Functioning of the Heart / Nodal System

The functioning of the heart regulates by two nodes SAN (Sinoatrial node) which is also known as Heartbeat initiating Centre/ Contraction center/ Heart of the heart/ Keith & Flock Node. The discovery of the SA Node was done by Arther Keith and Martin black. The second node is the AVN (Atrioventricular node) also known as Pacesetter. The discovery of the AV Node was done by Mr. Hiss. These two nodes make a major part of the nodal system.



Nodal System of the Heart


SA Node - Nodal System

SinoAtrial Node or the SA Node is present on the right upper corner of the right atrium. It is auto excitable because it does not require any external stimulus. SA node controls/ regulates contraction of both the Atrium. It stimulates by the high pressure of the Atrium (internal stimulus).


AV Node - Nodal System

The AtrioVentricular Node or the AV Node is present on the lower-left corner of the right Atrium close to the atrioventricular septum. AV node controls the contraction of both ventricles. Throttle’s bundle carries the information from the SA Node to the AV node. Atrioventricular bundles arise from the AV node. Then these pass through the atrioventricular septum and emerges at the top of the interventricular septum (IVS) and immediately divides into right and left bundles.

Right and Left bundles pass through the interventricular septum and divide into fine branches called Purkinje fibers. These spread in the walls of the ventricle of their side. Right and left bundles and Purkinje fibers are altogether known as BUNDLE OF HISS. SA Node, AV Node and Bundle of HISS comprise of specialized cardiac muscle fibers. But these functions as nerves because they have lost the contraction property.

Note

Actually, SAN and AVN do not control the contraction of cardiac muscles but they regulate the functioning of the heart in two ways. It maintains rhythmic contractile activities of the heart. When a particular type of node simulates (SAN/AVN), all the muscles of the atrium & ventricles contract at the same time. Secondly, Nodal Musculature has a tendency to generate an action potential. A number of action potential generated at different rates at the different parts of the nodal system. The maximum action potential generates at SA node which is 72-75 times/minute.


SA node initiates Heartbeat and maintains the rhythmic contractile activities of the heart and is therefore known as Pacemaker.

A.J de Bola and H. Sonnenberg discovered that the heart secretes a local hormone known as Atrial Natriuretic Factor (ANF). All the functioning of the heart is under the self-control of cardiac muscle.



Note

In general, the Atrial Natriuretic Factor acts as a vasodilator and reduces blood pressure.

Functioning of the Heart - Artificial pacemaker

An artificial pacemaker helps in Functioning of the Heart. The artificial pacemaker was first discovered by Mr. Chardac in 1960. It has a pulse generator and an electrode. The pulse generator has a Lithium halide battery which provides energy for more than 30 years. The electrode is of high-quality metal (titanium) and has a covering of biological protein.
The transplantation of the Pulse generator occurs either just above S.A Node or transvenous transplant occurs. And the tip of the electrode is inserted deep inside the right ventricle.

Artificial Pacemaker

The artificial pacemaker is of two types -
Fixed-rate: In this SA Node is more damaged.
Demand rate: SA Node performs some functions but there is missing some Heartbeats.


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