What Is SA Node and What Is the Function of SA Node?
A group of myocytes with pacemaker activity is represented by the SA (sinoatrial) node. It produces electrical impulses that, under normal circumstances, regulate the heart's rhythm and pace. The SA node, also called the sinus node, is a cluster of myocytes resembling a crescent spread over a few square millimeters. It is split by connective tissue. It is situated where the superior vena cava opening and the crista terminalis in the right atrium's top wall converge. These cells possess the capacity to produce an electrical impulse on their own.
Because of its modest bulk, the electrocardiogram (ECG) cannot detect a significant electrical signal from the sinus node. Rather, P waves produced by atrial activity must be used as an indirect indicator of SA nodal pacemaker activity. Any sinus node abnormality might impact the heart's pace and rhythm. The SA node comprises the coordinated actions of these so-called pacemaker cells.
After passing across the right atrium and the remainder of the heart's electrical conduction system, this electrical impulse is carried by perinodal cells, also known as transitional (T) cells. This ultimately causes myocardial contraction and the distribution of blood throughout the body. The sinus node maintains a healthy heart's regular rhythm and heart rate by continuously producing electrical impulses. As a result, the SA node is known as the heart's natural pacemaker.
The heart rate significantly varies based on physiological and environmental factors. At rest, the intrinsic rate at which the SA nodal myocytes depolarize is typically a normal heart rate, ranging from 60 to 100 beats per minute. The autonomic nervous system strictly regulates the sinus node's input. The pace of action potential production is slowed by parasympathetic input, which lowers the heart rate; the rate of action potential production is increased by sympathetic input, which raises the heart rate. The sinus node's precise and controlled regulation enables the heart to adjust to different physiological stimuli experienced by the body.
What Is AV Node and What Is the Function of AV Node?
A tiny structure in the heart called the atrioventricular (AV) node is situated in the interatrial septum, close to the coronary sinus, in the Koch triangle. The right coronary artery supplies the atrioventricular node in a right-dominant heart. This structure links the atria's electrical system and the ventricles' electrical system, delivering electrical impedance through the atria and an intrinsic pacemaker in the event of its absence. The AV node has an intrinsic rate between 40 and 60 beats per minute (bpm).
The right atrium provides the AV node with two inputs: anteriorly through the interatrial septum and posteriorly through the crista terminalis. Heart muscle cells' cell membranes must depolarize and then repolarize for them to contract. These things happen because of ions moving across cell membranes. The AV node and the cardiac conduction system work together to coordinate the mechanical activity of myocytes. A wave of excitement travels through the atria via specific conduction channels from the sinoatrial node. The AV node is thus turned on. The atrioventricular node delays impulses by roughly 0.09 seconds. The heart pulse must be delayed. It ensures that the atria have released their blood into them before the ventricles contract.
The term "atrioventricular conduction disease" (AV block) refers to a condition in which the atria and ventricles' electrical continuity is compromised. It happens when atrial depolarization does not reach the ventricles or when it is conducted unusually slowly. It may be a genetically inherited illness or the consequence of an injury.
Atrioventricular nodal re-entry tachycardia (AVNRT) is a condition that exclusively affects those with dual AV node physiology, accounting for approximately half of the population overall. Exclusively, a small percentage of these individuals will have AVNRT at some point. Atrioventricular nodal region cystic tumor (CTAVN), the AV node, tricuspid valve, and interatrial septum are the only locations where CTAVN, which is endodermal in origin, can arise.
What Is the Difference Between SA Node and AV Node?
SA node functions as a pacemaker. It is close to the superior vena cava opening on the right auricle wall. It can sustain a maximal rhythm. The medulla oblongata's heart centers are in charge of it. While the AV node does not play that role. It is located close to the interauricular septa at the right auricle. It has less rhythm capacity. The SA node controls it. Although they serve different purposes, the sinoatrial node and the atrioventricular node are crucial components of the cardiac conduction system.
The electrical impulse that the SA node sends into the atria causes them to constrict, as does the AV. The heart chamber can contract due to the electrical impulse that the node sends to the ventricles. Every component of the heart's electrical circuitry reset itself after contracting. A collection of cells called the sinoatrial node, and the atrioventricular node is responsible for heart chamber contraction. The primary role of the SA is to produce cardiac impulses, and the AV nodes relay the response that the SA nodes provide. In other words, the impulse produced by the sinoatrial nodes controls the action of the AV nodes.
Conclusion:
The sinoatrial (SA) node, a specialized cluster of myocardial conducting cells found between the right atrium's superior and posterior walls at the superior vena cava orifice, establishes a normal heart rhythm. Within the atrioventricular septum, in the inferior part of the right atrium, is a second cluster of specialized myocardial conducting cells known as the atrioventricular (AV) node. The impulse cannot propagate to the ventricles without first going via the AV node due to the septum.
