Digestive Physiology Quiz
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Questions and Answers

What are the primary components broken down during digestion?

  • Proteins, carbohydrates, and triacylglycerols (correct)
  • Carbohydrates, vitamins, and fiber
  • Proteins, minerals, and sugars
  • Fats, sugars, and carbohydrates

Which type of saliva is primarily secreted by the submaxillary glands?

  • High in protein and acidic
  • Low in potassium and isotonic
  • Rich in electrolytes and hypotonic (correct)
  • Rich in mucin and hypertonic

What is the role of parasympathetic stimulation in salivary secretion?

  • Promotes the secretion of mucin-rich saliva
  • Increases the release of watery saliva (correct)
  • Inhibits the function of acinar cells
  • Decreases the viscosity of saliva

What enzymes are found in saliva that aid in digestion?

<p>Salivary amylase and lingual lipase (C)</p> Signup and view all the answers

What is one of the minor roles of saliva in the digestive process?

<p>Excreting drugs and ions (A)</p> Signup and view all the answers

Which enzyme is primarily responsible for the hydrolysis of triacylglycerols at positions 1 and 3?

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

Which amylase has a cleavage site at the last α-1,4 glycosidic bond?

<p>γ-amylase (C)</p> Signup and view all the answers

What is the optimum pH range for β-amylase activity?

<p>5.4–5.5 (D)</p> Signup and view all the answers

Lactase activity in most mammals tends to decrease after which life stage?

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

What role do bile salts play in lipid digestion?

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

What is the primary role of co-lipase in the digestion of lipids?

<p>It binds lipase in a 1:1 molar ratio and anchors to triglycerides. (C)</p> Signup and view all the answers

Which statement accurately describes the action of phospholipase A2?

<p>It produces lysophospholipids, which act as powerful detergents. (B)</p> Signup and view all the answers

What is one of the functions of bile in lipid digestion?

<p>It performs emulsification of lipids and activation of digestive enzymes. (C)</p> Signup and view all the answers

How does bile acid contribute to cholesterol homeostasis?

<p>By regulating bile acid production as a determinant of cholesterol levels. (D)</p> Signup and view all the answers

What characteristic of bile acids allows them to function as detergents?

<p>Their solubility in both lipids and water due to polar and nonpolar regions. (A)</p> Signup and view all the answers

What mechanism is primarily responsible for the secretion of gastric acid by gastrin?

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

Which of the following statements about pepsin is correct?

<p>It can autocatalyze the activation of more pepsinogen. (B)</p> Signup and view all the answers

What is the role of rennin in the stomach?

<p>Converts milk casein to paracasein. (C)</p> Signup and view all the answers

What is unique about the intrinsic factor produced by parietal cells?

<p>It is essential for vitamin B12 absorption. (C)</p> Signup and view all the answers

Which statement about gastric lipase is accurate?

<p>It digests most triglycerides in the stomach. (A)</p> Signup and view all the answers

What effect does carbonic anhydrase have in the gastric secretions process?

<p>It catalyzes the formation of bicarbonate and protons from CO2. (D)</p> Signup and view all the answers

What is the physiological consequence of the alkaline tide after a meal?

<p>Increased alkalinity of urine. (D)</p> Signup and view all the answers

Which type of digestion occurs primarily in the stomach?

<p>Enzymatic hydrolysis of proteins. (A)</p> Signup and view all the answers

What is the primary rate-limiting enzyme in the synthesis of bile acids?

<p>7-α-hydroxylase (C)</p> Signup and view all the answers

Which bile acid undergoes bacterial modification in the intestine resulting in secondary bile acids?

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

What percentage of secreted bile acids is efficiently reabsorbed in the enterohepatic circulation?

<p>98-99% (B)</p> Signup and view all the answers

Which two bile acids are classified as primary bile acids?

<p>Cholic acid and chenodeoxycholic acid (C)</p> Signup and view all the answers

Which bile acid is primarily eliminated in the feces and is not reabsorbed due to its solubility?

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

What is the primary effect of conjugation on bile acids?

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

Which bile acid is produced in greater quantity from bacterial transformation compared to others?

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

Which of the following statements is true regarding the typical ratio of glycine and taurine conjugates in bile salts?

<p>Glycine conjugates predominate 3-4:1 (A)</p> Signup and view all the answers

What regulates the activity of 7--hydroxylase?

<p>Increased bile acid pool size suppresses its activity. (A), Decreased bile acid pool size enhances its activity. (D)</p> Signup and view all the answers

Which of the following secretions are produced by the Brush border of the small intestine?

<p>Aminopetidase and Nucleosidase (A), Sucrase and Lactase (C)</p> Signup and view all the answers

Which nutrient absorption occurs through tight junctions between epithelial cells?

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

What distinguishes L- and D-amino acids in their transport process?

<p>L-amino acids are actively transported; D-amino acids are not. (B)</p> Signup and view all the answers

What is the end product of sucrase activity?

<p>Fructose + Glucose (D)</p> Signup and view all the answers

Which statement about cholesterol's role in bile acid synthesis is accurate?

<p>Cholesterol stimulates 7--hydroxylase activity. (C)</p> Signup and view all the answers

How are fatty acids and monoglycerides processed after absorption?

<p>Reassembled into triglycerides and coated with proteins (B)</p> Signup and view all the answers

What is the mechanism for glucose transport in the small intestine?

<p>Na+ dependent cotransport and Na+ independent intake (D)</p> Signup and view all the answers

Flashcards

Digestion process

Breakdown of food into absorbable forms

Digestion phases

Neurogenic, gastric, intestinal

Saliva composition

Rich in K+, HCO3-, hypotonic, has enzymes and mucus

Saliva role

Aids mastication, swallowing, and food break-down, excretion of some substances.

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Salivary glands

Parotid, sublingual, submaxillary. Secrete saliva.

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α-amylase

An enzyme that breaks down starch randomly at α-1,4 glycosidic bonds, producing maltose, dextrin, and other shorter chains.

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β-amylase

An enzyme that breaks down starch sequentially from the non-reducing end, releasing maltose units.

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γ-amylase

An enzyme that breaks down starch from the non-reducing end, releasing glucose.

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Lactase

An enzyme that breaks down lactose (milk sugar) into glucose and galactose.

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Lipase

An enzyme that breaks down triglycerides into fatty acids and glycerol.

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Gastric Acid Secretion

Secretion of hydrochloric acid (HCl) in the stomach controlled by neurocrine (vagus/reflexes), endocrine (gastrin), and paracrine (histamine) mechanisms.

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HCI Secretion by Parietal Cell

Active transport of H+ ions against a concentration gradient by parietal cells; produces HCO3- creating an alkaline tide.

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Pepsinogen

Inactive precursor of pepsin, produced by chief cells, converted to pepsin via cleavage by HCI, activates other pepsinogens (autocatalysis).

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Pepsin Function

Endopeptidase that breaks down peptide bonds adjacent to Glu, Phe, Tyr, Trp, or Leu, most effective on collagen.

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Rennin Function (Infants)

Changes casein in milk to paracasein by using Ca2+. The paracasein is then broken down by pepsin.

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Intrinsic Factor

Essential stomach secretion: produced by parietal cells, required for B12 absorption in the ileum

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Gastric Lipase

Enzyme produced by chief cells, important in newborns, digests triglycerides into fatty acids and 1,2 dag, works at higher pH.

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Fat Digestion Steps

Emulsification (breaking down lipids into smaller droplets), enzymatic digestion (using pancreatic lipase), micelle formation (with bile salts) for absorption.

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Co-lipase's Role

Co-lipase binds to lipase in a 1:1 ratio, preventing inhibition by bile salts and anchoring lipase to the bile salt-coated triglyceride (TG) surface, facilitating efficient fat digestion.

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Lipase's Action on Triglycerides

Lipase primarily hydrolyzes triglycerides, breaking them down into fatty acids and either 2-monoacylglycerol (75%) or glycerol (25%).

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What are Lysophospholipids?

Lysophospholipids are the products of phospholipase A2's activity, which breaks down phospholipids. They have strong detergent properties.

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Bile's Functions

Bile emulsifies lipids, activates digestive enzymes, conjugates bilirubin, excretes cholesterol and toxins, neutralizes stomach acid, and forms micelles that aid in lipid absorption.

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Bile Acids' Role

Synthesized from cholesterol, bile acids have both polar and nonpolar regions, allowing them to reduce surface tension at lipid-water interfaces. They form micelles for lipid solubilization and enable cholesterol and dietary lipid digestion and excretion.

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Bile acid synthesis

The process of creating bile acids from cholesterol in the liver. It involves several enzymatic steps, including hydroxylation and side-chain cleavage.

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7-α-hydroxylase

The enzyme responsible for the first and rate-limiting step in bile acid synthesis. It introduces a hydroxyl group at the 7-α position of cholesterol.

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Conjugation of bile acids

The process of adding glycine or taurine to bile acids, increasing their solubility in water and making them more effective for digestion.

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Primary bile acids

Bile acids synthesized in the liver, such as cholic acid and chenodeoxycholic acid.

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Secondary bile acids

Bile acids modified by bacteria in the intestine, such as deoxycholic acid and lithocholic acid.

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Enterohepatic circulation

The cycle of bile acids being secreted into the intestine, reabsorbed in the ileum, and returned to the liver for reuse.

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Bile salt reabsorption

The process where most bile salts are reabsorbed in the terminal ileum, ensuring their efficient use for digestion and excretion.

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Lithocholic acid excretion

The main pathway for eliminating cholesterol from the body, where lithocholic acid, a secondary bile acid, is not reabsorbed and is eliminated in feces.

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Bile Acid Synthesis Regulation

The enzyme responsible for bile acid synthesis, 7--hydroxylase, is regulated by the Farnesoid X Receptor (FXR). When bile acid levels in the enterohepatic circulation rise, FXR is activated, suppressing the activity of 7--hydroxylase, slowing down bile acid production.

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Brunner's Glands

These glands are located solely in the duodenum, the first part of the small intestine. They produce a watery mucous secretion that helps protect the intestinal lining from the acidic chyme coming from the stomach.

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Crypts of Lieberkuhn

These invaginations in the small intestine lining are home to cells that produce and secrete water, bicarbonate, and various digestive enzymes. They play a vital role in digestion and nutrient absorption.

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Brush Border

The surface of the intestinal lining cells is covered in microscopic projections called microvilli, forming the 'brush border'. This structure vastly increases the surface area for absorption and also houses many essential digestive enzymes.

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Aminopeptidase Function

This brush border enzyme breaks down polypeptide chains, releasing single amino acids from the 'N-terminus', the beginning end of the polypeptide chain.

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Dipeptidase Function

Found in the brush border, dipeptidase breaks down dipeptides - short chains of two amino acids - into individual amino acids.

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What are Chylomicrons?

These are small, spherical particles made up of triglycerides coated with proteins. They are formed in the intestinal cells and are responsible for transporting dietary fats to the rest of the body via the lymph system.

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Monosaccharide Absorption

Glucose enters the intestinal cells using a sodium-dependent transporter (SGLT-1). Other monosaccharides can also be absorbed through carrier-mediated diffusion or simple diffusion.

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Study Notes

Digestion, Transport and Absorption of Nutrients

  • Digestion breaks down naturally occurring food into assimilable forms.
  • Proteins are broken down into amino acids.
  • Carbohydrates are broken down into monosaccharides.
  • Triacylglycerols are broken down into fatty acids and glycerol.
  • Minerals and vitamins also become assimilable.
  • Digestion has three phases: neurogenic, gastric, and intestinal.

Digestion in the Oral Cavity

  • Salivary glands (parotid, sublingual, submaxillary) produce most saliva.
  • Acinar cells create saliva similar to plasma composition (Na+, K+, Cl-, HCO3-).
  • Duct cells alter the ionic content of saliva.
  • Saliva is rich in K+, HCO3-, hypotonic, and contains amylase, lingual lipase, and lysozyme.
  • Parasympathetic stimulation increases watery saliva release.
  • Saliva helps with mastication, swallowing, and dissolving food molecules.
  • Saliva is a medium for hydrolases to act on food.
  • Aids in excretion of some drugs.
  • Lingual lipase is not significant in humans.

Digestion in the Stomach

  • Sight, smell, and taste of food stimulate cerebral cortex and vagal nuclei.
  • These stimulate gastric parietal and chief cells.
  • Gastric secretions include gastrin, HCl, and H2O.
  • Other secretions include pepsin, rennin, and gastric lipase.
  • Mucin and inorganic salts are also secreted.
  • HCl secretion is controlled by neurocrine (vagus/local reflexes), endocrine (gastrin), and paracrine (histamine) mechanisms.
  • Mucus forms a physical barrier between the lumen and epithelium.
  • Bicarbonate buffers stomach acid to prevent damage.
  • Pepsinogen is an inactive precursor to pepsin which is activated by HCl.
  • Pepsin is an endopeptidase that breaks down proteins.
  • Rennin is important in infants.
  • Gastric lipase is produced by chief cells.
  • It's important during the neonatal period.

Digestion in the Intestines

  • Chyme moves to the duodenum.
  • Pancreatic and biliary secretions neutralize pH and inactivate pepsin.
  • Bile acids emulsify fats & enable fat-soluble vitamin absorption.
  • Bile acids neutralize chyme and excrete cholesterol, bile pigments, and drugs.

Pancreatic Secretions

  • Pancreatic secretions include various zymogens (inactive enzymes).
  • These activate into active enzymes.
  • Different enzymes digest different substrates (peptides, phospholipids, triglycerides, starch, glycogen, RNA, DNA).
  • Zymogens are activated by enteropeptidase.

Carbohydrate Digestion

  • Starch and glycogen are broken down into glucose.
  • Amylase breaks down starch/glycogen.
  • Maltase, sucrase, and lactase further break down disaccharides into monosaccharides.
  • Monosaccharides are absorbed in the intestines.

Disaccharidases

  • Brush border enzymes (maltase, sucrase-isomaltase, lactase, trehalase) act on disaccharides.
  • Lactase activity usually declines after weaning in most mammals.

Fat Digestion

  • Lipids are emulsified by bile salts.
  • Pancreatic lipase hydrolyzes triglycerides.
  • Bile salts, colipase, and phospholipids are required for lipase action.
  • Short- and medium-chain fatty acids can be absorbed directly, while longer chains dissolve in lipid droplets.

Intestinal Secretions

  • Intestinal secretions contain various enzymes for breaking down peptides, and disaccharides, organic and nucleic acids.
  • Enzymes are found in the brush border

Absorption in Small Intestine

  • All nutrients pass through epithelial cells.
  • Tight junctions prevent movement between cells
  • Amino acids, monosaccharides, and fatty acids are transported through membranes and into blood capillaries.
  • Fatty acids and monoglycerides are reassembled into triglycerides and coated with proteins to form chylomicrons.
  • Chylomicrons are transported to lymphatic capillaries (lacteal).

Lipid Absorption

  • Intestinal epithelial cells synthesize triacylglycerols, cholesterol esters, phospholipids, and apoproteins.
  • These are packaged into chylomicrons.
  • Free fatty acids (<10 carbons) are transported unesterified in the portal vein.
  • Chylomicrons are too large to pass through capillary beds.
  • They are secreted into the lymph and enter the bloodstream via the thoracic duct.

Colon

  • No digestion occurs in the colon.
  • The colon absorbs water and ions.
  • It contains bacteria that synthesize vitamin K.
  • Bacterial fermentation produces gases and various acids.
  • Ammonia (NH3) is absorbed and removed by the liver.

Bacteria in the Intestine

  • Bacteria produce various gases (CO2, methane, H2S) and organic acids.
  • Bacterial activity generates considerable amounts of ammonia (NH3).
  • The liver removes ammonia.
  • Bacteria synthesize vitamin K and biotin.

Defects in Digestion and Absorption

  • Lactose intolerance, sucrase deficiency, and monosaccharide deficiency can result in issues with carbohydrate absorption.
  • Chyluria, chylothorax, and co-lipase deficiency affect lipid digestion/absorption.
  • Deficiencies in protein digestion may result from incomplete digestion of polypeptides or issues with mucosal permeability.

Diseases Resulting From Defects in Digestion and Malabsorption

  • Anemia (iron, vitamin B12, folic acid deficiency), edema (protein digestion/absorption), and tetany (Ca2+, Mg2+, vitamin D deficiency) may arise.
  • Osteoporosis (Ca2+, vitamin D deficiency), lactose intolerance, bleeding/bruising (vitamin K deficiency), steatorrhea (lipid digestion/absorption issues), and Hartnup disease (neutral amino acid carrier defect) are other possible illnesses.

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Description

Test your knowledge on the primary components of digestion and the secretions involved. This quiz covers various aspects of saliva's role, enzyme functions, and lipid digestion processes. Perfect for students studying digestive physiology or related fields.

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