The Structure And Function Of Ventricular Myocytes And Their Regulation Essay Example

Morphological analyses have revealed that there are three specific types of myocytes which constitutes the human bodily tissues. The skeletal, smooth and cardiac myocytes are composed of distinct cell types that are either under voluntary or involuntary control. (Anderson et al. 2008). Various descriptions of the structure of ventricular myocytes have been advanced ranging from laminated sheets, layered fibers, and complex nested syncytium to a unique band-like arrangement (Mall 1911). The ventricular myocytes are single-nucleated and are held loosely in a matrix of fibrous tissue. A cluster of myocytes surrounded by condensations of endomysial weave constitutes a myofiber (Sztajzel 2004).
Figure 1: The structure of a muscle cell with long tubular cells. Myocytes can be specialized to form cardiac, smooth or skeletal muscle (Adapted from Anderson et al. 2008).
The human heart has two pairs of valves: atrioventricular (AV) valves and semilunar valves that opens and closes as the heart goes through its cardiac cycle of rest (diastole) and contraction (systole). The cardiac cycle is a complex and well regulated process that ensures that there is unison in how the cells contract based on the blood pumping through the arteries and valves. In diastolic state, blood returns to the resting heart through veins into the right and left atria, this results in high pressure and subsequently opening of the AV valves to allow blood into the ventricles. Contraction of ventricles occurs during systolic state, this leads to increase in pressure within each chamber and cause the AV valves to forcefully close thereby preventing blood for flowing back into the atria. (Sengupta et al. 2006)This process is well coordinated wihin the heart and therefore allows the specialized myocyte cells to operate in unison within the human heart.
Figure 2: A simplified picture of the electrical system of the human heart.The direction of the activation is indicated by the arrows and is: SAN (= sinoatrial node), AM (= atrial myocardium), AVN (= atrioventricular node), PF (= Purkinje fibers), VM (= ventricular myocardium). (Adapted from Sengupta et al., 2006).
The contraction of the heart muscle is stimulated by depolarization and the heart contains specialized autogenic cells; sinoatrial (SA) node. The SA node serves as a pacemaker regulator by producing spontaneous depolarization at a faster rate than other autogenic cardiac cells (Sztajzel 2004). The SA node in the right atrium produces waves of depolarization which leads to stimulation of the atria and then causes the ventricles to contract. Although various cardiac tissues have intrinsic pacemaker capabilities, the contraction of atria and ventricles is largely modulated by the autonomous nervous system (ANS). The ANS regulates the heart rate through interplay of two systems with opposing actions: efferent sympathetic and parasympathetic. Sympathetic system increases automaticity while on the other hand, parasympathetic systems inhibit it. These two systems regulate the rate of pacemaker depolarization (Sztajzel 2004)
In conclusion, ventricular myocytes plays a critical role in regulation of heart rate by maintaining myocytes action potential which occurs by inactivation of Na+ channels. They are structurally adapted and designed as specialized cells that can form cardiac, skeletal or smooth muscles. These muscles are critical in regulating voluntary and involuntary actions in the human body.

Reference

Anderson R. H, Sanchez-Quintana D, Niederer P & Lunkenheimer P. P 2008, ‘Structural–functional correlates of the 3-dimensional arrangement of the myocytes making up the ventricular walls,’ The Journal of thoracic and cardiovascular surgery, vol.136, no.1, pp.10-18.
Mall F 1911, ‘On the muscular architecture of the ventricles of the human heart,’ American Journal of Anatomy, vol. 11, pp. 211-266.
Sengupta P. P, Korinek J, Belohlavek M, Narula J, Vannan M. A, Jahangir A & Khandheria B. K 2006, ‘Left ventricular structure and function: basic science for cardiac imaging,’ Journal of the American College of Cardiology, vol. 48, no.10, pp. 1988-2001.
Sztajzel, J 2004, ‘Heart rate variability: a noninvasive electrocardiographic method to measure the autonomic nervous system’, Swiss medical weekly, vol.134, pp.514-522.