Heart Anatomy PDF

Septum of heart The cardiac septum consists of two parts, the first part is the interatrial septum and the second part is the interventricular septum. The ventricular septum consists of two parts, the first part, which contains no myocardium and is called the membranous part of interventricular s...

Septum of heart The cardiac septum consists of two parts, the first part is the interatrial septum and the second part is the interventricular septum. The ventricular septum consists of two parts, the first part, which contains no myocardium and is called the membranous part of interventricular septal membrane, and the other part, which contains strong and thick myocardium and is called the muscular part of interventricular septal membrane. The interatrial septum and the interventricular septum separate the left and right atria and the left and right ventricles, respectively, preventing blood flow from the left and right halves of the heart from each other. Because the left and right halves of the heart flow arterial and venous blood, respectivelyza Interatrial septum There is a weak oval structure in the atrial septum, called the fossa ovalis, which is a remnant of the embryonic atresia(闭锁) of the foramen ovale（卵圆孔）. If the foramen ovale does not close 6 months after birth, it is called patent foramen ovale(卵圆孔未闭) and is one of the congenital heart diseases. The fossa ovale is the site of atrial septal defect Koch’s triangle In the anteroinferior part of the interatrial septum, there is a triangular region formed by the extension line of the inferior vena cava valve, the medial edge of the coronary sinus ostium, and the attachment edge of the lateral tip of the tricuspid annulus, called Koch's triangle, whose deep endocardium contains the atrioventricular node. Interatrial septum Defects of the interventricular septum tend to occur in the membranous septum, because this is the weakest part of the ventricular septum and contains no myocardium. Oxygen deficit When there is a patent fossa ovale or a ventricular septal defect, blood flows between the left and right halves of the heart. For example, when a patent foramen ovale or a ventricular septal defect occurs, during the course of arterial blood entering the left atrium via the left and right pulmonary veins and then the left ventricle, some of the arterial blood will pass through the foramen ovale to the right atrium or through the portion of the ventricular septal defect (most of which is in the membranous septum) to the right ventricle, thus mixing with the venous blood of the left halves of the heart. And finally reduce the amount of arterial blood delivered to the tissues of the whole body through the aorta and its branches, resulting in hypoxia. Conducting system of the heart Modified cardiac muscle cells have an intrinsic ability to automatically generate and conduct impulses that signal these ordinary working cardiac cells to contract rhythmically. These properties are intrinsic to the heart muscle itself and do not depend on extrinsic nerve impulses. Even if all nerve connections to the heart are severed, the heart continues to beat rhythmically.  The conducting system of the heart consists of a series of specialized cardiac muscle cells that carries impulses throughout the heart musculature, signaling the heart chambers to contract in the proper sequence. It also initiates each contraction sequence, thereby setting basic heart rate. The components of the conducting system of the heart are the sinoatrial node, internodal fibers, atrioventricular node, atrioventricular bundle, right and left bundle branches, and Purkinje fibers. Sinoatrial node A crescent-shaped mass of cardiac muscle cells. Lies in the wall of the right atrium, just inferior to the entrance of the superior vena cava. Sets the basic heart rate: the peacemaker of the heart. Internodal fibers Conduct impulses to signal atrial contraction. Conduct impulses to atrioventricular node. Atrioventricular node Lies on right side of the interatrial septum, just anterior & superior to the opening of the coronary sinus. Conduct impulses & delay them for a fraction of a second. Generates impulses after injury of the sinoatrial. The atrioventricular node receives impulses from the sinus node through the three internodal bundles, delays the impulses, and conducts them to the ventricle through the atrioventricular bundle and the left and right bundle branches Atrioventricular bundle Arises from AV bundle. Divides into left & right bundle branches Left & right bundle branches & Purkinje fibers Run along both sides of interventricular septum Continues to Purkinje fibers when they approach the apex Purkinje fibers signal ventricular contraction Branches of the left and right bundle branches interweave subendocardial Purkinje fibers. The branches from the subendocardial fiber network enter the ventricular wall at right or obtuse angles to form the Purkinje fiber network, which eventually connects with the contracting myocardium（original myocardium）. Blood supplies of the heart Although the heart is filled with blood, this contained blood provides little nourishment to the heart walls, which are too thick to obtain much nutrition by diffusion alone. Instead, the functional blood supply of the heart is delivered by the right and left coronary arteries. These systemic arteries arise from the base of the aorta and run in the coronary groove. Left Coronary Artery It arises from the left side of the aorta, passes posterior to the pulmonary trunk, then divides into two branches. One is the anterior interventricular artery, the other is the circumflex artery. The anterior interventricular artery descends in the anterior interventricular groove toward the apex of the heart, sending branches into the interventricular septum and onto the anterior walls of both ventricles. The circumflex artery follows the coronary groove posteriorly and supplies the left atrium and the posterior part of the left ventricle Right Coronary Artery It emerges from the right side of the aorta and descends in the coronary sulcus on the anterior wall of the heart, between the right atrium and right ventricle. At the inferior border of the heart, it branches to form the marginal artery. Continuing into the posterior part of the coronary groove, the right coronary artery gives off a large branch called the posterior interventricular artery in the posterior interventricular groove, and several posterior left ventricular branches on the inferior wall of the left ventricle. Overall, the branches of the right coronary artery supply the right atrium and almost all of the right ventricle Dominance of the coronary arteries Dominance of the coronary arterial system is defined by which artery gives rise to the posterior interventricular artery. Dominance of the right coronary artery is typical, with the right coronary artery supplying most of the diaphragmatic surface. The left coronary artery is dominant in approximately 10% of people, and there is codominance in 15% of people. Veins of the heart The heart is drained by the coronary sinus, anterior cardiac veins, the smallest cardiac veins The largest of these veins, the coronary sinus, occupies the posterior part of the coronary sulcus and returns almost all the venous blood from the heart to the right atrium. Draining into the coronary sinus are three large tributaries: the great cardiac vein in the anterior interventricular sulcus, the middle cardiac vein in the posterior interventricular sulcus, the small cardiac vein running along the heart’s inferior margin. Coronary Sinus The largest of these veins, the coronary sinus, occupies the posterior part of the coronary groove and returns almost all the venous blood from the heart to the right atrium. Draining into the coronary sinus are three large tributaries: the great cardiac vein in the anterior interventricular groove, the middle cardiac vein in the posterior interventricular groove, the small cardiac vein running along the heart’s inferior margin. Anterior Cardiac Veins  Several small anterior cardiac veins begin over the anterior surface of the right ventricle, cross over the coronary groove, and usually end directly in the right atrium; sometimes they enter the small cardiac vein. Smallest Cardiac Veins The smallest cardiac veins are minute vessels that begin in the capillary beds of the myocardium and open directly into the chambers of the heart, chiefly the atria. Although called veins, they are valveless communications with the capillary beds of the myocardium and may carry blood from the heart chambers to the myocardium. They may also provide a collateral circulation for parts of the heart musculature. Pericardium The pericardium is a triple-layered sac that encloses the heart The outer layer of this sac, called the fibrous pericardium, is a strong layer of dense connective tissue. It adheres to the diaphragm inferiorly, and superiorly it is fused to the roots of the great vessels that leave and enter the heart. The fibrous pericardium acts as a tough outer coat that holds the heart in place and keeps it from overfilling with blood. Deep to the fibrous pericardium is the double-layered serous pericardium, a closed sac sandwiched between the fibrous pericardium and the heart. The outer, parietal layer of the serous pericardium adheres to the inner surface of the fibrous pericardium. At a superior reflection, the parietal layer is continuous with the visceral layer of the serous pericardium or epicardium, which lies on the heart and is considered a part of the heart wall (discussed shortly).Between the parietal and visceral layers of serous pericardium is a slit-like space, called the pericardial cavity, which contains a lubricating film of serous fluid that reduces friction between the beating heart and the outer wall of the pericardial sac pericardial sinus In the pericardial cavity, the gap at the reflection of the two layers of the visceral- pericardial visceral wall, called pericardial sinus, mainly includes: transverse pericardia sinus: it is the space between the pericardial cavity behind the aorta and pulmonary artery, the superior vena cava, and the anterior wall of the left atrium. Two transverse fingers can be inserted from the left and right entrances of the transverse sinus. When it is necessary to block the blood flow of the aorta and pulmonary artery during open heart surgery, the two large arteries can be clamped from the front to the back through the transverse sinus. oblique pericardial also called Haller sinus is located in the pericardial cavity between the posterior wall of the left atrium, the left and right pulmonary veins, the inferior vena cava and the posterior wall of the pericardium. When it is necessary to block the blood flow of the inferior vena cava, the operation can be performed through the lower part of the oblique sinus.