Module 8: Thorax 2: Cardiovascular Structures PDF

Module 8: THORAX 2: CARDIOVASCULAR STRUCTURES Alarde, Aritrangco, Escalante, Gampong, Jarumahom, Patacsil, Silagan 1 EMBRYOLOGY...

Module 8: THORAX 2: CARDIOVASCULAR STRUCTURES Alarde, Aritrangco, Escalante, Gampong, Jarumahom, Patacsil, Silagan 1 EMBRYOLOGY On day 23, the primitive heart tube elongates, Cardiac Loop. Because the bulbus cordis and primitive The heart begins its development from mesoderm on ventricle grow more rapidly than other parts of the tube day 18 or 19 following fertilization. and because the atrial and venous ends of the tube are confined by the pericardium, the tube begins to loop Progenitor heart cells lie in the and fold. epiblast, immediately adjacent to the cranial end of the primitive streak. From there, they migrate through the streak and into the visceral layer of lateral plate mesoderm where some form a horseshoe-shaped cluster of cells called the primary heart On about day 28, thickenings of mesoderm of the field (PHF) inner lining of the heart wall, called Endocardial cushions, These cells form portions of the atria and the entire left appear. They grow toward each other, fuse, and divide ventricle. the single atrioventricular canal (region between atria and ventricles) into smaller, separate left and right The right ventricle and atrioventricular canals. outflow tract (conus cordis and truncus arteriosus) are Also, the interatrial septum begins its growth derived from the secondary toward the fused endocardial cushions. Ultimately, the heart field (SHF), which also interatrial septum and endocardial cushions unite and an contributes cells to formation opening in the septum, the foramen ovale of the atria at the caudal end of the heart On the 22nd day, the Primitive heart tube develops into five distinct regions and begins to pump blood. From tail end to head end (and in the same direction as blood flow (1) sinus venosus, (2) primitive atrium, (3) primitive ventricle, (4) bulbus cordis, (5) truncus arteriosus. MOLECULAR REGULATION OF CARDIAC DEVELOPMENT Signals from anterior endoderm induce a heart-forming region in overlying visceral mesoderm  2 by inducing the transcription factor NKX2.5. The signals require secretion of bone morphogenetic proteins (BMPs) 2 and 4 secreted by the endoderm and lateral plate mesoderm. The activity of WNT proteins (3a and 8), secreted by the neural tube, must be blocked because they normally inhibit heart development. 2. Atrial Septal Defect The combination of BMP activity and WNT inhibition by ASD is a congenital heart abnormality with an incidence CRESCENT and CERBERUS causes expression of NKX2.5, the of 6.4/10,000 births and with a 2:1 prevalence in female master gene for heart development. to male infants. BMP expression also upregulates expression of fibroblast growth factor 8 (FGF8) that is important for the expression One of the most significant defects is the ostium of cardiac-specific proteins. secundum defect, characterized by a large opening The combination of BMP activity and WNT inhibition by between the left and right atria. It may be caused by Crescent and Cerberus causes expression of NKX2.5, the excessive cell death and resorption of the septum master gene for heart development. primum or by inadequate development of the septum BMP expression also upregulates expression of fibroblast secundum growth factor 8 (FGF8) that is important for the expression of cardiac-specific proteins. Congenital Heart Defects 3. Ebstein Anomaly is a condition where the tricuspid 1. Hypoplastic right heart syndrome [HRHS] and valve is displaced toward the apex of the right ventricle, Hypoplastic left heart syndrome are rare defects that and as a result, there is an expanded right atrium and a cause an underdevelopment of the right or left sides of small right ventricle. the heart, respectively. The valve leaflets are abnormally positioned, and the anterior one is usually enlarged.  3 is an example of the 22q11 deletion syndrome characterized by a pattern of malformations that have 4. Tetralogy of Fallot their origin in abnormal neural crest development. the most frequently occurring abnormality of the conotruncal region, is due to an unequal division of the These children have facial defects, thymic hypoplasia, conus resulting from anterior displacement of the parathyroid dysfunction, and cardiac abnormalities conotruncal septum. involving the outflow tract, such as persistent truncus arteriosus and tetralogy of Fallot. Craniofacial malformations. HISTOLOGY LAYERS OF THE HEART WALL 5. A patent ductus arteriosus [PDA] one of the most frequently occurring Endocardium abnormalities of the Consists of: great vessels [8/I0,000 - a very thin layer of endothelium and supporting births], especially in connective tissue - middle myoelastic layer of smooth muscle fibers and premature infants, connective tissue either may be an - deep layer of connective tissue called the isolated abnormality or subendocardial layer may accompany other *small blood vessels and Purkinje fibers found in heart defects. subendocardial layer - lines the chambers of the heart and extends over In particular, defects that cause large differences projecting structures such as the valves, chordae between aortic and pulmonary pressures may cause tendineae, and papillary muscles increased blood flow through the ductus, preventing its Myocardium normal closure. - consists mainly of cardiac muscle with its fibers arranged spirally around each heart chamber 6.DiGeorge sequence - thickness: ventricle walls (particularly left) > atrial walls reason: strong force is needed to pump blood through the systemic and pulmonary circulations - facilitate the contraction and relaxation of the heart walls in order to receive and pump the blood into the systemic circulation *myocardial cells provide a scaffold for heart chambers and conduct electrical stimuli  4 Epicardium Tunica media - covered by the simple squamous mesothelium that also - intermediate predominantly muscular layer lines the pericardial space - consists primarily of concentric sheets of smooth muscle *mesothelial cells secrete a lubricant fluid that which during: prevents friction as the beating heart contacts the 1) contraction - vessel diameter decreased: parietal pericardium on the other side of the vasoconstriction pericardial cavity- consists of loose connective tissue 2) relaxation - vessel diameter increased: vasodilation containing autonomic nerves and variable amounts - particularly broad and extremely elastic of fat - at high magnification, it consists of the following: - consists of an underlying subepicardial layer of a) concentric fenestrated sheets of elastin, connective tissue separated by collagenous tissue; *subepicardial layer contains coronary blood vessels, b) and smooth muscle fibres nerves, and adipose tissue - typically thickest in artery Tunica adventitia/externa LAYERS OF BLOOD VESSELS - intermediate pr - outer connective tissue layer - consists of elastic and collagen fibers - contains numerous nerves and, especially in larger vessels, tiny blood vessels that supply the tissue of the vessel walls *vasa vasorum - small blood vessels which supply blood to the vessel tissues (vessels to vessels) - easily seen on large vessels such as the aorta - supplies the vessel wall with nerves and self-vessels Tunica intima/interna - helps anchor the vessels to surrounding tissues - forms the inner lining of a blood vessel, and is in direct contact with the blood as it flows through the lumen LAYERS OF ELASTIC ARTERIES, MUSCULAR ARTERIES, AND - single layer of flattened endothelial cells supported by a ARTERIOLES BASED ON THEIR DIAMETER, TUNICS AND ROLE layer of collagenous tissue rich in elastin disposed in the IN THE CIRCULATORY SYSTEM form of both fibres and discontinuous sheets - two components: 1) endothelium - innermost layer, continuous with the endocardial lining of the heart, thin layer of flattened cells that lines the inner surface of the entire cardiovascular system 2) basement membrane - deep to the endothelium, provides a physical support base for the epithelial layer - internal elastic lamina, its outermost part forms its boundary with the tunica media  5 VEINS postcapillary venules and cause extravasation(leaking from vessel to surrounding tissue/area) of white blood cells during inflammation and allergic reactions. High endothelial venules are specialized postcapillary venules in lymphoid tissue, they are lined by cuboidal endothelial cells. Locations: Lymph nodes, tonsils, lymph nodules. High endothelial venules are not present in the spleen. Small veins (0.1–1 mm diameter) drain blood from Veins carry blood toward the heart. muscular venules. They are lined by endothelium, Based on diameter, veins are classified as: 2– 3 layers of smooth muscle cells, and connective tissue adventitia. Medium-Sized Veins Venules, small veins, medium-sized veins, and large veins. 1-10 mm Has Tunica intima,Tunica media, and Tunica Venules and Small Veins adventitia Smallest veins are called venules.They collect ○ Tunica intima(consists) blood from capillaries. Endothelium Diameter are two types: Basal lamina ○ Post-capillary venules (10-50 µm) Thin subendothelial connective Receive blood from capillaries tissue Lined by endothelium and Discontinuous internal elastic pericytes lamina ○ Muscular venules (50-100 µm) ○ Tunica media Lined by endothelium, 1-2 layers Thin of smooth muscles and Consists of few layers of smooth surrounded by thick layer of muscle cells connective tissue ○ Tunica adventitia Histamine and serotonin act mainly on Thick layer of connective tissue  6 containing collagen and elastic contains few smooth muscle cells fibers ○ Tunica media Accompany medium-sized arteries (e.g. radial Consists of concentrically vein, tibial vein, popliteal vein, etc.) arranged smooth muscle cells, Presence of valves in lumen to prevent collagen fibers, and fibroblasts retrograde flow of blood Boundary between tunica media Venous valves are more in veins of lower limb to and tunica intima is difficult to counteract effect of gravity decide ○ Tunica adventitia Thickest layer of large vein Consists of longitudinally arranged smooth muscle cells Also contains collagen fibers, elastic fibers, and fibroblast (e.g. Superior vena cava, inferior vena cava) Larger Veins >10 mm CAPILLARIES Presence of three layer vessels: ○ Tunica intima The smallest blood vessels Consists of vascular endothelium, Form a network that connects arterioles with basal lamina, and thin venule and nourishes tissue subendothelial connective tissue Average diameter of 8 µm (4-10 µm) Subendothelial connective tissue Human body has ~50,000 miles of capillaries  7 (80467.2 km) (>10 kDa) Lumen at some place is narrower than the Locations: found in connective tissue, muscles, diameter of RBCs (7.2 µm). RBCs need to get skin, lungs, and central nervous system folded on themselves for passage through such capillaries Consists of endothelium and its basal lamina NO Tunica media and Tunica adventitia In some capillaries, pericytes are present Pericyte lie embedded in basal lamina of endothelium Pericyte has long oval euchromatic nuclei and several cytoplasmic processes that clasp capillary Pericyte can get differentiated into smooth muscle cell or fibroblast TYPES Fenestrated Capillaries (Visceral) endothelial cells have numerous circular openings called fenestrations (fenestrations = aperture or pores) Size of fenestrations: 50–80 nm Basal lamina is continuous and covers entire capillary Fenestrations are developed because of pinched off process of pinocytosis. Thin endothelium loses its portion on pinocytosis leaving behind a fenestration (gap) Fenestrations are closed by a nonmembranous Continuous Capillaries (Somatic) diaphragm that consists of thin layer of cytoplasm Edges of endothelial cells fuse completely with and basal lamina. Diaphragm closes filtration adjoining cells by tight junctions (uninterrupted pores or fenestrations vascular endothelium) Locations: renal glomeruli, pancreas, endocrine Basement membrane completely surrounds the glands, intestinal villi, choroid plexus, ciliary endothelium (continuous basal lamina) process of eye, and gallbladder exchange of nutrients takes place through cytoplasm of endothelial cells Transcytosis: Endothelial cells of continuous capillaries show pinocytic vesicles in the cytoplasm (mode of transepithelial transport) Tight junction restricts passage of large molecules  8 LYMPHATIC VESSEL carry large molecules and excess extracellular fluid to main bloodstream (lymph) Lymph is a fluid that flows through lymphatic vessels and lymph nodes It is a pale fluid that is generated from transudate (extravascular fluid) and contains plasma proteins. Lymph also contains white blood cells, predominantly lymphocytes also contains large fat molecules called chylomicrons that are absorbed from intestine. Such lymph containing large amount of fat molecules looks similar to milk; hence, it is also called chyle Discontinuous Capillaries (Sinusoids) Lymph may also contains cancerous cells, viruses, large, irregular gaps are present in the wall bacteria, and foreign material (dyes) Endothelial cells have large pores or slits. Most of Lymphatic vessels include: lymph capillaries, large these pores are not closed by basal lamina lymphatic vessels, and thoracic duct (discontinuous basal lamina) Because of sluggish blood flow, sinusoids provide a chance of exchanging of bigger molecules easily Locations:Liver, spleen, lymph nodes, bone marrow, endocrine glands (adrenal cortex, hypophysis cerebri, parathyroid gland), and carotid bodies In liver, sinusoidal wall shows two special cells: ○ Kupffer cells - Phagocytic (macrophage) cells ○ Ito cells - Vitamin A storing cells In spleen, endothelial cells have unique Lymph Capillaries elongated shape and have gaps between adjacent cells begin in tissue as blind-ended sacs lined by lymphatic endothelium are more permeable than blood capillaries, thus they permit entry to absorbed larger lipid molecules in intestine Most of the tissues have lymph capillaries absent in: Epidermis, cornea, cartilage, hair, nails, splenic pulp, bone marrow, choroid, internal ear, meninges, and nervous tissue Most of the lymph capillaries carry lymph toward lymph nodes through afferent lymph vessels Lymph leave the lymph nodes through efferent lymph vessels  9 Lymph Node Large Lymph Vessels is a small kidney-shaped structure that filters the lymph Lymph capillaries join to form lymph vessels has convex surface and concave area (hilum) include: thoracic duct, right lymphatic duct, Each lymph node receives lymph through many jugular lymph trunk, subclavian trunk, afferent lymphatic vessels broncho-mediastinal trunk, intestinal lymph trunks, Each lymph node has efferent lymphatic vessels and lumbar lymph trunks through which filtered lymph leave through hilum. show tunica intima, media, and adventitia (similar Lymph node receives blood vessels through to veins) hilum Differences of lymphatic vessels from veins are as Shows capsule, subscapular sinus, outer cortex, follows: paracortex, and medulla Elastic fibers are present in all layers of lymphatic vessel Circular smooth muscles are present in both tunica media and adventitia of lymphatic vessels In thoracic duct, smooth muscles are arranged longitudinally  10 Capsule thymus-dependent cortex ○ Lymph node is covered by connective tissue capsule. It is made up of dense Sinuses of Lymph Node connective tissue ○ three types of sinuses in lymph node: ○ Trabeculae extend from capsule in the Subcapsular sinus/cortical sinus substance of lymph node Just beneath the ○ Reticular meshwork capsule, a zone called Reticular tissue forms subcapsular sinus is supporting meshwork present consists of reticular cells, It receives lymph from follicular dendritic cells, afferent lymphatic macrophages, and reticular vessels fibers Intermediate/trabecular cells synthesize type III sinuses collagen/ reticular fibers Trabecular sinuses are cells are elongated cells with present adjacent to fine cytoplasmic processes trabeculae Dendritic cells are Trabecular sinuses antigen-presenting cells that connect subcapsular present antigens to T-cells sinus with medullary Parenchyma sinuses ○ Outer darkly stained cortex Medullary sinuses ○ Inner lightly stain medulla Medullary sinuses lie Cortex among the It is darkly stained outer anastomosing part of parenchyma medullary cords. They It consists of: receive lymph from ○ Superficial trabecular sinus and nodular cortex: drain it into efferent It shows lymph vessels presence of ○ Sinuses are filled with reticular numerous meshwork that helps in filtration of lymphatic lymph, trapping of cellular debris and follicles microorganisms, and antigen ○ Deep cortex or presentation to immune cells paracortex: It Medulla lies between ○ Medulla is an inner part of the lymph nodular cortex node. It consists of: and medulla Medullary cords: These are Nodular cortex contains mainly anastomosing cords of lymphocytes, B lymphocytes macrophages, and plasma cells Lymphatic nodules have Medullary sinuses: These are spaces central lightly stained germinal that separate adjacent medullary center and outer darkly cords. They converge at hilum and stained corona or mantle form efferent lymphatic vessels zone. Germinal center is the Medullary cords mainly consist of B zone of B cell proliferation cells, in addition to plasma cells and Paracortex mainly consists of T macrophages cells; hence, it is also called  11 GROSS ANATOMY: PERICARDIUM DEFINITION A PERICARDIUM IS A FIBROSEROUS SAC THAT ENCLOSES THE HEART AND THE ROOTS OF THE GREAT VESSELS AND OCCUPIES THE MIDDLE MEDIASTINUM. POSTERIOR TO THE BODY OF THE STERNUM AND THE SECOND TO THE SIXTH COSTAL CARTILAGES AND FUNCTION: ANTERIOR TO THE FIFTH TO THE EIGHT THORACIC TO RESTRICT EXCESSIVE MOVEMENT OF THE HEART AS A VERTEBRAE WHOLE AND TO SERVE AS A LUBRICATED CONTAINER IN WHICH THE DIFFERENT PARTS OF THE HEART CAN RECEIVES BLOOD FROM THE PERICARDIOPHRENIC, CONTRACT FREE FROM THE SURROUNDING STRUCTURES BRONCHIAL AND ESOPHAGEAL ARTERIES LAYERS: IS INNERVATED BY VASOMOTOR AND SENSORY FIBERS FROM THE PHRENIC AND VAGUS NERVE AND THE FIBROUS PERICARDIUM SYMPATHETIC TRUNK. IS THE STRONG, FIBROUS OUTER LAYER OF THE SAC. The pericardium lies within the middle mediastinum, posterior to the body of the sternum and the second ATTACHES FIRMLY BELOW TO THE CENTRAL to the sixth costal cartilages and anterior to the fifth to TENDON OF THE DIAPHRAGM the eight thoracic vertebrae. IT FUSES WITH THE OUTER COATS OF THE GREAT BLOOD VESSELS PASSING THROUGH IT- NAMELY, THE AORTA, PULMONARY TRUNK, SUPERIOR AND INFERIOR VENA CAVA, AND THE PULMONARY VEINS. (SNELL) ATTACHES IN FROM OF THE STERNUM BY FIBROUS BANDS CALLED THE STERNOPERICARDIAL LIGAMENT (MOORE)  12 A CONTINUOUS SUPERIORLY WITH THE TUNICA epicardium. The slit-like space between the ADVENTITIA OF THE GREAT VESSELS ENTERING AND parietal and visceral layers is referred to as the LEAVING THE HEART AND FUSING WITH pericardial cavity. Normally, the cavity contains PRETRACHEAL LAYER OF DEEP CERVICAL FASCIA (MOORE) a small amount of tissue fluid (about 50 mL), the pericardial fluid, which acts as a lubricant to THE INFERIOR WALL(FLOOR) OF THE FIBROUS facilitate movements of the heart. (SNELL) PERICARDIAL SAC IS FIRMLY ATTACHED AND CONFLUENT (PARTIALLY BLENDED) CENTRALLY PERICARDIAL SINUSES WITH THE CENTRAL TENDON OF THE DIAPHRAGM. (reference:https://slideplayer.com/slide/7887489 /) THE SITE OF CONTINUITY HAS BEEN REFERRED TO AS THE PERICARDIACOPHRENIC LIGAMENT HOWEVER, THE FIBROUS PERICARDIUM AND CENTRAL TENDON ARE NOT TWO SEPARATE STRUCTURES THAT FUSED TOGETHER SECONDARILY, NOR ARE THEY SEPARABLE BY DISSECTION (reference:https://slideplayer.com/slide/7887489 /) SEROUS PERICARDIUM The pericardial sinuses are spaces posterior to the heart formed by the reflections of the serous pericardium around the great vessels. TRANSVERSE SINUS - relatively short horizontal space between the reflection of the serous pericardium around the aorta and pulmonary trunk and the reflection around the large veins OBLIQUE SINUS - The reflection around the large veins forms an inverted U-shaped cup-de-sac. The serous pericardium lines the fibrous - Runs along the axis of the heart, from apex to the pericardium and coats the heart. It is divided into ascending aorta parietal and visceral layers. (SNELL) Parietal layer lines the inner surface of the fibrous pericardium and reflects around the roots of the great vessels to become continuous with the visceral layer of serous pericardium that closely covers the heart. (SNELL) Visceral layer is closely applied to the superficial surface of the heart and is often called the  13 serous pericardium. (SNELL) HEART OVERVIEW: THE RIGHT SIDE RECEIVES OXYGEN-POOR BLOOD FROM THE BODY AND TISSUES AND THEN PUMPS IT TO THE LUNGS TO PICK UP OXYGEN AND DISPEL CARBON DIOXIDE ITS LEFT SIDE RECEIVES OXYGENATED BLOOD RETURNING FROM THE LUNGS AND PUMPS THIS BLOOD THROUGHOUT THE BODY TO SUPPLY OXYGEN AND NUTRIENTS TO THE BLOOD SUPPLY OF THE PERICARDIUM (NOTE: INFOS BELOW BODY TISSUES CAN BE FOUND IN KENHUB AND MOORE) The arterial supply of the pericardium comes -MOORE- predominantly from the pericardiacophrenic -SLIGHTLY LARGER THAN ONE’S LOOSELY CLENCHED FIST artery (a branch of the internal thoracic artery). - A DOUBLE, SELF-ADJUSTING SUCTION AND PRESSURE This artery is located within the fibrous PUMP pericardium on its passage through the thoracic - CONSISTS OF FOUR CHAMBERS: cavity. 1. RIGHT ATRIUM 2. LEFT ATRIUM Additionally, the musculophrenic artery (a 3. RIGHT VENTRICLE terminal branch of the internal thoracic), 4. LEFT VENTRICLE bronchial, esophageal, and superior phrenic arteries (branches of the thoracic aorta) LAYERS OF THE HEART (DEEP TO SUPERFICIAL) contribute to vascularisation of the pericardium. ENDOCARDIUM- A THIN LAYER (ENDOTHELIUM AND SUBENDOTHELIAL CONNECTIVE TISSUE) OR LINING Note that coronary arteries also take part in MEMBRANE OF THE HEART THAT ALSO COVERS ITS VALVES arterial supply, but only to the visceral layer of the serous pericardium. MYOCARDIUM- A THICK, HELICAL MIDDLE LAYER COMPOSED OF CARDIAC MUSCLE NERVE SUPPLY OF THE PERICARDIUM -MOORE- EPICARDIUM- A THIN EXTERNAL LAYER (MESOTHELIUM) PHRENIC NERVE (C3-C5): FORMED BY THE VISCERAL LAYER OF SEROUS - PRIMARY SOURCE OF SENSORY FIBERS; PAIN PERICARDIUM. SENSATIONS CONVEYED BY THESE NERVES ARE COMMONLY REFERRED TO THE SKIN (C3-C5 STRUCTURE DERMATOMES) OF THE IPSILATERAL -SNELL- SUPRACLAVICULAR REGION (TOP OF THE SHOULDER OF THE SAME SIDE. TWO INTERNAL SEPTA (DIVIDES THE HEART INTO 4 VAGUS NERVES CHAMBERS) - FUNCTION UNCERTAIN 1. ATRIAL (INTERATRIAL)SEPTUM- SEPARATES THE SYMPATHETIC TRUNKS RIGHT AND LEFT ATRIA - VASOMOTOR 2. VENTRICULAR (INTERVENTRICULAR) SEPTUM - SEPARATES THE RIGHT AND LEFT Phrenic nerves carry sensory fibers from the pericardium VENTRICLES and the parietal layer of the serous pericardium. Visceral - LIES OBLIQUELY, WITH THE RIGHT SURFACE afferent fibers travel with branches of the sympathetic FACING FORWARD AND TO THE RIGHT trunks and the vagus nerve from the visceral layer of the  14 AND LEFT SURFACE FACING BACKWARD AND TO THE LEFT - HAS A LOWER, THICKER AND MUSCULAR PART AND A SMALLER UPPER, THINNER MEMBRANOUS PART. BORDERS -SNELL AND MOORE- RIGHT BORDER (SLIGHTLY CONVEX) -COMPOSE OF THE RIGHT ATRIUM AND EXTENDING BETWEEN THE SVC AND THE APEX OF THE HEART THE IVC IS FORMED BY THE INFEROLATERAL PART OF THE LEFT VENTRICLE (MOORE) LEFT BORDER (OBLIQUE, NEARLY VERTICAL)- COMPOSE LIES AT THE LEVEL OF THE 5TH LEFT INTERCOSTAL OF THE LEFT AURICLE AND LEFT VENTRICLE SPACE, 3.5 in. (9cm) FROM THE MIDLINE (SNELL) NORMALLY REMAINS MOTIONLESS THROUGHOUT INFERIOR (LOWER) BORDER (NEARLY HORIZONTAL)- THE CARDIAC CYCLE (MOORE) MAINLY FORMED BY THE RIGHT VENTRICLE IS WHERE THE SOUNDS OF MITRAL VALVE CLOSURE ARE MAXIMAL (APEX BEAT); THE APEX UNDERLIES SUPERIOR BORDER- FORMED BY THE RIGHT AND LEFT ATRIA THE SITE WHERE THE HEARTBEAT MAY BE AND AURICLES IN AN ANTERIOR VIEW; THE ASCENDING AUSCULTATED ON THE THORACIC WALL. (MOORE) AORTA AND PULMONARY TRUNK EMERGE FROM THIS BORDER AND THE SVC ENTERS ITS RIGHT SIDE. POSTERIOR THE BASE OF THE HEART (MOORE) TO THE AORTA AND PULMONARY TRUNK AND ANTERIOR IS THE HEART’S POSTERIOR ASPECT (OPPOSITE THE TO THE SVC, THIS BORDER FORMS THE INFERIOR APEX) BOUNDARY OF THE TRANSVERSE PERICARDIAL SINUS. IS FORMED MAINLY BY THE LEFT ATRIUM, WITH A LESSER CONTRIBUTION BY THE RIGHT ATRIUM FACE POSTERIORLY TOWARD THE BODIES OF VERTEBRAE T6-T9 AND IS SEPARATED FROM THEM BY THE PERICARDIUM, OBLIQUE PERICARDIAL SINUS, ESOPHAGUS, AND AORTA EXTENDS TO THE BIFURCATION OF THE PULMONARY TRUNK SUPERIORLY, AND INFERIORLY TO THE CORONARY SULCUS RECEIVES PULMONARY VEINS ON THE RIGHT AND LEFT SIDES OF ITS LEFT ATRIAL PORTION AND THE SUPERIOR AND INFERIOR VENAE CAVAE AT THE SUPERIOR AND INFERIOR ENDS OF ITS RIGHT ATRIAL PORTION THE BASE OF THE HEART IS CALLED THE BASE OF BECAUSE THE HEART IS PYRAMID SHAPED AND THE BASE LIES OPPOSITE THE APEX. (SNELL) NOTE! THE HEART DOES NOT REST ON ITS BASE: IT RESTS ON ITS DIAPHRAGMATIC (INFERIOR) SURFACE ADDITIONAL LEARNING:  15 The fibrous skeleton of the heart, also called the cardiac skeleton, consists of four fibrous rings (anuli fibrosi, singular: annulus fibrosis) and the membranous portions of the septa of the heart. This skeleton is located at the base of the ventricles, between the atria and the ventricles. The rings of the fibrous skeleton are composed of dense, fibrous connective tissue that encircle the orifices of the heart valves. These fibrous rings are interconnected by connective tissue called the right and left trigones and form the structural support for the heart on which the valvular leaflets and cardiac muscle fibers are anchored. (KENHUB) A. RIGHT ATRIUM FORMS THE RIGHT BORDER OF THE HEART AND RECEIVES VENOUS BLOOD FROM THE SVC, IVC, AND CORONARY SINUS.(MOORE) CONSISTS OF TWO PARTS: (SNELL) - MAIN CAVITY (ATRIUM PROPER) - smooth walled and forms from the embryonic sinus venosus - AURICLE- A SMALL EARLIKE OUTPOUCHING; roughened or (PHOTO FROM MOORE) SURFACES: (MOORE) 1. STERNOCOSTAL (ANTERIOR) - FORMED MAINLY BY THE RIGHT VENTRICLE 2. DIAPHRAGMATIC (INFERIOR)- FORMED MAINLY BY THE LEFT VENTRICLE AND PARTLY BY THE RIGHT VENTRICLE; IT IS RELATED MAINLY TO THE CENTRAL TENDON OF THE DIAPHRAGM 3. BASE(POSTERIOR) RIGHT PULMONARY SURFACE- FORMED MAINLY BY THE RIGHT ATRIUM LEFT PULMONARY SURFACE- FORMED MAINLY BY trabeculated by bundles of muscle fibers, THE LEFT VENTRICLE; IT FORMS THE CARDIAC the musculi pectinati (pectinate muscle IMPRESSION IN THE LEFT LUNG. THE INTERIOR OF THE RIGHT ATRIUM (MOORE) CHAMBERS OF THE HEART  16 SMOOTH, THIN-WALLED, POSTERIOR PART (THE SINUS VENARUM)ON WHICH THE VENA CAVA AND CORONARY SINUS OPEN, BRINGING POORLY OXYGENATED BLOOD INTO THE HEART ROUGH, MUSCULAR ANTERIOR WALL COMPOSED OF PECTINATE MUSCLES (L. MUSCULI PECTINATI) RIGHT AV ORIFICE THROUGH WHICH THE RIGHT ATRIUM DISCHARGES THE POORLY OXYGENATED BLOOD IT HAS RECEIVED INTO THE RIGHT VENTRICLE RIGHT ATRIOVENTRICULAR VALVE (TRICUSPID VALVE) REGULATES THE RIGHT ATRIOVENTRICULAR ORIFICE, SULCUS TERMINALIS(TERMINAL GROOVE)- EXTERNALLY WHICH LIES ANTERIOR TO THE INFERIOR VENA CAVA SEPARATES THE SMOOTH AND ROUGH PARTS OF THE OPENING. ATRIAL WALL. B. LEFT ATRIUM CRISTA TERMINALIS- A VERTICAL RIDGE THAT INTERNALLY SEPARATES THE SMOOTH AND ROUGH PARTS OF THE ATRIAL WALL. FORMS MOST OF THE BASE OF THE HEART ADDITIONAL: (MOORE) THE OPENING OF THE CORONARY SINUS-A SHORT THE VALVELESS PAIRS OF RIGHT AND PULMONARY VENOUS TRUNK RECEIVING MOST OF THE VEINS ENTER THE SMOOTH- WALLED ATRIUM CARDIAC VEINS; BETWEEN THE RIGHT AV ORIFICE (MOORE) AND THE IVC ORIFICE. TWO PARTS: (SNELL) THE INTERATRIAL SEPTUM- HAS AN OVAL, - ATRIUM PROPER (MAIN CAVITY) THUMBPRINT-SIZED DEPRESSION, THE OVAL FOSSA - AURICLE AND SEPARATES THE ATRIA. SITUATED BEHIND THE RIGHT ATRIUM AND FORMS THE GREATER PART OF THE BASE OF THE HEART. THE SVC OPENS INTO THE SUPERIOR PART OF THE RECEIVES OXYGENATED BLOOD FROM THE LUNGS RIGHT ATRIUM AT THE LEVEL OF THE RIGHT 3RD VIA THE PULMONARY VEINS (4 OSTIA) COSTAL CARTILAGE. THICKER WALLS ITS LEFT AURICLE CONTAINS PECTINATE MUSCLE THE IVC OPENS INTO THE INFERIOR PART OF THE LANDMARKS: T5-58 (SUPINE), T6-T9(ERECT) RIGHT ATRIUM ALMOST IN LINE WITH THE SVC AT APPROXIMATELY THE LEVEL OF THE 5TH COSTAL THE INTERIOR OF THE LEFT ATRIUM CARTILAGE ❖ A LARGER SMOOTH-WALLED PART AND A SMALLER MUSCULAR AURICLE CONTAINING PECTINATE MUSCLE ❖ FOUR PULMONARY VEINS (TWO SUPERIOR AND 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  17 RECEIVES BLOOD FROM THE RIGHT ATRIUM AND PUMPS IT VIA PULMONARY TRUNK INTO THE LUNGS FOR BLOOD OXYGENATION THE WALLS ARE MUCH THICKER THAN THOSE RIGHT ATRIUM AND SHOW MANY INTERNAL PROJECTING RIDGES FORMED OF MUSCLE FIBERS THE INTERIOR OF THE RIGHT VENTRICLE HAS IRREGULAR MUSCULAR ELEVATIONS (TRABECULAE CARNEA). SUPRAVENTRICULAR CREST, A THICK MUSCULAR RIDGE (FOUND IN RIGHT VENTRICLE) SEPARATES THE RIDGED MUSCULAR WALL OF THE INFLOW PART OT THE CHAMBER FROM THE SMOOTH WALL OPENINGS INTO THE LEFT ATRIUM OF THE CONUS ARTERIOSUS OR OUTFLOW PART. THE FOUR PULMONARY VEINS, TWO FROM EACH LUNG, THE INFLOW PART OF THE VENTRICLE RECEIVES OPEN THROUGH THE POSTERIOR WALL AND HAVE NO BLOOD FROM THE RIGHT ATRIUM THROUGH THE VALVES. THE LEFT ATRIOVENTRICULAR ORIFICE IS RIGHT AV (TRICUSPID) ORIFICE GUARDED BY THE MITRAL VALVE. VALVES SNELL) C. RIGHT VENTRICLE (MOORE AND SNELL) RIGHT ATRIOVENTRICULAR (TRICUSPID) VALVE GUARDS THE RIGHT ATRIOVENTRICULAR ORIFICE CONSISTS OF THREE CUSPS FORMED BY A FOLD OF ENDOCARDIUM WITH SOME CONNECTIVE TISSUE ENCLOSED: 1. ANTERIOR 2. SEPTAL 3. INFERIOR (POSTERIOR) CUSPS VENTRICULAR VALVE GUARDS THE PULMONARY ORIFICE AND CONSISTS OF THREE SEMILUNAR CUSPS THAT FORMED OF ENDOCARDIUM WITH SOME CONNECTIVE TISSUE ENCLOSED: 1. ANTERIOR 2. RIGHT 3. LEFT CUSPS TAKES UP THE MAJORITY OF THE ANTERIOR SURFACE OF THE HEART, A SMALL PART OF THE DIAPHRAGMATIC SURFACE, AND MOST THE ENTIRE THREE PAPILLARY MUSCLES (CORRESPOND TO THE CUSPS INFERIOR BORDER OF THE HEART OF THE TRICUSPID VALVE) SUPERIORLY, IT TAPERS INTO AN ARTERIAL CONE, 1. ANTERIOR PAPILLARY MUSCLE THE CONUS ARTERIOSUS (INFUNDIBULUM), WHICH LARGEST AND MOST PROMINENT LEADS INTO THE PULMONARY TRUNK. ARISES FROM THE ANTERIOR WALL OF THE RIGHT VENTRICLE  18 ITS TENDINOUS CORDS ATTACH TO THE INTERVENTRICULAR SEPTUM (IVS)- (MOORE) ANTERIOR AND POSTERIOR CUSPS OF THE COMPOSED OF MUSCULAR AND MEMBRANOUS TRICUSPID VALVE PARTS 2. POSTERIOR PAPILLARY MUSCLE SMALLER THAN THE ANTERIOR MUSCLE A STRONG, OBLIQUELY PLACED PARTITION CONSIST OF SEVERAL PARTS BETWEEN THE RIGHT AND LEFT VENTRICLES ARISES FROM THE INFERIOR WALL OF THE FORMING PART OF THE WALLS OF EACH OTHER. RIGHT VENTRICLE ITS TENDINOUS CORDS ATTACH TO THE MUSCULAR PART OF (IVS)- FORMS THE MAJORITY POSTERIOR AND SEPTAL CUSPS OF THE OF THE SEPTUM ; HAS THE THICKNESS OF THE TRICUSPID VALVE REMAINDERS OF THE WALL OF THE LEFT VENTRICLE 3. SEPTAL PAPILLARY MUSCLE AND BULGES INTO THE CAVITY OF THE RIGHT ARISES FROM THE INTERVENTRICULAR VENTRICLE ITS TENDINOUS CORDS ATTACH TO THE MEMBRANOUS PART OF THE (IVS)- FOUND ANTERIOR AND SEPTAL CUSPS OF THE SUPERIORLY AND INFERIORLY; A THIN MEMBRANE TRICUSPID VALVE. AND A PART OF THE FIBROUS SKELETON OF THE HEART SEPTOMARGINAL TRABECULA (MODERATOR BAND) A CURVED MUSCULAR BUNDLE THAT TRANSVERSES THE RIGHT VENTRICULAR CHAMBER FROM THE INFERIOR PART OF THE IVS TO THE BASE OF THE ANTERIOR PAPILLARY MUSCLE D.LEFT VENTRICLE FORMS THE APEX OF THE HEART, NEARLY ALL ITS LEFT (PULMONARY) SURFACE AND BORDER AND MOST OF THE DIAPHRAGMATIC SURFACE. ITS WALLS ARE SUBSTANTIALLY THICKER THAN THOSE OF THE RIGHT VENTRICLE MORE POWERFUL PUMP THAN THE LEFT VENTRICLE THE LARGEST OF ALL THE CHAMBERS, MAINLY DUE TO THE THICKNESS OF ITS MUSCULAR WALL OCCUPIES MOST OF THE PULMONARY AND INFERIOR SURFACES OF THE HEART, INCLUDING ITS APEX ADDITIONAL INFO ABOUT RV PERFORM MORE WORK THAN THE RIGHT VENTRICLE DUE TO ITS ARTERIAL HIGH PRESSURE. TRICUSPID VALVE- GUARDS THE RIGHT AV ORIFICE. THE INTERIOR OF THE LEFT VENTRICLE HAS: MOORE TENDINOUS CORDS- ATTACH TO THE FREE EDGES AND VENTRICULAR SURFACES OF THE ANTERIOR, POSTERIOR AND SEPTAL CUSPS. VENTRICULAR DIASTOLE- BLOOD FLOW BACK TOWARD THE HEART AND ENTERS THE SINUSES;THE VALVE CUSPS FILL, COME INTO APPOSITION IN THE CENTER OF THE LUMEN, AND CLOSE THE PULMONARY ORIFICE. (SNELL)  19 WALLS THAT ARE TWO TO THREE TIMES AS THICK AS REVERSAL OF FLOW TAKES PLACE AROUND THE ANTERIOR THOSE OF THE RIGHT VENTRICLE CUSP OF THE MITRAL VALVE. WALLS ARE MOSTLY COVERED WITH A MESH OF AORTIC VALVE- OBLIQUELY PLACED BETWEEN THE LEFT TRABECULAE CARNEAE THAT ARE FINER AND VENTRICLE AND THE ASCENDING AORTA; LOCATED MORE NUMEROUS THAN THOSE OF THE RIGHT POSTERIOR TO THE LEFT SIDE OF THE STERNUM AT THE LEVEL VENTRICLE OF THE 3RD RIB. (SNELL) 3 CUSPS: A CONICAL CAVITY THAT IS LONGER THAN THAT 1. RIGHT CORONARY OF THE RIGHT VENTRICLE 2. LEFT CORONARY 3. POSTERIOR (NONCORONARY) ANTERIOR AND POSTERIOR PAPILLARY MUSCLES THAT ARE LARGER THAN THOSE IN THE RIGHT VENTRICLE A SMOOTH-WALLED, NONMUSCULAR, SUPERO-ANTERIOR OUTFLOW PART, THE AORTIC VESTIBULE , LEADING FROM THE VENTRICULAR CAVITY 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 POSTEROSUPERIOR PARTS AND IS SURROUNDED BY (KEY POINTS OF LEFT VENTRICLE: TABLE FROM KENHUB) A FIBROUS RING TO WHICH THE RIGHT POSTERIOR AND LEFT CUSPS OF THE AORTIC VALVE ARE GREAT VESSELS ATTACHED; THE ASCENDING AORTA BEGINS AT 1. Ascending Aorta THE AORTIC ORIFICE. LEFT ATRIOVENTRICULAR (MITRAL) VALVE (MOORE) LOCATED POSTERIOR TO THE STERNUM AT THE LEVEL OF THE 4TH COSTAL CARTILAGE GUARDS THE ATRIOVENTRICULAR ORIFICE AND HAS TWO CUSPS: 1. ONE ANTERIOR- LARGER AND INTERVENES begins at the base of the left ventricle and runs BETWEEN THE ATRIOVENTRICULAR AND AORTIC upward and forward to come to lie behin ORIFICE d the right half of the sternum at the level of the 2. ONE POSTERIOR sternal angle it becomes continuous with the arch of the aorta (EACH CUSPS RECEIVES TENDINOUS CORDS FROM MORE THAN ONE PAPILLARY MUSCLE. THE CORDS BECOME TAUT Aortic Sinuses JUST BEFORE AND DURING SYSTOLE, PREVENTING THE at the root of ascending aorta possess 3 bulges CUSPS FROM BEING FORCED INTO THE LEFT ATRIUM.AS IT called Aortic Sinuses TRANSVERSES THE LEFT VENTRICLE, THE BLOODSTREAM One aortic sinus is located behind each aortic UNDERGOES TWO RIGHT ANGLE TURNS, WHICH TOGETHER valve cusp RESULTS IN 180 DEGREES CHANGE IN DIRECTION.THIS  20 Arteries originate from these Aortic Sinus into the iliac arteries just above the pelvis. 3. Ligamentum Arteriosum Right coronary artery arises from the right aortic sinus runs forward between the right side of the - is a fibrous band that connects the bifurcation of pulmonary trunk and the right auricle, and the pulmonary trunk to the lower concave descends almost vertically in the right surface of the aortic arch atrioventricular groove (coronary sulcus) - The ligamentum arteriosum is the remnant of the At the inferior border of the heart, it continues ductus arteriosus, which in the fetus conducts posteriorly along the atrioventricular groove to blood from the pulmonary trunk to the aorta, thus anastomose with the left coronary artery in the bypassing the lungs. posterior interventricular groove. - The left recurrent laryngeal nerve hooks around Left coronary artery arises from the left aortic sinus the lower border of the ductus which closes after usually larger than the right coronary artery birth. supplies the major part of the heart - Should it remain patent, aortic blood will enter the pulmonary circulation.Surgical ligation of the passes forward between the left side of the ductus is then necessary, and the surgeon must pulmonary trunk and the left auricle, enters the take care to preserve the left recurrent laryngeal atrioventricular groove (coronary sulcus), and nerve. divides into an anterior interventricular branch and a circumflex branch 2. Course of Aorta 4. Flow of Blood The aorta is the largest blood vessel in the body and is responsible for transporting oxygen rich blood from your heart to the rest of your body. It begins at the left ventricle of the heart, extending upward (Ascending Aorta) into the chest to form an Aortic Arch. It then continues 1. Oxygen-poor blood returns from the body to the downward (Descending Aorta) into the heart through the superior vena cava (SVC) and abdomen (Abdominal Aorta), where it branches  21 inferior vena cava (IVC), the two main veins that Brachiocephalic artery- passes upward and to bring blood back to the heart. the right of the trachea and divides into the right 2. The oxygen-poor blood enters the right atrium subclavian and right common carotid arteries (RA), or the right upper chamber of the heart. behind the right sternoclavicular joint. 3. From there, the blood flows through the tricuspid valve (TV) into the right ventricle (RV), or the right Left common carotid artery - arises on the left lower chamber of the heart side of the brachiocephalic artery. It runs upward 4. The right ventricle (RV) pumps oxygen-poor and to the left of the trachea and enters the blood through the pulmonary valve (PV) into the neck behind the left sternoclavicular joint. main pulmonary artery (MPA). 5. From there, the blood flows through the right and Left subclavian artery - arises from the aortic left pulmonary arteries into the lungs. arch behind the left common carotid artery. It 6. In the lungs, oxygen is put into the blood and runs upward along the left side of the trachea carbon dioxide is taken out of the blood during and the esophagus to enter the root of the neck. the process of breathing. After the blood gets It arches over the apex of the left lung and oxygen in the lungs, it is called oxygen-rich continues toward the left upper limb. blood. 7. Oxygen-rich blood flows from the lungs back into the left atrium (LA), or the left upper chamber of Descending Thoracic Aorta- lies in the posterior the heart, through four pulmonary veins. mediastinum. It begins as the continuation of the arch of 8. Oxygen-rich blood then flows through the mitral the aorta on the left side of the lower border of the body valve (MV) into the left ventricle (LV), or the left of the fourth thoracic vertebra. lower chamber. 9. The left ventricle (LV) pumps the oxygen-rich blood through the aortic valve (AoV) into the aorta (Ao), the main artery that takes oxygen-rich blood out to the rest of the body. AORTIC ARCH/ DESCENDING THORACIC AORTA Aortic Arch- is the continuation of the ascending aorta. Branches: Bronchial arteries- supply the lungs Pericardial arteries- supply dorsal portion of pericardium Superior phrenic arteries- support the diaphragm Esophageal arteries- supply the esophagus Posterior intercostal arteries- supply the intercostal spaces Subcostal arteries- supply the flat abdominal wall Branches: muscles Subclavian artery  22 -Is a paired arterial vessel of the thorax. -is a long, paired vessel that originates from the proximal -Main function of the subclavian artery is to supply blood part of the subclavian artery. to the upper limbs, thorax, neck, and brain. Origin Subclavian artery Branches Anterior collaterals: -Anterior intercostal branches -Perforating branches -Medial mammary arteries Posterior collaterals: -Mediastinal branches -Thymic branches Branches: -Pericardiacophrenic artery Vertebral artery- is the first branch of the -Sternal branches subclavian artery. It courses superiorly along -Bronchial branches each side of the neck region and ultimately -Tracheal branches merges with its counterpart at the Terminal branches: pontomedullary junction to form the basilar artery. The vertebral artery supplies the upper -Superior epigastric artery spinal cord, brainstem, cerebellum and posterior -Musculophrenic artery part of the brain. Supply Skin and muscles of the anterior Internal thoracic artery- in contrast to the aspect of the thoracic cage and vertebral artery, descends along the inner superior aspect of the abdominal surface of the anterior chest wall. It gives rise to wall, typical ribs, breasts, parietal several branches along its course to supply the pleura, sternum, pericardium and anterior thoracic wall and the breast. thymus. Thyrocervical trunk- is a short and wide branch that arises close to the medial border of the anterior scalene muscle. Its major branch, the SUPERIOR VENA CAVA inferior thyroid artery, supplies several important structures in the neck including the larynx, The two brachiocephalic pharynx, trachea, platysma, esophagus, thyroid veins join to form the superior and parathyroid glands). vena cava, which conveys all Costocervical trunk- this short artery that supplies the venous blood from the the posterior cervical muscles and upper thorax. head and neck and both Dorsal scapular artery-this artery provides arterial upper limbs. It passes downward to end in the right supply for muscles of the upper back and atrium of the heart. shoulder including the trapezius muscle, levator scapulae muscle and rhomboid muscle The azygos vein joins the posterior aspect of the The internal thoracic artery (internal mammary artery) superior vena cava just before it enters the  23 pericardium Left brachiocephalic vein It is a large vein, with a wide diameter of up to 2cm and The tributaries of the a length of approximately 7cm. left brachiocephalic vein are the left After Circulating through the body systemically, vertebral, internal Deoxygenated Blood returns to the Right Atrium of the thoracic, inferior heart through either the SVC, which drains the upper thyroid and superior Body, or the IVC that drains everything below the intercostal veins. Diaphragm. In addition, it often receives the thymic, supreme intercostal, pericardiacophrenic and the left posterior intercostal vein of the 1st intercostal space. The SVC receives tributaries from several minor vein Right brachiocephalic groups: The tributaries of the right Mediastinal veins brachiocephalic vein are the Oesophageal veins right vertebral, internal Pericardial veins thoracic and inferior thyroid veins, and occasionally the Brachiocephalic vein (Innominate vein) right posterior intercostal vein of the 1st intercostal space. The brachiocephalic vein, also known as the innominate vein, is a paired vein of the superior mediastinum that drains the venous blood from the head and neck, upper limbs and the upper part of the thorax. Azygos Vein The azygos venous system It is formed by the is located on either side of confluence of the the vertebral column and internal jugular and drains the viscera within subclavian veins on the mediastinum, as well each side, just as the back and posterior to the thoracoabdominal walls. sternoclavicular joint. This system consists of the azygos vein and its two main tributaries: the hemiazygos vein and the  24 accessory hemiazygos vein. Tributaries The azygos vein has two tributaries, which are referred to as the hemiazygos vein and the accessory hemiazygos vein. The hemiazygos vein is often connected to the left renal vein. It is formed by the oesophageal and mediastinal tributaries, the Tributaries common trunk of the left The subclavian vein receives venous blood from the ascending lumbar vein and internal and external jugular veins of the lateral cervical left subcostal vein, and by region, as well as the dorsal scapular vein which drains the lower three posterior the region of the same name, as well as the anterior intercostal veins. It ascends jugular vein, which lies on the front of the neck. anterior to the vertebral column before crossing the column posterior to the aorta, esophagus and thoracic duct at the level of T8. The accessory hemiazygos vein is formed by veins from the fourth to eighth intercostal spaces and sometimes by the left bronchial veins. It descends to the left of the vertebral column before crossing T7, where it joins with the azygos vein. Sometimes it joins the hemiazygos vein and, in this case, their common trunk drains into the azygos vein. Subclavian vein The subclavian vein is the major vein of the arm, shoulder and neck. Its name means ‘under the CORONARY CIRCULATION clavicle’, due to the Arterial Supply course it takes when The 2 main coronary arteries are the left main entering the thorax. and right coronary arteries: ○ Left main coronary artery (LMCA). The left main coronary artery supplies blood to the left side of the heart muscle (the left ventricle and left atrium). The left main coronary divides into branches: The left anterior descending artery branches off the left coronary artery and supplies blood to the front of the left side of the heart.  25 The circumflex artery branches The venous drainage of the heart is mostly off the left coronary artery and through the coronary sinus – a large venous encircles the heart muscle. This structure located on the posterior aspect of the artery supplies blood to the outer heart. The cardiac veins drain into the coronary side and back of the heart. sinus, which in turn, empties into the right atrium. ○ Right coronary artery (RCA). The right There are also smaller cardiac veins which pass coronary artery supplies blood to the directly into the right atrium. right ventricle, the right atrium, and the Tributaries SA (sinoatrial) and AV (atrioventricular) ○ Great cardiac vein (anterior nodes, which regulate the heart rhythm. interventricular vein) – the largest The right coronary artery divides into tributary of the coronary sinus. It smaller branches, including the right originates at the apex of the heart and posterior descending artery and the ascends in the anterior interventricular acute marginal artery. Together with the groove. It then curves to the left and left anterior descending artery, the right continues onto the posterior surface of coronary artery helps supply blood to the the heart. Here, it gradually enlarges to middle or septum of the heart. form the coronary sinus. Smaller branches of the coronary arteries ○ Small cardiac vein – located on the include: obtuse marginal (OM), septal perforator anterior surface of the heart, in a groove (SP), and diagonals. between the right atrium and right ventricle. It travels within this groove onto the posterior surface of the heart, where it empties into the coronary sinus. ○ Middle cardiac vein (posterior interventricular vein) – begins at the apex of the heart and ascends in the posterior interventricular groove to empty into the coronary sinus. ○ Posterior cardiac vein – located on the posterior surface of the left ventricle. It lies to the left of the middle cardiac vein and empties into the coronary sinus. Anterior View PHYSIOLOGY: GUYTON 1. STATE THE PHASIC CHANGES IN CORONARY BLOOD FLOW DURING SYSTOLE AND DIASTOLE IN RELATION TO THE EFFECT OF CARDIAC MUSCLE COMPRESSION. Posterior View Venous Supply  26 FLOW IN RELATION TO THE EFFECT OF INTRAMYOCARDIAL PRESSURE. Figure demonstrates the special arrangement of the coronary vessels at different depths in the heart muscle, showing on the outer surface Figure shows the changes in blood flow epicardial coronary arteries which supply most of through the nutrient capillaries of the left the muscle. ventricular coronary system in ml/min in Smaller intramuscular arteries derived from the the heart during systole and diastole, as epicardial arteries penetrate the muscle, extrapolated from studies in experimental supplying the needed nutrients. animals. Lying immediately beneath the endocardium is a Note from this diagram that the coronary plexus of subendocardial arteries. capillary blood flow in the left ventricle During systole, blood flow through the muscle falls to a low value during systole, subendocardial plexus of the left ventricle, where which is opposite to flow in vascular beds the intramuscular coronary vessels are elsewhere in the body. compressed greatly by ventricular muscle The reason for this phenomenon is strong contraction, tends to be reduced. compression of the intramuscular blood However, the extra vessels of the subendocardial vessels by the left ventricular muscle plexus normally compensate for this reduction. during systolic contraction. Later in the chapter, we explain how this peculiar During diastole, the cardiac muscle difference between blood flow in the epicardial relaxes and no longer obstructs blood and subendocardial arteries plays an important flow through the left ventricular muscle role in certain types of coronary ischemia. capillaries, so blood flows rapidly during all of the diastole. SOURCE: GUYTON AND HALL. 14TH ED. PAGE 263. Blood flow through the coronary capillaries of the right ventricle also undergoes phasic changes during the 3. DISCUSS THE DIFFERENT FACTORS CONTROLLING cardiac cycle but, because the force of CORONARY BLOOD FLOW IN RELATION TO: contraction of the right ventricular A. LOCAL MUSCLE METABOLISM (PRIMARY muscle is far less than that of the left CONTROLLER OF CORONARY BLOOD ventricular muscle, the inverse phasic FLOW) changes are only partial, in contrast to Blood flow through the coronary those in the left ventricular muscle. system is regulated mostly by local arteriolar vasodilation in SOURCE: GUYTON AND HALL. 14TH ED. PAGE response to the nutritional needs 262-263. of cardiac muscle. That is, whenever the vigor of 2. STATE THE DIFFERENCE BETWEEN EPICARDIAL cardiac contraction is increased, VERSUS SUBENDOCARDIAL CORONARY BLOOD the rate of coronary blood flow  27 also increases. prostaglandins, and nitric oxide. Conversely, decreased heart The mechanisms of coronary vasodilation during activity is accompanied by increased cardiac activity have not been fully decreased coronary flow. explained by adenosine. This local regulation of coronary Pharmacologic agents that block or partially blood flow is similar to that which block the vasodilator effect of adenosine do not occurs in many other tissues of completely prevent coronary vasodilation the body, especially in the caused by increased heart muscle activity. skeletal muscles. Studies in skeletal muscle have also shown that the continued infusion of adenosine maintains Oxygen Demand Is a Major Factor in Local Coronary vascular dilation for only 1 to 3 hours, yet muscle Blood Flow Regulation. activity still dilates the local blood vessels, even when the adenosine can no longer dilate them. Blood flow in the coronary arteries usually is Therefore, the other vasodilator mechanisms regulated almost exactly in proportion to the listed earlier should be remembered. need of the cardiac musculature for oxygen. Normally, about 70% of the oxygen in the B. NERVOUS CONTROL coronary arterial blood is removed as the blood flows through the heart muscle. Because not Stimulation of the autonomic nerves to the heart much oxygen is left, little additional oxygen can can affect coronary blood flow directly and be supplied to the heart musculature unless the indirectly. coronary blood flow increases. The direct effects result from action of the Fortunately, the coronary blood flow increases nervous transmitter substances acetylcholine almost in direct proportion to any additional from the vagus nerves and norepinephrine from metabolic consumption of oxygen by the heart. the sympathetic nerves on the coronary vessels. The exact means whereby increased oxygen The indirect effects result from secondary consumption causes coronary dilation has not changes in coronary blood flow caused by been determined. increased or decreased activity of the heart. Many researchers have speculated that a The indirect effects, which are mostly opposite to decrease in oxygen concentration in the heart the direct effects, play a far more important role causes vasodilator substances to be released in the normal control of coronary blood flow. from the muscle cells and that these substances Thus, sympathetic stimulation, which releases dilate the arterioles. norepinephrine from the sympathetic nerves and A substance with great vasodilator propensity is epinephrine, as well as norepinephrine from the adenosine. In the presence of very low adrenal medullae, increases both heart rate and concentrations of oxygen in the muscle cells, a heart contractility and increases the rate of large proportion of the cell’s ATP degrades to metabolism of the heart. adenosine monophosphate (AMP). In turn, the increased metabolism of the heart Small portions of this substance are then further sets off local blood flow regulatory mechanisms degraded and release adenosine to the tissue for dilating the coronary vessels and blood flow fluids of the heart muscle, with a resultant increases approximately in proportion to the increase in local coronary blood flow. metabolic needs of the heart muscle. After adenosine causes vasodilation, much of it is In contrast, vagal stimulation, with its release of reabsorbed into the cardiac cells to be reused acetylcholine, slows the heart and has a slightly for production of ATP. depressive effect on heart contractility. Adenosine is not the only vasodilator product These effects decrease cardiac oxygen that has been identified; others include consumption and, therefore, indirectly constrict adenosine phosphate compounds, potassium the coronary arteries. ions, hydrogen ions, carbon dioxide,  28 Direct Effects of Nervous Stimuli on Coronary Vasculature. However, glycolysis consumes large quantities of The distribution of parasympathetic (vagal) nerve the blood glucose and, at the same time, forms fibers to the ventricular coronary system is not large amounts of lactic acid in the cardiac tissue. very great. However, the acetylcholine released This is probably one of the causes of cardiac pain by parasympathetic stimulation has a direct in cardiac ischemic conditions, as discussed later effect to dilate the coronary arteries. in this chapter. Much more extensive sympathetic innervation of As is true in other tissues, more than 95% of the the coronary vessels occurs. In Chapter 61, we metabolic energy liberated from foods is used to see that the sympathetic transmitter substances form ATP in the mitochondria. norepinephrine and epinephrine can have This ATP in turn acts as the conveyer of energy for vascular constrictor or vascular dilator effects, cardiac muscular contraction and other cellular depending on the presence or absence of functions. constrictor or dilator receptors in the blood vessel In severe coronary ischemia, the ATP degrades walls. first to adenosine diphosphate and then to AMP The constrictor receptors are called alpha and adenosine. receptors, and the dilator receptors are called Because the cardiac muscle cell membrane is beta receptors. Both alpha and beta receptors slightly permeable to adenosine, much of this exist in the coronary vessels. agent can diffuse from the muscle cells into the In general, the epicardial coronary vessels have circulating blood. a preponderance of alpha receptors, whereas The released adenosine is believed to be one of the intramuscular arteries may have a the substances that causes dilation of the preponderance of beta receptors. coronary arterioles during coronary hypoxia, as Therefore, sympathetic stimulation can, at least discussed earlier. theoretically, cause slight overall coronary However, loss of adenosine also has a serious constriction or dilation, but usually c