Anatomy of the Heart 1 Kirsten Bazemore 2 2 Circuits Pulmonary Heart lungs heart Systemic Heart body heart 3 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 body tissues The heart=a muscular double pump with 2 functions 4 Arteries Carry blood away from heart Except pulmonary arteries (carries deoxygenated blood) Veins Carry blood to heart Except pulmonary veins (carries oxygenated blood) 5 simplified Cone shaped muscle Four chambers Two atria, two ventricles Double pump the ventricles Two circulations Systemic circuit: blood vessels that transport blood to and from all the body tissues Pulmonary circuit: blood vessels that carry blood to and from the lungs 6 Heart s position in thorax 7 In mediastinum behind sternum and pointing left, lying on the diaphragm It weighs gm (about 1 pound) Feel your heart beat at apex (this is of a person lying down) 8 Coverings of the Heart Fibrous PericardiumVisceral Layer Parietal Layer 9 Layers of the Heart PericardiumMyocardiumEndocardium 10 Pericardium (double-walled sac) Protects against infection Provides lubrication to the heart Fixes the heat to the medicstinum Myocardium Middle layer Contains many capillaries & nerve endings Has cardiac muscle forming the bulk of the heart thickest layer Layer that contracts Endocardium Has an endothelial layer that lines the heart chambers Contains Perkinje fibers (specialized nerve fibers used during the heart beat) 11 12 How Pericardium is Formed Around the Heart Pericardial Cavity Between the parietal and visceral layer of the serous pericardium Contains serous fluid lubricates membranes to reduce friction *Pericarditis : inflammation of the pericardium that roughens the serous membrane surface 13 The Heart is enclosed within a double-walled sac called the pericardium. Consists of 2 layers Fibrous pericardium Serous pericardium Fibrous pericardium: Composed of dense connective tissue (protects the heart) Anchors to surrounding walls Prevents the heart from overfilling with blood Serous pericardium Located deep to fibrous pericardium Contains 2 layers function to lubricate the heart to prevent friction during activity 14 Heart Chambers There are 4 chambers in the heart 2 superior ventricles 2 inferior atria Atriums known as the receiving chamber Ventricle s known as the discharging chambers 15 Chambers of the heart sides are labeled in reference to the patient facing you Two atria Right atrium Left atrium Two ventricles Right ventricle Left ventricle 17 Chambers of the heart divided by septae: Two atria-divided by interatrial septum Right atrium Left atrium Two ventricles-divided by interrventricular septum Right ventricle Left ventricle Relative thickness of muscular walls LV thicker than RV because it forces blood out against more resistance; the systemic circulation is much longer than the pulmonary circulation Atria are thin because ventricular filling is done by gravity, requiring little atrial effort 18 Auricle Pectinate muscles +Fossa ovalis +Foramen ovale Atria 19 The Fossa Ovalis is an embryonic remnant of the foramen ovale, which normally closes after birth. Following birth, the foramen ovale is covered by a fibrous sheet. Failure of the foramen ovale to close results in a disorder called patent foramen ovale. 20 Trabecular carneae Chordae tendineae Papillary muscles Ventricles 21 22 23 Heart Valves: Atrioventricular (AV) Valves Prevent backflow into the atria when the ventricles contract Both valves contains 3 cusps Tricuspid valve (right AV valve) has 3 flexible cusps Mitral valve (left AV valve) has 2 cusps a.k.a. bicuspid valve 24 Function of the AV Valves 25 Heart Valves: Semilunar (AV) Valves Prevent backflow into associated ventricles Aortic valve protects the orifice between the left ventricle and the aorta Pulmonary valve guards the orifice between the right ventricle and the pulmonary artery 26 Function of the Semilunar Valves 27 Homeostatic Imbalance of Heart Valves Heart valves can function with leaky valves as long as the impairment is not too severe. Severe valve deformities can seriously hamper cardiac function. Problems with Valves: An incompetent valve forces the hear to pump the same blood over and over because the valve does not close properly. When stenosis occurs, the valve flaps become stiff and constrict the opening heart contracts more than normal In both conditions, the hearts workload increases weakens the heart overtime Treatment: Heart valve is replaced with: Mechanical Heart Pig or cow valve (chemically treated to reduce rejection) Cyroperserved valves from human cadavers 28 Blood Return to R-atrium Superior vena cava (SVC)Inferior vena cava (IVC)Coronary sinus (CS) Pathway of Blood Through the Heart 30 Pathway of Blood (cont.) Superior vena cava, Inferior vena cava, Coronary sinus Right Atrium Right Ventricl e Rest of the Body Left Atrium Lungs Aorta Pulmonary Artery & Trunk Left Ventricle Tricuspid valve Pulmonary Semilunar valve 4 pulmonary veins Mitral Valve Aortic Semilunar valve 31 Coronary Artery Circulation Even though the heart is filled with blood, the blood provides little nourishment to the heart (the myocardium tissue is too thick). Blood is supplied to the heart via Coronary Circulation which is the shortest circulation in the body. 32 Branching of Coronary Arteries Right Coronary Artery (RCA) Branches into: Right marginal artery Posterior descending artery Supplies: Right atrium Bottom portion of both ventricles and back of septum Together the RCA and its branches supply the R. Atrium and nearly all the ventricles. Left Coronary Artery (Left Main Trunk) Branches into: Circumflex artery Anterior interventricular artery Supplies: Circumflex Artery: left atrium, side and back of the left ventricle Anterior interventricular artery: front and bottom of the left ventricle and front of the septum 33 *What happens when a coronary artery is blocked? Angina Pectoris Myocardial Infarction (MI) 34 Homeostatic Imbalance of Coronary Blood Flow Partial blockade Decreased blood flow ischemia angina Treatment:???? Complete blockade No blood flow myocardial infarction Treatment: ????? 35 Therapeutic Relevance Medical management Percutaneous coronary intervention (PCI) Surgery (CABG) Cardiac Muscle Cell Characteristics Striated Involuntary control Short, fat branched, and interconnected One to two large, centrally located nuclei 37 Adjacent cardiac cells interlock at intercalated discs Desmosomes (prevents cell separation during contraction) Gap junctions (allow cells to chemically communicate) Mitochondria account for 25-35% of volume of cardiac cells highly resistant to fatigue Cardiac Muscle Cell 38 39 Cardiac Muscle Cell T-Tubules Transverse to the surface Increases surface area Allows Extracellular Ca 2+ ions to cross the membrane into the cell Sarcoplasmic Reticulum Contains a supply of Ca 2+ ions Extracellular Ca 2+ binds to its receptors --> SR releases its own Ca 2+ ions (Extracellular Ca 2+ SR Ca 2+ ) 40 Sarcomere Sarcomere : smallest contractile unit of a muscle (the region between two Z-lines) Thick filament = Myosin Thin filament = Actin A band = length of the myosin filament Distance between Z line and H zone = length of actin filament Length of actin and myosin filament does not change during contraction 41 Unique Characteristic of the Heart Some cardiac fibers are auto-rhythmic. These fibers have the ability to depolarize spontaneously and pace the heart. The bulk of the heart consists of contractile muscle cells that are responsible for the hearts pumping activity. All cells of the heart MUST contract as a unit or the heart doesnt contract at all. Gap junctions electrically tie all cardiac muscle together into a single contractile unit. 42 QUESTIONS? 43 Physiology of the Heart 44 Kirsten Bazemore Types of Cardiac Muscle Cells 45 Contractile Cells 99% of cardiac muscle cells Do mechanical work of pumping Normally do not produce action potentials Autorhythmic Cells 1% or cardiac muscle cell Do not contract Generate and conduct action potentials Unstable membrane potential (never rests, continues depolarization) 46 Action Potential of Contractile Cells 47 Contraction in Contractile Cells Transmission of depolarization from Na + ions channels Cross Bridge Formation. Energized myosin head attached to an action myofilament, forming a cross bridge. 2. The power (working stroke). ADP and P i are released and the myosin head pivots and bends, changing to its bent low-energy state. As a result it pulls the action filament toward the M line Cross bridge detachment. After ATP attaches to myosin, the link between myosin and actin weakens, and the myosin head detaches (the cross bridge breaks) Cocking of the myosin head. As the ATP is hydrolyzed to ADP and P i, the myosin head returns to its prestroke high-energy, or cocked, position. *This cycle will continue as long as ATP is available and Ca 2+ is bound to troponin. 49 Contraction in Contractile Cells Intrinsic Cardiac Conduction System (autorhythmic cells) 50 The intrinsic cardiac conduction system consist of noncontractile cardiac cells specialized to initiate and distribute impulses throughout the heart, so that is depolarizes and contracts in an orderly, sequential manner. Action Potentials of Pacemaker Cells Where Are Pacemaker Cells Found? 51 52 Sequence of Excitation Pacemaker Cells 1. SA Node Generates ~75 times/min Sets pace for the heart Faster depolarization rate (considered hearts pacemaker) It rhythm, sinus rhythm, determines the heart rate 2. AV Node Delays impulse for 0.1 s to allow the atria to respond and complete their contraction before the ventricles contract 3./4. AV Bundle/ Bundle brances Since the atria and ventricles are not connected by gap junctions, the AV bundle is the only electrical connection between them The bundles branches into 2 directions along the interventricular septum toward the apex 53 5. Subendocardinal Conducting Network also called Purkinje fibers Excites the septal cells More elaborate on the left ventricle since it is much larger than the right side of the heart *Slower pacemakers can dominate when the faster pacemakers stop functioning. Homeostatic Imbalance Arrhythmias Uncoordinated atrial and ventricular contractions Fibrillations Heart block Sequence of Excitation Pacemaker Cells 54 Electrocardiography (EKG/ECG) Electrocardiogram (EKG ) Recording of heart electrical activities Electrocardiograph Device that records electrical current of heart 55 Sequence of EKG Events 56 Whats wrong with the EKG? Elevated ST wave 57 58 The Cardiac Cycle Systole Emptying of ventricles Diastole Filling of ventricles The heart undergoes some dramatic writhing movements as it alternately contracts, forcing blood out of its chambers, and then relaxes, allowing its chambers to refill with blood. Heart Sounds Lub Closing of AV valves Dub Closing of SL valves 60 Cardiac Output (CO) Cardiac output (C) is the amount of blood that is pumped out by each ventricle is 1 minute. The equation to calculate CO is shown below. CO = HR X SV The average adult cardiac output is ~ 5 mL. (equation shown below using the normal resting values for HR and SV) 61 Cardiac Output (CO) Cardiac output (C) is the amount of blood that is pumped out by each ventricle is 1 minute. The equation to calculate CO is shown below. CO = HR X SV The average adult cardiac output is ~ 5 mL. (equation shown below using the normal resting values for HR and SV) 62 Cardiac Output (CO) Cardiac output is highly variable and increases markedly in response to special demands. Homeostatic Imbalance of Heart Rate 63 Tachycardia : an abnormally fast heart rate (more than 100 beats/min) that may result from elevated body temperature, stress, certain drugs, or heart disease. Persistent tachycardia is considered pathological because tachycardia occasionally promotes fibrillation. Bradycardia : a heart rate slower than 60 beats/min. It may result from low body temperature, certain drugs, or parasympathetic nervous activation. In poorly conditioned people, persistent bradycardia may result in grossly inadequate blood circulation to body tissues. It is a known, and desirable, consequence of endurance training. With physical and cardiovascular conditioning, the heart hypertrophies and SV increases, allowing a lower resting heart rate while still providing the same cardiac output. 64 Stroke volume (SV) represents the difference between end diastolic volume (EDV), the amount of blood that collects in a ventricle during diastole, and end systolic volume (ESV), the volume of blood remaining in a ventricle after it has contracted. Formula for Stroke volume: Although many factors affect SV by altering EDV or ESV, the three most important are preload (EDV), contractility, and afterload (ESV). Preload & Afterload Preload Amount of blood returning to RA the load, or stretch, put on the ventricle by the amount of entering blood volume. The ventricle will tolerate only so much volume before the ventricle is stretched too far and thus reduces stroke volume. Afterload Force against which ventricles have to pump to eject blood one can still have a normal cardiac function but have an afterload that negatively affects stroke volume Therapeutic Significance Preload reducers Venodilators (nitroglycerin) Cause peripheral edema, HA (headache) Afterload reducers Arterial vasodilators (hydralazine) cause Reflex tachycardia Homeostatic Imbalance of Cardiac Output 67 In congestive heart failure (CHF), the heart is such an inefficient pump that blood circulation is inadequate to meet tissue needs. The disorder reflects weakening of the myocardium. Certain conditions that the myocardium include: Coronary atherosclerosis Multiple myocardial infarctions Dilated cardiomyopathy (DCM) In peripheral congestion the right side of the heart fails stagnate blood in body organs and pooled fluid in tissue impair cells due to a lack on nutrients. Failure on one side can lead to heart failure and the heart become irreparable. Treatment: use diuretics, reduce afterload (reduce pressure), heart transplants QUESTIONS? 68 Additional Help Contact Info: Layers of the Heart: https://www.khanacademy.org/science/health-and- medicine/circulatory-system/circulatory-system-introduction/v/layers-of-the-hearthttps://www.khanacademy.org/science/health-and- medicine/circulatory-system/circulatory-system-introduction/v/layers-of-the-heart Flow of blood : https://www.youtube.com/watch?v=7XaftdE_h60https://www.youtube.com/watch?v=7XaftdE_h60 Normal sinus rhythm of EKG : https://www.youtube.com/watch?v=lRHq7sMRWpUhttps://www.youtube.com/watch?v=lRHq7sMRWpU Heart cells/Heart contraction: https://www.youtube.com/watch?v=__afuK1CMpQ https://www.youtube.com/watch?v=__afuK1CMpQ 69