Advanced Dental Admission Test (ADAT)

What is the effect of Beta 1 adrenergic receptors on cardiac output?

1. Decrease cardiac output

2. Increase heart rate and contractility

3. No effect on contractility

4. Decrease heart rate

The correct answer is: Increase heart rate and contractility

Beta 1 adrenergic receptors play a crucial role in the regulation of cardiac output by influencing heart rate and the strength of heart contractions, known as contractility. When these receptors are activated, typically by catecholamines like norepinephrine and epinephrine, they lead to several physiological responses: 1. **Increase in Heart Rate**: The activation of Beta 1 receptors in the sinoatrial (SA) node of the heart accelerates depolarization, leading to an increase in heart rate. This is particularly significant during times of stress or physical activity when the body needs to boost blood flow and oxygen delivery. 2. **Increase in Contractility**: Beta 1 receptors also enhance the force of cardiac muscle contraction. This is achieved through increased intracellular calcium levels, which improve the contractile strength of the myocardium. The more forceful contractions contribute to a larger stroke volume, thereby elevating cardiac output. Given these mechanisms, it is evident that the stimulation of Beta 1 adrenergic receptors directly contributes to an increase in both heart rate and contractility, which consequently raises cardiac output. This effect is essential for meeting the body's increased demands during exercise, stress, or other situations that require heightened physiological response.