Assignment 1: The cardiovascular system
The cardiac conduction system comprises of a specialized network of cells located in the heart which produce and spread electrical signals through the heart to facilitate contraction. In other words, the pumping process of the heart is regulated by the cardiac conduction system. On the other hand, the cardiac cycle refers to series of events which take place when the heart beats. The cardiac cycle is driven by the force of cardiac conduction which comprises of an electrical system whose role is to power the cardiovascular system and the cardiac cycle. Blood is circulated throughout the body through the pulmonary and systemic circuits as the heart beats. The cardiac cycle encompasses two phases; the diastole and the systole phase.in the diastole phase. In the diastole phase, contraction of the ventricle occurs and blood is forced out of the heart to the arteries. In the diastole phase, relaxation of ventricles occurs and blood is filled in the heart.
The heart comprises of two specialized cells which trigger the conduction of the heart. Heart conduction involves depolarization and repolarization which are electrical sequences. This cardiac tissue property is known as inherent rhythmicity. The electrical signal is produced by the Sino atrial node (SA node) and spreads through particular conducting pathways to the ventricular muscle. The conducting pathways include the intermodal pathways, the antrioventricular node, the atria fibers, the bundle of His, the left and the right bundle branches (Lepeschkin 1950, p280) when the depolarization electrical signal reaches the contractile cell, contraction takes place. On the other hand, when the reporalization signal spreads to the myocardial cells, relaxation occuers. In his essence, the electrical signals leads to the mechanical pumpin action of the heart.
Each electrical and mechanical cycle is initaiated by the SA node which acts as the normal heart pacemaker. After the depolarization of the SA node, electrical stimulus extends through the the atrial muscle, triggering the contraction of the muscle. Therefore, the depolarization of the SA node is accompanied by the contraction of the atrial. Additionally, The SA node extends to the AV node through the nternodal fibres. However, the depolarization wave does not extend to the ventricles right away due to the presence of a non-conducting tissue which separates the atria from the ventricles. The electricla signal stuck in the AV node for about 0.20 seconds after the contraction of the atria, evetually, the signal is sspread to the ventricles through the bundle of His, left and right bundle branches and then to the purkinje fibres. The purkinje fibres then transmit the electrical signals to the ventricuar muscles directly, causing the ventricles to contract (ventricular systole). The SA node repolarization is also transmitted via the atria and then the ventricles, trigering the relaxation phase (ventricular diastole). Even though the heart creates its own beat, physiological foundation of the heart rate and the contraction strength is generated from the parasympathetic and sympsthetic divisions located within the nervous system (Boer et al. 1985, p150).
The sympathetic system perfoms as an accelarator, it speeds up and increases to contaction force of the heart. When more oxygen is needed in the body for instance during exercise or in the case of a drop in the blood pressure, the sympathetic input increases, leading a faster heart rate and increase in the contraction strength. Sympathetic influence fastens during inhalation. On the other hand, the parasympathetic input acts as a break, it slows down the heart. During relaxation, the parasympathetic inputs takes full control and the rate of heart beat in turn slows down. The parasympathetic influence increases during the process of exhalation as the heart muscles relax.
Generally, the conducting pathway integrates together with the cardiac cycle processes to facilitate movement of blood throughout the body. The conducting system initiates a normal cardiac cycle as well as the contraction of the cardiac chambers through which blood and various electrical impulses are transmitted throughout the body. The conducting system provides the heart its automatic rhythmic beat. Ultimately, for an effective blood pumping process and the pulmonary and systemic circulations to take place effectively and in synchrony the events in the cardiac cycle must be coordinated with the heart’s conducting system.