Pericardium Heart Thorax Unit Lecture 5 6 Pericardium

Pericardium & Heart Thorax Unit Lecture 5 & 6 ﺣﻴﺪﺭ ﺟﻠﻴﻞ ﺍﻷﻌﺴﻢ. ﺩ

Pericardium It is a fibroserous sac enclosing heart and roots of great vessels. Pericardium lies within middle mediastinum, posterior to body of sternum and 2 nd - 6 th costal cartilages and anterior to 5 th - 8 th thoracic vertebrae. It is composed of two layers A. Fibrous Pericardium B. Serous Pericardium

Pericardium Fibrous pericardium is strong fibrous part of the sac. It is firmly attached below to central tendon of the diaphragm. It fuses with outer coats of great blood vessels passing through it (aorta, pulmonary trunk, superior and inferior venae cavae, and pulmonary veins). Fibrous pericardium is attached in front to sternum by sternopericardial ligaments.

Pericardium Serous Pericardium It lines fibrous pericardium and coats heart. It is divided into parietal & visceral layers. Parietal layer lines fibrous pericardium & is reflected around roots of great vessels to become continuous with visceral layer of serous pericardium that closely covers heart. Visceral layer is called epicardium. Pericardial cavity is a slit-like space between parietal & visceral layers that contains a small amount of tissue fluid, pericardial fluid To facilitate heart movements

Pericardium Pericardial Sinuses They are recesses in pericardium cavity formed by reflection of serous pericardium on posterior surface of heart. Oblique sinus formed around large veins. Transverse sinus lies between reflection of serous pericardium around aorta and pulmonary trunk and reflection around large veins.

Pericardium Nerve Supply of Pericardium Fibrous pericardium and parietal layer of serous pericardium are supplied by phrenic nerves. Visceral layer of the serous pericardium is innervated by branches of sympathetic trunks and vagus nerves.

Heart hollow muscular & pyramid shaped organ that lies freely within pericardium in mediastinum and is connected at its base to great blood vessels. Heart has apex and 3 surfaces Apex of heart: is formed by left ventricle, is directed downward, forward, and to the left. It lies at level of 5 th left intercostal space, 9 cm from midline where apex beat can usually palpated in living patient. Surfaces of the Heart: Anterior, Inferior, Posterior

Heart Surfaces Sternocostal (Anterior) surface: is formed mainly by right atrium and right ventricle, which are separated from each other by vertical atrioventricular groove. Right border is formed by right atrium; left border, by left ventricle and part of left auricle. Right & left ventricles are separated by anterior interventricular groove.

Heart Surfaces Diaphragmatic (inferior) surface: is formed mainly by right and left ventricles separated by posterior interventricular groove. Inferior surface of right atrium and inferior vena cava also forms part of this surface.

Heart Surfaces Base of heart, or (posterior surface): is formed mainly by left atrium, into which open four pulmonary veins. The base of heart lies opposite apex.

Heart Borders of the Heart Right border is formed by right atrium; left border by left auricle; and below, by left ventricle. Lower border mainly by right ventricle but also by right atrium; apex is formed by left ventricle.

Chambers of the Heart is divided by vertical septa into four chambers: right & left atria and right & left ventricles. Right atrium lies anterior to left atrium, and right ventricle lies anterior to left ventricle. Walls of the heart are composed of cardiac muscle, myocardium; covered externally with serous pericardium, epicardium; and lined internally with a layer of endothelium, endocardium.

Chambers of the Heart Right Atrium It consists of a main cavity and a small out-pouching, auricle. There is a vertical groove on outside of the heart at junction between right atrium and right auricle called sulcus terminalis, which on the inside forms a ridge called crista terminalis. Main part of atrium that lies posterior to this ridge is smooth walled and is derived embryologically from sinus venosus. Part of atrium in front of this ridge is roughened or trabeculated by bundles of muscle fibers, musculi pectinati, which run from crista terminalis to auricle. This anterior part is derived embryologically from primitive atrium.

Chambers of the Heart Openings into the Right Atrium: Superior vena cava opens into upper part of right atrium; it has no valve. It returns blood to heart from upper half of body. Inferior vena cava opens into lower part of right atrium; it is guarded by a rudimentary, nonfunctioning valve. It returns blood to heart from lower half of the body. Coronary sinus, which drains most of blood from the heart wall, opens into right atrium between inferior vena cava and atrioventricular orifice. It is guarded by a rudimentary, nonfunctioning valve. Right Atrioventricular Orifice lies anterior to inferior vena cava opening and is guarded by tricuspid valve.

Chambers of the Heart Fetal Remnants of right atrium: Rudimentary valve of inferior vena cava Fossa ovalis & Anulus ovalis: lie on atrial septum. Fossa ovalis is a shallow depression, which is site of foramen ovale in fetus. Anulus ovalis forms upper margin of fossa. Floor of the fossa represents persistent septum primum of heart of embryo, and anulus is formed from lower edge of septum secundum.

Chambers of the Heart Right Ventricle It communicates with right atrium through atrioventricular orifice and with pulmonary trunk through pulmonary orifice. Its cavity becomes funnel shaped near pulmonary orifice called (infundibulum). Walls of right ventricle are much thicker than those of right atrium and show several internal projecting ridges formed of muscle bundles trabeculae carneae. One type of these trabeculae carneae are Papillary muscles: which project inward, being attached by their bases to ventricular wall; their apices are connected by fibrous chords (chordae tendineae) to cusps of tricuspid valve.

Chambers of the Heart Tricuspid valve guards atrioventricular orifice and consists of 3 cusps formed by a fold of endocardium with some connective tissue enclosed: Anterior, Septal & Inferior (posterior) cusps. Bases of cusps are attached to fibrous ring of heart skeleton, whereas their free edges & ventricular surfaces are attached to chordae tendineae. When ventricle contracts, papillary muscles contract and prevent cusps from being forced into atrium and turning inside out as intraventricular pressure rises. Chordae tendineae of one papillary muscle are connected to adjacent parts of two cusps.

Chambers of the Heart Pulmonary valve guards pulmonary orifice and consists of 3 semilunar cusps formed by folds of endocardium with some connective tissue enclosed. Open mouths of cusps are directed upward into pulmonary trunk. No chordae or papillary muscles are associated with these cusps; attachments of sides of cusps to arterial wall prevent cusps from prolapsing into ventricle. At root of pulmonary trunk are 3 dilatations (sinuses) each one is situated external to each cusp.

Chambers of the Heart Left Atrium It consists of a main cavity and a left auricle. Left atrium is situated behind right atrium and forms greater part of base (posterior surface) of heart. Behind it lies oblique sinus of serous pericardium, and fibrous pericardium separates it from esophagus. Interior of left atrium is smooth, but left auricle possesses muscular ridges. Openings into the Left Atrium: Four pulmonary veins: two from each lung, open through posterior wall with no valves Left Atrioventricular Orifice: is guarded by mitral valve.

Chambers of the Heart Left Ventricle It communicates with left atrium through atrioventricular orifice and with aorta through aortic orifice. Walls of left ventricle are three times thicker than those of right ventricle. In cross section, left ventricle is circular; right is crescentic because of bulging of ventricular septum into cavity of right ventricle. There are well-developed trabeculae carneae, two large papillary muscles. Part of ventricle below aortic orifice is called aortic vestibule. .

Chambers of the Heart Mitral valve guards atrioventricular orifice. It consists of two cusps, one anterior and one posterior, which have a structure similar to that of tricuspid valve. Anterior cusp is the larger and intervenes between atrioventricular and aortic orifices. Aortic valve guards aortic orifice and is similar to pulmonary valve. Behind each cusp aortic wall bulges to form an aortic sinus. Anterior aortic sinus gives origin to right coronary artery, and left posterior sinus gives origin to left coronary artery

Structure of the Heart Walls of the heart: are composed of thick layer of cardiac muscle, myocardium, covered externally by epicardium and lined internally by endocardium. Atria are thin-walled and divided by atrial (interatrial) septum into right and left atria. Ventricles are thick-walled and divided by ventricular (interventricular) septum into right and left ventricles. Septum is placed obliquely, with one surface facing forward and to the right and the other facing backward and to the left. Lower part of septum is thick and formed of muscle and smaller upper part of septum is thin & membranous and attached to fibrous skeleton.

Structure of the Heart Skeleton of the heart: consists of fibrous rings that surround atrioventricular, pulmonary, and aortic orifices and are continuous with membranous upper part of ventricular septum. Fibrous rings around atrioventricular orifices separate muscular walls of atria from those of ventricles but provide attachment for muscle fibers. Fibrous rings support bases of valve cusps and prevent valves from stretching and becoming incompetent. Skeleton of heart forms basis of electrical discontinuity between atria and ventricles.

Structure of the Heart Conducting System of the Heart: Sinuatrial Node: is located in wall of right atrium in upper part of sulcus terminalis just to right of opening of superior vena cava. Atrioventricular Node: is strategically placed on lower part of atrial septum just above attachment of septal cusp of tricuspid valve. Atrioventricular Bundle of His: It descends through fibrous skeleton of heart behind septal cusp of tricuspid valve to reach upper border of muscular part of septum, then divides into two branches, one for each ventricle. • Right bundle branch (RBB) • Left bundle branch (LBB) Subendocardial plexus of Purkinje fibers:

Arterial Supply of Heart It is provided by right and left coronary arteries, which arise from ascending aorta immediately above aortic valve. Coronary arteries and their major branches are distributed over surface of heart, lying within subepicardial connective tissue. Right coronary artery arises from anterior aortic sinus of ascending aorta & runs forward between pulmonary trunk & right auricle. It descends almost vertically in right atrioventricular groove, and at inferior border of heart it continues posteriorly along atrioventricular groove to anastomose with left coronary artery in posterior interventricular groove. It supplies right atrium and right ventricle and parts of left atrium and left ventricle and atrioventricular septum.

Branches of right coronary artery: 1. Right conus artery: supply pulmonary conus 2. Atrial branches supply anterior and lateral surfaces of right atrium. One branch supplies posterior surface of both right and left atria. Artery of sinuatrial node supplies node and right and left atria; in 35% of individuals it arises from left coronary artery. 3. Ventricular Branches: Anterior ventricular branches: supply anterior surface of right ventricle. Marginal branch: is the largest & runs along lower margin of costal surface to reach apex. Posterior ventricular branches: supply diaphragmatic surface of right ventricle. Posterior interventricular (descending) artery: runs in posterior interventricular groove. It supply inferior wall & posterior part of ventricular septum. Large septal branch supplies AV node.

Arterial Supply of Heart Left coronary artery supplies major part of heart, including greater part of left atrium, left ventricle, and ventricular septum. It arises from left posterior aortic sinus of ascending aorta and passes forward between pulmonary trunk and left auricle. It then enters atrioventricular groove & divides into an anterior interventricular branch & circumflex branch. Anterior interventricular (descending) branch: runs downward in anterior interventricular groove. In most individuals it passes around apex of heart to enter posterior interventricular groove & anastomoses with terminal branches of right coronary artery. It supplies right & left ventricles with numerous branches that also supply anterior part of ventricular septum. One of these ventricular branches (left diagonal artery) may arise directly from trunk of left coronary artery. A small left conus artery supplies pulmonary conus.

Arterial Supply of Heart Circumflex artery: same size as anterior interventricular artery. It winds around left margin of heart in atrioventricular groove. Left marginal artery is a large branch supplying left margin of left ventricle down to apex. Anterior & posterior ventricular branches supply left ventricle. Atrial branches supply left atrium. Coronary Artery Anastomoses between terminal branches of right & left coronary arteries exist, but not large to provide an adequate blood supply to cardiac muscle if one of large branches becomes blocked. A sudden block of one of larger branches of either coronary artery usually leads to myocardial infarction, although sometimes collateral circulation is enough to sustain muscle.

Arterial Supply of Heart Variations in the Coronary Arteries Variations in blood supply to heart do occur, and most common variations affect blood supply to diaphragmatic surface of both ventricles. Here origin, size, and distribution of posterior interventricular artery are variable. In right dominance, posterior interventricular artery is a large branch of right coronary artery. Right dominance is present in most individuals (90%). In left dominance, posterior interventricular artery is a branch of circumflex branch of left coronary artery (10%).

Venous Drainage of the Heart Most blood from heart wall drains into right atrium through coronary sinus, which lies in posterior part of atrioventricular groove and is a continuation of great cardiac vein. It opens into right atrium to left of inferior vena cava. Small and middle cardiac veins are tributaries of coronary sinus. Remainder of blood is returned to right atrium by anterior cardiac vein and by small veins that open directly into heart chambers.

Nerve Supply of Heart is innervated by sympathetic and parasympathetic fibers of autonomic nervous system via cardiac plexuses situated below arch of aorta. Sympathetic supply arises from cervical & upper thoracic portions of sympathetic trunks, and parasympathetic supply comes from vagus nerves. Sympathetic fibers terminate on SA & AV nodes, cardiac muscle fibers & coronary arteries. These nerves results in cardiac acceleration, increased contraction of cardiac muscle, and dilatation of coronary arteries. Parasympathetic fibers terminate on SA & AV nodes and on coronary arteries. These fibers results in a reduction in rate and force of contraction of heart and a constriction of coronary arteries.

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