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Physiology & Biochemistry: INBDE study notes and practice questions

These are the biomedical foundations that explain why patients present as they do: how organ systems work, how metabolism and nutrition affect oral tissues, and how inherited conditions are passed on and show up in the mouth.

150 practice questions · 5 patient cases

Practice Physiology & Biochemistry

Where it fits in the official INBDE blueprint

Foundation Knowledge (FK 1, 2, 4). Nearest foundation knowledge areas: FK 1, FK 2, FK 4. See the content outline for the official weights. This mapping is approximate: real items combine a clinical area with a foundation area.

What this area tests

High-yield checklist

Common traps

These notes are original study aids, not official exam content. Confirm clinical details against current guidelines.

Sample questions

1. Which of the following is an example of a Type III hypersensitivity reaction?

  1. Graves disease
  2. Contact dermatitis
  3. Systemic lupus erythematosus (SLE)
  4. Erythroblastosis fetalis
Show answer and explanation

Correct answer: C. Systemic lupus erythematosus (SLE)

Type III hypersensitivity involves immune complex deposition and includes SLE, serum sickness, and post-streptococcal glomerulonephritis. Graves disease and erythroblastosis fetalis are Type II (antibody directly targeting a cell-surface antigen/receptor), and contact dermatitis is Type IV (delayed, T-cell mediated).

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2. Multiple Sclerosis (MS) is a demyelinating disease involving oligodendrocytes. How is it classified?

  1. Reactive (inflammatory response to infection)
  2. Developmental (abnormal development of the nervous system)
  3. Autoimmune (immune-mediated attack on myelin/oligodendrocytes)
  4. Hereditary (single gene mutation)
Show answer and explanation

Correct answer: C. Autoimmune (immune-mediated attack on myelin/oligodendrocytes)

Multiple Sclerosis (MS) is classified as an autoimmune disease. The immune system attacks the myelin sheath produced by oligodendrocytes in the CNS, causing demyelinating plaques. This leads to impaired nerve conduction and the characteristic relapsing-remitting or progressive neurological symptoms. While genetic susceptibility exists, it is not a single-gene hereditary condition — it is the autoimmune attack that defines its pathophysiology.

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3. A decrease in Carbon Dioxide (CO2) in your blood (hypocapnia) will lead to:

  1. Increased tidal volume
  2. Decreased respiratory rate
  3. Bronchoconstriction
  4. Vasodilation
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Correct answer: B. Decreased respiratory rate

CO2 is the PRIMARY driver of respiration. When CO2 DECREASES (hypocapnia — e.g., during hyperventilation), the respiratory drive is REDUCED, leading to DECREASED tidal volume and respiratory rate (the body slows breathing to allow CO2 to build back up). Increased tidal volume (A) would occur with HIGH CO2. Hypocapnia causes vasoconstriction (not vasodilation — D wrong) and cerebral vasoconstriction (causes lightheadedness in hyperventilation). B is the best answer among options.

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4. A patient with pre-auricular pain, 45mm opening, and 'pop-and-click' most likely has:

  1. Myofascial pain dysfunction syndrome
  2. Internal derangement with reduction
  3. Auriculotemporal syndrome
  4. Coronoid hyperplasia
Show answer and explanation

Correct answer: B. Internal derangement with reduction

The 'pop-and-click' is pathognomonic for internal derangement with reduction u2014 the disc displaces anteriorly but recaptures during opening. Normal mouth opening (45mm) confirms reduction is occurring. MPDS is a muscular disorder without clicking.

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5. A patient with cancer, hyperparathyroidism, and hyperkalemia — what is the most likely cause of the hyperkalemia?

  1. The underlying malignancy
  2. Vitamin D deficiency
  3. Hyperparathyroidism itself
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Correct answer: A. The underlying malignancy

Hyperparathyroidism's primary metabolic effect is on calcium and phosphate (causing hypercalcemia), not potassium — it is not a direct, expected cause of hyperkalemia. The underlying malignancy (through mechanisms like tumor lysis, paraneoplastic effects, or renal involvement) is the most plausible explanation for hyperkalemia among the choices given.

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6. Which fiber is responsible for contraction of the vessels (vasoconstriction)?

  1. A gamma
  2. A beta
  3. C fibers
  4. A delta
Show answer and explanation

Correct answer: A. A gamma

A GAMMA (Aγ) fibers are efferent fibers innervating intrafusal muscle spindle fibers AND are associated with sympathetic vasoconstriction. Sympathetic adrenergic fibers controlling vasomotion are classified as A-gamma efferents. A-beta fibers are large myelinated sensory fibers for touch/pressure. C fibers are unmyelinated, associated with slow/burning pain and postganglionic autonomic. A-delta are small myelinated fibers for sharp pain. A gamma is correct for vessel contraction.

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7. What is the most common chromosomal anomaly / defect?

  1. Trisomy 13 (Patau syndrome)
  2. Trisomy 21 (Down syndrome)
  3. Trisomy 18 (Edwards syndrome)
  4. Monosomy X (Turner syndrome)
Show answer and explanation

Correct answer: B. Trisomy 21 (Down syndrome)

Trisomy 21 (Down syndrome) is the MOST COMMON chromosomal abnormality in live births, occurring in approximately 1 in 700 live births. It is caused by nondisjunction during meiosis, resulting in three copies of chromosome 21. Dental features: hypodontia, delayed eruption, macroglossia, bruxism, increased periodontal disease. Trisomy 18 and 13 are more severe but much less common. Turner syndrome affects females only.
  • A. CORRECT. Trisomy 21 (Down syndrome) is the most common chromosomal abnormality in live-born children — approximately 1:700 live births.
  • B. Incorrect. Trisomy 18 (Edwards syndrome) occurs in approximately 1:5,000 live births — much less common than Trisomy 21.
  • C. Incorrect. Monosomy X (Turner syndrome, 45,X) affects 1:2,500 females — less common than Trisomy 21.
  • D. Incorrect. Trisomy 13 (Patau syndrome) occurs in about 1:10,000–20,000 live births — much rarer than Trisomy 21.

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8. Which is the most common chromosomal abnormality compatible with survival?

  1. Trisomy 18 (Edwards syndrome)
  2. Trisomy 21 (Down syndrome)
  3. Trisomy 16
  4. Trisomy 13 (Patau syndrome)
Show answer and explanation

Correct answer: B. Trisomy 21 (Down syndrome)

Trisomy 21 (Down syndrome): most common viable trisomy (~1/700 live births). Oral findings: macroglossia, hypodontia, delayed eruption. Trisomies 13/18: severe anomalies, high infant mortality.

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Patient cases

All Physiology & Biochemistry questions (150)