Heart

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The heart is the driving force of the Cardiovascular System and is found in the human body in the left of the centre (between the lungs). The heart is found between level T5-T9 which is a description of the location of the heart in relation to the levels of the vertebrae[1]. The heart's function is to pump oxygenated blood around the body through arteries and to accept deoxygenated blood through the veins. These two processes are separated into the heart's left and right-hand side respectively[2] which are subdivided into four chambers[3]. Temporal dispersion of recovery of excitability, measured as the range of local refractory period durations at numerous sites on the atrial and ventricular surfaces, was found to be a direct function of the basic cycle length except at very rapid driving frequencies[4].The Upper chambers are known as the Atria, and the lower chambers are called ventricles[5]. The wall separating the ventricles is known as the ventricular septum[6]. The heart is essentially a muscle, known as the cardiac muscle. The ventricles have a thick muscular wall in comparison the atria. However, the left side is thicker than the right side because the left ventricle is required to send the blood all around the body (systemic circulation) rather than just to the lungs which is what the right ventricle does (pulmonary circulation). The left ventricle requires a greater force, so hence more muscle is required to provide this[7]

The ventricles are the bottom two chambers of the heart with the atria being the top two chambers of the heart. The left atrium is located on the left posterior side[8]. Its main roles are to act as a holding chamber for blood returning from the lungs as well as to act as a pump to transport blood to other areas of the heart. The right atrium is located on the top right-hand side next to the superior vena cava. Its primary function is to allow deoxygenated blood to enter via the inferior and superior vena cava. The right side of the heart then pumps this deoxygenated blood from the heart to the lungs via the pulmonary artery where it then circulates back to the heart through the pulmonary veins, carrying oxygenated blood. Deoxygenated blood enters the right atrium through the inferior and superior vena cava[9].

The heartbeat is initiated by a bundle of nerves called the SA node, this is located in the right atrium of the heart. The SA node sends out electrical impulses which travel the walls of the atria, causing it to contract, pushing the atrioventricular valves open with the pressure of blood, and allowing blood to travel into the ventricles[10]. As the arteries contract, electrical impulses from the SA node continue to travel to the atrioventricular node (AV node), which is another relay point[11]. The AV node is located in the wall between the left and right atria, and here, there is a 0.1 second delay before the electrical impulse travels further to the apex of the heart[12]. This delay ensures that all the blood is emptied out of the atria and into the ventricles for effective ventricular contraction to be carried out[13]. The electrical impulses travel from the AV node to the atrioventricular bundle, which splits into two branches called bundle branches[14]. From here, the electrical impulses move down the apex through bundle branches and up the ventricular walls through Purkinje fibres[15]. These impulses cause the ventricles to contract, pushing blood out from the ventricles, through the pulmonary valves and into the aorta, before bringing it to the rest of the body[16].

For the heart to function properly it should be healthy. A healthy heart will circulate blood throughout the body at the right pace providing sufficiently to all parts of the body. This vital organ is unable to perform this necessary function if weakened by disease or injury[17].

References

  1. https://web.duke.edu/anatomy/Lab03/Lab4_preLab.html
  2. Parker S. (2007) The Human Body Book, 1st edition, London: Dorling Kindersley Limited.
  3. http://www.gknmhospital.org/ctvs/hevaldis.html
  4. Han et al. Temporal Dispersion Of Recovery Of Excitability In Atrium And Ventricle As A Function Of Heart Rate'. American Heart Journal 71.4 (1966): 481-487
  5. http://inspirations786.wordpress.com/2011/11/15/four-chambers-of-heart-islamic-polygamy-of-up-to-four-wives-and-miracle-of-allah/
  6. http://www.gknmhospital.org/ctvs/hevaldis.html
  7. http://www.nhlbi.nih.gov/health/health-topics/topics/hhw/anatomy
  8. http://www.healthline.com/human-body-maps/left-atrium
  9. http://www.healthline.com/human-body-maps/right-atrium
  10. Rakesh K.p (2014).Electrical System of the Heart.[1]
  11. Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V. and Jackson, R. B.. Campbell Biology. 10th Edition, Boston: Pearson. 2014
  12. Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V. and Jackson, R. B.. Campbell Biology. 10th Edition, Boston: Pearson. 2014
  13. Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V. and Jackson, R. B.. Campbell Biology. 10th Edition, Boston: Pearson. 2014
  14. Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V. and Jackson, R. B.. Campbell Biology. 10th Edition, Boston: Pearson. 2014
  15. Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V. and Jackson, R. B.. Campbell Biology. 10th Edition, Boston: Pearson. 2014
  16. Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V. and Jackson, R. B.. Campbell Biology. 10th Edition, Boston: Pearson. 2014
  17. http://www.nhlbi.nih.gov/health/health-topics/topics/hhw
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