Transcript The Heart
The Cardiovascular System: The Heart Chapter 19 Introduction The heart is the pump of our circulatory system The cardiovascular system provides the transport system of the body Using blood as the transport medium, the heart continually propels oxygen, nutrients, wastes, and many other substances into the interconnecting blood vessels that move past the body cells Heart Size, Location and Position The heart is about the size of a fist It weighs between 250 350 grams (less than a pound) Located in the medial cavity of the thorax, the mediastinum It extends from the 2nd rib to 5th intercostal space Rests on the superior surface of diaphram Heart Size, Location and Position The lungs flank the heart laterally and partially obscure it Heart Size, Location and Position The heart lies anterior to the vertebral column and posterior to the sternum Two thirds of the heart lies to the left of the midsternal line; the balance projects to the right Its broad flat base, or posterior surface, points to right shoulder The apex points toward the left hip Coverings of the Heart The heart is enclosed in a double-walled sac called the pericardium The loose fitting superficial part of the sac is the fibrous pericardium – This tough, dense connective tissue layer 1) protects the heart; 2) anchors the heart; and 3) prevents overfilling Coverings of the Heart The loose fitting superficial part of the sac is the fibrous pericardium This tough, dense connective tissue layer – Protects the heart – Anchors it to surrounding structures (diaphragm/large vessels) – Prevents overfilling of the heart with blood Coverings of the Heart Deep to the fibrous pericardium is the serous pericardium, a thin slippery serous membrane composed of two layers – Parietal layer – Visceral layer Coverings of the Heart The parietal layer lines the internal surface of the fibrous pericardium At the superior margin of the heart, the parietal layer attaches to the large arteries exiting from the heart It then turns inferiorly and continues over the external heart surface as the visceral layer Coverings of the Heart The visceral layer, also called the epicardium, is an integral part of the heart wall The layer membrane conforms around the heart much like pushing your fist into a double layer membrane with an air pocket in between Coverings of the Heart Between the two layers of serous pericardium is the slitlike pericardial cavity The cavity contain pericardial fluid The serous membranes, lubricated by fluid, glide smoothly against one another during heart activity, creating a relatively friction-free environment Inflammation Inflammation of the heart can lead to serious problems – Pericarditis / hinders production of serous fluid production causing the heart to rub – Cardiac tamponade / inflammatory fluid seep into the pericardial cavity, compressing the heart and limiting its ability to pump blood Layers of the Heart Wall The heart wall is composed of three layers – Superficial layer of epicardium – Middle layer of myocardium – Deep layer of endocardium All three layers are richly supplied with blood vessels Layers of the Heart Wall The epicardium is the visceral layer of the serous pericardium The epicardium is often infiltrated with fat, especially in older people Layers of the Heart Wall The myocardium is the layer of cardiac muscle that forms the bulk of the heart It is the layer that actually contracts Layers of the Heart Wall Within the myocardium, the branching cardiac muscle cells are tethered to each other by crisscrossing connective tissue fibers arranged in spiral or circular bundles These interlacing bundles effectively link all parts of the heart together Layers of the Heart Wall The connective tissue forms a dense network called the internal skeleton of the heart It reinforces the myocardium internally and anchors the cardiac muscle This network of fibers is thicker in some areas than in others to reinforce valves and where the major vessels exit Layers of the Heart Wall The internal skeleton prevents overdilation of vessels due to the continual stress of blood pressure Additionally, since connective tissue is not electrically excitable, it limits action potentials across the heart to specific pathways Layers of the Heart Wall The endocardium is a glistening white sheet of endothelium (squamous epithelium) resting on a thin layer of connective tissue Layers of the Heart Wall Located on the inner myocardial surface, it lines the heart chambers and covers the connective tissue skeleton of the valves The endocardium is continuous with the endothelial linings of the blood vessels leaving and entering the heart Chambers and Great Vessels The heart has four chambers Atria – Two superior atria – Two inferior ventricles The longitudinal wall separating the chambers is called the – Interartial septum • Between atria – Interventricular septum • Between ventricles Septum Chambers and Great Vessels The right ventricle forms most of the anterior surface of the heart The left ventricle dominates the inferioposterior aspect of the heart and forms the heart apex Left Ventricle Right Ventricle Chambers and Great Vessels Two grooves visible on the surface of the heart indicate the boundaries of its four chambers and carry the blood vessels that supply myocardium Atrioventricular groove or coronary sulcus encircles the junction of the atria and ventricles Coronary Sulcus Chambers and Great Vessels The anterior interventricular sulcus, separates the right and left ventricles It continues as the posterior interventricular sulcus which provides a similar landmark on the heart’s posterioinferior surface Posterior Interventricular Sulcus Anterior Interventricular Sulcus Atria: The Receiving Chambers Except for the small, wrinkled, protruding appendages called auricles, the atria are free of distinguishing surface features The auricles increase the atrial volume slightly Atria Auricles Atria: The Receiving Chambers Internally, the posterior walls are smooth, but the anterior walls are ridged by bundles of muscle tissue These muscle bundles are called pectinate muscles Pectinate Muscle Atria: The Receiving Chambers The interatrial septum bears a shallow depression, the fovea ovalis This landmark marks the spot where an opening, the foramen ovale, existed in the fetal heart Fovea Ovalis Atria: The Receiving Chambers Functionally, the atria are receiving chambers for blood returning to the heart from the circulation Because they need to contract only minimally to push blood into the ventricles, the atria are relatively small, thin walled chambers As a rule they contribute little to the propulsive pumping of the heart Atria: The Receiving Chambers Blood enters the right atrium via three veins Superior vena cava – Superior vena cava • Returns blood from body regions superior to diaphragm – Inferiorn vena cava • Returns blood from body areas below the diaphragm Coronary – Coronary sinus sinus • Collects blood draining from the myocardium itself Inferior vena cava Atria: The Receiving Chambers Blood enters the left atrium via four veins – Right and left pulmonary veins The pulmonary veins transport blood from the lungs back to the heart Left pulmonary veins Right Pulmonary veins Posterior view Ventricles: Discharging Chambers Marking the internal walls of the ventricle chambers are irregular ridges of muscle called trabeculae carneae The papillary muscles project into the cavity and play a role in valve function Papillary muscles Trabeculae carneae Ventricles: Discharging Chambers The ventricles are the discharging chambers of the heart Note the difference in thickness of the wall When the ventricles contract blood is propelled out of the heart and into circulation Atrial Wall Ventricular Wall Ventricles: Discharging Chambers The right ventricle pumps blood into the pulmonary trunk, which routes blood to the lungs for gas exchange The left ventricle pumps blood into the aorta, the largest artery in the systemic circulation Aorta Left ventricle Right ventricle Pulmonary trunk Pathway of Blood: Heart The heart is actually two pumps, each serving a separate blood circuit Blood vessels that carry blood to the lung form the pulmonary circuit (gas exchange) Vessels carrying blood to the body form the systemic circuit Pathway of Blood: Heart The right side of the heart forms the pulmonary circuit Blood returning from the body enters the right atrium and passes into the right ventricle The ventricle pumps the blood to the lungs via the pulmonary trunk Pathway of Blood: Heart Blood in the pulmonary circuit is oxygen poor and carbon dioxide rich Once in the lungs the blood unloads carbon dioxide and picks up oxygen Freshly oxygenated is carried back to the heart by the pulmonary veins Pathway of Blood: Heart Note that the circulation of the pulmonary circuit is unique Typically veins carry oxygen poor blood to the heart and arteries carry oxygen rich blood The pattern is reversed in the pulmonary circuit with the pulmonary arteries carrying oxygen poor blood to the lungs and the pulmonary veins carrying oxygen rich blood back to the heart Pathway of Blood: Heart The left side of the heart is the systemic system pump Freshly oxygenated blood leaving the lungs enters the left atrium and passes into the left ventricle The left ventricle pumps blood into the aorta and from there into many distributing arteries Pathway of Blood: Heart Smaller distributing arteries carry the blood to all parts of the body Gases, wastes and nutrients are exchanged across capillary walls Blood then returns to the right atrium of the heart via systemic veins and the cycle continues Pathway of Blood: Heart Although equal volumes of blood are flowing in the pulmonary and systemic circuits at any one moment the two ventricles have very unequal work loads The pulmonary circuit, served by the right ventricle, is a low pressure circulation The systemic circuit, served by the left ventricle, circulates through the entire body and encounters about five times as much resistance to blood flow Ventricles: Discharging Chambers The difference in system work load is revealed in the comparative anatomy of the two ventricles The walls of the left ventricle are three times as thick as those of the right ventricle Left ventricle Ventricles: Discharging Chambers The cavity of the left ventricle is circular The right ventricle wraps around the left and is crescent shaped The left can generate much more pressure than the right and is a far more powerful pump Left ventricle Pathway of Blood: System Blood flows through the heart and other parts of the circulatory system in one direction – Right atrium right ventricle pulmonary arteries lungs – Lungs pulmonary veins left atrium left ventricle body This one way flow of blood is controlled by four heart valves Heart Valves Heart valves are positioned between the atria and the ventricles and between the ventricles and the large arteries that leave the heart Valves open and close in response to differences in blood pressure Tricuspid valve Bicuspid (mitral) valve Aortic valve Pulmonary valve Atrioventricular (AV) Valves The AV valves are located at each atrial-ventricular junction The valves are positioned to prevent a backflow of blood into the atria when the ventricles are contracting The valves are the – Tricuspid valve – Bicuspid valve Tricuspid valve Bicuspid (mitral) valve Atrioventricular (AV) Valves The right AV valve, the tricuspid, has three flexible cusps The left AV valve, the bicuspid, has two flexible cusps The cusps are flaps of endocardium reinforced by connective tissue Tricuspid valve Bicuspid (mitral) valve Atrioventricular (AV) Valves Attached to each of the AV valve flaps are tiny collagen cords called chordae tendoneae The cords anchor the cusps to the papillary muscles protruding from the ventricular walls Papillary muscles Chordae tendoneae Atrioventricular (AV) Valves When the heart is completed relaxed, the AV valve flaps hang limply into the ventricular chambers Blood flows into the atria and then through the open AV valves into the ventricles Papillary muscles Chordae tendoneae Atrioventricular (AV) Valves When the ventricles begin to contract, compressing the blood in the chambers, intraventricular pressure rises forcing blood superiorly against the valve flaps The chordae tendoneae and the papillary muscles anchor the flaps in their closed Papillary muscles position Chordae tendoneae Semilunar (SL) Valves The aortic and pulmonary semilunar valves are located at the bases of the large arteries exiting the ventricles The valves prevent backflow of blood from the aorta and pulmonary trunk into the associated ventricles Aortic valve Pulmonary valve Semilunar (SL) Valves Each semilunar valve is made up of three pocketlike cusps Their mechanism of closure differs from that of the AV valves When the ventricles contract intraventricular pressure exceeds the blood pressure in the aorta and pulmonary trunk Aortic valve Pulmonary valve Semilunar (SL) Valves Blood pressure from the ventricle forces the semilunar valves open and blood is forced past the valve and into the artery When the ventricles relax, and the blood flows backward toward the heart it fills the cusps which closes the valves Aortic valve Pulmonary valve Coronary Circulation The coronary circulation, the functional blood supply of the heart, is the shortest circulation in the body The arterial supply of the coronary circulation is provided by the right and left coronary arteries Coronary Circulation The left coronary artery runs toward the left side of the heart and then divides into its major branches Anterior interventricular artery follows the sulcus and supplies blood to the interventricular septum and walls of ventricle Coronary Circulation The right coronary artery courses to the right side of the heart where it divides The marginal artery serves the myocardium of the lateral part of the right side of the heart The posterior interventricular artery runs to the apex of the heart Coronary Circulation There are many merging blood vessels that delivery blood to the heart muscle This explains how the heart can receive an adequate supply when one of its coronary arteries is almost entirely occluded Coronary Circulation The coronary arteries provide an intermittent pulsating flow to the myocardium These vessels and their main branches lie in the epicardium and send branches inward to nourish the myocardium Although the heart represents only about 1/200 of body weight, it requires 1/20 of the body’s blood supply The left ventricle receives the largest proportion of the blood supply Coronary Circulation After passing through the myocardium, the venous blood is collected by the cardiac veins The veins join together to form an enlarged vessel called the coronary sinus which empties into the right atrium End of Material Chapter 19 Blood Supply to the Heart: Coronary Circulation Properties of Cardiac Muscle Fibers Microscopic Anatomy Energy Requirements Mechanism and Events of Contraction Heart Physiology Developmental Aspects of the Heart