Dental MCQ
Cells and fluids · Endocrine & Neuromuscular Physiology · INBDE Patient Cases

Cell Physiology & Body Fluids INBDE Patient Cases

By Dr. Isaac Sun, DDS

7 ADA INBDE-format patient cases on cell physiology & body fluids. Each case is a shared patient box (chief complaint, history, medications, allergies, exam) followed by linked multiple-choice questions with full distractor explanations. Practice the way the real exam is structured.

7 patient cases35 linked questionsADA INBDE formatFull distractor explanations

Seven ADA INBDE-format patient cases on cell physiology and body fluids: why local anesthetic fails in inflamed tissue (Henderson-Hasselbalch, ionized vs unionized LA, block proximal to inflammation), choosing 0.9% isotonic saline for IV fluid (sterile water hemolysis and 3% saline only for severe symptomatic hyponatremia), ACE inhibitor angioedema as a bradykinin-mediated Starling-force problem with airway-first management, the Na+/K+ ATPase (3 Na+ out, 2 K+ in) setting up the resting membrane potential that local anesthetics interrupt at the voltage-gated Na+ channel, tonicity and red blood cell behavior (isotonic/hypotonic/hypertonic), why IV bioavailability is 100% and why oral and sublingual differ, and elderly body fluid compartments with the NSAID + ACE inhibitor + diuretic 'triple whammy' that raises acute kidney injury risk. Topics include the cell membrane, membrane transport (passive, facilitated, primary active, secondary active), the Na+/K+ ATPase, SGLT2 inhibitors, resting membrane potential, body fluid compartments (60-40-20 rule), osmolality and tonicity, and the Starling forces that produce edema.

Case Coverage Map
What each case is testing
Why local anesthetic fails in inflamed tissue:
Ionized vs unionized LA, Henderson-Hasselbalch, acidic inflamed tissue, and block-proximal-to-inflammation technique.
Choosing 0.9 percent saline for IV fluid:
Isotonic vs hypertonic vs hypotonic; sterile water causes hemolysis; 3% saline for severe symptomatic hyponatremia (specialist setting only).
ACE inhibitor angioedema as a Starling-force problem:
Bradykinin increases capillary permeability; airway-first management; multiple edema mechanisms.
Why the Na+/K+ ATPase keeps the nerve at rest:
Pump stoichiometry (3 Na+ out, 2 K+ in), K+ permeability dominance at rest, voltage-gated Na+ depolarization, LA block.
Tonicity and red blood cells:
Isotonic maintains volume, hypotonic swells, hypertonic shrinks, sterile water causes hemolysis.
Why IV bioavailability is 100 percent:
IV bypasses absorption; oral reduced by first-pass; sublingual nitroglycerin bypasses first-pass.
Body fluid compartments and dehydration:
TBW lower in elderly; ECF affected first; thiazide + ACEi + NSAID 'triple whammy' raises AKI risk.
Patient case: Why local anesthetic fails in inflamed tissue
0 of 5 answered, 0 correct
Patient
Male, 35 years old
Chief Complaint
Severe acute pulpitis with periapical inflammation; routine local anesthesia provides incomplete numbness.
Background and/or Patient History
  • Acute pulpitis with surrounding inflammation
  • Standard infiltration with lidocaine + epinephrine 2% produces incomplete anesthesia
  • Discussion of why
Allergies
NKDA
Medications
  • None
Current Findings
  • Incomplete anesthesia in inflamed tissue
  • Cell membrane / pH-pKa relevance
  1. Question 1
    Moderate
    Local anesthetics cross the nerve membrane MORE EASILY in their:
  2. Question 2
    Hard
    Inflamed tissue is more ACIDIC than normal tissue, which:
  3. Question 3
    Moderate
    The relationship between pH and ionization is described by:
  4. Question 4
    Moderate
    Practical strategies in inflamed tissue include:
  5. Question 5
    Easy
    The teaching point is that cell membrane crossing of drugs:

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Patient case: Choosing 0.9 percent saline for IV fluid
0 of 5 answered, 0 correct
Patient
Female, 50 years old
Chief Complaint
Routine IV access for a sedation case.
Background and/or Patient History
  • Healthy adult receiving conscious IV sedation
  • IV access established with 0.9% NaCl ('normal saline')
  • Discussion of why isotonic saline is the default
Allergies
NKDA
Medications
  • None
Current Findings
  • Routine IV with isotonic saline
  1. Question 1
    Moderate
    0.9% NaCl is chosen because it is:
  2. Question 2
    Hard
    If sterile water alone were given IV in significant volume, the most likely consequence is:
  3. Question 3
    Hard
    HYPERTONIC 3% saline is used clinically for:
  4. Question 4
    Moderate
    Normal plasma osmolality is approximately:
  5. Question 5
    Easy
    The teaching point is that IV fluid choice depends on:

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Patient case: ACE inhibitor angioedema as a Starling-force problem
0 of 5 answered, 0 correct
Patient
Female, 62 years old
Chief Complaint
Sudden lip and tongue swelling on lisinopril.
Background and/or Patient History
  • Hypertension on lisinopril
  • Sudden lip and tongue swelling without urticaria
  • Mild stridor
Allergies
NKDA reported
Medications
  • Lisinopril
Current Findings
  • ACE inhibitor angioedema with airway involvement
  1. Question 1
    Moderate
    ACE inhibitor angioedema is mediated by:
  2. Question 2
    Hard
    In Starling-force terms, ACE inhibitor angioedema represents:
  3. Question 3
    Moderate
    Immediate management is:
  4. Question 4
    Moderate
    Other classes of edema include:
  5. Question 5
    Easy
    The teaching point is that edema is:

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Patient case: Why the Na+/K+ ATPase keeps the nerve at rest
0 of 5 answered, 0 correct
Patient
Mixed (educational case)
Chief Complaint
Local anesthesia case used as the entry to discuss the resting membrane potential.
Background and/or Patient History
  • Routine dental local anesthesia
  • Discussion of how the Na+/K+ ATPase sets up the gradients that local anesthetics ultimately interrupt
Allergies
NKDA
Medications
  • None
Current Findings
  • Conceptual case linking pump activity to nerve excitability
  1. Question 1
    Moderate
    The Na+/K+ ATPase pumps:
  2. Question 2
    Moderate
    The resting membrane potential is set MOSTLY by:
  3. Question 3
    Moderate
    Action potentials are driven by:
  4. Question 4
    Moderate
    Local anesthetics block:
  5. Question 5
    Easy
    The teaching point is that the Na+/K+ ATPase:

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Patient case: Tonicity and red blood cells
0 of 5 answered, 0 correct
Patient
Mixed (educational case)
Chief Complaint
Discussion of tonicity using red blood cell behavior.
Background and/or Patient History
  • Conceptual case: red blood cells placed in different solutions
  • Tonicity decides cell volume change
Allergies
NKDA
Medications
  • None
Current Findings
  • Conceptual case on tonicity
  1. Question 1
    Easy
    A red blood cell placed in 0.9% NaCl will:
  2. Question 2
    Moderate
    A red blood cell placed in 0.45% NaCl will:
  3. Question 3
    Moderate
    A red blood cell placed in 3% NaCl will:
  4. Question 4
    Moderate
    A red blood cell placed in sterile water will:
  5. Question 5
    Easy
    The teaching point of tonicity is that:

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Patient case: Why IV bioavailability is 100 percent
0 of 5 answered, 0 correct
Patient
Female, 28 years old
Chief Complaint
Routine IV midazolam for a sedation case.
Background and/or Patient History
  • Routine IV midazolam for sedation
  • Discussion of why the IV route gives 100% bioavailability
Allergies
NKDA
Medications
  • None
Current Findings
  • IV sedation case as bioavailability anchor
  1. Question 1
    Moderate
    IV administration gives 100 percent bioavailability because it:
  2. Question 2
    Moderate
    ORAL drugs have lower bioavailability primarily because of:
  3. Question 3
    Moderate
    Drugs given by routes that BYPASS first-pass include:
  4. Question 4
    Moderate
    Sublingual nitroglycerin is given that way because:
  5. Question 5
    Easy
    The teaching point is that bioavailability:

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Patient case: Body fluid compartments and dehydration
0 of 5 answered, 0 correct
Patient
Male, 80 years old
Chief Complaint
Mild dehydration in an elderly patient; planning a dental procedure.
Background and/or Patient History
  • Mild dehydration from inadequate fluid intake
  • Skin tenting, dry mucous membranes
  • Dental procedure planned
Allergies
NKDA
Medications
  • Lisinopril
  • Hydrochlorothiazide
Current Findings
  • Elderly dehydrated patient
  1. Question 1
    Moderate
    Total body water in the elderly is typically:
  2. Question 2
    Hard
    Mild dehydration affects the ECF first because:
  3. Question 3
    Moderate
    Antihypertensive medications in this patient that increase dehydration risk include:
  4. Question 4
    Hard
    An NSAID added to this patient's regimen would:
  5. Question 5
    Easy
    The teaching point is that fluid status:

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Keep studying
Cell Physiology & Body Fluids core recall

Refresh the anatomy facts these cases depend on: nerve numbers, foramina, functions, and lesion findings.

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