THE HEART

The Heart

The Heart

Introduction

The heart is a conical muscular organ located in the thoracic cavity, in the center of the chest between the lungs. Heart is the pumping organ of the cardiovascular system that pushes blood throughout the body (Gilbert, 2000). The heart is essential to the life of any animal that depends on blood circulation to supply oxygen and food to the various cells of the body. If the heart stops beating for two to four minutes, irreversible damage may be done to the brain, with death occurring shortly thereafter. A normal adult heart is thus 3 to 5 inches (8 to 13 cm) long. It weighs 8 to 14 ounces (230 to 400 g) (Martini et al., 2001). The heart is enclosed in a fibrous sac called the pericardium. The normal heartbeat of an adult at rest occurs 70 to 80 times a minute.

Parts of the Heart

The human heart has four chambers, two on the right side, and two on the left. These chambers are called atria and ventricles. Left part of the heart contains two chambers, which include left ventricle and left atrium. However, right part of the heart also contains two chambers, which include right ventricle and right atrium (Marieb & Hoehn, 2010). Right and left atria split from their respective ventricles by atrioventricular (AV) valves, folds of tough tissue that open in one direction only (Gilbert, 2000).

The flow of blood between the chambers on the right is controlled by the tricuspid valve. Contrastingly, flow of blood between the chambers on the left is controlled by the mitral valve. The muscle cells of the atria secrete hormones that are called atrial natriuretic factors (Opie, 2004). These hormones help regulate blood volume and pressure. Atrium is the receiving chambers of the heart as it receives the blood flowing towards the heart, whereas ventricles are the chambers that pump the blood out of the heart (Opie, 2004).

The right section of the heart pumps blood to the lungs, where carbon dioxide is removed and blood becomes oxygen enriched (Opie, 2004). Right part of the heart also receives blood from all parts of the body, except the lungs (Vander, 1998). The left side of the heart receives the oxygen-bearing blood from the lungs and sends it out to the rest of the body (Katz, 2010). The atria receive blood from the lungs and from the body tissues; it pumps that blood into the ventricles (Marieb & Hoehn, 2010). The ventricles are the muscular pumps of the heart, because they must generate enough force to propel the blood out into circulation against the pressures existing in the two circuits. Muscular walls of the left ventricle are thicker the walls of the right ventricle because it generate higher propulsion force to overcome the higher pressure existing in the systemic circuit and propel blood for longer distances (Katz, 2010). The right ventricle supplies the pulmonary circuit, where the distance traveled by the blood is short, and blood pressure is lower (Gilbert, ...