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Chapter 4.3 · Renal & GI

Digestive System — INBDE Review

GI anatomy and physiology with the dental-relevant pieces emphasized: enzyme sites, intrinsic factor + B12, accessory organs, and oral signs of malabsorption (glossitis, enamel erosion, scurvy). 11 board-style MCQs.

11 practice MCQsQuick-reference tableMnemonics + clinical pearlsFull distractor explanations
High-yield review

Concept summary & clinical relevance.

Quick-reference structure first, then nerve-by-nerve detail. Mnemonics in amber, clinical pearls in blue.

Digestive physiology questions on the INBDE focus on which enzyme acts where, where each nutrient is absorbed, and the oral signs of GI disease. The mouth itself is the start of digestion (salivary amylase, lingual lipase) — and many systemic GI conditions surface as oral findings (glossitis, enamel erosion, aphthous ulcers, gingival bleeding).

Digestive enzymes — site & substrate
EnzymeSourceSubstrate
Salivary amylaseSalivary glands (mouth)Starch (carbohydrate)
Lingual lipaseLingual glands (mouth)Triglycerides (fat)
PepsinStomach chief cells (from pepsinogen)Protein
Pancreatic amylasePancreas → small intestineStarch
Pancreatic lipasePancreas → small intestineTriglycerides
Trypsin / chymotrypsinPancreas → small intestineProtein
Stomach cells & secretions
CellSecretesNotes
ParietalHCl + intrinsic factorPPI side effect: ↓ B12 absorption
ChiefPepsinogen (→ pepsin)Protein digestion
MucousMucus + bicarbonateProtective barrier against HCl
G cellsGastrinStimulates parietal cell HCl
Enterochromaffin-like (ECL)HistamineStimulates HCl release
Where each nutrient is absorbed
NutrientSiteDental relevance if deficient
IronDuodenumGlossitis, angular cheilitis, anemia
Carbohydrates, proteins, most fatsJejunum (main absorption)Generalized malnutrition signs
Vitamin B12 (with IF)IleumGlossitis, burning mouth, megaloblastic anemia
Bile saltsIleum (recycled)Fat malabsorption if resected
Fat-soluble vitamins (A, D, E, K)Small intestine, requires bileBleeding (vit K), bone issues (vit D)
Water & electrolytesColon—
Vitamin K (some)Colon (synthesized by gut flora)Antibiotics → bleeding tendency
Clinical pearl — Oral signs of GI disease
Iron deficiency → atrophic glossitis, angular cheilitis. B12 deficiency (PPI users, gastrectomy, ileal resection, vegans) → smooth red tongue, burning mouth. Vitamin C deficiency (scurvy) → spongy bleeding gums, delayed wound healing. GERD → enamel erosion on palatal surfaces. Crohn's/celiac → recurrent aphthous ulcers, enamel hypoplasia. The mouth is often where systemic GI disease shows up first.
Clinical pearl — Vitamin K + dental bleeding risk
Vitamin K is needed for clotting factors II, VII, IX, X (and proteins C, S). Patients on long-term broad-spectrum antibiotics (which kill colonic flora that synthesize vitamin K) or with severe liver disease can have prolonged bleeding after extractions. Warfarin works by interfering with vitamin K — that's why warfarin patients need INR monitoring before surgical dental procedures.
Clinical pearl — Why intrinsic factor matters
Parietal cells make BOTH HCl and intrinsic factor (IF). Long-term proton pump inhibitor (PPI) use, autoimmune gastritis (pernicious anemia), gastrectomy, or ileal resection all impair B12 absorption — the IF–B12 complex needs the ileum. B12 deficiency causes glossitis and burning mouth before classic anemia is obvious; dentists sometimes flag it first.
Mnemonic — Stomach cells
“Parietal = Proton pump + IF. Chief = Cooks (Pepsinogen).” Parietal makes acid and intrinsic factor; chief makes pepsinogen for protein digestion.
Mnemonic — Fat-soluble vitamins
“ADEK require bile salts.” Vitamins A, D, E, K need bile-emulsified fat to absorb. Cholestasis or bile salt loss → deficiency risk.
Mnemonic — Small bowel division
“Duodenum: digestion + iron. Jejunum: juicy nutrients (most absorption). Ileum: intrinsic factor + B12 + bile salts.”

Mouth & esophagus

  • Salivary amylase begins starch digestion; lingual lipase starts fat digestion (more important in infants).
  • Esophagus moves the bolus by peristalsis; the lower esophageal sphincter (LES) prevents reflux.
  • GERD erodes enamel — characteristically on palatal surfaces of upper anteriors.

Stomach

  • Parietal cells: HCl + intrinsic factor.
  • Chief cells: pepsinogen, activated to pepsin in acid.
  • Mucous cells: mucus + bicarbonate barrier protecting the gastric lining.
  • G cells: gastrin (stimulates HCl).

Small intestine

  • Duodenum: digestion (pancreatic enzymes + bile salts) and iron absorption.
  • Jejunum: main site of nutrient absorption — carbs, proteins, fats.
  • Ileum: bile salt recycling and vitamin B12 absorption (with intrinsic factor).

Large intestine & accessory organs

  • Colon: absorbs water, electrolytes; gut flora synthesize some vitamin K.
  • Liver: produces bile, synthesizes clotting factors, clears many drugs.
  • Gallbladder: stores and releases bile.
  • Pancreas: exocrine (digestive enzymes) + endocrine (insulin, glucagon).
KYT INBDE
KYT INBDE: Anatomy & Physiology for Dentistry
900 MCQs · Volume 1 · Available on Amazon
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Self-assessment · Core Recall

11 board-style MCQs.

Active recall is the highest-yield study method for the INBDE. Pick an answer, check it, and read why every distractor is wrong — that's where the learning compounds.

In the book — different question type

The MCQs above are Core Recall — testing what you've memorized. The book adds a full Clinical Integration set: board-style patient scenarios where you apply this anatomy to real clinical reasoning. That's the section the INBDE actually weights heaviest.

  1. Question 1
    Easy
    Which enzyme begins carbohydrate digestion in the mouth?
  2. Question 2
    Easy
    What is the primary function of the esophagus?
  3. Question 3
    Easy
    Which stomach cell produces hydrochloric acid and intrinsic factor?
  4. Question 4
    Easy
    Which substance is necessary for vitamin B12 absorption in the ileum?
  5. Question 5
    Easy
    Where does most digestion and absorption of nutrients occur?
  6. Question 6
    Moderate
    Which intestinal section is the main site of vitamin B12 absorption?
  7. Question 7
    Easy
    Which organ produces bile?
  8. Question 8
    Easy
    What is the main function of bile salts?
  9. Question 9
    Easy
    Which vitamin is partly synthesized by colonic bacteria?
  10. Question 10
    Easy
    Which dental finding is most characteristic of chronic vomiting or gastroesophageal reflux?
  11. Question 11
    Easy
    Which vitamin deficiency develops if intrinsic factor is absent (e.g., long-term PPI use, gastrectomy, autoimmune gastritis)?
KYT INBDE
Anatomy & Physiology
Volume 1
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KYT INBDE: Anatomy & Physiology for Dentistry
Head & Neck Anatomy · Neuroanatomy & CNS · Cardiovascular & Respiratory · Renal & GI

900 INBDE-style MCQs with full explanations across 18 chapters — Core Recall plus board-style Clinical Integration scenarios — alongside Learning Summaries, Integration Bridges, and Review Boxes. Built by Dr. Isaac Sun for dental students who want to think like a clinician, not just memorize.

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Author
Dr. Isaac Sun, DDS

Founder, KYT Dental Services · Author, KYT INBDE series. These MCQs and Learning Summaries are part of a structural-thinking framework Dr. Sun uses with patients in the chair.

About Dr. Sun
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