Duodenal Function Quiz
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Questions and Answers

What is the primary function of the bicarbonate secreted into the small intestine?

  • To lubricate the intestinal contents
  • To neutralize acidic chyme (correct)
  • To produce digestive enzymes
  • To aid in fat digestion

The pancreas solely produces endocrine secretions.

False (B)

What are the two main types of secretory epithelium found in the pancreas?

Endocrine and exocrine

The fastest pacemaker in the small intestine is located in the ______.

<p>duodenum</p> Signup and view all the answers

Which enzyme secretion process involves inactive forms called zymogens?

<p>Pancreatic enzyme secretion (C)</p> Signup and view all the answers

Match the following pancreatic secretions with their purposes:

<p>Insulin = Regulates blood sugar levels Glucagon = Increases blood sugar levels Digestive enzymes = Break down nutrients Bicarbonate = Neutralizes stomach acid</p> Signup and view all the answers

Mucus secreted from intestinal goblet cells helps to protect the epithelium and lubricate gut contents.

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

Name the structure in the pancreas where digestive enzymes are produced.

<p>Acinar cells</p> Signup and view all the answers

What is the primary transport mechanism for fructose absorption in the intestine?

<p>Facilitated diffusion via GLUT5 (D)</p> Signup and view all the answers

What is the primary role of bile salts in fat digestion?

<p>Facilitate enzymatic fat digestion (B)</p> Signup and view all the answers

Cellulose is digestible by humans.

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

Bicarbonate secretion from the pancreas helps to neutralize stomach acid.

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

What role does amylase play in carbohydrate digestion?

<p>It breaks down long glucose polymers into smaller glucose chains and maltose.</p> Signup and view all the answers

Chylomicrons are absorbed into __________, the lymph vessels of the villi.

<p>lacteals</p> Signup and view all the answers

What enzyme converts inactive trypsinogen to active trypsin?

<p>enteropeptidase</p> Signup and view all the answers

Match the following types of digestive enzymes with their function:

<p>Endopeptidases = Attack peptide bonds within protein chains Exopeptidases = Release single amino acids from the ends of peptides Amylase = Breaks down starches into sugars Disaccharidases = Digest disaccharides into monosaccharides</p> Signup and view all the answers

The gallbladder stores and concentrates ________.

<p>bile</p> Signup and view all the answers

Which of the following best describes the primary product of protein digestion?

<p>Free amino acids, dipeptides, and tripeptides (B)</p> Signup and view all the answers

Match the following components with their roles in digestion:

<p>Trypsin = Activates pancreatic zymogens Bicarbonate = Neutralizes stomach acid Lipase = Digests triglycerides Cholesterol = Absorbed intact without digestion</p> Signup and view all the answers

What happens to bile salts when they reach the terminal section of the small intestine?

<p>They are reabsorbed and returned to the liver (B)</p> Signup and view all the answers

Shorter fatty acids can enter the bloodstream directly after absorption.

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

What type of transporters are used for glucose and galactose absorption in the intestine?

<p>Na+-dependent transporters</p> Signup and view all the answers

Colipase is required for the proper function of lipase in fat digestion.

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

Pancreatic and intestinal enzymes digest nucleic acids into __________ and __________.

<p>nucleotides, monosaccharides</p> Signup and view all the answers

What are the waste products of hemoglobin degradation found in bile?

<p>bilirubin</p> Signup and view all the answers

Match the following carbohydrates with their properties:

<p>Starch = Digestible storage carbohydrate in plants Cellulose = Indigestible fibrous component of plants Glycogen = Digestible storage carbohydrate in animals Sucrose = Disaccharide made of glucose and fructose</p> Signup and view all the answers

Bile salts may be converted back to bile acids by ________ in the colon.

<p>bacteria</p> Signup and view all the answers

What happens to the majority of oligopeptides once they enter intestinal epithelial cells?

<p>They are digested into individual amino acids. (C)</p> Signup and view all the answers

Which of the following is not a component of pancreatic secretion?

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

Match the process with its description:

<p>Emulsification = Breaks fat droplets into smaller particles Digestion = Chemical breakdown of nutrients Absorption = Uptake of nutrients into cells Secretion = Release of digestive enzymes and fluids</p> Signup and view all the answers

Dietary fiber is fully digested and absorbed by the human body.

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

The gallbladder is essential for normal digestion.

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

What main source of energy do enterocytes use instead of glucose?

<p>Glutamine</p> Signup and view all the answers

Name the channel responsible for bicarbonate secretion in the pancreas.

<p>CFTR</p> Signup and view all the answers

The pancreas secretes ___________ to neutralize stomach acid in the duodenum.

<p>bicarbonate</p> Signup and view all the answers

The initial coarse emulsion of fat is formed from the ________ leaving the stomach.

<p>aqueous chyme</p> Signup and view all the answers

Flashcards

Duodenal Secretions

The duodenum receives and mixes secretions from the liver, pancreas, and intestine, including digestive enzymes, bile, bicarbonate, mucus, and isotonic NaCl solution.

Intestinal Brush Border Enzymes

Enzymes that are anchored to the luminal cell membranes of intestinal epithelium and aid in digestion.

Pancreatic Enzymes

Digestive enzymes produced by the exocrine pancreas, often secreted as inactive precursors (zymogens).

Pancreatic Bicarbonate

The pancreas secretes sodium bicarbonate (NaHCO3) to neutralize acidic chyme from the stomach.

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Bile Role

Bile, produced by the liver and stored in the gallbladder, aids in fat digestion.

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Zymogens Activation

Pancreatic enzymes are often secreted as inactive precursors (zymogens) and activated in the duodenum.

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Duodenal Contractions

Phasic contractions in the duodenum propel chyme and mix it with digestive secretions.

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Slow Waves in Small Intestine

Slow waves generated from interstitial cells of Cajal (ICCs) regulate the frequency of contractions in the small intestine; specifically, they establish the rhythm of contractions.

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Enteropeptidase activation

Brush border enzyme converts inactive trypsinogen to active trypsin, initiating a cascade of pancreatic enzyme activation.

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Pancreatic enzyme triggers

Intestinal distension, presence of food, neural signals, and CCK hormone stimulate pancreatic enzyme release.

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Bicarbonate secretion

Pancreatic and duodenal bicarbonate neutralizes stomach acid, crucial for enzyme function in the small intestine.

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Bile composition

Bile is a non-enzymatic fluid containing salts, pigments, cholesterol, and other waste/drugs for fat digestion and excretion.

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Bile salt function

Bile salts act as detergents, emulsify fats, and are recycled through the liver and intestines, crucial for fat digestion.

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Bile recirculation

Bile salts are reabsorbed and reused multiple times in the digestive process, optimizing fat digestion efficiency.

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Fat digestion trigger

Bile salts break down fat into smaller droplets, increasing the surface area for lipase action.

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Fat digestion enzymes

Lipases break down triglycerides into monoglycerides and fatty acids. Colipase helps lipase access the fats.

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Micelle formation

Fatty acids, monoglycerides, bile salts, and cholesterol form small droplets that carry fats to the intestinal lining.

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Fat absorption mechanism

Fatty acids and monoglycerides are absorbed by simple diffusion; cholesterol absorption is energy-dependent.

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Chylomicron formation

Inside intestine cells, fats recombine with cholesterol and proteins to form large droplets called chylomicrons.

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Protein digestion completion

Pancreatic and brush border enzymes complete protein, carbohydrate, and fat digestion.

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Chyme entry affects digestion

Pepsin inactivation in the higher pH of the small intestine signifies a shift from stomach protein digestion to pancreatic protein digestion.

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Fat digestion complication

Lipase cannot penetrate the bile salt coating, so colipase is necessary to expose fats to lipase.

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Bile essential for digestion

Mechanical and enzymatic digestion in the intestines and the liver are needed for good digestion

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Chylomicron Absorption

Large fat molecules (chylomicrons) are absorbed into lymphatic vessels (lacteals) rather than directly into blood capillaries, due to their size.

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Short-Chain Fatty Acid Absorption

Fatty acids with 10 or fewer carbons can directly enter the bloodstream by crossing the capillary basement membrane.

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Starch Digestion

Starch is broken down first by salivary amylase in the mouth, then by pancreatic amylase in the small intestine to produce maltose.

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Disaccharide Digestion

Disaccharides (like maltose) are further broken down into monosaccharides (glucose, galactose, fructose) by disaccharidases in the small intestine.

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Carbohydrate Absorption

The body only absorbs monosaccharides (glucose, galactose, fructose).

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Cellulose Digestion

Humans lack enzymes to digest cellulose, so it passes through the digestive system as dietary fiber.

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Glucose and Galactose Absorption

Glucose and galactose are absorbed via sodium-dependent co-transport mechanisms (SGLT) and then transported to the bloodstream (GLUT2).

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Fructose Absorption

Fructose is absorbed by facilitated diffusion (GLUT5) and then moves to the bloodstream (GLUT2).

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Protein Digestion (general)

The digestion of proteins breaks down ingested polypeptides into smaller fragments, ultimately into individual amino acids.

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Endopeptidases

Enzymes that break peptide bonds within the polypeptide chain.

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Exopeptidases

Enzymes that break peptide bonds at the ends of the polypeptide chain.

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Protein Absorption

Amino acids, dipeptides, and tripeptides are absorbed in the small intestine, entering the bloodstream.

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Oligopeptides Transport

Some small peptide fragments (oligopeptides) are transported across the membranes and are later digested into amino acids.

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Carbohydrate digestion location

Digested in the mouth and stomach then duodenum

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Study Notes

Duodenal Function (Intestinal Phase)

  • Movement: Phasic contractions (contraction-relaxation cycles) occur in the posterior stomach and small intestine, driven by slow waves generated by Interstitial Cells of Cajal (ICCs).
  • Slow Wave Frequency: 12 waves per minute in the duodenum.
  • Secretions (overview): Liver, pancreas, and intestines produce over 3 liters daily of secretions for nutrient digestion, including enzymes, bile, bicarbonate, mucus, and an isotonic NaCl solution.
  • Digestive Enzymes: Produced by intestinal epithelium and the exocrine pancreas. Brush border enzymes remain attached to luminal cell membranes. Release is controlled by neural, hormonal, and paracrine signals. Parasympathetic stimulation enhances enzyme release.
  • Bile: Non-enzymatic, liver-produced solution crucial for fat digestion, released from the gallbladder during fat intake.
  • Bicarbonate: Neutralizes stomach acid, primarily from the pancreas (released in response to neural stimuli and secretin), and duodenal cells.
  • Mucus: Protects intestinal epithelium and lubricates gut contents, from goblet cells.
  • NaCl solution: Mixed with mucus for lubrication.

Pancreas Function

  • Dual Function: The pancreas contains endocrine (insulin, glucagon) and exocrine tissues (digestion).
  • Exocrine Function: Consist of acini releasing enzymes and duct cells releasing bicarbonate solution delivered via ducts to the duodenum.
  • Enzyme Secretion (important): Most pancreatic enzymes are released as inactive zymogens (e.g., trypsinogen) activated by enterokinase (brush border enzyme). Trypsin then activates other zymogens. Signals for release include intestinal distension, the presence of food, neural signals, and CCK (a gut hormone).
  • Bicarbonate Secretion (Important): Neutralization of stomach acid relies on carbonic anhydrase and chloride-bicarbonate exchanger. Sodium-hydrogen exchangers are also involved. Crucial for normal digestion, pancreatic insufficiency impacts this function. CFTR defects can disrupt the process as seen in cystic fibrosis.
  • Water & Sodium Secretion: Passive processes driven by electrochemical and osmotic gradients. Watery bicarbonate solution is the outcome.

Liver Function

  • Bile Production: Bile is a non-enzymatic solution produced by hepatocytes (liver cells).
  • Bile Composition: Bile salts for fat digestion, bilirubin (waste), cholesterol, and drugs/xenobiotics.
  • Bile Salt Recycling: Bile salts are reabsorbed in the ileum return to the liver via the hepatic portal vein via a crucial recycling, returning to the liver for secretion, critical for fat digestion. The body recycles bile salts 2-5 times per meal.
  • Gallbladder Function: Stores and concentrates bile. Not essential for digestion but important.

Digestion in the Small Intestine

  • General Overview: Chemical digestion of chyme. -Neutralization of stomach acid, carbohydrate breakdowns, protein digestion, fat emulsification and digestion. All needed for the absorption process.
  • Fat Digestion and Absorption: -Emulsification involves bile salts increasing the surface area for lipase action. -Lipase breaks triglycerides into monoglycerides and free fatty acids, with colipase displacing bile salts for lipase access. Phospholipids are digested by pancreatic phospholipase. -Absorption: Simple diffusion for fatty acids and monoglycerides; cholesterol is transported by proteins. -Chylomicrons (fatty acids, cholesterol, and protein) are formed, transported into the lymphatic system (lacteals), and eventually enter the bloodstream.
  • Carbohydrate Digestion & Absorption: -Starches are broken down by pancreatic amylase and brush border enzymes (maltase, sucrase, and lactase). -Glucose, galactose, and fructose are absorbed using sodium-dependent cotransporters (for glucose and galactose) and facilitated diffusion (fructose). Intestinal cells primarily use glutamine for energy.
  • Protein Digestion & Absorption: -Endopeptidases and Exopeptidases break down proteins to oligopeptides, dipeptides, and tripeptides through activation, and splitting of peptide chains.
    -Absorption: amino acids absorbed via sodium-dependent transporters; dipeptides & tripeptides are absorbed, digested, and transported across the membrane as a whole unit.

Nucleic Acid Digestion

  • Nucleic acids (DNA and RNA) are digested into nucleotides, then nitrogenous bases and monosaccharides. The bases are actively transported, and sugars are absorbed via facilitated and secondary active transport.

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Description

Test your knowledge on the duodenal function during the intestinal phase. This quiz covers the physiological aspects, secretions, and enzyme functionality involved in digestion. Challenge yourself to recall details about movements, bile production, and more.

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