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You are watching: Which of the following is the most superficial layer surrounding the heart?

StatPearls . Endowment Island (FL): StatPearls Publishing; 2021 Jan-.


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Introduction

Located within the mediastinum between the third and 6th costal cartilages, the heart functions to it is provided tissues transparent the body through oxygenated blood. While the precise position is variable among patients, the heart has tendency to lie reasonably horizontally, with the apex directed toward the patient’s left side.

In order to maintain appropriate function, the heart and also roots the the good vessels room encased within a double-walled fibrous sac termed the pericardium. On each side that the heart, the pericardium acts as the medial border of the pleural space. The most superficial layer, the fibrous pericardium, is robust and also composed of many layers the connective tissue. The serous pericardium is separated into the parietal pericardium, i beg your pardon is straight fused with the fibrous pericardium, and also the visceral pericardium, i beg your pardon adheres straight to the heart. In enhancement to the collagen and also elastic yarn that comprise the parietal pericardium, the visceral pericardium is additionally composed that mesothelial cells. The 2 layers are directly linked at the good vessels, whereby the pericardium reflects back on itself.<1><2><3>


Structure and also Function

The heart"s capacity to adequately pump blood transparent the human body is straight dependent on its structure and also pressure differences within that is chambers. Merely put, blood circulation through the heart can be visualized as 2 interwoven circuits. Deoxygenated blood return to the ideal atrium, through the exceptional or worse vena cava, and also moves with the tricuspid valve right into the best ventricle of the heart during diastole. The tricuspid valve closes during the systolic phase, and also 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, ultimately moving into the left ventricle with the mitral (bicuspid) valve. Because of the high push within the ventricle, oxygenated blood is ejected v the aortic valve and into the systemic circulation. <4>

The heart’s ability to perfuse organization throughout the human body is sustained by the lot of physiological features of the pericardium. The strong fibrous pericardium protects the love by acting together a barrier versus pathogens. Because of its non-compliant structure, the fibrous pericardium also serves to hinder severe dilation that the heart once intracardiac volume increases. The pericardium additionally functions come anchor cardiac frameworks through its plenty of layers the connective tissue. By attaching to the sternum, diaphragm, and tunica adventitia, the fibrous pericardium boundaries the heart’s motion within the mediastinum. The pericardium plays a role by encasing pericardial fluid (usually 20 to 25 mL) in ~ its 2 layers, which reduces friction throughout heartbeats by lubricating the surfaces involved. The fluid is well-off in prostacyclin, which also helps to regulate coronary artery ton in the area. Compared to serum, the pericardial liquid has a lower osmolality, containing much less protein and more albumin. It is secreted through mesothelial cells within the serosal layer.<5>


Embryology

Heart advance begins in ~ the fetus throughout the center of the third week and also begins come beat spontaneously by the end of the fourth week. The process of myocardiogenesis begins with the formation of endocardial tube by lateral bowl mesoderm. Body folding bring the endocardial tubes come the thorax, where the tube fuse right into a major heart tube. Quickly after, the myocardium, obtained from the splanchnic mesoderm, consist of the love tube and also the facility begins come loop.<6>

Once love looping is finish at the end of main 4, separation of love chambers begins. The development of a septum primum starts to different the atria if a muscular septum forms in between the ventricles. Further separation occurs as result of the development of endocardial cushions, which construct on the atrioventricular canal. While an important for the development of a four-chambered heart, the endocardial cushions likewise play a significant role in valve formation. By mainly 7, the formation of a foramen secundum and a foramen ovale occurs between the atria. In the following weeks, the coronary sinus is formed, and also the semilunar and also atrioventricular valves are completed.

The pericardium creates simultaneously with the breakthrough of the heart. Together the love tubes fuse and also attach to anterior and posterior walls, the left and right intraembryonic coelomic cavities technique each other. Quickly after, the cavities 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 ~ above coronary arteries, i beg your pardon are normally installed within epicardial fat. Left and right coronary arteries arise indigenous their particular aortic sinuses, located simply superior come the aortic valve. The left coronary artery moves for a small period within the coronary sulcus prior to dividing into the left anterior diminish (LAD) and also circumflex coronary arteries. The LAD runs anteroinferior, giving the anterior two-thirds that the interventricular septum before commonly anastomosing through the posterior diminish artery. The circumflex artery continues within the coronary sulcus toward the crux of the heart. Branches of this arteries adequately supply the left ventricle v blood and also nutrients. The right coronary artery operation in the coronary sulcus towards the posterior ar of the heart and is critical for perfusing the best ventricle with its marginal branches. ~ above its path, it often perfuses the SA node. Close to the crux of the heart, the AV nodal artery generally comes turn off the RCA. In end 70% that humans, the RCA continues and also supplies the posterior one-third that the interventricular septum as the posterior diminish artery.

Lymph within the heart drains from the subendocardial organization within the atria and also ventricles into an epicardial plexus. From here, the lymph runs in multiples vessels within the AV groove till combining and also moving away from the love in the mediastinal lymphatic plexus.

Blood it is provided to and from the pericardium is dependency on the pericardiophrenic branches that the interior thoracic ship (formerly the internal mammary vessels). The pericardiophrenic artery runs between the pericardium and the pleura alongside the phrenic nerve.

Lymphatic drainage the the visceral pericardium makes use of the tracheal and bronchial lymph chain while the parietal pericardium drains an in similar way to the sternum and diaphragm.


Nerves

Cardiac role is dependence on properly timed contractions that the atria and ventricles. In a healthy and balanced heart, the advertise originates in ~ the sinoatrial node (SA node), i beg your pardon is a mass of muscle yarn in the right atrium wall. Conduction move to the atrioventricular (AV) node within an inferior ar of the interatrial septum. Here, the impulse is momentarily delayed, which allows for filling of the ventricles, prior to traveling through the bundle that His in the interventricular septum. The bundle the His bifurcates into right and left bundle branches as it moves inferiorly. The impulse is then distributed through the Purkinje yarn (subendocardial branches), i m sorry transmit the signal come papillary muscles and the ventricular wall. Coordinated convulsion of the ventricles begins at the apex and moves towards the base.

The price (chronotropic) and force (inotropy) that cardiac contractions are regulated through sympathetic and also parasympathetic innervation. Cell bodies for sympathetic innervation are located within the an initial 5 thoracic level of the spinal cord when parasympathetic innervation works through branches that the vagus nerve (CN X).

The fibrous pericardium and serous pericardium room innervated by the phrenic nerve, i m sorry is acquired primarily indigenous cervical nerve 4 but additionally has contributions from the 3 and also 5. Due to its origin, pericarditis and other cardiac complications can cause referred pain come the shoulder. The serous pericardium has actually branches of innervation native the vagus nerve via the esophageal plexus. The pericardium has an extensive set of mechanoreceptors and chemoreceptors that are responsible for specific reflexes. The Bezold-Jarisch reflex describes a triad that bradycardia, hypotension, and apnea that occurs because of receptors in this area.


Muscles

Moving superficially, the heart wall can be divided into the endocardium, myocardium, and epicardium. The endocardium is a thin layer of sustaining connective tissue and smooth muscle fibers, which line the love chambers and also valves. Connective tissue builds up within the subendocardial layer, i m sorry attaches come the myocardium and contains branches the the heart’s conduction system. The myocardium is the thickest of the three layers, an especially within the left ventricle, and is responsible because that the ejection that blood throughout contractions. The epicardium (visceral pericardium) is responsible for the manufacturing of pericardial fluid and the defense of the various other heart layers.


Physiologic Variants

Dextrocardia describes the congenital problem where the apex of the love is directed towards the right side of the chest. The defect is regularly attributed to Kartagener syndrome (primary ciliary dyskinesia).

A patent foramen ovale wake up if the septum primum and also septum secundum fail come fuse throughout embryogenesis. This deserve to lead come paradoxical emboli that go into systemic circulation instead of the lungs.

Tetralogy the Fallot (TOF) is a congenital heart defect due to the anterior deviation of the aorticopulmonary septum. The malalignment leads to pulmonary stenosis, an overriding aorta, a ventricular septal defect, and right ventricular hypertrophy.

Ventricular septal defects are the most common congenital cardiac anomaly. They often occur within the membranous part of the ventricular septum and can result in a left-to-right shunt in ~ the newborn.

While the pericardium serves many physiological roles, its presence is not a necessity. Congenital absence of the pericardium or its operation removal (pericardiectomy) walk not have tendency to cause symptom in patients.

Defects the the pericardium space infrequent (approximately 1 in 10,000 patients) and also have a left side predominance (70%). They can occasionally compress cardiac structures, such as coronary arteries or the left atrial appendage.


Surgical Considerations

Coronary artery bypass grafting (CABG) is a procedure to restore cardiac tissue perfusion after ~ a coronary artery i do not care occluded. Two typical approaches including rerouting the left interior thoracic artery come the LAD or using the great saphenous vein native the patient’s leg.  

Pericardiocentesis is a clinical procedure where the fluid is aspirated native the pericardial cavity. Typically, the needle is placed just left that the xiphoid process and worse to the left costal margin. Echocardiography is frequently utilized to avoid puncturing the heart.

Due to their ar on each side that the pericardium, phrenic nerves need to be figured out during thoracic surgeries. Damage can bring about paralysis the the diaphragm.

At your lines the reflection, the visceral and also parietal pericardium layers create two sinuses. The transverse pericardial sinus, situated posterior to the ascending aorta and anterior to the premium vena cava, is an essential landmark to identify structures during CABG procedures. A 2nd pericardial sinus, the tilt sinus, is located posterior come the left atrium and allows for distension the the chamber.


Clinical Significance

Pericardial effusion refers to abnormal level of fluid within the pericardial space. This is frequently attributed come a to decrease in fluid resorption, which can happen with a lymphatic obstruction or venous hypertension. In acute cases, the sudden rise of volume deserve to lead to love dysfunction if the pressure increases enough. However, slow accumulation of liquid can cause the pericardium come stretch, which permits the cavity to withstand higher pressures. When a variety of clinical features exists, effusions commonly present through chest ache or dyspnea.<7><8>

Pericarditis refers to inflammation that the pericardium, which frequently presents v chest pain and fever. Typically, the pain aggravates with incentive or coughing and is alleviated by leaning front or sitting. ~ above auscultation, a friction rub is frequently present. Acute pericarditis can be attributed come both infectious and also non-infectious causes. While often idiopathic, many situations are thought to it is in viral with echovirus and coxsackievirus being the most common. Noninfectious causes of pericarditis incorporate neoplasms and damage caused by myocardial infarction. Electrocardiograms in patients with pericarditis generally show ST-segment key in all leads as well as aVR and V1.

Dressler syndrome is a form of pericarditis, believed to it is in an autoimmune reaction to details myocardial antigens, that occurs at least 2 come 3 weeks after myocardial infarction.

Constrictive pericarditis describes fibrosis and thickening that the pericardium. The succeeding loss the compliance to reduce the heart’s capability to pump blood adequately. The bulk of situations of constrictive pericarditis are taken into consideration idiopathic. In addition to decreased cardiac output and elevated venous pressures, Kussmaul’s authorize may likewise be observed. This describes a paradoxical increase in jugular venous distension throughout inspiration.

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Cardiac tamponade wake up when boost in pressure, early to reasons such together hemopericardium or pericarditis, compresses the heart and restricts sufficient cardiac output. By diminish compliance, normal venous go back to the right atrium is hindered. Acute cardiac tamponade can current with Beck’s Triad, which has hypotension, jugular venous distension, and also muffled love sounds ~ above auscultation. Pulsus paradoxus, an exaggerated decrease in systolic blood pressure throughout inspiration, is also often seen.<9><10>