Chronotropes Definition and Examples

Chronotropes Overview

• Chronotropes are factors that influence heart rate.
• Can be classified into positive and negative chronotropes.

Examples of Chronotropes

• The autonomic nervous system is a primary regulator.
• Hormones and various chemicals also serve as chronotropic agents.

Cardioinhibitory Mechanism

• Operated by the parasympathetic nervous system, acting as a negative chronotrope.
• Involves the release of acetylcholine (AcH).
• AcH binds to muscarinic receptors, opening potassium channels in the sinoatrial (SA) and atrioventricular (AV) nodes.
• This process makes it harder for these nodes to reach the depolarization threshold.

Cardioacceleratory Mechanism

• Function of the sympathetic nervous system, acting as a positive chronotrope.
• Characterized by the release of epinephrine, which binds to beta-adrenergic receptors.
• Activation of the cAMP second messenger system opens calcium and sodium channels in the SA and AV nodes.
• This mechanism facilitates depolarization, increasing heart rate.

Positive Chronotropes

• Defined as agents that increase heart rate.
• Play a crucial role in enhancing cardiac output during physical activity or stress.

Negative Chronotropes

• Defined as agents that decrease heart rate.
• Important in regulating heart function during rest or in response to certain conditions.

Cardiac Control Center

• Located in the medulla oblongata of the brain.
• Plays a vital role in regulating heart rate and overall cardiovascular function.

Effects of Potassium Levels

• Hypokalemia (low potassium levels) can lead to cardiac arrest.
• Hyperkalemia (high potassium levels) can also result in the heart ceasing to beat.