- The following statements were proposed by a researcher on the characteristic features of stretch receptors in atria and the effect of these receptors’ activity on blood pressure regulation:
A. The activity of type A receptors are increased by burst of impulses during atrial systole
B. The activity of type B receptors are increased by burst of impulses at the time of peak atrial filling during late diastole of atria
C. The discharge of type B atrial receptors is increased when venous return is increased
D. The activity of type B atrial receptors is increased by positive pressure breathing
E. The increased activity of most of the atrial receptors initiates reflex circulatory adjustment by increasing blood pressure
F. The heart rate is decreased reflexly by the increased activity of atrial receptors
Choose all CORRECT statements from the following options:
(1) A, B and C (2) B, C and D
(3) C, D and E (4) D, E and F
Introduction to Atrial Stretch Receptors
Atrial stretch receptors, found primarily at the junctions of the atria and large veins, are crucial for detecting changes in blood volume and pressure. These receptors, primarily myelinated vagal afferents, are categorized into two types based on their activity patterns and timing during the cardiac cycle:
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Type A receptors: Activated during atrial contraction (atrial systole), responding to wall tension caused by active contraction.
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Type B receptors: Activated during atrial filling (late diastole), responding to stretch caused by increased venous return.
Analysis of Each Statement
A. The activity of type A receptors is increased by bursts of impulses during atrial systole
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Correct. Type A receptors fire bursts during the contraction phase coinciding with the ‘a’ wave of the atrial pressure curve.
B. The activity of type B receptors is increased by bursts of impulses at peak atrial filling during late diastole
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Correct. Type B receptors activate during the ‘v’ wave of atrial pressure, corresponding to atrial filling.
C. The discharge of type B atrial receptors increases when venous return increases
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Correct. Enhanced venous return stretches the atrial walls more, increasing type B receptor firing.
D. The activity of type B atrial receptors is increased by positive pressure breathing
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Correct. Positive pressure in the thorax may enhance atrial pressures and receptor activation.
E. Increased activity of most atrial receptors initiates reflex circulatory adjustments by increasing blood pressure
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Incorrect. Increased atrial receptor activity usually leads to decreased blood pressure through reflex vasodilation and natriuresis.
F. Heart rate is decreased reflexly by increased activity of atrial receptors
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Incorrect. Increased atrial receptor activity via the Bainbridge reflex tends to increase heart rate.
Correct Statements From Options
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(1) A, B, and C — All correct.
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(2) B, C, and D — All correct.
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(3) C, D, and E — E is incorrect.
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(4) D, E, and F — E and F are incorrect.
Thus, the possible correct answers are either (1) A, B, and C or (2) B, C, and D.
Since A is indeed correct based on physiological firing patterns and D (effect of positive pressure breathing) is also supported in research but sometimes considered secondary, the better answer aligning with standard knowledge is:
(1) A, B, and C
Physiological Summary
Statement Correctness Explanation A Correct Type A receptors fire in bursts during atrial contraction B Correct Type B receptors fire during atrial filling (late diastole) C Correct Type B receptor activity increases with venous return D Correct but occasionally debated Positive pressure breathing increases pressure activating receptors E Incorrect Increased receptor activity usually decreases blood pressure F Incorrect Reflex heart rate typically increases via Bainbridge reflex
Conclusion
The correct choice is:
(1) A, B, and C
These statements accurately describe the behavior of atrial stretch receptors and their roles in hemodynamic regulation.
Further Insights
Atrial stretch receptors contribute to:
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Regulation of blood volume via natriuretic peptides release.
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Reflex modulation of systemic vascular resistance.
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Bainbridge reflex-mediated heart rate adjustments.
Understanding these functions helps comprehend cardiovascular homeostasis in health and disease.
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2 Comments
Varsha Tatla
September 17, 2025Easy
Aakansha sharma Sharma
October 3, 2025(1) A, B, and C