Cardiac systems and physiological function

Cardiac Cycle: Diastole and Systole Phases and Heart Disease

The objective of the research in this study is to examine the cardiac cycle from the anatomy and physiology perspective. Toward this end, literature in this area of inquiry, which for the purpose of this study is the cardiac cycle, is examined and reported.

Two Phases of the Cardiac Cycle

The work of Klabunde reports that the single cycle of cardiac activity may be divided into two primary phases stated to be those of: (1) the diastole phase; and (2) the systole phase. (Klabunde, 2012, p.1, p.1) Diastole is representative of the span of time when the "ventricles are relaxed…blood is passively flowing from the left atrium (LA) and right atrium (RA) into the left ventricle (LV) and right ventricle (RV), respectively." (Klabunde, 2012, p.1) The mitral and triscuspid or atrioventircular valves are reported to "separate the atria from the ventricles and to contain the blood flow. The right atrium is reported to receive the venous blood from the body via the superior vena cava (SVC) and inferior vena cava (IVC). The left atrium is reported in the work of Klabunde (2012) to be in receipt of the blood that is oxygenated via the lungs through four pulmonary veins entering the left atrium. When the diastole phase ends, both the left atria and the right atria, are reported to contract propelling more blood into the both the right and left ventricles.

The second phase of the cardiac cycle is the systole stage which is representative of the time "during which the left and right ventricles contract and eject blood into the aorta and pulmonary artery, respectively." (Klabunde, 2012, p.1) According to Klabunde, during the systole phase "…the aortic and pulmonic valves open to permit ejection into the aorta and pulmonary artery. The atrioventricular valves are closed during systole, therefore no blood is entering the ventricles; however, blood continues to enter the atria though the vena cavae and pulmonary veins." (2012, p.1)

II. Analysis of the Systole and Diastole

In order to conduct an analysis of the systole and diastole phases of the cardiac cycle, the cycle is divided into seven phases. Phase 1 begins with the P. wave of the electrocardiogram representing atrial depolarization, or the last phase of diastole. (Klabunde, 2012, paraphrased) Phases two through four represent systole and phases five through seven are reported to represent "early and mid-diastole. The final phase of the cardiac cycle is reported to end at the beginning of the following P. wave starting a new cycle. The seven stated phases in this analysis include the following stated phases: (1) atrial contraction; (2) isovolumetric contraction; (3) rapid ejection; (4) reduced ejection; (5) isovolumetric relaxation; (6) rapid filling; and (7) reduced filling. (Klabunde, 2012, p.1)

III. Diagnosis and Treatment of Abnormal Cardiac Activation on Cardiac Function

Resulting from abnormal cardiac activation on cardiac function are a variety of heart associated disorders including that known as congestive heart failure, as well as what is known as a heart murmur. (Limacher, 2004, Fukuta, and Little, 2008) The diastole and systole cardiac phase analysis assists the practitioner in understanding precisely what functions in the heart are affected and what treatment can be applied to maintain the health of the individual with cardiac phase disruption related disease.

There are layers of tissue in the heart including the endocardium, myocardium, and pericardium. Pericardium tissues are formed by the visceral peridardium, parietal pericardium and the pericardial fluid. The arteries of the heart are: (1) elastic arteries; (2) muscular arteries; and (3) arterioles. The elastic arteries are described as having thick walls near the heart, the aorta and its major branches. It is reported that large lumen enable low-resistance conduction of blood and that elastic is contained in all three tunics. The elastic arteries are reported to "withstand and smooth out large blood pressure fluctuations" and to "allow blood to flow fairly continuously through the body." (Chute, 2012, p.1) The muscular arteries are described as "distal to elastic arteries and to be those which deliver the blood to the organs of the body. These arteries have "thick tunic media with more smooth muscle and less elastic tissue and are active in vasoconstriction." (Chute, 2012, p.1) The arterioles are the smallest of all arteries and are reported to "lead to capillary beds" and to "control flow into the capillary beds via vasodilation and constriction." (Chute, 2012, p.1) Capillaries are walls that are comprised by "thin tunica interna, one cell thick" and are reported to allow "only a single RBC to pass at a time." (Chute, 2012, p.1) Capillaries have percytes located on the outer surface, which serve to provide stability to their walls. There are reported to be three structural types of capillaries including those stated as follows:

(1) Continuous -abundant in the skin and muscles, and have: (a) Endothelial cells that provide an uninterrupted lining; (b) Continuous capillaries of the brain; (c) Have tight junctions completely around the endothelium; and (d) Constitute the blood-brain barrier; (e) Adjacent cells that are held together with tight junctions; and (f) Intercellular clefts of unjoined membranes that allow the passage of fluids. (Chute, 2012, p.1)

(2) Fenestrated: These are reported as found "wherever active capillary absorption or filtrate formation occurs." These are located in the small intestines, endocrine glands and kidneys. These are reported to be characterized by:

(1) An endothelium riddled with pores (fenestrations); and (2) Greater permeability to solutes and fluids than other capillaries. (Chute, 2012, p.1)

(3) Sinusoids in which:

(1) Blood flows sluggishly, allowing for modification in various ways;

(2) Are found in the liver, bone marrow, lymphoid tissue, and in some endocrine organs;

(3) Are highly modified, leaky, fenestrated capillaries with large lumens;

(4) Allowed are large molecules (proteins and blood cells) to pass between the blood and surrounding tissues. (Chute, 2012, p.1)

The heart's capillary beds are reported to be a "microcirculation of interwoven networks of capillaries, consisting of the following:

(1) Vascular shunts - metarteriole-thoroughfare channel connecting an arteriole directly with a postcapillary venule;

(2) True capillaries - 10 to 100 per capillary bed, capillaries branch off the metarteriole and return to the thoroughfare channel at the distal end of the bed;

(3) Precapillary sphincter;

(4) Cuff of smooth muscle that surrounds each true capillary;

(5) Regulates blood flow into the capillary; and (6) Blood flow is regulated by vasomotor nerves and local chemical conditions, so it can either bypass or flood the capillary bed. (Chute, 2012, p.1)