University:
Kentucky State University
Course:
BIO 301 | Human Anatomy
Academic year:

2020
Views:

156

Pages:

43
Author:

Tyshawn Shaffer

Coronary Collateral Circulation The branches of the coronary arteries are generally considered to be Functional End arteries!!!!! arteries that supply regions of the myocardium lacking sufficient anastomoses from other large branches to maintain viability of the tissue should occlusion occur Some Anastomoses do exist  The calibre of coronary arteries, both main stems and larger branches, based on measurements of arterial casts or angiograms, ranges between 1.5 and 5.5 mm for the coronary arteries at their origins.  The left exceed the right in 60% of hearts, the right being larger in 17%, and both vessels being approximately equal in 23%.  The diameters of the coronary arteries may increase up to the 30th year BLOOD SUPPLY OF THE HEART from two coronary arteries The left coronary artery (LCA) The right coronary artery (RCA) The endocardium and some subendocardial tissue located immediately external to the endocardium receive oxygen and nutrients by diffusion or microvasculature directly from the chambers of the heart THE LEFT CORONARY ARTERY (LCA) The left coronary artery (LCA) originates from The left sinus of Valsalva (the left aortic sinus ) of the ascending aorta passes between the left auricle and the left side of the pulmonary trunk The LCA usually has a short (0.5-2 cm) common stem that left diagonal artery, may arise directly from the trunk of the left coronary artery 1-THE ANTERIOR INTERVENTRICULAR or LEFT ANTERIOR DESCENDING (LAD)  Runs downward in the anterior interventricular groove to the apex of the heart  In most individuals it then passes around the apex of the heart to enter the posterior interventricular groove and anastomoses with the terminal branches of the right coronary artery. In one third of individuals it ends at the apex of the heart  The anterior interventricular branch LEFT ANTERIOR DESCENDING (LAD) Supplies 2-THE CIRCUMFLEX ARTERY  It is the same size as the anterior interventricular artery  It winds around the left margin of the heart in the atrioventricular groove.  A left marginal artery is a large branch that supplies the left margin of the left ventricle down to the apex.  Anterior ventricular and posterior ventricular branches supply the left ventricle.  Atrial branches supply the left atrium Summary of the Overall Arterial Supply to the Heart from the LCA The right coronary artery (RCA) arises from The right anterior sinus of Valsalva of the aorta and runs along the right AV sulcus, embedded in fat. Summary of the Overall Arterial Supply to the Heart from the RCA in Most Individuals The right coronary artery supplies all of the right ventricle (except for the small area to the right of the anterior interventricular groove), the variable part of the diaphragmatic surface of the left ventricle, the posteroinferior third of the ventricular septum, the right atrium and part of the left atrium, and the sinuatrial node and the atrioventricular node and bundle. The LBB also receives small branches. Arterial Supply to the Conducting System 1-The sinuatrial node is usually supplied by the right but sometimes by the left coronary artery. From the RCA near its origin (in 60%) from Circumflex branch of LCA (in 40%) A common variation in the origin of the sinoatrial nodal artery. 2-The atrioventricular node and the atrioventricular bundle are supplied by THE RIGHT CORONARY ARTERY 3-The RBB of the atrioventricular bundle is supplied by the left coronary artery 4-the LBB is supplied by the right and left coronary arteries Variations in the Coronary Arteries The most common variations affect the blood supply to the diaphragmatic surface of both ventricles the origin, size, and distribution of the Posterior Interventricular Artery Can be variable In right dominance, the posterior interventricular artery is a large branch of the right coronary artery. Right dominance is present in most individuals (90%). In left dominance the posterior interventricular artery is a branch of the circumflex branch of the left coronary artery (10%). The term ‘dominant’ is used to refer to the coronary artery giving off the posterior interventricular (descending) branch In the so-called ‘balanced’ pattern, branches of both arteries run in or near the posterior interventricular groove The term ‘dominant Is misleading because the left artery almost always supplies a greater volume of tissue than the right. . intra- and inter-coronary anastomoses in vessels up to 100–200 μm in calibre. The most frequent sites of extramural anastomoses are: The apex The anterior aspect of the right ventricle The posterior aspect of the left ventricle Interatrial and interventricular grooves Between the sinoatrial nodal and other atrial vessels The functional value of such anastomoses must vary, but they appear to become more effective in slowly progressive pathological conditions. Extracardiac anastomoses May connect various coronary branches with other thoracic vessels via the pericardial arteries and arterial vasa vasora of vessels which link the heart with the systemic and pulmonary circulations. The effectiveness of these connections as collateral routes in coronary occlusion is unpredictable Coronary arteriovenous anastomoses and numerous connections between the coronary circulation and cardiac cavities, producing so-called ‘myocardial sinusoids’ and ‘arterioluminal’ vessels, have been reported; their importance in coronary disease is uncertain Venous Drainage of the Heart Most !blood from the heart wall drains into the right atrium through THE CORONARY SINUS which lies in the posterior part of the atrioventricular groove 19 tributaries of the coronary sinus. GREAT CARDIAC VEIN SMALL CARDIAC VEINS MIDDLE CARDIAC VEINS 20 1-3 counts for at least 85% of occlusions Read only and you will not enjoy?!!!! Innervation of the Heart The heart is supplied by autonomic nerve fibers from The cardiac plexus which is often quite artificially divided into superficial and deep portions The cardiac plexus Leis on the anterior surface of the bifurcation of the trachea It is formed of both sympathetic and parasympathetic fibers as well as visceral afferent fibers conveying reflexive and nociceptive fibers from the heart The sympathetic supply is from Presynaptic Fibers, with cell bodies in the intermediolateral cell columns (IMLs) of the superior five or six thoracic segments of the spinal cord Postsynaptic Sympathetic Fibers, with cell bodies in the cervical and superior thoracic paravertebral ganglia of the sympathetic trunks. The postsynaptic fibers traverse cardio pulmonary splanchnic nerves and the cardiac plexus to end in the SA and AV nodes and in relation to the terminations of parasympathetic fibers on the coronary arteries. Adrenergic stimulation of the SA node and conducting tissue  increases the rate of depolarization of the pacemaker cells while increasing atrioventricular conduction causes increased heart rate impulse conduction force of contraction At the same time Increased blood flow through the coronary vessels!!!!!!!!! to support the increased activity are β -receptors, Most adrenergic receptors on coronary blood vessels 2 which, when activated, cause relaxation (or perhaps inhibition) of vascular smooth muscle and, therefore, dilation of the arteries (Wilson-Pauwels et al., 1997). This supplies more oxygen and nutrients to the myocardium during periods of increased activity. The parasympathetic supply  is from presynaptic fibers of the vagus nerves  Postsynaptic parasympathetic cell bodies (intrinsic ganglia) are located in • The atrial wall • Interatrial septum near the SA and AV node • Along the coronary arteries  Parasympathetic stimulation slows  The heart rate  reduces the force of the contraction  constricts the coronary arteries  Postsynaptic parasympathetic fibers release ACETYLCHOLINE which binds with muscarinic receptors to slow the rates of depolarization of the pacemaker cells and atrioventricular conduction and decrease atrial contractility. Cardiac Pain The nature of the pain varies considerably, from a severe crushing pain to nothing more than a mild discomfort Pain originating in the heart stimulate the sensory nerve endings in the myocardium. Cardiac referred pain is a phenomenon whereby noxious stimuli originating in the heart are perceived by a person as pain arising from a superficial part of the body—the skin on the left upper limb The afferent nerve fibers ascend to the central nervous system through the cardiac branches of the sympathetic trunk and enter the spinal cord through the posterior roots of the upper four thoracic nerves The pain is not felt in the heart, but is referred to the skin areas supplied by the upper four thoracic nerves The skin areas supplied by the upper four intercostal nerves and by the intercostobrachial nerve (T2) are therefore affected. The intercostobrachial nerve communicates with the medial cutaneous nerve of the arm and is distributed to skin on the medial side of the upper part of the arm A certain amount of spread of nervous information must occur within the central nervous system, for the pain is sometimes felt in the neck and the jaw. Myocardial infarction involving the inferior wall or diaphragmatic surface of the heart often gives rise to discomfort in the epigastrium. One must assume that the afferent pain fibers from the heart ascend in the sympathetic nerves and enter the spinal cord in the posterior roots of the seventh, eighth, and ninth thoracic spinal nerves and give rise to referred pain in the T7, T8, and T9 thoracic dermatomes in the epigastrium Synaptic contacts may also be made with commissural (connector) neurons, which conduct impulses to neurons on the right side of comparable areas of the spinal cord. This occurrence explains why pain of cardiac origin, although usually referred to the left side, may be referred to the right side, both sides, or the back THE CONDUCTING SYSTEM OF THE HEART consists of specialized cardiac muscle present in  THE SINUATRIAL NODE  THE ATRIOVENTRICULAR NODE  THE ATRIOVENTRICULAR BUNDLE RIGHT AND LEFT TERMINAL BRANCHES THE SUBENDOCARDIAL PLEXUS OF PURKINJE FIBERS 33 The sinu-atrial (SA) node  is located anterolaterally just deep to the epicardium at the junction of the SVC and right atrium, near the superior end of the sulcus terminalis  The SA node—a small collection of nodal tissue, specialized cardiac muscle fibers, and associated fibroelastic connective tissue— is the pacemaker of the heart  The SA node initiates and regulates the impulses for the contractions of the heartgiving off an impulse approximately 70 times per minute in most people most of the time The contraction signal from the SA node spreads myogenically (through the musculature) of both atria  The SA node is stimulated by the sympathetic division of the autonomic nervous system to accelerate the heart rate and is inhibited by the parasympathetic division to return to or approach its basal rate. The atrioventricular (AV) node  is a smaller collection of nodal tissue than the SA node.  The AV node is located in the posteroinferior region of the interatrial septum near the opening of the coronary sinus  Its anatomical landmarks are the boundaries of the triangle of Koch  The signal generated by the SA node passes through the walls of the right atrium, propagated by the cardiac muscle (myogenic conduction), which 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 (of His)  Sympathetic stimulation speeds up conduction, and parasympathetic stimulation slows it down. • At the junction of the membranous and muscular parts of the IVS, the AV bundle divides into right and left bundles • These branches proceed on each side of the muscular IVS deep to the endocardium and then ramify into subendocardial branches (Purkinje fibers) • which extend into the walls of the respective ventricles. • The subendocardial branches of the right bundle stimulate the muscle of the IVS, the anterior papillary muscle through the septomarginal trabecula (moderator band), and the wall of the right ventricle. • The left bundle divides near its origin into approximately six smaller tracts, which give rise to subendocardial branches that stimulate the IVS, the anterior and posterior papillary muscles, and the wall of the left ventricle. With a VSD, the AV bundle usually lies in the margin of the VSD. Obviously, this vital part of the conducting system must be preserved during surgical repair of the defect. Destruction of the AV bundle would cut the only physiological link between the atrial and ventricular musculature, also producing a heart block as described above. 38 • subendocardial branches • (Purkinje fibers) • which extend into the walls of the respective ventricles. • The subendocardial branches of the right bundle stimulate the muscle of the IVS, the anterior papillary muscle through the septomarginal trabecula (moderator band), and the wall of the right ventricle. 39 • The left bundle divides near its origin into approximately six smaller tracts, which give rise to subendocardial branches that stimulate the IVS, the anterior and posterior papillary muscles, and the wall of the left ventricle. 40 Internodal Conduction Paths This phenomenon has been explained by the description of special pathways in the atrial wall which have a structure consisting of a mixture of Purkinje fibers and ordinary cardiac muscle cells.

Coronary Collateral Circulation

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