MBBS Physiology 1 — Questions and Answers
Question 1: What is the normal resting membrane potential of a cardiac ventricular myocyte?
- -55 mV
- -70 mV
- -90 mV (Correct answer)
- -110 mV
Correct answer: -90 mV
The resting membrane potential of ventricular myocytes is approximately -90 mV, maintained primarily by K+ leak channels.
Question 2: Which of the following shifts the oxygen-hemoglobin dissociation curve to the right?
- Decreased temperature
- Decreased PCO2
- Increased 2,3-DPG (Correct answer)
- Increased pH
Correct answer: Increased 2,3-DPG
Increased 2,3-DPG reduces hemoglobin's affinity for oxygen, shifting the curve to the right and facilitating oxygen unloading to tissues.
Question 3: The Frank-Starling mechanism of the heart states that:
- Heart rate increases with increased venous return
- Stroke volume increases with increased end-diastolic volume (Correct answer)
- Cardiac output is independent of preload
- Contractility decreases with increased stretch
Correct answer: Stroke volume increases with increased end-diastolic volume
The Frank-Starling mechanism states that stroke volume increases as end-diastolic volume increases, up to a physiological limit.
Question 4: Which hormone is responsible for the long-loop negative feedback on the hypothalamo-pituitary axis in thyroid regulation?
- TSH
- TRH
- T3 and T4 (Correct answer)
- Calcitonin
Correct answer: T3 and T4
T3 and T4 exert negative feedback on both the pituitary (inhibiting TSH) and hypothalamus (inhibiting TRH) to regulate their own production.
Question 5: What is the GFR (glomerular filtration rate) in a healthy adult?
- 60 mL/min
- 90 mL/min
- 125 mL/min (Correct answer)
- 180 mL/min
Correct answer: 125 mL/min
The normal GFR in a healthy adult is approximately 125 mL/min (180 L/day), with approximately 99% of the filtrate reabsorbed.
Question 6: During exercise, which of the following best explains the increase in cardiac output?
- Increased vagal tone
- Increased sympathetic activity and venous return (Correct answer)
- Decreased heart rate with increased stroke volume only
- Peripheral vasoconstriction reducing afterload
Correct answer: Increased sympathetic activity and venous return
During exercise, sympathetic activation increases heart rate and contractility while increased venous return (via muscle pump) boosts stroke volume.
MBBS Physiology 1
What is the normal resting membrane potential of a cardiac ventricular myocyte?