Emergency Medical Technician (EMT) Basic Certification Practice Exam

Which receptor type is primarily responsible for increasing heart rate?

1. Alpha 1 receptors

2. Beta 1 receptors

3. Beta 2 receptors

4. Muscarinic receptors

The correct answer is: Beta 1 receptors

The primary receptor type responsible for increasing heart rate is the beta 1 receptor. These receptors are located mainly in the heart, and when they are stimulated, they promote an increase in the force and rate of cardiac contraction. This results in an elevated heart rate, facilitating improved blood flow and oxygen delivery to tissues during situations requiring heightened physical activity or in response to stressors. Beta 1 receptors are adept at responding to catecholamines, such as adrenaline and noradrenaline, which are released during sympathetic nervous system activation. This mechanism is crucial for the body's "fight or flight" response. Engaging these receptors leads not only to an increase in heart rate but also enhances the heart's contractility, which together contribute to a more efficient cardiovascular response to demands on the body. In contrast, alpha 1 receptors primarily mediate vasoconstriction and do not have a direct role in increasing heart rate. Beta 2 receptors generally influence smooth muscle relaxation, such as in the lungs, and have minimal effect on heart rate. Muscarinic receptors are involved in parasympathetic responses and typically decrease heart rate when activated. Thus, beta 1 receptors stand out as the key players in cardiac acceleration.