Correct option is C
Explanation-
Type A receptors: Activated during atrial systole (when atria contract).
Type B receptors: Activated during atrial filling (late diastole).
Both are low-pressure baroreceptors that monitor venous return and blood volume. Their stimulation generally causes reflex tachycardia and diuresis (Bainbridge reflex), not an increase in blood pressure.
Statement A - The activity of type A receptors is increased by burst of impulses during atrial systole - CORRECT
Type A receptors fire during atrial contraction, i.e., systole.
Statement B - The activity of type B receptors is increased by burst of impulses at the time of peak atrial filling during late diastole of atria - CORRECT
Type B receptors are activated by stretch due to venous return in late diastole.
Statement C - The discharge of type B atrial receptors is increased when venous return is increased - CORRECT
More venous return = more atrial filling, leading to greater stretch and increased discharge of type B receptors.
Statement D - The activity of type B atrial receptors is increased by positive pressure breathing - CORRECT
Positive pressure breathing increases intrathoracic pressure, influencing venous return and atrial stretch, which can stimulate B receptors.
Statement E - The increased activity of most of the atrial receptors initiates reflex circulatory adjustment by increasing blood pressure - INCORRECT
Their stimulation leads to vasodilation, natriuresis, and diuresis (not increased BP). They reduce blood volume and pressure, not increase it.
Statement F - The heart rate is decreased reflexly by the increased activity of atrial receptors - INCORRECT
This is opposite of the Bainbridge reflex. Increased atrial receptor activity → reflex increase in HR (not decrease).
Final Answer:
Correct statements: A, B, C, and D
So, the most appropriate option is Option c - A, B and C
