Anatomy of the Cardiovascular System PDF

2. Anatomy of the Cardiovascular System Learning Objectives By the end of this section, you will be able to: 1. Identify the major anatomical areas of the heart on a model or diagram 2. Trace the pathway of blood through the heart 3. Compare the pulmonary and systemic circulations 4. Explain th...

2. Anatomy of the Cardiovascular System Learning Objectives By the end of this section, you will be able to: 1. Identify the major anatomical areas of the heart on a model or diagram 2. Trace the pathway of blood through the heart 3. Compare the pulmonary and systemic circulations 4. Explain the functions of the heart valves Introduction The cardiovascular system is sometimes called, simply, the circulatory system. It consists of the heart, which is a muscular pumping device, and a closed system of vessels called arteries, veins, and capillaries. In response to this need, the cardiovascular system makes its appearance early in development and reaches a functional state long before any other major organ system. HEART LOCATION OF THE HEART The human heart is a four-chambered muscular organ, shaped and sized roughly like a person’s closed fist. It lies in the mediastinum, or middle region of the thorax, just behind the body of the sternum between the points of attachment of the second through the sixth ribs. Approximately two thirds of the heart’s mass are to the left of the midline of the body and one third to the right. Posteriorly the heart rests against the bodies of the fifth to the eighth thoracic vertebrae. Because of its placement between the sternum in front and the bodies of the thoracic vertebrae behind, it can be compressed by application of pressure to the lower portion of the body of the sternum using the heel of the hand. Rhythmic compression of the heart in this way can maintain blood flow in cases of cardiac arrest and, if combined with effective artificial respiration, the resulting procedure, called cardiopulmonary resuscitation (CPR), can be lifesaving. In the adult between puberty and 25 years of age the heart attains its adult shape and weight— about 310 g is average for the male and 225 g for the female. COVERINGS OF THE HEART Structure of the Heart Coverings The heart has its own special covering, a loose-fitting inextensible sac called the pericardium. The pericardial sac can be removed. The pericardium consists of two parts: a fibrous portion and a serous portion. This covering layer is known as the visceral layer of the serous pericardium or as the epicardium. The fibrous sac attaches to the large blood vessels emerging from the top of the heart but not to the heart itself. Therefore, it fits loosely around the heart, with a slight space between the visceral layer adhering to the heart and the parietal layer adhering to the inside of the fibrous sac. This space is called the pericardial space. It contains 10 to 15 ml of lubricating fluid secreted by the serous membrane and called pericardial fluid. The structure of the pericardium can be summarized as follows: Fibrous pericardium—tough, loo se-fitting, and inelastic sac around the heart Serous pericardium—consisting of two layers Parietal layer—lining inside of the fibrous pericardium Visceral layer (epicardium)—adhering to the outside of the heart; between visceral and parietal layers is a space, the pericardial space, which contains a few drops of pericardial fluid Function of the Heart Coverings The fibrous pericardial sac with its smooth, well- lubricated lining provides protection against friction. The heart moves easily in this loose-fitting jacket with no danger of irritation from friction between the two surfaces, as long as the serous pericardium remains normal and continues to produce lubricating serous fluid STRUCTURE OF THE HEART Wall of the Heart Three distinct layers of tissue make up the heart wall in both the atria and the ventricles: the epicardium, myocardium, and endocardium. Epicardium. The outer layer of the heart wall is called the epicardium, a name that literally means “on the heart.” The epicardium is actually the visceral layer of the serous pericardium already described. Myocardium. The bulk of the heart wall is the thick, contractile, middle layer of specially constructed and arranged cardiac muscle cells called the myocardium. Endocardium. The lining of the interior of the myocardial wall is a delicate layer of endothelial tissue known as the endocardium. Endothelium is the type of membranous tissue that lines the heart and blood vessels. Endothelium resembles simple squamous epithelium.  Chambers of the Heart The interior of the heart is divided into four cavities, or heart chambers. The two upper chambers are called atria (singular, atrium), and the two lower chambers are called ventricles. The left chambers are separated from the right chambers by an extension of the heart wall called the septum. Atria: The two superior chambers of the heart—the atria—are often called the “receiving chambers” because they receive blood from vessels called veins. Veins are the large blood vessels that return blood from various tissues to the heart so that the blood can be pumped out to tissues again. The atria alternately relax and contract to receive blood, then push it into the lower chambers. Because the atria need not generate great pressure to move blood such a small distance, the myocardial wall of each atrium is not very thick. Ventricles: The ventricles are the two lower chambers of the heart. Because the ventricles receive blood from the atria and pump blood out of the heart into arteries, the ventricles are considered to be the primary “pumping chambers” of the heart. Because more force is needed to pump blood such a distance, the myocardium of each ventricle is thicker than the myocardium of either atrium. The myocardium of the left ventricle is thicker than that of the right ventricle because the left ventricle pushes blood through most vessels of the body, whereas the right ventricle pushes blood only through the vessels that serve the gas exchange tissues of the lungs. Valves of the Heart The heart valves are mechanical devices that permit the flow of blood in one direction only. Four sets of valves are of importance to the normal functioning of the heart. Two of these, the atrioventricular (AV) valves, guard the openings between the atria and the ventricles (atrioventricular orifices). The atrioventricular valves are also called cuspid valves. The other two heart valves, the semilunar (SL) valves, are located where the pulmonary artery and the aorta arise from the right and left ventricles, respectively. Atrioventricular Valves: The atrioventricular valve guarding the right atrioventricular orifice consists of three flaps (cusps) of endocardium. The free edge of each flap is anchored to the papillary muscles of the right ventricle by several cordlike structures called chordae tendineae. Because the right atrioventricular valve has three flaps, it is also called the tricuspid valve. The valve that guards the left atrioventricular orifice is similar in structure to the right atrioventricular valve, except that it has only two flaps and is therefore also called the bicuspid or, more commonly, the mitral valve. The construction of both atrioventricular valves allows blood to flow from the atria into the ventricles but prevents it from flowing back up into the atria from the ventricles. Ventricular contraction forces the blood in the ventricles hard against the valve flaps, closing the valves and thereby ensuring the movement of the blood upward into the pulmonary artery and aorta as the ventricles contract. Semilunar Valves; The semilunar valves consist of half- moon–shaped flaps growing out from the lining of the pulmonary artery and aorta. The semilunar valve at the entrance of the pulmonary artery (pulmonary trunk) is called the pulmonary semilunar valve. Blood Supply of Heart Tissue Coronary Arteries: Myocardial cells receive blood by way of two small vessels, the right and left coronary arteries. Both right and left coronary arteries have two main branches Both ventricles receive their blood supply from branches of the right and left coronary arteries. Each atrium, in contrast, receives blood only from a small branch of the corresponding coronary artery. The most abundant blood supply goes to the myocardium of the left ventricle—an appropriate amount, because the left ventricle does the most work and so needs the most oxygen and nutrients delivered to it. The right coronary artery is dominant in about 50% of all hearts; the left coronary artery is dominant in about 20%; and in about 30%, neither right nor left coronary artery dominates. Cardiac Veins. After blood has passed through capillary beds in the myocardium, it enters a series of cardiac veins before draining into the right atrium through a common venous channel called the coronary sinus. Several veins that collect blood from a small area of the right ventricle do not end in the coronary sinus but instead drain directly into the right atrium. As a rule, the cardiac veins follow a course that closely parallels that of the coronary arteries. Pulmonary & Systemic Circulation | Circulatory Anatomy Superior and inferior vena cava  The inferior vena cava is the lower ("inferior") of the two venae cavae, the two large veins that carry deoxygenated blood from the body to the right atrium of the heart: the inferior vena cava carries blood from the lower half of the body whilst the superior vena cava carries blood from the upper half of the body.  The deoxygenated blood inter to right atrium, the blood is pumped through the tricuspid valve (or right atrioventricular valve), into the right ventricle. Deoxygenated blood leaves the right ventricle through the pulmonary artery to the Lungs. Oxygeneted leaves from the Lungs to the lets artia theought the Pulmanry Vein ‫شكرا لكم‬