6.2 Basic Concepts of the Cardiovascular and Renal Systems
6.2 Basic Concepts of the Cardiovascular and Renal Systems
To understand the effects of various classes of cardiovascular medications, it is important to first understand the anatomy and physiology of the cardiovascular and renal systems.
Review of Anatomy and Physiology of the Cardiovascular and Renal Systems
Location of the Heart
The human heart is located within the thoracic cavity, medially between the lungs in the space known as the mediastinum. The great veins (i.e., the superior and inferior venae cavae) and the great arteries (i.e., the aorta and pulmonary trunk) are attached to the superior surface of the heart, called the base. The base of the heart is located at the level of the third costal cartilage, as seen in Figure 6.1.[1] The inferior tip of the heart, the apex, lies just to the left of the sternum between the junction of the fourth and fifth ribs. It is important to remember the position of the heart when placing a stethoscope on the chest of a client and listening for heart sounds.[2]
Chambers and Circulation Through the Heart
The heart consists of four chambers: two atria and two ventricles. The right atrium receives deoxygenated blood from the systemic circulation, and the left atrium receives oxygenated blood from the lungs. The atria contract to push blood into the lower chambers, the right ventricle and the left ventricle. The right ventricle contracts to push blood into the lungs, and the left ventricle is the primary pump that propels blood to the rest of the body.
There are two distinct but linked circuits in the human circulation called the pulmonary and systemic circuits. The pulmonary circuit transports blood to and from the lungs, where it picks up oxygen and delivers carbon dioxide for exhalation. The systemic circuit transports oxygenated blood to virtually all of the tissues of the body and returns deoxygenated blood and carbon dioxide to the heart to be sent back to the pulmonary circulation. See Figure 6.2[3] for an illustration of blood flow through the heart and blood circulation throughout the body.[4] The blue areas indicate deoxygenated blood flow, and the red areas indicate oxygenated blood flow.
Blood also circulates through the coronary arteries with each beat of the heart. The left coronary artery distributes blood to the left side of the heart, and the right coronary distributes blood to the right atrium, portions of both ventricles, and the heart conduction system. See Figure 6.3[5] for an illustration of the coronary arteries. When a client has a myocardial infarction, a blood clot lodges in one of these coronary arteries that perfuse the heart tissue. If a significant area of muscle tissue dies from lack of perfusion, the heart is no longer able to pump.
Conduction System of the Heart
Contractions of the heart are stimulated by the electrical conduction system. The components of the cardiac conduction system include the sinoatrial (SA) node, the atrioventricular (AV) node, the left and right bundle