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📚 Guyton & Hall – Medical Physiology Question Bank

20 MCQs | Mixed Topics | Undergraduate Level Reference: Guyton and Hall Textbook of Medical Physiology (14th Ed.)

UNIT I – MEMBRANE PHYSIOLOGY & NERVE

Q1. A nerve fiber at rest has a membrane potential of −70 mV. When a stimulus depolarizes the membrane to threshold, rapid sodium influx occurs. What is the approximate threshold potential at which voltage-gated sodium channels open?

A) −90 mV
B) −70 mV
C) −55 mV ✅
D) 0 mV
E) +35 mV

Answer: C — −55 mV Guyton: "An action potential is triggered when a stimulus depolarizes the membrane to a threshold level, usually around −55 mV." (Ch. 5)

Q2. During the repolarization phase of the action potential, which event primarily restores the resting membrane potential?

A) Inward Na⁺ current through voltage-gated channels
B) Closure of K⁺ channels
C) Outward K⁺ current through voltage-gated K⁺ channels ✅
D) Inward Ca²⁺ current
E) Activation of Na⁺–K⁺–ATPase

Answer: C Guyton: "Rapid diffusion of potassium ions to the exterior reestablishes the normal negative resting membrane potential, which is called repolarization of the membrane." (Ch. 5)

Q3. After repolarization, the membrane potential briefly becomes more negative than −70 mV. This phenomenon is called:

A) Depolarization
B) Absolute refractory period
C) Threshold potential
D) Hyperpolarization (undershoot) ✅
E) Summation

Answer: D Guyton: "The potassium channels may remain open longer than needed to return the membrane to its resting potential, resulting in hyperpolarization (Fig. 5.6), also called undershoot." (Ch. 5)

UNIT II – CARDIOVASCULAR PHYSIOLOGY

Q4. At the normal equilibrium point of cardiac output and venous return curves, what is the approximate cardiac output and right atrial pressure in a resting adult?

A) 3 L/min; −5 mm Hg
B) 5 L/min; 0 mm Hg ✅
C) 7 L/min; +5 mm Hg
D) 5 L/min; +8 mm Hg
E) 2 L/min; 0 mm Hg

Answer: B Guyton: "In the normal circulation, the right atrial pressure, cardiac output, and venous return are all depicted by point A…giving a normal value for cardiac output of 5 L/min and a right atrial pressure of 0 mm Hg." (Ch. 20)

Q5. A sudden infusion of blood equal to 20% of the blood volume is administered. What is the expected immediate effect on cardiac output?

A) Decrease by 50%
B) Remain unchanged due to autoregulation
C) Increase 2.5 to 3 times normal ✅
D) Increase by 20%
E) Drop due to cardiac strain

Answer: C Guyton: "A sudden increase in blood volume of about 20% increases the cardiac output to about 2.5 to 3 times normal." (Ch. 20)

Q6. Following a large blood transfusion, which compensatory mechanism helps return cardiac output toward normal?

A) Decreased aldosterone secretion
B) Fluid transudation from capillaries due to increased capillary pressure ✅
C) Decreased sympathetic tone
D) Bradycardia
E) Renal arteriolar dilation

Answer: B Guyton: "The increased cardiac output increases the capillary pressure so that fluid begins to transude out of the capillaries." (Ch. 20)

Q7. A patient with increased peripheral resistance to venous return will show which change on the venous return curve?

A) Rightward shift with steeper slope
B) Leftward shift with no change in slope
C) Rotation downward (flatter slope) ✅
D) No change
E) Upward parallel shift

Answer: C Guyton describes that increased resistance to venous return rotates the venous return curve downward/flatter. (Ch. 20)

UNIT III – RENAL PHYSIOLOGY

Q8. Which of the following correctly describes the composition of the glomerular filtrate?

A) Rich in red blood cells and albumin
B) Similar to plasma, but almost devoid of proteins and cells ✅
C) High in fatty acids and calcium
D) Concentrated with plasma proteins
E) Contains only water and electrolytes

Answer: B Guyton: "The glomerular filtrate normally has only tiny amounts of protein and is devoid of cellular elements, including red blood cells. The concentrations of other constituents… are similar to the concentrations in the plasma." (Ch. 27)

Q9. The average GFR in a healthy adult is approximately:

A) 60 mL/min
B) 90 mL/min
C) 125 mL/min ✅
D) 200 mL/min
E) 50 mL/min

Answer: C Guyton: "In the average adult human, the GFR is about 125 mL/min, or 180 L/day." (Ch. 27)

Q10. Approximately what fraction of renal plasma flow is normally filtered (filtration fraction)?

A) 5%
B) 10%
C) 20% ✅
D) 35%
E) 50%

Answer: C Guyton: "The filtration fraction averages about 0.2, which means that about 20% of the plasma flowing through the kidney is filtered through the glomerular capillaries." (Ch. 27)

Q11. The glomerular capillary membrane differs from typical capillaries in having how many layers?

A) One layer (endothelium only)
B) Two layers
C) Three layers ✅
D) Four layers
E) Five layers

Answer: C Guyton: "The glomerular capillary membrane… has three (instead of the usual two) major layers: (1) endothelial cells… (2) a basement membrane; and (3) a layer of epithelial cells (podocytes)." (Ch. 27)

Q12. With normal aging from young adulthood to age 70–75 years, healthy adults lose approximately what fraction of nephrons?

A) One quarter
B) One third
C) One half ✅
D) Two thirds
E) Three quarters

Answer: C Guyton: "From young adulthood (18 to 29 years) to age 70 to 75 years, healthy adults lose almost half of their nephrons." (Ch. 27)

UNIT IV – RESPIRATORY PHYSIOLOGY

Q13. Under normal resting conditions, approximately what percentage of oxygen transported in the blood is carried bound to hemoglobin?

A) 50%
B) 70%
C) 97% ✅
D) 100%
E) 85%

Answer: C Guyton: "Normally, about 97% of the oxygen transported from the lungs to the tissues is carried in chemical combination with hemoglobin in the red blood cells." (Ch. 41)

Q14. In normal systemic arterial blood (PO₂ ≈ 95 mm Hg), hemoglobin saturation is approximately:

A) 50%
B) 75%
C) 85%
D) 97% ✅
E) 100%

Answer: D Guyton: "The blood leaving the lungs and entering the systemic arteries usually has a PO₂ of about 95 mm Hg, the usual O₂ saturation of systemic arterial blood averages 97%." (Ch. 41)

Q15. Each gram of normal hemoglobin can bind a maximum of approximately how much oxygen?

A) 0.5 mL
B) 1.0 mL
C) 1.34 mL ✅
D) 2.0 mL
E) 2.5 mL

Answer: C Guyton: "Each gram of hemoglobin can bind with a maximum of 1.34 mL of O₂." (Ch. 41)

Q16. Under normal resting conditions, about how many mL of O₂ are transported from lungs to tissues per 100 mL of blood flow?

A) 1 mL
B) 3 mL
C) 5 mL ✅
D) 10 mL
E) 20 mL

Answer: C Guyton: "Under normal conditions, about 5 mL of O₂ are transported from the lungs to the tissues by each 100 mL of blood flow." (Ch. 41)

UNIT V – ENDOCRINE & METABOLIC PHYSIOLOGY

Q17. Between meals, resting muscle depends primarily on which energy substrate?

A) Glucose
B) Amino acids
C) Ketone bodies
D) Fatty acids ✅
E) Lactate

Answer: D Guyton: "During much of the day, muscle tissue depends mainly on fatty acids for its energy, rather than glucose… because the normal resting muscle membrane is only slightly permeable to glucose, except when the muscle fiber is stimulated by insulin." (Ch. 79)

Q18. During moderate-to-heavy exercise, muscle glucose uptake increases without requiring large amounts of insulin. What mechanism explains this?

A) Activation of glucagon receptors on muscle
B) Increased GLUT-1 expression
C) Translocation of GLUT-4 to the cell membrane due to muscle contraction ✅
D) Increased Na⁺–K⁺–ATPase activity
E) Decreased fatty acid oxidation

Answer: C Guyton: "Muscle contraction increases translocation of glucose transporter 4 (GLUT 4) from intracellular storage depots to the cell membrane, which, in turn, facilitates diffusion of glucose into the cell." (Ch. 79)

Q19. How much can insulin increase the rate of glucose transport into resting muscle cells?

A) 2-fold
B) 5-fold
C) 10-fold
D) At least 15-fold ✅
E) 50-fold

Answer: D Guyton: "Insulin can increase the rate of transport of glucose into resting muscle cells by at least 15-fold." (Ch. 79)

Q20. A patient eats a carbohydrate-rich meal. Insulin is secreted in large quantities. Which of the following effects does insulin have on the liver?

A) Stimulates liver phosphorylase to break down glycogen
B) Promotes gluconeogenesis from amino acids
C) Inactivates liver phosphorylase and promotes glycogen storage ✅
D) Decreases glucose transport into hepatocytes
E) Stimulates ketogenesis

Answer: C Guyton: "Insulin inactivates liver phosphorylase, the principal enzyme that causes liver glycogen to split into glucose… [insulin] causes most of the glucose absorbed after a meal to be rapidly stored in the liver in the form of glycogen." (Ch. 79)

Summary Table

#	System	Topic	Answer
1	Neurophysiology	Action potential threshold	C (−55 mV)
2	Neurophysiology	Repolarization mechanism	C (K⁺ efflux)
3	Neurophysiology	Hyperpolarization / undershoot	D
4	Cardiovascular	Equilibrium cardiac output	B (5 L/min, 0 mmHg)
5	Cardiovascular	Blood volume & cardiac output	C (2.5–3×)
6	Cardiovascular	Compensation after transfusion	B
7	Cardiovascular	Venous return curve	C
8	Renal	Glomerular filtrate composition	B
9	Renal	Normal GFR	C (125 mL/min)
10	Renal	Filtration fraction	C (20%)
11	Renal	Glomerular membrane layers	C (3 layers)
12	Renal	Nephron loss with aging	C (half)
13	Respiratory	O₂ transport by Hb	C (97%)
14	Respiratory	Arterial Hb saturation	D (97%)
15	Respiratory	O₂ per gram Hb	C (1.34 mL)
16	Respiratory	O₂ delivery per 100 mL blood	C (5 mL)
17	Endocrine	Resting muscle energy substrate	D (fatty acids)
18	Endocrine	Exercise glucose uptake	C (GLUT-4)
19	Endocrine	Insulin & glucose transport	D (15-fold)
20	Endocrine	Insulin effect on liver	C (glycogen storage)

All questions are directly sourced from Guyton and Hall Textbook of Medical Physiology chapters 5, 20, 27, 41, and 79. Want more questions on a specific system, harder difficulty, or a different format (True/False, essay, clinical vignettes)?

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