Physician Assistant Scientific Knowledge 3 — Questions and Answers
Question 1: Which pharmacokinetic parameter describes the fraction of an administered drug that reaches systemic circulation unchanged?
- Bioavailability (F) (Correct answer)
- Volume of distribution (Vd)
- Clearance (CL)
- Half-life (t½)
Correct answer: Bioavailability (F)
Bioavailability (F) quantifies the proportion of an administered dose that reaches systemic circulation, accounting for first-pass metabolism and absorption.
Question 2: The complement system's membrane attack complex (MAC) is formed by which terminal complement components?
- C5b-9 (Correct answer)
- C3a and C5a
- C1q, C1r, C1s
- C4b2a3b
Correct answer: C5b-9
The MAC is assembled from C5b through C9, forming a pore in the target cell membrane that causes osmotic lysis.
Question 3: In a patient with metabolic alkalosis, which compensatory mechanism would you expect?
- Hypoventilation to retain CO2 (Correct answer)
- Hyperventilation to eliminate CO2
- Increased renal bicarbonate excretion only
- Decreased aldosterone secretion
Correct answer: Hypoventilation to retain CO2
Metabolic alkalosis is compensated by hypoventilation, which retains CO2 and increases carbonic acid to buffer the elevated pH.
Question 4: Which neurotransmitter is released at the neuromuscular junction to initiate skeletal muscle contraction?
- Acetylcholine (Correct answer)
- Norepinephrine
- Dopamine
- Glutamate
Correct answer: Acetylcholine
Acetylcholine is released from motor neuron terminals and binds nicotinic receptors on the motor end plate, triggering muscle depolarization.
Question 5: Which vitamin requires intrinsic factor for absorption and is deficient in pernicious anemia?
- Vitamin B12 (cobalamin) (Correct answer)
- Vitamin B1 (thiamine)
- Vitamin B6 (pyridoxine)
- Folate
Correct answer: Vitamin B12 (cobalamin)
Vitamin B12 binds intrinsic factor produced by gastric parietal cells for absorption in the terminal ileum; autoimmune destruction of parietal cells causes pernicious anemia.
Question 6: The zone of inhibition in a Kirby-Bauer disk diffusion test is used to determine which microbiological property?
- Antibiotic susceptibility of a bacterial isolate (Correct answer)
- Bacterial growth rate
- Minimum bactericidal concentration (MBC)
- Bacterial virulence factors
Correct answer: Antibiotic susceptibility of a bacterial isolate
The Kirby-Bauer test measures zones of inhibited bacterial growth around antibiotic-impregnated disks to classify organisms as susceptible, intermediate, or resistant.
Question 7: Preload in cardiac physiology refers to which hemodynamic parameter?
- End-diastolic ventricular volume (or pressure) (Correct answer)
- Systemic vascular resistance
- Aortic diastolic pressure
- Heart rate at rest
Correct answer: End-diastolic ventricular volume (or pressure)
Preload represents the degree of ventricular stretch before contraction, best approximated by end-diastolic volume, and follows the Frank-Starling mechanism.
Physician Assistant Scientific Knowledge 3
Which pharmacokinetic parameter describes the fraction of an administered drug that reaches systemic circulation unchanged?