Cardiovascular System Gross Anatomy PDF

CARDIOVASCULAR SYSTEM  Outline  Overview of the thorax  Mediastinum and its classification  Gross Anatomy of the Heart  Neurovascular supply of the Heart  Some clinical associations Introduction: The thorax  Cont… ...

CARDIOVASCULAR SYSTEM  Outline  Overview of the thorax  Mediastinum and its classification  Gross Anatomy of the Heart  Neurovascular supply of the Heart  Some clinical associations Introduction: The thorax  Cont…  Is the region b/n the neck and the abdomen.  It has the shape of a truncated cone  Is narrow superiorly but circumference increase inferiorly.  It is flattened in front & behind but rounded at the sides.  Cont…  The thoracic cavity enclosed by the thoracic wall and the diaphragm is subdivided into three major compartments:  Left and right pleural cavity, mediastinum  The mediastinum is a thick, flexible soft tissue partition oriented longitudinally in a median sagittal position..  The pleural cavities are completely separated from each other by the mediastinum.  Therefore, abnormal events in one pleural cavity do not necessarily affect the other cavity. This also means that the mediastinum can be entered surgically without opening the pleural cavities  Relationship of thorax to other body regions  Neck: the superior thoracic aperture opens directly into the root of the neck  Upper limb: An axillary inlet, or gateway to the upper limb, lies on each side of the superior thoracic aperture  Cont…  Abdomen: The diaphragm separates the thorax from the abdomen. Structures that pass between the thorax and abdomen either penetrate the diaphragm or pass posteriorly to it  The inferior vena cava pierces the central tendon of the diaphragm to enter the right side of the mediastinum near vertebral level TVIII  The esophagus penetrates the muscular part of the diaphragm to leave the mediastinum and enter the abdomen just to the left of the midline at vertebral level TX  The aorta passes posteriorly to the diaphragm at the midline at vertebral level TXII  Breast: The breasts, consisting of secretory glands, superficial fascia, and overlying skin, are in the pectoral region on each side of the anterior thoracic wall Cont…  Boundaries of thoracic wall  Consists of: A. Skeletal elements(thoracic cage )  Anteriorly- sternum (manubrium, body, & xiphoid process). This side is flat  Posteriorly-all thoracic vertebrae & their intervening IVDs  Laterally -ribs (12 pairs) B. Skin  Mammary glands of breasts lie within the subcutaneous tissue of thoracic wall on the anterior side. Skeletal framework :Ribs, costal cartilages, and intercostal spaces  Clinical significance: Sternal angle  Used to find the position of rib II as a reference for counting ribs (because of the overlying clavicle, rib I is not palpable);  Separates the superior mediastinum from the inferior mediastinum and marks the position of the superior limit of the pericardium;  Marks where the arch of the aorta begins and ends;  The site where the superior vena cava penetrates the pericardium to enter the heart;  The level at which the trachea bifurcates into right and left main bronchi  Marks the superior limit of the pulmonary trunk.  Thoracic apertures  The thoracic cavity is open superiorly and inferiorly  The much smaller superior opening is a passageway that allows communication with the neck and upper limb.  The larger inferior opening (partially closed by diaphragm) provides the ring-like origin of the diaphragm, which completely occludes the opening.  Superior thoracic apertures  The superior thoracic aperture is bounded:  Posteriorly, by vertebra T1( its body)  Laterally, by the 1st pair of ribs  Anteriorly, by the superior border of the manubrium.  Cont…  Sometimes we refer to the superior thoracic aperture as the thoracic inlet because non-circulating substances (air and food) may enter the thorax only through this aperture  Structures that pass through superior thoracic aperture include the trachea, esophagus, nerves, and vessels.  The adult superior thoracic aperture measures approximately 6.5 cm anteroposteriorly and 11 cm transversely  Because of the obliquity of the 1st pair of ribs, the aperture slopes antero-inferiorly Cont…  Inferior thoracic aperture It is bounded by:  Posteriorly by the 12T(its body ).  Posterolaterally, by 11th & 12th ribs.  Anterolaterally, by the joined costal cartilages of ribs 7–10,forming the costal margins.  Anteriorly, by the xiphisternal joint.  Cont…  The inferior thoracic aperture is larger than the superior thoracic aperture  It is oblique b/c the posterior thoracic wall is much longer than the anterior wall  Structures passing b/n the abdomen & thorax pass through openings of the diaphragm, or pass posterior to it  The domes of the diaphragm rise to the level of the 4th intercostal space, and abdominal viscera, including the liver, spleen, and stomach, lie superior to the plane of the inferior thoracic aperture, within the thoracic wall  Mediastinum  Is the central compartment of the thoracic cavity  Occupied by the mass of tissue  It extends from the superior thoracic aperture to the diaphragm & from the sternum to the bodies of the T. vertebrae  It serves as a passageway for structures from the neck & head to the abdomen  Is covered on each side by mediastinal pleura  Contains all the thoracic viscera except the lungs Cont…  Cont…  A horizontal plane passing through the sternal angle & to the intervertebral disc b/n vertebrae TIV and TV divides the mediastinum into superior and inferior parts.  Inferior mediastinum further partitioned into the anterior, middle, and posterior mediastinum by the pericardial sac. Cont…  Superior mediastinum Boundaries of superior mediastinum:  Upper boundary - jugular notch,1st rib,T1 vertebra.  Lower boundary --plane of sternal angle(sternal angle to lower border of 4th thoracic vertebra)  Lateral boundaries -- mediastinal pleurae  Anterior boundary -- manubrium of sternum  Posterior boundary -- bodies of thoracic vertebrae: T1 thru T4  Contents of the superior mediastinum  From anterior to posterior, the contents of the superior mediastinum are.  Glandular plane (Thymus).  Venous plane contains (brachiocephalic veins and SVC)  Arterial-nervous plane contains arteries (arch of aorta & roots of its major branches—the brachiocephalic trunk, left common carotid artery & left subclavian artery) & related nerves (vagus & phrenic nerves & the cardiac plexus of nerves).  Visceral plane contains (trachea anteriorly and esophagus posteriorly) and related nerves (left recurrent laryngeal nerve).  Lymphatic plane. Cont…  Inferior mediastinum  Is divided by the pericardial sac into the:  Anterior(2)  Middle (3)  Posterior (4) mediastinum  Anterior mediastinum  Boundaries of anterior mediastinum(2):  Anteriorly -- body and xiphoid of sternum  Posteriorly -- pericardium  Laterally -- mediastinal pleura  Superiorly -- plane of sternal angle  Inferiorly ---diaphragm  Cont…  The anterior mediastinum, is the smallest subdivision of the mediastinum.  It is continuous with the superior mediastinum at the sternal angle and is limited inferiorly by the diaphragm.  It consists of loose connective tissue (sternopericardial ligaments), fat, lymphatic vessels, a few lymph nodes & branches of the internal thoracic vessels.  In infants and children, the anterior mediastinum contains the inferior part of the thymus.  Middle mediastinum  Middle mediastinum: boundaries  Anterior -- pericardium  Posterior -- pericardium  Lateral -- mediastinal pleura  Superior -- plane of sternal angle  Inferior -- diaphragm  Cont… The contents of middle mediastinum includes:  The pericardium,  Heart  Roots of its great vessels  Ascending aorta,  Pulmonary trunk  SVC  Pericardium  The pericardium is a fibroserous sac surrounding the heart and the roots of the great vessels  The pericardium is a closed sac composed of 2 layers, outer fibrous pericardium & an inner smooth, serous pericardium.  Fibrous pericardium  The fibrous pericardium is a tough connective tissue outer layer that defines the boundaries of the middle mediastinum  Superiorly: Continuous with the tunica adventitia of the great vessels entering & leaving the heart  Anteriorly: Attached to the posterior surface of the sternum by the sternopericardial ligaments  Posteriorly: Bound by loose connective tissue to structures in the posterior mediastinum  Inferiorly: Continuous with the central tendon of the diaphragm  Cont…  The inferior wall (floor) of the fibrous pericardial sac is firmly attached and confluent centrally with the central tendon of the diaphragm  The site of continuity has been referred to as the pericardiacophrenic ligament but the fibrous pericardium & central tendon are not separable  Phrenic nerves(C3 to C5), & pericardiacophrenic vessels are located within/pass thru fibrous pericardium & supply it.  Cont...  Fibrous pericardium  Stabilizes the heart  Prevent heart from over dilating  Protects the heart against sudden overfilling  Serous pericardium  Serous pericardium forms a closed sac similar to the pleura: containing  Parietal layer: lines the inner surface of the fibrous pericardium  Visceral layer (epicardium): of serous pericardium adheres to the heart and forms its outer covering.  Narrow space b/n the two layers, containing a thin film of fluid, is the pericardial cavity.  Cont…  The visceral and parietal layer of serous pericardium becoming continuous together where  The aorta and pulmonary trunk leave the heart  The SVC, inferior vena cava (IVC), and pulmonary veins enter the heart  Clinical: Pericardial effusion  Normally, only a tiny amount of fluid is present between the visceral and parietal layers of the serous pericardium.  In certain situations, this space can be filled with excess fluid (pericardial effusion).  Because the fibrous pericardium is a 'relatively fixed' structure that cannot expand easily, a rapid accumulation of excess fluid within the pericardial sac compresses the heart (cardiac tamponade), which resulting in biventricular failure.  Pericardial Sinuses  The transverse sinus is posterior to the intrapericardial parts of the pulmonary trunk and ascending aorta, anterior to the SVC, and superior to the atria of the heart  Surgical significance of transverse pericardial sinus  Is especially important to cardiac surgeons. After the pericardial sac is opened anteriorly, a finger can be passed through the transverse pericardial sinus posterior to the ascending aorta and pulmonary trunk Cont…  Cont…  The oblique sinus is bounded laterally by the pericardial reflections surrounding the pulmonary veins and IVC and posteriorly by the pericardium overlying the anterior aspect of the esophagus.  Arterial supply of the pericardium  Is mainly from branch's of the internal thoracic artery, the pericardiacophrenic artery - Smaller contributions of blood come from the:  Musculophrenic artery- a terminal branch of the internal thoracic artery  Bronchial, esophageal, and superior phrenic arteries, branches of the thoracic aorta  Coronary arteries (visceral layer of serous pericardium only), the first branches of the aorta.  Venous drainage  The venous drainage of the pericardium is into the:  Pericardiacophrenic veins, tributaries of the brachiocephalic (or internal thoracic) veins.  Variable tributaries of the azygos venous system.  Nerve supply of the pericardium The nerve supply of the pericardium is from the:  Phrenic nerves (C3–C5), primary source of sensory fibers; pain sensations conveyed by these nerves are commonly referred to the skin (C3–C5 dermatomes) of the ipsilateral supraclavicular region (top of the shoulder of the same side).  Vagus nerves, function uncertain.  Sympathetic trunks, vasomotor Heart The heart is a funnel-shaped, hollow, muscular organ that is responsible for pumping blood to all parts of the body. 11/01/2024  Cont… The heart, slightly larger than one’s loosely clenched fist and weighs about 350 g in adults  Is a double, self-adjusting suction & pressure pump.  The general shape of the heart pyramidal.  The right side of the heart receives poorly oxygenated blood through the SVC and IVC and pumps it through the pulmonary trunk to the lungs for oxygenation.  The left side of the heart (Lt heart) receives well-oxygenated (arterial) blood from the lungs through the pulmonary veins& pumps it into the aorta for distribution.  Cont… Cardiac orientation:  The apex projects forward, downward, & to Lt  The base is opposite the apex & faces in a posterior direction.  Surfaces of the heart Anterior (sternocostal) : consists mostly of Rt ventricle with some of Rt atrium & some of Lt ventricle. Diaphragmatic surface: consists of Lt ventricle & a small portion of Rt ventricle.  Heart in the anatomic position rests on diaphragmatic surface.  Cont… Left pulmonary surface: consists of Lt ventricle & a portion of Lt atrium & faces Lt lung. Right pulmonary surface: consists of Rt atrium & faces Rt lung. Apex – formed by Lt ventricle: is directed downward, forward & to the left.  Borders of the heart  The four borders of the heart are the: 1. Right border (slightly convex), formed by the right atrium and extending between the SVC and the IVC. 2. Inferior border (nearly horizontal), formed mainly by the right ventricle and slightly by the left ventricle. 3. Left border (oblique, nearly vertical), formed mainly by the left ventricle and slightly by the left auricle. 4. Superior border, formed by the right and left atria and auricles in an anterior view; the ascending aorta and pulmonary trunk emerge from this border and the SVC enters its right side. Cont…  Cardiac cycle  Is the complete movement of the heart /heartbeat & includes the period from the beginning of one heartbeat to the beginning of the next one.  The cycle consists of diastole (ventricular relaxation and filling) and systole (ventricular contraction and emptying).  The right heart (blue side) is the pump for the pulmonary circuit; the left heart (red side) is the pump for the systemic circuit.  Heart sound  Two heart sounds are heard with a stethoscope:  The first (“lub”) sound is caused by the closure of the tricuspid and mitral valves(as the blood is transferred from the atria into the ventricles(end of diastole and beginning of systole)  The second (“dub”) sound is caused by the closure of the aortic and pulmonary valves, as the ventricles expel blood from the heart (end of systole and beginning of diastole)  The heart sounds are produced by the snapping shut of the one way valves that normally keep blood from flowing backward during contractions of the heart.  Fibrous skeleton of the heart  Is a collection of dense, fibrous connective tissue in the form of four rings with interconnecting areas in a plane between the atria and the ventricles.  The cardiac muscle fibers are anchored to the fibrous skeleton of the heart  This is a complex framework of dense collagen forming:  4 fibrous rings that surround the orifices of the valves  A right and left fibrous trigone (formed by connections between rings), and the membranous parts of the interatrial and interventricular septa Cont…  Cont…  The fibrous skeleton of the heart functions in:  Keeps the orifices of the AV and semilunar valves patent& prevents over distention  Provides attachments for the leaflets or cusps of the valves.  Provides attachment for the myocardium  Forms an electrical “insulator,” by separating the myenterically conducted impulses of the atria and ventricles, so that they contract independently.  Internal partitions of the Heart  Internal partitions divide the heart into four chambers (i.e. two atria and two ventricles) and produce surface or external grooves referred to as sulci  Coronary sulcus / AV groove/ circles the heart, separating the atria from the ventricles. As it circles the heart, it contains the Rt CA , small cardiac vein, coronary sinus, and the circumflex branch of the left coronary artery.  The anterior and posterior interventricular sulci separate the two ventricles-  Ant. interventricular sulcus: is on the anterior surface of the heart and contains the ant. IVC artery and the great cardiac vein  Post. interventricular sulcus: is on the diaphragmatic surface of the heart and contains the post. IVC artery and the middle cardiac vein Cont…  Clinical: Septal defect Atrial septal defect (ASD)  Allows oxygenated blood to flow from the left atrium (higher pressure) across the ASD into the right atrium (lower pressure)  Many patients with ASD are asymptomatic, but in some cases the ASD may need to be closed surgically or by endovascular devices.  Occasionally, increased blood flow into the right atrium over many years leads to right atrial and right ventricular hypertrophy and enlargement of the pulmonary trunk, resulting in pulmonary arterial hypertension.  Cont… Ventriculoseptal defect (VSD)  These lesions are most frequent in the membranous portion of the septum and they allow blood to move from the left ventricle (higher pressure) to the right ventricle (lower pressure);  This leads to right ventricular hypertrophy and pulmonary arterial hypertension.  Right atrium  Blood returning to the right atrium enters thru: the superior & inferior venae cavae, (which together deliver blood to the heart from the body); & coronary sinus, (which returns blood from walls of the heart itself).  SVC enters upper posterior portion of Rt atrium.  IVC & coronary sinus enter the lower posterior portion of Rt atrium.  From Rt atrium, blood passes into Rt ventricle thru Rt AV. orifice.  Rt atrioventricular orifice is closed during ventricular contraction by tricuspid valve.  Interior of the right atrium  Interior of Rt atrium is divided into two continuous parts : 1) Smooth, thin-walled, posterior part (the sinus venarum) on w/c the SVC, IVC& coronary sinus open. 2) Rough, muscular anterior wall composed of pectinate muscles.  The smooth &rough parts are separated externally by the sulcus terminalis & internally by the crista terminalis.  The SVC opens into the superior part of the Rt atrium at the level of Rt 3rd costal cartilage.  The IVC opens into the inferior part of the right atrium almost in line with the SVC at approximately the level of the 5th costal cartilage. Cont…  Cont…  The coronary sinus, opens b/n the orifices of Rt AV& IVC.  The interatrial septum separating the atria has an oval, depression, the oval fossa (L. fossa ovalis), w/c is a remnant of the oval foramen (L. foramen ovale) & its valve in the fetus.  Right ventricle  The Rt ventricle forms the largest part of the anterior surface of the heart, a small part of the diaphragmatic surface& most inferior border of the heart.  The outflow tract of the right ventricle, which leads to the pulmonary trunk, is the conus arteriosus (infundibulum).  The interior of the Rt ventricle has irregular muscular elevations (trabeculae carneae)  A thick muscular ridge, the supraventricular crest, separates the muscular wall of the inflow part, from the smooth wall of the conus arteriosus, or outflow part. Cont…  Cont… The papillary muscles begin to contract before contraction of the right ventricle, tightening the tendinous cords and drawing the cusps together and prevent backflow of the blood  Cont…  The inflow part of the ventricle receives blood from the right atrium through the Rt AV (tricuspid) orifice located at the level of the 4 th& 5th intercostal spaces  The walls of the inflow part of the Rt ventricle have numerous muscular, irregular structures called trabeculae carneae.  A few trabeculae carneae (papillary muscles) have only one end attached to the ventricular surface, while the other end serves as the point of attachment for tendon-like fibrous cords (the chordae tendineae), which connect to the free edges of the cusps of the tricuspid valve.  Cont…  Tendinous cords attach to the anterior, posterior & septal cusps.  The tendinous cords arise from the apices of papillary muscles.  Cont…  There are 3 papillary muscles in the Rt ventricle.  They are named relative to their point of origin on the ventricular surface. These are: 1. Anterior papillary muscle: is the largest& most prominent, arises from the anterior wall of the right ventricle; its tendinous cords attach to the anterior and posterior cusps of the tricuspid valve. 2. Posterior papillary muscle: smaller than the anterior muscle,; it arises from the inferior wall of the right ventricle, and its tendinous cords attach  Cont… 3. Septal papillary muscle: arises from the interventricular septum, and its tendinous cords attach to the anterior and septal cusps of the tricuspid valve.  Cont…  The interventricular septum (IVS),has muscular & membranous parts, is a strong, obliquely placed partition b/n the Rt & Lt ventricles.  The muscular part of the IVS forms the majority of the septum  The septomarginal trabecula (moderator band) is a curved muscular bundle that traverses the right ventricular chamber from the inferior part of the IVS to the base of the anterior papillary muscle.  It carries a portion of the cardiac conduction system, right bundle of the atrioventricular bundle, to the anterior wall of the right ventricle.  The pulmonary valve at the apex of the conus arteriosus is at the level of the left 3rd costal cartilage  Left atrium  The left atrium forms most of the base of the heart  The valveless pairs of Rt and Lt pulmonary veins enter the smooth- walled atrium.  The part of the wall derived from the embryonic pulmonary vein is smooth walled.  The tubular, muscular left auricle, its wall trabeculated with pectinate muscles. It represents the remains of the left part of the primordial atrium  Cont…  A semilunar depression in the interatrial septum indicates the floor of the oval fossa; the surrounding ridge is the valve of the oval fossa (L. valvulae foramen ovale).  Interior of the left atrium  A larger smooth-walled part and a smaller muscular auricle containing pectinate muscles  Four pulmonary veins (two superior and two inferior) entering its smooth posterior wall  A slightly thicker wall than that of the right atrium  An interatrial septum that slopes posteriorly and to the right.  A left AV orifice through which the left atrium discharges the oxygenated blood it receives from the pulmonary veins into the left ventricle  Left ventricle  The left ventricle forms the apex of the heart, nearly all its left (pulmonary) surface and border, and most of the diaphragmatic surface.  Interior of the left ventricle  Walls that are two to three times as thick as those of the right ventricle.  Walls that are mostly covered with a mesh of trabeculae carneae that are finer and more numerous than those of the right ventricle.  A conical cavity that is longer than that of the right ventricle.  Anterior & posterior papillary muscles that are larger than those in the right ventricle.  Cont…  A smooth-walled, non-muscular, supero-anterior outflow part, the aortic vestibule, leading to the aortic orifice and aortic valve.  A double-leaflet mitral valve that guards the left AV orifice.  An aortic orifice that lies in its right postero superior part and the ascending aorta begins at the aortic orifice  Cont…  The Lt atrioventricular orifice opens into the posterior Lt side of the superior part of the left ventricle.  It is closed during ventricular contraction by the mitral valve (Lt atrioventricular valve),w/c is also referred to as the bicuspid valve b/c it has 2 cusps, the anterior & posterior cusps.  The mitral valve is located posterior to the sternum at the level of the 4th costal cartilage. Cont… Cont…  Myocardial Thickness and Function  The thickness of the myocardium of the four chambers varies according to the function of each chamber.  The atria walls are thin because they deliver blood to the ventricles  The ventricle walls are thicker because they pump blood to greater distances  The right ventricle walls are thinner than the left because they pump blood into the lungs, which are nearby and offer very little resistance to blood flow.  The left ventricle walls are thicker because they pump blood through the body where the resistance to blood flow is greater 11/01/2024  Semilunar valve  The aortic vestibule, or outflow tract of the left ventricle, is continuous superiorly with the ascending aorta.  The opening from the left ventricle into the aorta is closed by the aortic valve.  It consists of three semilunar cusps.  The aortic valve is located posterior to the left side of the sternum at the level of the 3rd intercostal space. Cont…  Cont…  The outflow opening tract of the right ventricle into the pulmonary trunk is closed by the pulmonary valve.  Each of 3 semilunar cusps of the pulmonary valve (anterior, right & left), is concave when viewed superiorly.  Semilunar cusps do not have tendinous cords to support them.  They are smaller in area than the cusps of the AV valves & the force exerted on them is less than half that exerted on the cusps of the tricuspid & mitral valves.  The cusps project into the artery but are pressed toward its walls as blood leaves the ventricle  Cont…  After relaxation of the ventricle (diastole), the elastic recoil of the wall of the pulmonary trunk or aorta forces the blood back toward the heart.  However, the cusps snap closed like an umbrella caught in the wind as they catch the reversed blood flow.  They come together to completely close the orifice, supporting each other as their edges meet, and preventing any significant amount of blood from returning to the ventricle. Vasculature of heart  Cont…  The blood vessels of the heart comprise the coronary arteries & cardiac veins, which carry blood to & from most of the myocardium.  The endocardium & some subendocardial tissue receive oxygen & nutrients by diffusion or microvasculature directly from the chambers of the heart.  The blood vessels of the heart, normally embedded in fat, course across the surface of the heart just deep to the epicardium.  Cont…  The coronary arteries, the 1st branches of the aorta, supply the myocardium & epicardium  The Rt & Lt coronary arteries arise from the corresponding aortic sinuses at the proximal part of the ascending aorta.  The coronary arteries supply both the atria &the ventricles but the atrial branches are usually small.  The ventricular distribution of each coronary artery is not sharply demarcated.  Right coronary artery (RCA)  The RCA arises from the Rt aortic sinus of the ascending aorta & passes to the Rt side of the pulmonary trunk.  Near its origin, the RCA usually gives off an ascending sinu-atrial nodal branch then RCA descends in the coronary sulcus & gives off the Rt marginal branch.  After giving off this branch, the RCA turns to the Lt & continues in the coronary sulcus to the posterior aspect of the heart.  RCA….  At the posterior aspect of the crux of the heart the junction of the inter atrial & IV septa b/n the 4 heart chambers the RCA gives rise to the atrioventricular nodal branch, which supplies the AV node.  Dominance of the coronary arterial system is defined by which artery gives rise to the posterior IV branch (posterior descending artery).  Dominance of the RCA is approximately 67%; the RCA gives rise to the large posterior IV branch w/c supplies adjacent areas of both ventricles & sends perforating IV septal branches into the IV septum.  RCA….  Typically, the RCA supplies :  The right atrium  Most of right ventricle  Part of the left ventricle (the diaphragmatic part)  Part of the IV septum, usually the posterior 3rd  The SA node (in approximately 60% of people)  The AV node (in approximately 80% of people) RCA…  Left coronary artery (LCA)  The LCA arises from the left aortic sinus of the ascending aorta & passes b/n the Lt auricle & the Lt side of the pulmonary trunk before entering the coronary sulcus.  As it enters the coronary sulcus, at the superior end of the anterior IV groove, the LCA divides into 2 branches, the anterior IV branch & the circumflex branch,  Anterior IV branch passes along the IV groove to the apex of the heart  In approximately 40% of people, the SA nodal branch arises from the circumflex branch of the LCA.  LCA…  Anterior IV artery around the inferior border of the heart it anastomoses with the posterior IV branch of the right coronary artery.  The anterior IV branch supplies adjacent parts of both ventricles and, via IV septal branches, the anterior 2/3rd of the IVS.  In many people, the anterior IV branch gives rise to a lateral branch (diagonal artery), which descends on the anterior surface of the heart  The left marginal branch of the circumflex branch follows the left margin of the heart and supplies the left ventricle  LCA…  Typically, the LCA supplies:  The left atrium.  Most of the left ventricle.  Part of the right ventricle.  Most of the IVS (usually its anterior two thirds), including the AV bundle of the conducting system of the heart, through its perforating IV septal branches.  The SA node (in approximately 40% of people) Cont…  Variations of the coronary arteries  Variations in the branching patterns and distribution of the coronary arteries are common.  In the most common Rt dominant pattern, present in approximately 67% of people, the RCA and LCA share about equally in the blood supply of the heart.  In approximately 15% of hearts, the LCA is dominant.  There is codominance in approximately 18% of people, in which branches of both the Rt &Lt CA reach the crux of the heart & give rise to branches that course in the posterior IV groove.  In other people, the circumflex branch arises from the right aortic sinus.  Approximately 4% of people have an accessory coronary artery.  Coronary collateral circulation  The branches of the coronary arteries are generally considered to be functional end arteries (lacking sufficient anastomoses)  However, anastomoses do exist between branches of the coronary arteries, subepicardial or myocardial, and between these arteries and extracardiac vessels such as thoracic vessels.  Anastomoses exist between the terminations of the right and the left coronary arteries in the coronary sulcus and between the IV branches around the apex in approximately 10% of apparently normal hearts.  Clinical: Coronary artery disease  Occlusion of a major coronary artery leads to an inadequate oxygenation of an area of myocardium and cell death (i.e. myocardial infarction).  The severity depends on the size and location of the artery involved and whether or not the blockage is complete.  Partial blockages may produce pain (angina) during or after exercise.  Typically cardiac pain is a deep central sternal pain radiating into the left arm and the lower neck  The severity of ischemia and infarction depends on the rate at which the occlusion or stenosis has occurred and whether or not collateral channels have had a chance to develop  Venous drainage of the heart  About 2/3rd the heart is drainaged by the coronary sinus in the coronary sulcus, located posteriorly.  The coronary sinus opens into the right atrium. Veins that drain into the coronary sinus include: 1. Great cardiac vein – accompanies anterior interventicular artery 2. Middle cardiac vein – accompanies posterior interventricular artery 3.Small cardiac vein – accompanies right marginal artery 4. Posterior left ventricular vein 5. Oblique vein of left atrium  Cont… Few of the blood drains by small veins directly into the cardiac cavity, usually the atria: i) anterior cardiac vein --- drain into right atrium, ii) venae cordis minimae (Thebesian veins) --- drain into all chambers, mainly atria  Lymphatic drainage of the heart  Lymphatic vessels in the myocardium and subendocardial connective tissue pass to the subepicardial lymphatic plexus.  Vessels from this plexus pass to the coronary groove and follow the coronary arteries  A single lymphatic vessel, formed by the union of various vessels from the heart, ascends between the pulmonary trunk and left atrium and ends in the inferior tracheobronchial lymph nodes, usually on the right side.  Innervation of the heart  The heart is supplied by autonomic nerve fibers from the cardiac plexus  The cardiac plexus is formed of both sympathetic and parasympathetic fibers en route to the heart  This nerve network is most commonly described as lying on the anterior surface of the bifurcation of the trachea  Cont…  Autonomic nervous system (ANS) is directly responsible for regulating: heart rate; force of each contraction; cardiac output:  Both parasympathetic & sympathetic parts are involved.  Sympathetic fibers arise from segments T2-T4 of the spinal cord & are distributed thru middle cervical & stellate ganglia  Cont…  Sympathetic fibers pass into cardiac plexus & from there to SA node and cardiac muscle.  Effect of sympathetic nerves at SA node is an increase in heart rate.  Effect on the muscle is an increase in rise of pressure within the ventricle, thus increasing stroke volume, dilatation of coronary aa.  Cont…  Parasympathetic stimulation:  decreases heart rate; reduces force of contraction; constricts the coronary arteries: 1. Effect of vagus n. at the SA node is the opposite of sympathetic nerves  decreases the heart rate. 2. It also decreases excitability around the AV node: slows down transmission. 3. Effect on the muscle is decrease in force of contraction.  Stimulating and conducting system of the heart  In the cardiac cycle, the atrium and ventricle work together as one pump.  The conducting system of the heart generates and transmits the impulses.  The conduction system consists of nodes and networks of specialized cardiac muscle cells organized into four basic components:  Sinu-atrial node(SA)  Atrioventricular node(AV)  Atrioventricular bundle with its right and left bundle branches;  Subendocardial plexus of conduction cells (the Purkinje fibers) Cont…  Cont…  The conducting system initiates by nodal tissue that & propagated by the cardiac striated muscle cells.  The sinu-atrial (SA) node is located anterolaterally at the junction of the SVC& Rt atrium near the superior end of the sulcus terminalis.  The SA node, specialized cardiac muscle fibers & associated fibroelastic connective tissue, is the pacemaker of the heart.  The SA node initiates and regulates the impulses for the contractions of the heart, giving off an impulse approximately 70 times per minute in most people most of the time.  Cont..  The SA node is stimulated by the sympathetic division to accelerate the heart rate & is inhibited by the parasympathetic autonomic nervous system division.  The AV node is located in the posteroinferior region of the interatrial septum.  The signal generated by the SA node passes through the walls of the Rt atrium, propagated by the cardiac muscle (myogenic conduction) w/c transmits the signal rapidly from the SA node to the AV node.  The AV node then distributes the signal to the ventricles through the AV bundle.  Cont…  The AV bundle, the bridge b/n the atrial& ventricular myocardium, passes from AV node thru the fibrous skeleton of the heart& along the membranous part of the IVS.  At the junction of the membranous & muscular parts of the IVS, the AV bundle divides into right and left bundles.  These branches then ramify into subendocardial branches (Purkinje fibers), w/c extend into the walls of the respective ventricles and the subendocardial branches of the right bundle stimulate the muscle of the IVS.  Impulse generation and conduction can be summarized as follows  The SA node initiates an impulse that is rapidly conducted to cardiac muscle fibers in the atria, causing them to contract.  The impulse spreads by myogenic conduction, which rapidly transmits the impulse from the SA node to the AV node.  The signal is distributed from the AV node through the AV bundle and its branches (the right and left bundles) w/c pass on each side of the IVS to supply subendocardial branches to the papillary muscles and the walls of the ventricles Principal Arteries of the body 11/01/2024  Cont… Aorta – has 3 parts: 1. Ascending aorta  Ascends from the heart (left ventricle)  The coronary arteries are the only branch of the ascending aorta that supplies the heart 2. Aortic arch Three vessels arise from the aortic arch:  Brachiocephalic artery  Left common carotid artery  Left subclavian artery 3. Descending aorta Continuation of aortic arch Lies posterior to the heart and continues down ward to become thoracic aorta 11/01/2024  Cont…  Brachiocephalic artery(trunk) Bifurcates into: The right common carotid artery and right subclavian artery supplies the right side of head and neck & the right upper limb The left common carotid artery and the left subclavian artery branch directly from the aortic arch. 11/01/2024  Surface anatomy of the heart & great vessels  Surface features in the thorax are fundamental to a physical examination.  Heart & great vessels are in middle of thorax, surrounded laterally by lungs & anteriorly by sternum & central part of thoracic cage.  Borders of heart are variable & depend on position of diaphragm & physical condition of the person.  Surface landmarks can be palpated to visualize the outline of the heart  Cont…  Outline of the heart can be traced on anterior surface of thorax by using the following guidelines:- 1. The superior border – corresponds to a line connecting inferior border of 2nd left costal cartilage (3 cm to the Lt of median plane) to the superior border of the 3rd Rt costal cartilage (2 cm from the median plane )  Cont… 2.The right border: corresponds to a line drawn from 3rd Rt costal cartilage (2 cm from median plane) to 6th Rt costal cartilage (2 cm from the median plane): this border is slightly convex to the right. 3.The left border: corresponds to a line connecting to the left ends of the lines representing the superior & inferior borders.  Cont… 4.The inferior border: corresponds to a line drawn from inferior end of Rt border to a point in 5th inter costal space close to Lt MCL ( 9 cm from median plane); Left end of this line corresponds to the location of apex of heart & apex beat. Cont…  Cont…  Upper limit of the heart reaches as high as 3rd costal cartilage on Rt side of sternum & 2nd intercostal space on Lt side of sternum.  Rt margin of the heart extends from Rt 3rd costal cartilage to near Rt 6th costal cartilage.  Lt margin of the heart descends laterally from 2nd intercostal space to the apex located near the MCL in 5th intercostal space.  Lower margin of the heart extends from sternal end of Rt 6 th costal cartilage to the apex in the 5th intercostal space near the MCL line  Surface anatomy of the great vessels Thoracic aorta:  Begins on the left side of the inferior border of the body of T4 vertebra & descends in the posterior mediastinum on the left sides of the T5- T12 vertebrae. Superior vena cava (SVC):  Passes inferiorly deep to the manubrium and manubriostrenal junction; a finger breadth to the right of the margin of the bony structures.  The SVC enters the right atrium of the heart opposite the right 3 rd costal cartilage.  It is essential to know the surface anatomy of this large vein to insert catheters into the SVC for feeding extremely ill patients & other purposes  Cont… Inferior vena cava (IVC):  Begins anterior to L5 vertebra by union of common iliac veins, about 2.5 cm to the right of the median plane, inferior to bifurcation of aorta & posterior to proximal part of common iliac artery.  Ascends on the right sides of bodies of L3 –L5 vertebrae & on the right psoas major to the right of aorta.  Leaves the abdomen by passing thru caval opening in the diaphragm to enter thorax at T8 vertebral level.