SBM2 Cardiovascular System 1 PDF

SBM2 Cardiovascul ar System 1 DR. JENNIFER RAYBURN MTSU PHYSICIAN ASSISTANT STUDIES  Objectives Illustrate Illustrate the ordered flow of blood through the circulatory system. Inventory Inventory the anatomic structures of the heart wall, chambers, and valv...

SBM2 Cardiovascul ar System 1 DR. JENNIFER RAYBURN MTSU PHYSICIAN ASSISTANT STUDIES  Objectives Illustrate Illustrate the ordered flow of blood through the circulatory system. Inventory Inventory the anatomic structures of the heart wall, chambers, and valves. Distinguish the anatomy and function of the great vessels: vena cava, pulmonary arteries, Distinguish and veins, and aorta. Debate Debate the anatomy and function of the coronary vessels. Relate Relate the anatomy and function of the cardiac conduction system. Distinguish the mechanisms that cause the generation and conduction of action potentials in Distinguish cardiac tissue. Interpret Interpret the waves of a basic ECG Apply Apply the mechanisms that cause automaticity and rhythmicity of cardiac tissue Analyze Analyze the phases and events of the cardiac cycle. Relate Relate the structure and mechanism of cardiac muscle contraction  Pulmonary and Systemic Circulation ▪ Each heartbeat pumps blood into two closed circuits: pulmonary and systemic circulations. ▪ Pulmonary circulation: blood vessels that carry blood from the right side of the heart to the alveoli (air sacs) of the lungs and then back to the left side of the heart. ▪ Systemic Circulation: blood vessels that carry blood from the left side of the heart to all organs and tissues of the body, except the alveoli, and then back to the right side of the heart. ▪ https://www.youtube.com/watch?v=NDk8fmIl9V8 (Pulmonary and Systemic Circulation; great refresher video!!)  Pulmonary and Systemic Circulation ▪ Parallel Flow: in the systemic circulation, blood flows through pathways that are parallel to each other. ▪ A given portion of blood flows through an artery to only one organ and enters only one set of capillaries before returning to the heart through a vein (same portion of blood does not flow from one organ to the next). ▪ This allows: ▪ 1. Each organ to receive its’ own freshly oxygenated blood supply ▪ 2. Allows blood to flow to different organs to be regulated independently Surface Anatomy of the Heart ▪ Heart is a hollow, cone-shaped, muscular organ about the size of a closed fist ▪ Lies mostly to the left of the midline in the thoracic cavity ▪ Heart Borders: anteriorly by sternum; lungs laterally; vertebral column posteriorly; diaphragm inferiorly ▪ Apex (tip): Tip of the L ventricle. Points inferiorly, anteriorly, and to the left ▪ Base (posterior surface): atria (mainly left atria). Lies between the lung hila ▪ Anterior surface: R atrium and R ventricle ▪ Inferior Surface: Both ventricles (mainly left). Lies along the diaphragm  Anatomy of the Heart Pericardium ▪ Pericardium: Membranous (fibroserous) sac that encloses the heart and roots of the great vessels ▪ Confines the heart to its’ position in the thoracic cavity (attaches to the sternum and mediastinal portions of the right and left pleurae) but also allows freedom of movement for vigorous and rapid contraction ▪ Two layers of pericardium: ▪ 1. Parietal layer (outer): tough fibrous coat of connective tissue that anchors the heart in place by attaching to nearby structures in the thoracic cavity ▪ 2. Visceral Layer (inner): Also called epicardium. Adheres to the surface of the heart (considered the outer layer of the heart wall) ▪ Pericardial Cavity: The space between the parietal and visceral pericardium. Filled with a thin film of lubricating fluid (pericardial fluid) that reduces friction within the pericardium as the heart moves  Anatomy of the Heart Heart Wall ▪ Three layers: ▪ 1. Epicardium: outer layer aka visceral pericardium. Consists of epithelium and connective tissue ▪ 2. Myocardium: Forms the bulk of the heart wall. Consists of cardiac muscle that provides the pumping action of the heart. ▪ 3. Endocardium: thin layer of epithelium that lines the chambers of the heart and covers the heart valves (also continuous with the epithelial cells that line the blood vessels attached to the heart).  Heart Anatomy Heart Chambers ▪ Four Chambers of the Heart: Two atria (R&L) and Two Ventricles (R&L) ▪ R side heart serves as the pump for the pulmonary circulation ▪ L side heart serves as the pump for the systemic circulation ▪ The heart is two separate pumps located within the same organ (separated by a septum) ▪ Atria have thin walls (deliver blood under less pressure) ▪ Ventricles have thick walls (deliver blood under higher pressure; especially the L ventricle)  Heart Anatomy Heart Valves ▪ Four Heart Valves (prevent backward flow of blood in the heart ensuring one-way flow of blood) – composed of connective tissue covered by endocardium ▪ Valves open and close due to pressure changes as the heart contracts and relaxes ▪ Two Atrioventricular valves (AV ): (lie between the atria and ventricles) ▪ 1. Tricuspid valve (TV): Lies between the R atria and R ventricle. Has three cusps (flaps) ▪ 2. Mitral valve (MV) aka bicuspid valve: Lies between the L atria and L ventricle. Has two cusps (flaps) ▪ Two Semilunar Valves: (lie between ventricle and vessel) ▪ 1. Pulmonary Valve (PV): Lies between the R ventricle and pulmonary trunk. Has three cusps ▪ 2. Aortic valve (AV): Lies between the left ventricle and aorta. Has three cusps  Heart Anatomy Great Vessels ▪ Superior Vena Cava (SVC): receives deoxygenated blood and returns it to the right atrium from the upper parts of the body above the heart ▪ Inferior Vena Cava (IVC): receives deoxygenated blood and returns it to the right atrium from the lower parts of the body below the heart ▪ Pulmonary Trunk: takes deoxygenated blood from the right ventricle to the lungs. Divides into the left and right pulmonary arteries ▪ Pulmonary Veins: carry oxygenated blood from the lungs to the left atrium of the heart (have four) ▪ Aorta: carries oxygenated blood from the left ventricle to all parts of the body except the alveoli  Coronary (Cardiac) Circulation ▪ The heart wall has its’ own circulation called the coronary circulation to supply nutrients through all layers of the heart wall. ▪ Coronary Arteries: branch from the root of the aorta just above the aortic valve cusps & encircles the heart like a crown ▪ Left Main Coronary artery: passes between the left atrium and pulmonary trunk to reach the AV groove. It divides into the left anterior descending (LAD) and the left circumflex arteries ▪ Right Coronary Artery (RCA): Supplies blood to the right ventricle via acute marginal branches. Gives off the posterior descending artery that supplies the inferior and posterior walls of the ventricles and one-third of the interventricular septum. Also gives off the AV nodal artery. Most of the time also supplies the SA node Blood Flow Through The Heart https://www.youtube.com/watch?v=DNNFA0-fozE (The Heart and Systemic Circuit)  Cardiac Muscle Fibers ▪ Cardiac muscle fibers: ▪ 1. Shorter in length & smaller in diameter than skeletal muscle fibers ▪ 2. They branch (stair step appearance) ▪ 3. Striated like skeletal muscle (thick and thin filaments with regular pattern of overlap ▪ 4. Thick filaments (myosin) & thin filaments (actin, troponin & tropomyosin) ▪ 5. Ends connected to each other by intercalated discs (contain desmosomes & gap junctions) unlike skeletal muscle ▪ 6. Act as a Functional Syncytium ▪ 7. Mitochondria are larger and more numerous than in skeletal muscle ( means cardiac muscle depends largely on aerobic respiration) Cardiac Conduction System ▪ Autorhythmicity: Cardiac muscle does not require external stimulation to contract. Contractions occur because action potentials within cardiac muscle itself are spontaneously generated on a periodic basis. ▪ Cardiac muscle (as a functional syncytium) has two types of muscle fibers: ▪ 1. Autorhythmic Fibers (pacemaker cells): small in number and grouped together. Spontaneously generate action potentials. Unable to contract. ▪ 2. Contractile Fibers: great majority of cardiac muscle fibers. Contract but do not generate action potentials. ▪ Autorhythmic Fibers include: 1. Sinoatrial Node (SA Node): wall of R atrium close to opening of the superior vena cava 2. Atrioventricular Node (AV Node): in the interatrial septum 3. Atrioventricular Bundle (Bundle of His): upper part of the interventricular septum 4. Right and Left Bundle branches: in the interventricular septum 5. Purkinje Fibers: in the ventricular wall  Cardiac Conduction System Autorhythmic Fibers ▪ Autorhythmic Fibers can initiate their own action potentials because the have unstable resting membrane potentials. ▪ The membrane potential starts at about -60mV and then spontaneously depolarizes to threshold (-40mV), at which point the action potential is generated. ▪ Pacemaker Potential: is the spontaneous depolarization to threshold that occurs in an autorhythmic fiber of the cardiac muscle Cardiac Conduction System Autorhythmic Fibers  Cardiac Conduction System Contractile Fibers ▪ Contractile Cardiac Muscle Fibers: Have a stable resting membrane potential of about -90mV. Resting contractile fibers are highly permeable to K+ and not very permeable to other ions. ▪ Once a cardiac muscle fiber is depolarized to threshold by an action potential from an autorhythmic fiber, the cardiac muscle fiber generates its’ own action potential. ▪ Four Phases of Contractile Muscle Fiber Action Potentials: ▪ 1. Depolarizing phase ▪ 2. Initial repolarizing phase ▪ 3. Plateau phase ▪ 4. Final Repolarizing phase  Cardiac Conduction System Contractile Fibers  Cardiac Conduction System The Electrocardiogram ▪ As action potentials propagate through the heart, they generate electrical currents that can be detected on the surface of the body. ▪ Electrocardiogram (ECG or EKG) is a recording of these electrical signals. It is a composite record of action potentials produced by all of the heart muscle fibers during each heartbeat. ▪ Three waves of the ECG (in order of appearance): ▪ 1. P wave: small upward deflection that represents atrial depolarization ▪ 2. QRS complex: begins as a downward deflection & continues as a large, upright, triangular wave and ends as a downward wave that represents ventricular depolarization ▪ 3. T wave: dome shaped upward deflection that represents ventricular repolarization ▪ Where is atrial repolarization? It gets buried in the QRS complex ▪ Intervals or segments of ECG: time spans between waves ▪ 1. P-R interval (P-Q): From the beginning of the P wave to the beginning of the QRS complex; represents conduction time between beginning of atrial excitation to the beginning of ventricular excitation (AV Node delay). Normal is between 120-200 ms. ▪ 2. S-T segment: end of the S wave to the beginning of the T wave; time when ventricular contractile fibers are depolarized during the plateau phase of the action potential (depolarized state of ventricular muscle). ▪ 3. Q-T interval: Start of QRS complex to the end of the T wave; time from the beginning of Phases of Cardiac Conduction on the ECG ▪ Systole: Phase of contraction ▪ Diastole: Phase of relaxation ▪ The ECG waves predict the timing of atrial and ventricular systole and diastole.  The Cardiac Cycle Passive Isovolumetric Isovolumetric Ventricular Ventricular Atrial Ventricular Ventricular Ejection Filling Contracti Contraction Relaxation on  The Cardiac Cycle https://www.youtube.com/watch?v=IS9TD9fHFv0 (cardiac cycle) ▪ Two Major Heart Sounds heard during a cardiac cycle: ▪ 1. First Sound S1 (lub): louder and a bit longer than S2. Caused by vibrations associated with closure of the AV valves (tricuspid and mitral) soon after ventricular systole begins ▪ 2. Second Sound S2 (dub): shorter and not as loud. Caused by vibrations associated with closure of the semilunar valves (aortic and pulmonic) at the beginning of ventricular diastole  Definitions ▪ End-Diastolic Volume (EDV): Amount of blood each ventricle contains at the end of diastole ( approx. 130mL) ▪ End-Systolic Volume (ESV): Amount of blood in each ventricle at the end of systole (approx. 60mL) ▪ Stroke Volume (SV): Volume of blood ejected per beat from each ventricle (approx. 70 mL) SV=EDV-ESV ▪ Ejection Fraction (EF): The percentage of the end-diastolic volume that is ejected with each stroke volume EF= (SV/EDV) x 100 *changes in stroke volume alter the ejection fraction Questions???