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Located within the mediastinum in between the third and 6th costal cartilages, the heart attributes to supply tissues transparent the body v oxygenated blood. While the specific position is variable among patients, the heart has tendency to lie fairly horizontally, with the apex directed towards the patient’s left side.
In order to maintain proper function, the heart and roots the the great vessels are encased within a double-walled fibrous sac termed the pericardium. On every side that the heart, the pericardium acts as the medial border that the pleural space. The most superficial layer, the fibrous pericardium, is robust and also composed of countless layers the connective tissue. The serous pericardium is split into the parietal pericardium, which is directly fused v the fibrous pericardium, and the visceral pericardium, i m sorry adheres straight to the heart. In enhancement to the collagen and also elastic yarn that comprise the parietal pericardium, the visceral pericardium is likewise composed of mesothelial cells. The 2 layers space directly associated at the an excellent vessels, where the pericardium reflects back on itself.<1><2><3>
Structure and also Function
The heart"s ability to adequately pump blood transparent the body is directly dependent on its structure and pressure differences within the chambers. Just put, blood circulation through the heart deserve to be visualized as 2 interwoven circuits. Deoxygenated blood returns to the ideal atrium, v the remarkable or inferior vena cava, and also moves v the tricuspid valve into the best ventricle of the heart during diastole. The tricuspid valve closes during the systolic phase, and blood is funneled with the pulmonic valve right into the pulmonary circulation. Blood will end up being oxygenated and move right into the left atrium, subsequently moving right into the left ventricle v the mitral (bicuspid) valve. Due to the high press within the ventricle, oxygenated blood is ejected through the aortic valve and into the systemic circulation. <4>
The heart’s ability to perfuse tissues throughout the human body is sustained by the multiple physiological attributes of the pericardium. The strong fibrous pericardium protects the heart by acting together a barrier against pathogens. Because of its non-compliant structure, the fibrous pericardium additionally serves come hinder severe dilation of the heart when intracardiac volume increases. The pericardium additionally functions come anchor cardiac frameworks through its countless layers the connective tissue. By attaching to the sternum, diaphragm, and tunica adventitia, the fibrous pericardium boundaries the heart’s activity within the mediastinum. The pericardium dram a role by encasing pericardial liquid (usually 20 come 25 mL) within its 2 layers, i beg your pardon reduces friction throughout heartbeats through lubricating the surface involved. The liquid is well-off in prostacyclin, which likewise helps to control coronary artery ton in the area. Contrasted to serum, the pericardial liquid has a reduced osmolality, containing less protein and more albumin. It is secreted through mesothelial cells within the serosal layer.<5>
Heart advance begins within the fetus throughout the center of the third week and begins come beat spontaneously through the end of the fourth week. The procedure of myocardiogenesis begins with the formation of endocardial pipe by lateral key mesoderm. Human body folding brings the endocardial tubes come the thorax, whereby the pipe fuse into a major heart tube. Quickly after, the myocardium, acquired from the splanchnic mesoderm, consists the heart tube and the complicated begins to loop.<6>
Once love looping is complete at the end of mainly 4, separation of heart chambers begins. The formation of a septum primum begins to different the atria while a muscular septum forms between the ventricles. More separation occurs because of the development of endocardial cushions, which develop on the atrioventricular canal. While vital for the creation of a four-chambered heart, the endocardial cushions likewise play a far-reaching role in valve formation. By mainly 7, the development of a foramen secundum and also a foramen ovale occurs between the atria. In the adhering to weeks, the coronary sinus is formed, and the semilunar and also atrioventricular valves room completed.
The pericardium creates simultaneously v the advancement of the heart. As the heart tubes fuse and attach come anterior and also posterior walls, the left and right intraembryonic coelomic cavities strategy each other. Soon after, the caries fuse and kind the pericardial cavity, enveloping the heart pipe within that is dorsal wall.
Blood Supply and Lymphatics
Perfusion of the myocardium and epicardium is dependent top top coronary arteries, i m sorry are normally embedded within epicardial fat. Left and also right coronary arteries arise indigenous their corresponding aortic sinuses, located just superior to the aortic valve. The left coronary artery moves because that a small period within the coronary sulcus prior to dividing into the left anterior descending (LAD) and circumflex coronary arteries. The LAD runs anteroinferior, giving the anterior two-thirds that the interventricular septum prior to commonly anastomosing v the posterior to decrease artery. The circumflex artery continues within the coronary sulcus towards the crux that the heart. Branches of this arteries adequately supply the left ventricle through blood and also nutrients. The appropriate coronary artery runs in the coronary sulcus towards the posterior section of the heart and is an essential for perfusing the best ventricle with its marginal branches. Top top its path, it frequently perfuses the SA node. Close to the crux of the heart, the AV nodal artery frequently comes turn off the RCA. In over 70% the humans, the RCA continues and also supplies the posterior one-third the the interventricular septum together the posterior diminish artery.
Lymph within the love drains indigenous the subendocardial tissue within the atria and also ventricles right into an epicardial plexus. From here, the lymph runs in multiples vessels within the AV groove until combining and also moving far from the heart in the mediastinal lymphatic plexus.
Blood supply to and also from the pericardium is dependency on the pericardiophrenic branches of the interior thoracic ship (formerly the interior mammary vessels). The pericardiophrenic artery runs between the pericardium and the pleura together the phrenic nerve.
Lymphatic drainage that the visceral pericardium utilizes the tracheal and also bronchial lymph chain when the parietal pericardium drains similarly to the sternum and diaphragm.
Cardiac role is dependency on correctly timed contractions that the atria and ventricles. In a healthy heart, the impulse originates within the sinoatrial node (SA node), i beg your pardon is a massive of muscle fibers in the best atrium wall. Conduction moves to the atrioventricular (AV) node within an inferior ar of the interatrial septum. Here, the advertise is momentarily delayed, which allows for pour it until it is full of the ventricles, before traveling with the bundle that His in the interventricular septum. The bundle that His bifurcates right into right and left bundle branches as it move inferiorly. The advertise is then dispersed through the Purkinje fibers (subendocardial branches), which transmit the signal to papillary muscles and the ventricular wall. Coordinated convulsion of the ventricles begins at the apex and also moves toward the base.
The price (chronotropic) and also force (inotropy) the cardiac contractions are regulated through sympathetic and parasympathetic innervation. Cell bodies because that sympathetic innervation are situated within the an initial 5 thoracic levels of the spinal cord while parasympathetic innervation works through branches of the vagus nerve (CN X).
The fibrous pericardium and serous pericardium room innervated through the phrenic nerve, i m sorry is obtained primarily indigenous cervical nerve 4 but additionally has contributions from the 3 and 5. Because of its origin, pericarditis and also other cardiac symptom can reason referred pain come the shoulder. The serous pericardium has actually branches of innervation from the vagus nerve via the esophageal plexus. The pericardium has an extensive set of mechanoreceptors and chemoreceptors that are responsible for particular reflexes. The Bezold-Jarisch reflex refers to a triad that bradycardia, hypotension, and apnea that occurs due to receptors in this area.
Moving superficially, the heart wall can be divided into the endocardium, myocardium, and epicardium. The endocardium is a slim layer of sustaining connective tissue and also smooth muscle fibers, which line the heart chambers and also valves. Connective tissue builds up in ~ the subendocardial layer, i m sorry attaches come the myocardium and contains branches of the heart’s conduction system. The myocardium is the thickest of the 3 layers, an especially within the left ventricle, and is responsible because that the ejection the blood during contractions. The epicardium (visceral pericardium) is responsible for the production of pericardial fluid and also the security of the other heart layers.
Dextrocardia describes the congenital problem where the apex of the heart is directed toward the ideal side that the chest. The defect is often attributed come Kartagener syndrome (primary ciliary dyskinesia).
A patent foramen ovale occurs if the septum primum and septum secundum fail come fuse throughout embryogenesis. This deserve to lead come paradoxical emboli that get in systemic circulation instead of the lungs.
Tetralogy of Fallot (TOF) is a congenital love defect due to the anterior deviation the the aorticopulmonary septum. The malalignment leader to pulmonary stenosis, an overriding aorta, a ventricular septal defect, and right ventricular hypertrophy.
Ventricular septal defects space the most common congenital cardiac anomaly. They frequently occur within the membranous portion of the ventricular septum and can bring about a left-to-right shunt within the newborn.
While the pericardium serves plenty of physiological roles, its visibility is no a necessity. Congenital absence of the pericardium or its operation removal (pericardiectomy) does not tend to cause symptom in patients.
Defects of the pericardium are infrequent (approximately 1 in 10,000 patients) and also have a left side predominance (70%). They can occasionally compress cardiac structures, such together coronary arteries or the left atrial appendage.
Coronary artery bypass grafting (CABG) is a procedure to gain back cardiac organization perfusion after a coronary artery i do not care occluded. Two typical approaches including rerouting the left internal thoracic artery come the LAD or using the good saphenous vein from the patient’s leg.
Pericardiocentesis is a clinical procedure whereby the fluid is aspirated from the pericardial cavity. Typically, the needle is put just left that the xiphoid process and inferior to the left costal margin. Echocardiography is regularly utilized to prevent puncturing the heart.
Due come their location on every side the the pericardium, phrenic nerves must be figured out during thoracic surgeries. Damages can cause paralysis of the diaphragm.
At their lines that reflection, the visceral and parietal pericardium layers create two sinuses. The transverse pericardial sinus, situated posterior come the ascending aorta and anterior to the premium vena cava, is critical landmark to determine structures during CABG procedures. A second pericardial sinus, the tilt sinus, is located posterior come the left atrium and enables for distension that the chamber.
Pericardial effusion describes abnormal levels of fluid within the pericardial space. This is regularly attributed to a diminish in liquid resorption, which can happen with a lymphatic obstruction or venous hypertension. In acute cases, the sudden boost of volume can lead to heart dysfunction if the pressure rises enough. However, slow accumulation of fluid can reason the pericardium to stretch, which allows the cavity come withstand greater pressures. When a selection of clinical attributes exists, effusions commonly present through chest pain or dyspnea.<7><8>
Pericarditis describes inflammation that the pericardium, which frequently presents v chest pain and also fever. Typically, the pain aggravates with impetus or coughing and is alleviated by leaning front or sitting. ~ above auscultation, a friction obstacle is frequently present. Acute pericarditis have the right to be attributed to both infectious and non-infectious causes. While often idiopathic, many situations are believed to it is in viral through echovirus and also coxsackievirus gift the many common. Noninfectious reasons of pericarditis encompass neoplasms and damage resulted in by myocardial infarction. Electrocardiograms in patients with pericarditis generally show ST-segment key in every leads besides aVR and also V1.
Dressler syndrome is a kind of pericarditis, believed to it is in an autoimmune reaction to particular myocardial antigens, that occurs at the very least 2 to 3 weeks ~ myocardial infarction.
Constrictive pericarditis refers to fibrosis and thickening the the pericardium. The subsequent loss that compliance decreases the heart’s capability to pump blood adequately. The bulk of instances of constrictive pericarditis are taken into consideration idiopathic. In addition to diminished cardiac output and also elevated venous pressures, Kussmaul’s sign may additionally be observed. This refers to a paradoxical boost in jugular venous distension throughout inspiration.
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Cardiac tamponade wake up when rise in pressure, due to reasons such as hemopericardium or pericarditis, compresses the heart and restricts enough cardiac output. By diminish compliance, typical venous go back to the ideal atrium is hindered. Acute cardiac tamponade can present with Beck’s Triad, which has hypotension, jugular venous distension, and also muffled heart sounds top top auscultation. Pulsus paradoxus, an exaggeration decrease in systolic blood pressure throughout inspiration, is additionally often seen.<9><10>