the last part of the small intestine).

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Lipid digestion in stomach

Limited lipid digestion happens in the stomach, primarily catalyzed by lingual and gastric lipases. These enzymes are acid-stable and function best at a pH of 4-6.

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Lingual lipase

An enzyme located in the mouth (tongue) that aids in breaking down dietary fats.

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Gastric lipase

An enzyme found in the stomach that assists in the breakdown of dietary fats.

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Dietary lipids

Lipids consumed through food, primarily triacylglycerols, cholesterol, cholesteryl esters, phospholipids, and free fatty acids.

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Triacylglycerols (TAGs)

The primary fat in our diet, composed of three fatty acids attached to a glycerol molecule.

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Dietary Lipids

Lipids consumed through foods, mainly triacylglycerols (TAGs), cholesterol, cholesteryl esters, phospholipids, and free fatty acids (FFAs).

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Triacylglycerols (TAGs)

The primary fat in our diet, composed of three fatty acids attached to a glycerol molecule.

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Lipid Digestion

The process where dietary fats are broken down into smaller molecules for absorption.

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Small Intestine

Part of the digestive system where most lipid digestion occurs.

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Bile Salts

Substances that emulsify fats, breaking them into smaller droplets, increasing enzyme accessibility.

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Pancreatic Enzymes

Enzymes produced by the pancreas to break down dietary lipids into their components.

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Micelles

Aggregates of fatty acids, monoglycerides, cholesterol, and other products of lipid digestion, that facilitate absorption by cells.

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Free Fatty Acids

Individual fatty acids released from triglycerides during digestion.

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2-Monoacylglycerol

A glycerol molecule with one fatty acid attached, a product of fat digestion.

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Cholesterol

A type of lipid crucial for cell structure and hormone production, broken down during digestion.

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Lipid absorption mechanism

Mixed micelles facilitate the transport of hydrophobic fats through the unstirred water layer to the brush border membrane for absorption.

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Bile salts absorption site

Bile salts are absorbed in the terminal ileum (the last part of the small intestine).

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Study Notes

Lipid Metabolism Overview

  • Lipids are hydrophobic organic molecules
  • Important for energy, cell membrane structure, and hormone production
  • Imbalances can cause major health issues like atherosclerosis, diabetes, and obesity

Lipid Digestion, Absorption, Secretion, and Utilization

  • Digestion in the stomach: Limited lipid digestion by lingual and gastric lipases. Acid stable, optimal pH 4-6
  • Digestion in the small intestine: Emulsification is crucial for increasing surface area for enzyme action.
    • Bile salts (from liver and gallbladder) act as detergents, emulsifying lipids
    • Pancreatic lipase breaks down triacylglycerols (TAGs) into fatty acids (FAs) and 2-monoacylglycerols (2-MAGs)
    • Colipase anchors lipase to lipid-aqueous interface.
    • Orlistat, a drug, inhibits lipases to decrease fat absorption.

Degradation by pancreatic enzymes

  • TAG degradation: Pancreatic lipase breaks down TAGs into 2-MAG and fatty acids.
  • Cholesterol ester degradation: Pancreatic cholesterol ester hydrolase breaks down cholesteryl esters into cholesterol and fatty acids
  • Phospholipid degradation: Phospholipase A2 breaks down phospholipids, produces lysophospholipids
  • Control of enzyme secretion: Hormone-regulated processes (cholecystokinin (CCK) and secretin).

Absorption by Enterocytes

  • Mixed micelles: Formed by FAs, 2-MAG, cholesterol, bile salts, vitamins form mixed micelles to allow lipid absorption.
  • Absorption of FA: Short- and medium-chain FAs are absorbed directly by enterocytes into the blood
  • Absorption of TAG and Cholesterol esters: Resynthesized into TAG and cholesterol esters, packaged into chylomicrons, enter lymphatic system, then blood
  • Removal of chylomicrons: Degraded by lipoprotein lipase in the capillaries
  • Fate of fatty acids: Can be used for energy production or storage in adipose tissue.
  • Fate of glycerol: Can be used in glycolysis or gluconeogenesis, involved in energy production & storage
  • Fate of Chylomicron remnants: Recycled back to liver

Lipid Malabsorption

  • Causes:
    • Cystic fibrosis (CF)
    • Short bowel syndrome
  • Results in increased lipid (including fat-soluble vitamins) in the feces (steatorrhea)

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Lippincott's Biochemistry Chapter 15 - Dietary Lipid Metabolism PDF

Description

This quiz covers the essential aspects of lipid metabolism, including digestion, absorption, and the roles of enzymes and bile salts. Understand the implications of lipid imbalances and the impact on health conditions such as diabetes and obesity. Test your knowledge on how lipids are processed in the body and their significance in energy and hormone production.

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