Composition of blood and the cardiac cycle
Composition of blood
Whole blood is a mixture of cellular components, formed elements and the plasma. Formed elements are comprised of red blood cells (RBC), white blood cells (WBC), and platelets. Plasma constituents are mostly water, plasma proteins, and other minute particles (Basu et al., 2014, p.531). RBC constitutes 99% of formed elements, and the structural integrity of these proteins is essential. RBC are responsible for delivering macronutrients and the oxygen to tissue cells and the bicarbonate that keeps our blood in homeostatic levels. Also, RBC removes cellular waste and CO2. RBC is almost entirely composed of protein hemoglobin (Hb), which is the main job of binding O2. Another critical player in blood composition is WBC or the leukocytes, which only account for about 1% of formed elements. These cells’ job is to protect the host and play a role in immunity and inflammation. Also, formed elements comprised of platelets or the thrombocyte (Moloney et al., 2021, p.4). These cells are responsible for blood coagulation to prevent the host from bleeding if there is damage to the blood vessels internally or externally (Marieb et al., 2018, p.643). The plasma portion of whole blood is mainly water, which helps transport formed elements and delivers nutrients to tissue cells. Also, plasma consists of proteins that help maintain fluid balance, osmotic pressure, blood pH, and the transport of fat-soluble molecules. (Marieb et al., 2018, p.643-660).
Explain the cardiac cycle
The cardiac cycle is comprised of two very distinct phases, the systole, and the diastole, the contraction and the relaxation of the heart. These cardiac phases controlled by the conduction system of the heart which provides the electrical impulses to the heart muscle. There are two periods in the systole phase and two periods in the diastole phase. The diastole periods are the isovolumetric relaxation period when ventricles are relaxed and the filling period when ventricles are in the process of being filled with blood. The systole periods are isovolumetric contraction and ejection. During isovolumetric contraction heart contracts in preparation for blood ejection but only during the contraction period, heart ejects blood from the left and right ventricles. Blood is ejected to the pulmonary circulation and systemic circulation. Systemic circulation delivers oxygenated blood to tissues and the pulmonary circulation delivers deoxygenated blood to lungs to remove CO2 (Zhao et al., 2015, p.3). Heart valves play a very important role in the cardiac cycle. Heart valves are responsible for proper and in-time blood delivery to the heart’s chambers, control of blood flow from each chamber, prevention of backflow, and generation of proper pressure in the chambers (Marieb et al., 2018, p.679). For the heart to contract, relax and eject blood, the heart relies on the electrical impulses of the conduction system which is the part of the autonomic nervous system. The cardiac cycle is achieved in a series of steps; it begins with action potentials that spread rapidly through conducting cells in a specific pattern. Sinoatrial node initiates the signal, the signal passes through atria and initiates contraction, atrioventricular node delays the signal, atrioventricular bundle fires the signal and bundle branches convey that signal for the apex of the hearts, then Purkinje fibers stimulate contraction that leads to blood ejection from left and right ventricles of the heart (Marieb et al., 2018, p.687).
Basu, D., & Kulkarni, R. (2014). Overview of blood components and their preparation. Indian journal of anaesthesia, 58(5), 529–537. https://doi.org/10.4103/0019-5049.144647
Camici, Olivotto, I., & Rimoldi, O. E. (2011). The coronary circulation and blood flow in left ventricular hypertrophy. Journal of Molecular and Cellular Cardiology, 52(4), 857–864. https://doi.org/10.1016/j.yjmcc.2011.08.028
Marieb, E. N. (2018). The function of blood and its constituents. In Human Anatomy and Physiology (pp. 643–690). Pearson.
Moloney, O’Riordan, E. ., McGee, M., Carberry, C. ., Moran, L., McMenamin, K., & Monahan, F. . (2021). Growth, efficiency and the fatty acid composition of blood and muscle from previously grazed late-maturing bulls fed rumen protected fish oil in a high concentrate finishing ration. Livestock Science, 244, 104344–. https://doi.org/10.1016/j.livsci.2020.104344
Zhao, Abuhamad, S., Sinkovskaya, E., Mlynarczyk, M., Romary, L., & Abuhamad, A. (2015). Cardiac axis shift within the cardiac cycle of normal fetuses and fetuses with congenital heart defect. Ultrasound in Obstetrics & Gynecology, 46(5), 558–563. https://doi.org/10.1002/uog.14768
