10. Mucosal Digestion

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Questions and Answers

What is a key characteristic of carbohydrate absorption?

  • It primarily occurs through active transport of oligosaccharides.
  • It is a relatively inefficient process.
  • It is a very efficient process. (correct)
  • It bypasses the portal vein and liver.

Where does the final digestion of oligosaccharides and disaccharides primarily occur?

  • Within the lumen of the stomach.
  • In the liver.
  • In the portal vein.
  • At the brush border. (correct)

How is fructose absorbed through the luminal membrane?

  • Through simple diffusion.
  • Through osmosis.
  • Via active transport using the SGLT 1 transporter.
  • By facilitated diffusion. (correct)

What is the immediate destination of monosaccharides after absorption in the small intestine?

<p>The portal vein leading to the liver. (D)</p> Signup and view all the answers

Based on the diagram, what transporter is located adjacent to the site of final digestion of carbohydrates?

<p>SGLT 1 (A)</p> Signup and view all the answers

Why is lactase activity high at birth in mammals?

<p>To prevent the digestion of maternal immunoglobulins found in colostrum. (C)</p> Signup and view all the answers

What is the primary reason for the decline in lactase activity with age in many mammalian species?

<p>It prevents adults from consuming dam's milk. (D)</p> Signup and view all the answers

Which of the following best describes the state of digestive enzyme concentrations at birth in domestic species?

<p>Low concentrations of all digestive enzymes except for lactase. (C)</p> Signup and view all the answers

What is the consequence of reduced lactase activity in older animals that continue to consume lactose?

<p>Lactose intolerance, potentially leading to diarrhea. (C)</p> Signup and view all the answers

How does the delayed development of digestive enzymes (other than lactase) immediately after birth aid in the absorption of maternal antibodies?

<p>It prevents the enzymatic breakdown of immunoglobulins in colostrum. (B)</p> Signup and view all the answers

Which of the following proteases is active in the stomach?

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

Where does the digestion of di- and tri-peptides into amino acids primarily occur?

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

Which of the transport mechanisms facilitates the absorption of amino acids and peptides in the intestinal brush border?

<p>Na+- and H+-coupled transport (C)</p> Signup and view all the answers

What is the primary destination of amino acids after absorption from the intestinal brush border?

<p>Portal vein to the liver (A)</p> Signup and view all the answers

Which of the following enzymes is NOT a pancreatic protease?

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

Why is the digestion of dietary protein considered a less efficient process in the stomach?

<p>Poor access of enzymes to the 3D structure (A)</p> Signup and view all the answers

Which of the following is the only instance when digestion occurs within epithelial cells?

<p>Di, tripeptides (B)</p> Signup and view all the answers

Which of the following is a product of protein digestion in the intestinal lumen?

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

What primary stimulus triggers the release of cholecystokinin (CCK) during fat digestion?

<p>Presence of fat in the duodenal lumen (C)</p> Signup and view all the answers

What is the primary function of bile salts in the process of fat digestion?

<p>To emulsify lipids and form micelles, increasing the surface area for lipase action (A)</p> Signup and view all the answers

Which structural feature of bile salts allows them to effectively emulsify lipids?

<p>Their amphipathic nature, possessing both hydrophobic and hydrophilic regions (C)</p> Signup and view all the answers

Inside a micelle, what is the arrangement of the hydrophobic and hydrophilic components?

<p>Hydrophobic components form the interior, while hydrophilic components form the exterior (A)</p> Signup and view all the answers

What is the role of lipases in the digestion of triglycerides?

<p>To hydrolyze ester bonds at the 1 and 3 positions of triglycerides (C)</p> Signup and view all the answers

Which of the following is a key difference in fat digestion in horses compared to other mammals with gallbladders?

<p>Horses continuously secrete bile directly from the biliary ducts in response to feeding. (D)</p> Signup and view all the answers

What characteristic defines a medium-chain triglyceride (MCT)?

<p>Having fatty acids with fewer than 16 carbon atoms (D)</p> Signup and view all the answers

Why are medium-chain triglycerides (MCTs) sometimes used in pharmaceutical applications?

<p>They can increase energy intake in individuals with pancreatic and liver diseases. (A)</p> Signup and view all the answers

What happens to bile salt absorption after ileal resection?

<p>Bile salt absorption decreases, leading to potential colitis. (B)</p> Signup and view all the answers

Which of the following statements about fat absorption after ileal resection is true?

<p>Overall fat absorption decreases, causing potential steatorrhea. (A)</p> Signup and view all the answers

What is a consequence of reduced fluid and electrolyte absorption after colon resection?

<p>Increased likelihood of diarrhea. (C)</p> Signup and view all the answers

How does the intestinal mucosa adapt after injury?

<p>It compensates over time, potentially adapting to maintain absorption. (C)</p> Signup and view all the answers

What dietary change may be recommended for a patient with impaired vitamin B12 absorption due to ileal resection?

<p>Reduce dietary fat and consider B12 injections. (A)</p> Signup and view all the answers

What is the primary purpose of chylomicra entering the liver in a diluted form?

<p>To prevent excessive fat from entering the liver (D)</p> Signup and view all the answers

What cellular structure is primarily involved in the packaging of triglycerides with apolipoproteins?

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

What happens to the surface area of the small intestinal mucosa after damage, such as from viral infections?

<p>It undergoes villous hyperplasia (C)</p> Signup and view all the answers

What factor limits the extent of adaptation in the small intestine after injury?

<p>The presence of intact crypt epithelium (A)</p> Signup and view all the answers

What is the consequence of intestinal resection on the absorptive surface area?

<p>Surfaces area can increase by a limited percentage (A)</p> Signup and view all the answers

How do luminal nutrients affect the adaptation process after intestinal injury?

<p>They enhance adaptation (D)</p> Signup and view all the answers

Which of the following diets leads to the formation of black fat droplets?

<p>High fat diet (A)</p> Signup and view all the answers

What are the consequences if the crypt epithelium is damaged?

<p>Adaptation to injury is hindered (B)</p> Signup and view all the answers

Flashcards

Carbohydrate Digestion

The breakdown of carbohydrates into simpler sugars for absorption.

Absorption of Fructose

Fructose is absorbed by facilitated diffusion on the luminal membrane.

Brush Border

The microvilli on the intestinal surface where final digestion occurs.

SGLT 1

A transporter that aids in the absorption of glucose and galactose.

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Portal Vein

The blood vessel that carries absorbed nutrients to the liver.

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Mucosal Brush Border Enzymes

Enzymes located on the intestinal lining that aid in digestion.

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Lactase

An enzyme necessary for breaking down lactose into glucose and galactose.

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Colostrum Absorption

The 'open' gut allows absorption of maternal antibodies from colostrum shortly after birth.

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Lactose Intolerance

A condition where lactase production decreases, causing difficulty digesting lactose.

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Increased Enzyme Concentration

As animals age, the levels of most digestive enzymes increase, except for lactase.

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Protein Digestion

The process of breaking down dietary protein into smaller peptides and amino acids.

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Stomach Role in Digestion

The stomach contributes by using acid hydrolysis and pepsin to begin protein breakdown.

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Pancreatic Proteases

Enzymes like trypsin and chymotrypsin released into the intestine to further digest proteins.

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Absorption of Amino Acids

Process where amino acids from digested proteins enter the bloodstream through the intestinal brush border.

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Oligopeptides

Short chains of amino acids formed during protein digestion before they are absorbed.

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Epithelial Cell Digestion

Digestion that occurs within epithelial cells, especially for di- and tri-peptides.

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Na+ and H+-coupled Transport

Mechanism that helps transport amino acids and peptides into intestinal cells.

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Portal Vein Function

Carries absorbed amino acids from the intestines to the liver for processing.

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Chylomicrons

Lipid particles formed in the intestinal lining to transport fats in the bloodstream.

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Intracellular Space (ICS)

The space within cells where substances like chylomicrons are found before exocytosis.

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Exocytosis

The process by which cells expel materials, including chylomicrons, into the bloodstream.

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Micelles

Structures that help in the absorption of fats by transporting fatty acids and monoglycerides to enterocytes.

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Intestinal Adaptation

The process by which the small intestine increases absorptive area following injury or resection.

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Villus Hyperplasia

The increase in the length and number of intestinal villi to enhance nutrient absorption.

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Apolipoproteins

Proteins that bind lipids to form lipoproteins, essential for lipid transport.

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Paracellular Transport

The movement of substances across the intestinal epithelium via the spaces between cells.

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Triglycerides

Main dietary fats composed of glycerol and three fatty acids.

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Micelle formation

Process where bile salts and lipids form a structure to aid fat digestion.

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CCK (Cholecystokinin)

Hormone released in response to fats, stimulating digestive enzyme release.

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Emulsification

The process of breaking down fats into smaller droplets, aided by bile.

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Amphipathic bile salts

Bile salts with a hydrophobic and hydrophilic part, emulsifying fats.

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Critical Micelle Concentration (CMC)

The concentration of bile salts necessary to form micelles in the bowel.

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Lipase digestion

Enzymatic breakdown of triglycerides by hydrolyzing ester links.

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Absorption at brush border

Process where digested fats are taken up by intestinal epithelial cells.

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Ileal Resection Effects

Ileal resection impair Vitamin B12 absorption and fat digestion.

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Fat Absorption

Resection of ileum decreases overall fat absorption, risk of steatorrhea.

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VFA Absorption

Colonic resection reduces absorption of volatile fatty acids, important in horses.

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Electrolyte Absorption

Fluid and electrolyte absorption is impaired after colon resection, leading to diarrhea.

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Post-Surgical Adaptation

Partial colectomy leads to adaptations like cecum enlargement for better absorption.

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Study Notes

Mucosal Digestion and Adaptation

  • At birth, most digestive enzymes are low, except lactase, which is present in high concentrations in many species.
  • Lactase aids in digesting lactose, the primary sugar in milk.
  • Low digestive enzyme levels initially prevent the digestion of colostrum containing immunoglobulins.
  • Enzyme concentrations increase with age, except lactase, which often declines.
  • Lactase activity decreases or disappears with age in some species early.
  • This phenomenon can cause issues like diarrhea in young animals, but can be avoided in many species, most concerning in adults who consume dam's milk (especially from the mother).
  • Enzyme activities differ in various species and are measured by units per gram of protein.
  • Charts show measurements of several digestive enzyme activities over time. These measure activity of the enzymes in units/g protein, over time in days, measuring results along a logarithmic scale.

Carbohydrate Digestion and Absorption

  • Carbohydrate digestion is an efficient process.
  • Digestion occurs extracellularly within the intestinal lumen involving various enzymes.
  • Carbohydrate breakdown products, such as oligosaccharides, disaccharides, and monosaccharides are absorbed.
  • Fructose absorption is facilitated by diffusion mechanisms
  • Final digestion of oligosaccharides and disaccharides occurs adjacent to monosaccharide transporters.

Protein Digestion and Absorption

  • Protein digestion is a less efficient process than carbohydrate digestion.
  • This is due to enzymes having poor access to 3D protein structures.
  • Digestion begins in the stomach and continues in the small intestine.
  • Final products are amino acids which are actively transported into the bloodstream

Fat Digestion and Absorption

  • Main dietary fat is triglycerides.
  • Bile salts aid in emulsifying fats (forming micelles), increasing surface area accessible to lipases.
  • Lipases hydrolyze ester links in triglycerides.
  • These digested products, including fatty acids, and glycerol are absorbed into epithelial cells.
  • Micelles increase surface area, aiding access by lipases.
  • Products are re-esterified and assembled into chylomicrons which enter lymphatic vessels, rather than the bloodstream,

Adaptation

  • Adaptation is enhanced, in cases where there's a limited damage/repair processes to the small intestine's mucosal surface.
  • Surface area is adapted in response to damages, including larger villi which are made, and more micorvilli for higher absorption rates.
  • Damaged intestinal mucosa can respond with villous hyperplasia (increased villi) to restore absorptive function.
  • Protein and carbohydrate digestion is more affected by intestinal resection or injury, compared to reactions to carbohydrate digestion.

Intestinal Resection

  • Digestion and absorption of carbohydrates may be less affected by intestinal resection or injury compared to protein digestion/absorption.
  • Overall fat absorption may decrease, with resultant fat in fecal matter which is referred to as steatorrhea. Also, B12 is impacted.
  • Reduced or impaired water and electrolyte absorption may occur after intestinal damage or resection.

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