Anatomy of the Heart PDF

Anatomy of the Heart The heart & pericardium (adapted from Mr Kris Phillips) Maryam Rajid Lecturer in Anatomy and Development [email protected] Learning Outcomes (LOs) MACRO LOs: MICRO Los: M1.I.CVS.ANA1 – Describe the anatomy and Describe...

Anatomy of the Heart The heart & pericardium (adapted from Mr Kris Phillips) Maryam Rajid Lecturer in Anatomy and Development [email protected] Learning Outcomes (LOs) MACRO LOs: MICRO Los: M1.I.CVS.ANA1 – Describe the anatomy and Describe the location of the heart within the thorax histology of the heart and major vessels, and its orientation, relating this to surface anatomy. including innervation. Describe the compartments and contents of the M1.I.CVS.ANA2 – Outline the arrangement mediastinum. of the coronary circulation, innervation, and Describe the structure of the pericardium and its role conduction of the heart. in heart function. M1.I.CVR.ANA1 – Understand specific Describe the structure of the heart, heart valves, and common clinical examples associated with heart wall, and recall key anatomical landmarks. the cardiorespiratory system. Describe the key histology features of the heart wall M1.I.CVR.RAD1 – Recognise the anatomical and valve structures of the cardiovascular system Describe the innervation and structure of the using chest X-ray (CXR), CT and angiogram. conduction pathway of the heart. Describe the arrangement of coronary circulation. Lecture Overview ❑PART 1: Heart location ❑PART 3: Heart vasculature o Surface anatomy o Coronary circulation o Mediastinum o Orientation ❑PART 4: Conduction ❑PART 2: Heart structure o Innervation of the Heart o Pericardium o Conduction of the Heart o The Heart & Pre-lab activity o Heart Valves o Heart wall histology Part 1: Heart Location ❑Surface Anatomy ❑The mediastinum ❑Orientation What is Surface Anatomy? The ability to visualise how anatomical structures in the thorax are related to surface features is fundamental to physical examinations. Surface Anatomy: Palpable Landmarks Bony palpable landmarks of the thoracic cage are useful to locate underlying structures. Outline of heart can be traced on the anterior surface of the thorax. Surface Anatomy: Palpable Landmarks Outline of heart can be traced on the anterior surface of the thorax. Surface Anatomy: Sternal angle STERNAL ANGLE: Junction between the manubrium and body of the sternum. Also known as Angle of Louis. Surface Anatomy: Sternal angle Q:What structures like at the sternal angle? Surface Anatomy: Sternal angle What structures lie at the sternal angle? (RATPLANT) R – Rib 2 A - Aortic arch T - Tracheal bifurcation (Carina) P – Pulmonary trunk L – Ligamentum arteriosum A – Azygous vein drains into SVC N – Nerves (Cardiac plexus, loop of recurrent laryngeal n. etc.) T – Thoracic duct (right-to-left movement before exiting thoracic inlet) Other: Pre-vertebral and pre-tracheal fascia of the neck end Oesophagus continuous past sternal angle Other acronyms include CLAPTRAP Surface Anatomy: Observable Landmarks What landmarks can be seen here? Things such as: Anterior axillary fold Posterior axillary fold Axillary fossa/Axilla Jugular notch Pectoralis major and other muscles Bony features and muscle borders can be used as both observable and palpable landmarks.  Surface Anatomy: Lines Imaginary lines can be drawn on the surface of the thorax in order to orientate yourself. Imaginary lines are useful for procedures and also knowing what anatomical structures is lying below. Surface Anatomy: Lines An example of practical use of imaginary lines is to demark the ‘safe triangle’. The ‘Safe Triangle’ is an important area to note for where chest drains could be inserted safely. Surface Anatomy: Heart Location: Usually between ribs 2 and 5th intercostal space. Extends from right medial border of the sternum to having its apex close to the midclavicular line on the left. Heart location can change due to pathology e.g. cardiomegaly or displaced by mediastinal or lung conditions. When displaced heart moves inferiorly and laterally towards the axilla. Surface Anatomy: Heart The heart is usually between vertebral levels T4-T9 When supine: T4/T5 – T8 When standing: T6 – T9 THINK: What structures are in motion within thorax region that can change the location of the heart? Surface Anatomy: Heart The heart is attached to the diaphragm via its pericardium. The borders of the heart are variable depending on the position of the diaphragm (i.e during respiration). Pericardium: fibro-serous sac that covers the heart and the roots of the great vessels.  Heart Location The Mediastinum  Mediastinal pleura encapsulates most of the Thorax: Divisions mediastinum. Thorax can be divided into: Blends with the parietal pleura of the lungs laterally. Blends with the pericardium internally. Mediastinum: Divisions The mediastinum is divided into superior and inferior mediastinum by the sternal angle. An imaginary plane that extends from the sternal angle to the intervertebral disc T4 and T5. Many structures lie in each area of the mediastinum. It also serves as a passageway for structures. Mediastinum: Divisions The mediastinum is divided into superior and inferior mediastinum by the sternal angle. The inferior mediastinum is further subdivided into anterior, middle, and posterior mediastinum. Mediastinum: Divisions Heart is located within the pericardium in the middle mediastinum. The inferior mediastinum is partitioned into anterior, middle and posterior mediastinum by the heart and its pericardial sac. The middle mediastinum is bordered: ANTERIORLY: Anterior mediastinum POSTERIORLY: Posterior mediastinum LATERALLY: Pleura of each lung SUPERIORLY: Sternal angle and Superior mediastinum INFERIORLY: Diaphragm. Mediastinum: Contents overview Superior Inferior Thymus Anterior Middle Posterior Trachea Oesophagus Thymus extends from Main content of the middle Posterior mediastinum contains Thoracic duct Superior mediastinum mediastinum is the heart in the lots of major vessels and Aortic arch (and associated In children – Thymus pericardium. structures, most of which will branches) In adults – Adipose go to pierce its inferior border Superior vena cava (and tissue Also contains the beginnings at – the diaphragm. associated convergent Internal thoracic vessels least of the associated vessels: veins) Lymph nodes – Main Ascending aorta Contents: Vagus nerve important structure Superior vena cava Descending aorta and its Phrenic nerve Pulmonary trunk branches Recurrent laryngeal nerve Azygos venous network Sympathetic trunk Also other structures including: Thoracic duct (ascending) Lymphatics Main/primary bronchi after Oesophagus Muscles bifurcation of trachea – Sympathetic trunk structures which go to the Nerves: hila of the lungs. Oesophageal plexus Phrenic nerve Vagus nerve branches Cardiac plexus Vagus nerve  Heart Location Orientation Orientation: Surfaces The heart is generally shaped like a wedge or a pyramid that has fallen over. It’s base lies posteriorly (hence the falling over). Geometrically, the heart has multiple surfaces that are in contract with specific structures. Inferior (diaphragmatic) surface: In contact with diaphragm Anterior (sternocostal) surface: Orientated towards the anterior thoracic cage (sternum and ribs) Right (pulmonary) surface: In contact with the right pleura and lung. Left pulmonary surface: In contact with the left pleura and lung. Orientation: Surfaces Orientation: Anterior surface Orientation: Anterior surface The anterior surface of heart faces anteriorly. It is in contact (via pericardium) with the sternum, costal cartilage, and ribs. Some parts have contact with the pleura and lungs. Made up of: Right ventricle Partially the right atrium https://3d4medic.al/8TXnXSCU Partially the left ventricle Roots of vessels entering/exiting the heart Orientation: Base Base surface is the posterior surface of the heart. Made up of: The whole of the left atrium and part of the right atrium. Majority of great heart vessels exit/enter the heart in this location. https://3d4medic.al/ekpXo4SJ Base of heart is one of the most difficult areas to visualise with an ECG. WHY? Orientation: Base Base surface is the posterior surface of the heart. Base of heart is one of the most difficult areas to visualise with an ECG. WHY? Orientation: Inferior Surface The diaphragmatic surface of the heart is the inferior surface. Projects from the base of the heart towards the apex of the heart. It is contact with the diaphragm via the pericardium. The coronary sinus acts as a landmark to divide the base from the inferior surface of the heart. Made up of: Left ventricle (including apex) Small portion of right ventricle https://3d4medic.al/5ACIezFV Coronary vessels (Including the posterior https://3d4medic.al/5ACIezFV interventricular groove). Orientation: Pulmonary surface The right and left pulmonary surface of the heart faces and is in contact with the right and left pleura and lung, respectively. Left pulmonary surface made up of: Mainly Left ventricle Partially left atrium https://3d4medic.al/ow1xvEQX https://3d4medic.al/ow1xvEQX Right pulmonary surface made up of: Mainly Right atrium Orientation: Pulmonary surface The right and left pulmonary surface of the heart faces and is in contact with the right and left pleura and lung, respectively. Left pulmonary surface made up of: Mainly Left ventricle Partially left atrium The heart pulmonary surface forms a cardiac Right pulmonary surface made up of: impression on medial surface of the lungs. Mainly Right atrium Orientation: Apex Apex of heart: part of the inferolateral portion of the left ventricle. It lies deep to the 5th intercostal space along the midclavicular line. Clinical importance: Palpating apex beat. Apex beat is the outermost and lowermost palpable cardiac impulse on the chest wall. The maximal impulse apical pulse can be palpated at the 5 th intercostal space at the mid-clavicular line. A displaced apex beat may indicate possible pathology. E.g. Cardiomegaly (enlarged heart) apex beat will be displaced more towards the axilla. Part 2: Heart Structure ❑Pericardium ❑ The Heart & Pre-lab activity ❑Heart Valves ❑Heart Wall  Heart Structure Pericardium Pericardium: Overview Pericardium: Fibro-serous membrane covering the heart and the origin of the great vessels. The pericardium can be divided into 3 layers: 1. Fibrous pericardium 2. Serous pericardium Parietal layer Visceral layer 3. Pericardial cavity: Space between the parietal and visceral layers of the serous pericardium. Pericardial fluid: contained within the pericardial cavity. Secreted by serous mesothelium Pericardium: Fibrous pericardium The fibrous pericardium extends from its inferior apex attachment at the diaphragm, all around the heart, and then blends with the adventitia (blood vessel layer) of the great vessels superiorly. Its attached anteriorly to the sternum. This helps keep the heart in position in the thoracic cavity. Its attached loosely posteriorly to structures within the posterior mediastinum. Somatic sensory innervation: Phrenic nerves. Phrenic nerves passes through the fibrous pericardium on the way to the diaphragm. Pericardium: Serous pericardium The serous pericardium is divided into two layers that are continuous (similar to the pleura of the lungs) around the roots of the great vessels. Parietal pericardium: Lines the inner surface of the fibrous pericardium. Visceral layer: Adheres to the heart and forms its outer covering. Also known as the epicardium. There is a space between these two layers known as the pericardial cavity. Pericardial cavity typically has 15-50ml of pericardial fluid. What is the function of this fluid? Pericardium: Clinical correlates Pericardial effusion: Fluid (including blood) build up in the pericardial sac. This can arise from aortic aneurysms, heart attacks, or penetrating injuries (most common) or inflammation of the pericardium (pericarditis). Puts pressure on the heart and hence heart functions impaired. In extreme cases, this can lead to Cardiac tamponade. When fluid accumulates too fast, increases pericardial pressure and compresses the heart. Leads to rapid breathing and shortness of breath, sharp stabbing chest pains and cyanosis. Treatment: pericardial tap/pericardiocentesis. Pericardium: Clinical correlates Pericardial effusion: Fluid (including blood) build up in the pericardial sac. This can arise from aortic aneurysms, heart attacks, or penetrating injuries (most common) or inflammation of the pericardium (pericarditis). Puts pressure on the heart and hence heart functions impaired. In extreme cases, this can lead to Cardiac tamponade. When fluid accumulates too fast, increases pericardial pressure and compresses the heart. Leads to rapid breathing and shortness of breath, sharp stabbing chest pains and cyanosis. Treatment: pericardial tap/pericardiocentesis. Heart Structure The Heart Heart: Chambers Heart: Chambers Heart is a 4 chambered structure divided in half by a septum. Right side: Takes deoxygenated blood from the body and sends to lungs to be oxygenated. Known as Pulmonary circuit. Left side: Takes newly oxygenated blood from lungs and sends to rest of the body. Known as Systematic circuit. There are one-way valves between each chamber and major onward vessels (Pulmonary artery and aorta) to prevent blood from flowing backwards. Heart: Chambers The 4 chambers of the heart are: Right atrium Right ventricle Left atrium Left ventricle  Heart: Blood flow through the heart 1. Right atria collects deoxygenated blood 4. Left atrium collects oxygenated from the body via superior vena cava, blood from lungs via the four inferior vena cava and coronary sinus. pulmonary veins. 5. Left atrium contracts to pass 2. Right atria contracts to pass blood blood through the AV valve into through the atrioventricular (AV) valve into left ventricle. the right ventricle. 6. Left ventricle contracts and blood 3. Right ventricle contracts and blood passes through the semilunar valves at passes through the semilunar valves at the the entrance of the aorta as it entrance of the pulmonary trunk and continues towards the rest of the body. continues towards the lungs to be oxygenated. As the ventricles contract, the atria fills, and as the atria contracts, the ventricles fill. This creates a continuous flow of blood. Heart: External features Sulci/Grooves of the heart: The structures that separate the chambers of the heart internally creates impressions on the external surface of the heart - known as sulci. Provides external demarcations that corresponds to the internal partitions that divide the heart into its chambers. Creates a passageway for the coronary arteries and veins and their main branches. Heart: External features Sulcus (plural: sulci) refers to grooves or depressions that mark the boundaries between different regions of the heart. These sulci house major blood vessels and help define the external anatomy. There are 3 main sulci: Coronary sulcus (Atrioventricular sulcus) (Pink https://3d4medic.al/HhLHQZvL line) https://3d4medic.al/HhLHQZvL Anterior interventricular sulcus (Green line) Note: The anterior and posterior interventricular sulci are Posterior interventricular sulcus (Blue line) continuous inferiorly towards the apex of the heart. Heart chambers: Right atrium Receives venous blood (poorly oxygenated) from 4 sources: 1. Superior vena cava 2. Inferior vena cava 3. Coronary sinus 4. Anterior cardiac veins (small veins along surface of the atrium) Pre-lab activity: Internal features of the heart chambers Heart chambers: Right atrium (blank copy) Heart chambers: Right atrium Internal aspect: Sinus venarum (smooth post. portion): both vena cave drain here, also known as sinus of venae cavae. Pectinate muscle (rough ant. portion): Atrium proper Crista terminalis: separates the two internal surfaces, seen internally. Sulcus terminalis: separates the two internal surfaces, seen externally. Coronary sinus opening Auricle: Helps atrium hold more blood during increased exertion. Interatrial septum: separates right atrium from the left atrium Fossa ovalis: oval shaped depression, a remnant of the foramen ovale (passageway for fetal circulation to short circuit away from the lungs during intrauterine development). Failure to close after birth can lead to a patent foramen ovale, where blood will pass straight into the left atrium. Tricuspid valve: Blood passes into the right ventricle through this right atrioventricular valve known as the tricuspid valve. Heart chambers: Right ventricle (blank copy) Heart chambers: Right ventricle Internal aspect: Trabeculae carnea: Majority of the surface of the right ventricle is covered in irregular muscular elevations. Some of the trabeculae carnea project as papillary muscles. Papillary muscles: 3 papillary muscle that correspond to the cusps of the tricuspid valve. Serve as attachment for the chordae tendineae. Chorda tendineae: Fibrous tendon-like cords that attach on the cusps of the tricuspid valve. Septomarginal trabecula: specialised curved mascular bundle that traverses the right ventricular wall from the lower portion of the interventricular septum to the papillary muscle. Also known as moderator band. Important in the cardiac condition. Interventricular septum Conus arteriosus: smooth walls that leads into the pulmonary trunk. Semilunar valve: at the apex of the conus arteriosus, also known as Pulmonary valve. Heart chambers: Left Atrium & Left Ventricle (blank copy) Q: Left ventricle is longer, larger and has a thicker layer of myocardium. WHY? Heart chambers: Left Atrium Internal aspect: Similar to the right atrium, left atrium has two distinct surfaces. Smooth post. Portion: inflow from pulmonary veins drain into here Rough ant. Portion: Pectinate muscle. However, there is no distinct structure to divide these two surfaces. Left auricle: same function to that of the right auricle. Interatrial septum Valve of the foramen ovale: this is the other side of the fossa ovalis on the interatrial septum from the left atrium. Bicuspid valve: Blood passes into the left ventricle through this left atrioventricular valve, also known as the mitral valve. Heart chambers: Left Ventricle Internal aspect: Much like the right ventricle, has similar structures. Trabeculae carneae: More delicate and fine than the right ventricle. Appears more tortuous. Papillary muscle: Larger than in the right ventricle. 2 papillary muscles corresponding to the cusps of the bicuspid valve. Chorda tendineae Interventricular septum: Has two parts: Muscular part – Thickest, largest part and forms lower part Membranous part – Thin and forms upper part Aortic vestibule: smooth walls that leads towards the ascending aorta. Semilunar valve: at the apex of the aortic vestibule, also known as the aortic valve. Heart chambers: great vessels (Blank copy) Heart Structure Heart valves  Structure: Cardiac skeleton Complex framework of dense collagen forming four fibrous rings. Located in between the atria and the onward great vessels of the heart. Acts as the strut for the attachment of the cusps of the valves. Keeps these orifices patent and prevent over distention. Fibrous cardiac skeleton made of: 2 atrioventricular rings Bicuspid (Mitral) valve Tricuspid valve Aortic ring – For aortic valve Pulmonary ring – for pulmonary valve Also known as anulus fibrosus. https://3d4medic.al/zX8vHhom https://3d4medic.al/zX8vHhom Structure: Cardiac skeleton Forms electrical “insulator”: It also separates the atrial and ventricular muscles. This is important in conduction, as this dense connective tissue acts as a partition to isolate the atria from the ventricles – meaning one electrical impulse for contraction won’t cause the other to contract also. Valves: Atrioventricular (AV) valves There are 2 AV valves, one on each side of the heart: Tricuspid valve – separates right atrium and right ventricle Bicuspid/Mitral valve – separates the left atrium and left ventricle The tricuspid valve has 3 cusps (leaflets), while the bicuspid/mitral valve has 2 cusps (leaflets). These valves open when the atria contract and send blood to the ventricles. As the ventricles fill up, these valves start to close. When the ventricles contract the pressure closes the valve. The chordae tendineae is tensed by contraction of papillary muscles and tension is maintained throughout the contraction – this prevents the cusps of the tricuspid or bicuspid valves from prolapsing when ventricular pressure rises (ventricular systole). The closure of these two AV valves together create the first heart sound (‘LUB’). https://3d4medic.al/bj41xlXu  Valves: Semi-lunar valves There are 2 semi-lunar valves, one on each side of the heart: Pulmonary valve – separates the right ventricle and the pulmonary trunk Aortic valve – separates the left ventricle and the ascending aorta. The semi-lunar valves have 3 crescent shaped cusps. The semilunar cusps of the aortic valves have opening to the right and left coronary arteries within their sinuses. Valves: Semi-lunar valves  Valves: Semi-lunar valves These valves open when the ventricles contract and send blood to the outward vessels. Initially there is a high amount of blood pressure causing these valves to stay open. As the ventricles empty and the blood pressure lessens these valves begin to slowly close. The closure of these valves is achieved when the pressure has dropped enough that blood tries to flow back into the ventricle. The blood pools in the sinuses of these cusps and close the valves. How does this help the coronary arteries? These valves function similar to the valves of veins. The closure of semilunar valves together creates the second heart sound (‘DUB’). Semilunar valves are heart valves consisting of cusps that prevent blood back flow. Heart Valves: Review ATRIUM ATRIUM AV valves S1 ‘LUB’ VENTRICLE VENTRICLE AORTA AORTA Semilunar valves S2 ‘DUB’ LV LV Heart Valves  Valves: Abnormalities There are two main types of abnormalities of the heart valves: Stenosis: A narrowing of the valves meaning they don’t open properly Regurgitation: The valve is compromised and cannot close properly. Also known as insufficiency. Can cause heart murmurs, which can be heard when auscultating the heart. Treatment: To fix these valves is through heart valve replacement surgery.  Valves: Auscultation Heart valves are generally auscultated close to their location, though depending on the type of murmur present it may be before of after the valve. Murmurs can also radiate to different locations, depending on You can only ever listen near the valve, not the direction of the vessels and also directly above it- why? the position of the heart. Heart Structure Heart Histology  Heart Wall: Layers The heart wall after the pericardial sac has multiple layers: Epicardium/Visceral pericardium Outermost layer Visceral pericardium, adipose tissue, and connective tissue. Myocardium Middle layer Muscular wall of the heart that is responsible for contraction of the heart. Thicker in certain areas, e.g. the left ventricle wall. Endocardium Inner layer Smooth layer lining the lumen of the heart chambers, in direct contact with circulation blood.  Heart Wall: Layers The heart wall after the pericardial sac has multiple layers: 1) Epicardium/Visceral pericardium Outermost layer Visceral pericardium, adipose tissue, and connective tissue. 2) Myocardium Middle layer Muscular wall of the heart that is responsible for contraction of the heart. Thicker in certain areas, e.g. the left ventricle wall. 3) Endocardium Transverse sectioning of myocardium. Key: (*) internal heart chamber. (En) Inner layer Enocardium innermost layer. (CT) Myocaridum-bulk of heart wall, consists of bundles of cardiac muscle cells, coursing in different directions and separated by (CT) loose connective tissue- endomysium. Thin (Ep) epicardium-fibrous Smooth layer lining the lumen of the heart chambers, in direct contact connective tissue covered by thin mesothelium. with circulation blood. Histology: Epicardium The Epicardium has two layers: 1. Serous membrane layer: Outer layer of epicardium – visceral layer of pericardium, made of mesothelium- simple squamous and cuboidal cells that secretes serous fluid. – In pericarditis, this smooth lining can be lost (immune cells convert this lining into fibrous tissue) and cause a characteristic pericardial friction rub (two layers scratch together due to abnormal roughening). 2. Subepicardial layer: Inner layer of the epicardium, made of loose connective tissue (fibrocollagenous and elastic tissue) and adipose tissue. Coronary vessels runs between adipose tissue – Adipose tissue acts as shock absorber and supports branches of coronary vessels. – Superficial location of coronary artery is significant as it allows coronary bypass grafts to be performed. Heart Wall: Epicardial Fat Epicardial fat is a common occurrence on the surface of the heart. Lies between the visceral pericardium (epicardium) and the myocardium of the heart. Acts to protect and support the heart during normal function. Aids in insulating the heart and its electrical activity. It generally covers about 80% of the heart. More abundant in the atrioventricular and interventricular grooves. Increased amounts are associated with age, obesity, diabetes, and it more common in females. An increase in epicardial fat is highly associated with conditions such as cardiovascular disease and atherosclerosis. Histology: Myocardium Myocardium is the middle and largest layer of the heart. Composed of specialised striated muscle fibres, same basic organisation as skeletal muscles. Cardiac muscle cells – myocytes (myocardial cells) Myocytes are branched and joined end to end and side to side at specialised sites, unique to cardiac muscles – intercalated discs. Intercalated discs – mechanically and electrically link the cells and allow them to function in a coordinated way. No satellite cells – regeneration of cardiac muscle cells after injury does not readily occur. Lipofuscin (age) pigment – wear and tear pigment, because cells are long lived with advancing age these pigment accumulate. Longitudinal section of cardiac muscle. Key: (CM) Cardiac muscle fibers branched with 1-2 centrally placed nucleus. (Lf) Lipofuscin pigment Cardiac muscle cells is the most richly vascularised among concentrated at nuclear poles. (Cap) cappilaries. the three muscle types. Histology: Myocardium The amount of myocardium and diameter of muscle fibres varies between chamber and cardiac workload. i.e. atria smaller than right ventricle. Left ventricle larger than right ventricle. Both images are transverse sectioning of cardiac muscles. Top image: Left atrium myocardium – Shows small muscle fibres separated by loose fibrocollagenous tissue (endomysium) Bottom image: Left ventricle myocardium – Shows larger muscles fibres (same magnification as top image) Key: (M) myocardial fibres; (E) endomysium. Histology: Myocardium Outer surface (in contact with epicardium) is smooth; however the inner surface (in contact with endocardium) is raised into trabeculation. In ventricles, the myocardium protrudes into chamber to form papillary muscles These serve at attachment for chordae tendineae. Histology: Endocardium Endocardium is the internal layer of the heart wall that is in direct contact with blood. It is composed of 3 layers: Innermost layer Endothelial layer – Flat endothelial cells, simple squamous epithelium Continuous with the endothelium of veins and arteries that enter and leave the heart Middle layer Subendothelial layer – Collagen fibres with variable number of elastic fibres. Key: (En) Endothelium – Innermost layer. (CT) Connective tissue – subendothelial (middle) layer, whose collagenous fibers and connective Layer in contact with myocardium. Collagen fibres merge with those tissue (N) cell nuclei. (PF) Purkinje fibers – scattered along the innermost part of myocardium adjacent to the endocardium. Third layer of the endocardium surrounding cardiac muscle fibres. borderers the (My) myocardium and is composed of looser connective tissue elements housing blood vessels, occasional adipocytes, and additional May contain Purkinje fibres – modified cardiac muscle cells, connective tissue cells. especially found in interventricular septum Histology: Endocardium Endocardium is thicker in atria than ventricles. Thicker middle layer due to elastic fibres needed in atria for expansion. Both slides same magnification. Top- Inner ventricular wall. Bottom-Inner atrial wall Key: (*) internal heart chamber (En) endothelial layer, innermost layer. (CT) deep subendocardial layer of connective tissue  Histology: Heart valves Heart valves originate from the cardiac skeleton. Central plate is fibrocollagenous (fibrosa) which extends from cardiac skeleton (annulus fibrosus). Avascular connective tissue core is dominated by a mixture of collagen and elastic fibres. Hence, The connective tissue cells receive their nutrients directly from the blood in the lumen of the heart via simple diffusion. Endocardium covers the leaflets or cusps – Endothelial cells cover the valve on both surfaces. Injury to endothelial cells can lead to infiltration of WBCs inducing calcium deposits e.g. Aortic valve stenosis. Thickness of layers varies between valves and also between different areas of each valve and with age and disease. AV valves are slightly thicker than the SL valves, and the left-sided valves are slightly thicker than the right-sided valves. Image A: H&E stained aortic valve. Dense area of elastic tissue superiorly. Image B: Elastic van Gieson stained aortic valve. Elastic tissue is black, collagen is red. Image C: Elastic van Gieson stained mitral valve. Shows attachment of chordae tendineae. Key: (En) flat endothelial cells; (EI) elastic tissue; (C) collagen; (CT) chordae tendineae. Part 3: Heart vessels ❑Coronary circulation Heart Vessels Coronary circulation Circulation: Overview The heart, like all areas of the body, needs oxygenated blood to function. It receives this from the coronary circulation. 2 Coronary arteries: Right and left coronary arteries The first branches of the aorta and arises from the right and left aortic sinus, in the proximal part of the ascending aorta. These arteries circle the heart in the coronary sulcus. They give off multiple branches in and around the interventricular sulci that converge towards the apex of the heart. Cardiac veins, drain blood and empties into the coronary sinus. The coronary sinus lies on the posterior aspect of the heart in the coronary sulcus. It drains into the right atrium near the tricuspid valves  Circulation: Right coronary artery The right coronary artery descends vertically in the coronary sulcus, between the right atrium and ventricle. It gives off multiple branches: Sinoatrial nodal or atrial artery Right marginal artery Small branch to AV node Posterior Interventricular artery o In the posterior interventricular sulcus o Also known as Posterior descending artery (PDA) o Anastomoses with the anterior interventricular artery near apex of the heart Supplies: Right atrium, Right ventricle, SA and AV nodes, interatrial septum, part of the left atrium, most of the interventricular septum, part of the left ventricle.  Circulation: Left coronary artery The left coronary artery enters the coronary sulcus and divides into two branches: Anterior interventricular and circumflex branch. 1. Anterior interventricular artery o The anterior interventricular branch continues towards the apex of the heart in the anterior interventricular sulcus. o Also known as Left anterior descending artery (LAD) o Gives off one or two large diagonal branches. 2. Circumflex artery o Curves around the left in the coronary sulcus and ends just before the posterior interventricular sulcus. o Gives off left marginal artery, which continuous across the Supplies: Left atrium, Left ventricle, part of the interventricular septum and the atrioventricular rounded obtuse edge of the heart bundle and its branches. Circulation: Coronary dominance & variation Major variations to the basic distribution of the coronary arteries often occurs. This is referred to as Coronary dominance. Majority of people origin of the PI artery is from the RCA (~80- Dominance depends on the origin of the posterior 85%). interventricular (PI) artery. Supplies a large portion of the posterior wall of left ventricle. This is called Right dominance. If circumflex artery of LCA is the origin of PI artery (~10%). Supplies most, if not all of the posterior wall of the left ventricle. This is called Left dominance. If both LCA and RCA have equally contributes as the PI artery origin, and with the circumflex a. (~20%). ~ 80-85% population ~10% population ~20% population Supplies the posterior wall of left ventricle equally. This is called co-dominance.  Coronary circulation: SA & AV node supply Important to know blood supply due to potential obstructions or infarctions SA Node: of the area – can affect Usually supplied by right coronary artery in ECGs. 60% of people In other 40% supplied by left circumflex coronary artery AV Node: Supplied by right coronary artery in around From the R 90% of people coronary artery Variations include supply by left circumflex coronary artery (90%) Coronary circulation: Imaging The best way to view the coronary arteries is via an arteriogram/angiogram. It is done by inserting a thin tube into an artery and injecting a contrast dye. It can be used to detect blockages in vessels and is particularly important in myocardial infarctions. Circulation: Venous return The coronary sinus is the primary drainage for the cardiac veins. Receives drainage from: Great cardiac v. Middle cardiac v. Small cardiac v. Posterior cardiac v. Anterior cardiac v. drain directly into the right atrium. Venous drainage generally mirrors the arterial supply. https://3d4medic.al/Pd8CGsOU https://3d4medic.al/Pd8CGsOU Coronary circulation: Review Anterior interventricular Diagonal a. a. (LDA) Left Coronary a. Circumflex a. Left marginal a. Sinoatrial nodal Ascending aorta a. Right marginal a. Right coronary a. AV node a. Post. Interventricular a. Coronary circulation: Distribution Left Anterior Descending Artery: Anterior interventricular artery Coronary circulation: Clinical correlates Coronary Artery Bypass Graft Coronary arteries sometimes become obstructed. Revascularisation must occur by grafting an artery from elsewhere in the body to bypass the obstructed artery. These include: Great saphenous vein (leg) Internal thoracic artery (thorax) Radial artery (arm) Angiogenesis Angiogenesis is the budding of new blood vessels to aid with revascularisation. Vital for establishing blood flow to damaged areas. Can create more capillary networks or even connect two blood vessels (anastomose) Part 4: Conduction ❑Innervation of the heart ❑Conduction of the heart Heart Conduction Overview: Conduction system Heart contracts involuntarily on average at 70 beats per minute. Higher for heart transplant patients (~100 bpm) Nerve impulses are not necessary for the heart to remain beating Set rhythmic contractions come from SA node and heart muscle. ANS can control the rate of heartbeat. Can also be controlled by hormones This takes longer than nerve control. Overview: Conduction system Starts at sinoatrial (SA) node. Located in the right atrium near the entrance of the SVC. Pacemaker of the heart. Internodal branches send impulses to AV node. SA node and branches stimulates contraction of right atrium. Branch to Bachmann’s bundle in left atrium stimulates contraction there at the same time. Atrioventricular (AV) node sends impulses into interventricular septum – as bundle of His to stimulate contraction of ventricles. AV node located in the right atrium just above the tricuspid valve Bundle of His – Collection of nerve fibres extending into the interventricular septum Bundle of His divides into main left and right branches Gives off many smaller terminal branches called Purkinje fibres Stimulates muscle cells to contract. Conduction: Cardiac cycle The cardiac cycle begins with atrial systole and ends with ventricular diastole. Systole: The period of contraction that the heart undergoes while it pumps blood. Diastole: The period of relaxation that occurs as the heart chambers fill with blood. Innervation of Heart Heart: Innervation Overview 1. Parasympathetic (Vagus nerve) Slows heart rate 2. Sympathetic Increases heart rate Pre-synaptic fibers: T1-T4 Post-synaptic fibers: Cervical and superior thoracic ganglia 3. Visceral afferent Travel with (hitchhike) sympathetic fibers Transmit noxious stimuli originating from the heart – Link to Referred pain. Heart: Innervation Overview 1. Parasympathetic (Vagus nerve) Slows heart rate 2. Sympathetic Increases heart rate Pre-synaptic fibers: T1-T4 Post-synaptic fibers: Cervical and superior thoracic ganglia 3. Visceral afferent Travel with (hitchhike) sympathetic fibers Transmit noxious stimuli originating from the heart – Link to Referred pain. Heart: Sympathetic innervation Spinal cord levels T1–T4 (and a bit of T5) become cervical cardiac & thoracic cardiac splanchnic nerves then become part of the cardiac plexus Branches to the SA & AV nodes and to myocardium. Releases neurotransmitter noradrenaline. = ↑ heart rate, conduction rate (excitability) & force of contraction CNS Spinal Cervical ganglia Cervical splanchnic nerves Cardiac Plexus Pre-sympathetic SYMPATHETIC CHAIN (Sympathetic cord T1- neurones Post-sympathetic neurones T4(5) Thoracic ganglia Thoracic splanchnic nerves innervation to heart) Heart: Parasympathetic innervation Vagus nerve branches to become cervical cardiac & thoracic cardiac branches which merge to become cardiac plexus. Branches to the SA & AV nodes Other branches directly to myocardium. Releases neurotransmitter acetylcholine. ↓ heart rate, conduction rate (excitability) & force of contraction Cervical cardiac Vagus nerve: branches Cardiac Plexus 10th cranial nerve (Parasympathetic Originates in medulla Thoracic cardiac innervation to heart) oblongata (brain stem) branches Heart: Innervation overview Heart: Referred pain The visceral sensory neurons from the myocardium enter the spinal cord at the same segmental level as T1-T4 spinal nerves which provide sensation to skin (dermatomes) Referred pain occurs because the brain cannot distinguish between sensory input from visceral sensory neurons within the ANS (supplying heart) and spinal nerves from the somatic nervous system (supplying skin sensation) CNS Cervical ganglia Cervical splanchnic nerves Cardiac Plexus Spinal (Sympathetic SYMPATHETIC CHAIN Visceral sensory neurones cord innervation to segmental Thoracic ganglia Thoracic splanchnic nerves heart) level Skin innervated by T1-T4 spinal nerves (outer chest, neck, shoulder, T1-T4 back, arms) in a DERMATOME distribution END