regulation of the force of heart contraction by cardiac conduction

Definition

Target type: biologicalprocess

A cardiac conduction process that modulates the extent of heart contraction, changing the force with which blood is propelled. [GOC:BHF, GOC:mtg_cardiac_conduct_nov11]

The regulation of the force of heart contraction, known as **contractility**, is intricately linked to the cardiac conduction system. This system, a network of specialized cardiac muscle cells, orchestrates the rhythmic beating of the heart by generating and propagating electrical impulses. The conduction system ensures coordinated contraction of the heart chambers, propelling blood efficiently throughout the body. Here's a detailed explanation of how the conduction system regulates heart contractility:

**1. Action Potential Generation and Conduction:**
- The heart's electrical activity begins in the **sinoatrial (SA) node**, the heart's natural pacemaker, located in the right atrium.
- The SA node spontaneously generates electrical impulses, triggering a rhythmic sequence of depolarization and repolarization in cardiac muscle cells. This electrical activity is represented as an **action potential**.
- The action potential spreads rapidly through the atrial muscle, causing atrial contraction.
- It then reaches the **atrioventricular (AV) node**, located at the junction between the atria and ventricles.
- The AV node acts as a gate, slowing down the conduction of the electrical impulse, allowing the ventricles to fill with blood before they contract.
- The impulse then travels through the **bundle of His**, a specialized conductive pathway, and branches into the **Purkinje fibers** which extend throughout the ventricular myocardium.
- The Purkinje fibers rapidly distribute the electrical impulse to all ventricular muscle cells, leading to synchronized ventricular contraction.

**2. Calcium-Mediated Contraction:**
- The arrival of the action potential at the ventricular muscle cells triggers the release of calcium ions (Ca2+) from the sarcoplasmic reticulum, the intracellular calcium store.
- The influx of Ca2+ into the cytoplasm initiates the process of muscle contraction by interacting with proteins called **troponin and tropomyosin**.
- These proteins regulate the interaction between the contractile proteins **actin and myosin**, which slide past each other to generate force.

**3. Modulation of Contractility:**
- The force of ventricular contraction, or contractility, can be modulated by several factors that influence calcium levels and the sensitivity of the contractile proteins to calcium:
- **Sympathetic Nervous System Activation:** The sympathetic nervous system, part of the autonomic nervous system, releases norepinephrine, a neurotransmitter that increases the rate and force of heart contractions. This is achieved by:
- Increasing the rate of action potential generation in the SA node.
- Accelerating conduction through the AV node.
- Enhancing calcium release from the sarcoplasmic reticulum.
- **Parasympathetic Nervous System Activation:** The parasympathetic nervous system, another part of the autonomic nervous system, releases acetylcholine, a neurotransmitter that decreases heart rate and force of contraction. This effect is primarily mediated by slowing down conduction through the AV node.
- **Hormonal Influences:** Hormones such as epinephrine (adrenaline) and thyroid hormones can also increase contractility by mechanisms similar to those of the sympathetic nervous system.
- **Drugs:** Medications like digitalis can increase contractility by enhancing calcium levels and sensitivity to calcium.

**4. Importance of Conduction Regulation:**
- The precise regulation of cardiac conduction is critical for maintaining normal heart function.
- Abnormalities in the conduction system can lead to irregular heart rhythms (arrhythmias), which can impair the heart's ability to pump blood effectively, potentially causing serious health problems.

**5. Summary:**
- The cardiac conduction system plays a crucial role in regulating the force of heart contraction.
- By generating and propagating electrical impulses, the conduction system ensures coordinated contraction of the heart chambers.
- The force of contraction can be modulated by factors like the autonomic nervous system, hormones, and drugs, affecting calcium levels and contractile protein sensitivity to calcium.
- The intricate interplay between electrical activity and calcium signaling within the heart muscle is fundamental to regulating heart contractility and maintaining cardiovascular health.'
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Proteins (1)

Compounds (9)