Contractility refers to the

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of the contraction of the heart muscle.

Correct answer:

• Stroke volume (SV) = 60 mL
• This stroke volume is within the normal expected range.

Stroke volume represents the amount of blood ejected from the ventricle with each heartbeat and is calculated using the formula:

SV = EDV – ESV

EDV (end-diastolic volume) = 150 mL
ESV (end-systolic volume) = 90 mL

SV = 150 mL – 90 mL

= 60 mL

An anatomically and physiologically normal adult stroke volume ranges from approximately 60–100 mL per beat. This measurement indicates that the ventricles are ejecting an adequate volume of blood during systole. The calculation reflects effective ventricular filling and contractility, suggesting that the patient’s heart is pumping a normal volume of blood per beat.

Correct answer: True

The Bainbridge reflex is a physiological response mediated by stretch receptors located in the walls of the right atrium and the venae cavae. When venous return increases, atrial stretch stimulates these proprioceptive receptors, sending signals via the vagus nerve to the cardiovascular centers in the medulla oblongata. In response, sympathetic activity to the sinoatrial node increases, resulting in an elevated heart rate. This reflex helps maintain homeostasis by ensuring that the increased blood volume returning to the heart is effectively ejected, preventing venous congestion and optimizing cardiac output.