Human Anatomy and Physiology - The Cardiac System PDF

Human Anatomy and Physiology The Cardiac System This slide deck contains animations. Please disable animations if they cause issues with your device. Copyright ©2021 John Wiley & Sons, Inc. Learning Objectives 1. Describe the structure of th...

Human Anatomy and Physiology The Cardiac System This slide deck contains animations. Please disable animations if they cause issues with your device. Copyright ©2021 John Wiley & Sons, Inc. Learning Objectives 1. Describe the structure of the heart. 2. List the arteries that supply blood to the heart muscle. 3. Describe the electrical excitation of the heart. 4. Describe the cardiac action potential. 5. Discuss the cardiac cycle. Cardiovascular System - Heart Cardiovascular System = Blood + Blood Vessels + Heart Heart: center of cardiovascular system ✓ Weighs of 250 to 390 g in men, 200 to 275 g in women (about the size of a closed fist) Heart Location Located in the mediastinum (the medial cavity of the thorax) Lies medially between two lungs and pleural membranes that cover them The base of the heart is tipped up medially and posteriorly, while the apex project inferiorly and laterally. Covering of the Heart – The Pericardium Pericardium: sac surrounding the heart, helps hold it in place. Is a double-walled sac around the heart composed of: 1. Outer fibrous pericardium 2. Inner serous pericardium = parietal layer (outer) + visceral layer (inner, called epicardium) 3. Space between the parietal and visceral Membranes called pericardial cavity (filled with pericardial fluid) Pericarditis: inflammation of the pericardium  Layers of the Heart Wall 1. Epicardium(outer layer): visceral layer of pericardium 2. Myocardium (middle layer): cardiac muscle. Circular and Spiral Arrangement of Cardiac Muscle Bundles. Fibrous skeleton of the heart : crisscrossing, interlacing layer of connective tissue 3. Endocardium (Inner layer) – endothelial layer of the innermost layer of heart wall The Fibrous Skeleton of the Heart Why dose the heart has fibrous skeleton (functions)? 1. Forms the foundation for which the heart valves attach 2. Serves as a point of insertion for cardiac muscle bundles 3. Prevents overstretching of the heart valves 4. Acts as an electrical insulator Chambers of the Heart (2 Atria = Receiving) Two upper Atria (Right Atrium and Left Atrium) separated by interatrial septum Atrial walls are thin; only have to push the blood into the ventricles Each atrium has an auricle (pouched-like extension), for increased volume. FT Chambers of the Heart (2 Atria = Receiving) Walls are ridged by pectinate muscles (are parallel ridges in the walls of the atria of the heart) (found more in the right atria) Vessels entering right atrium: 1. Superior vena cava 2. Inferior vena cava 3. Coronary sinus Vessels entering left atrium: 1. Right pulmonary veins 2. Left pulmonary veins Chambers of the Heart (2 Ventricles = Discharging) Two lower ventricles (Right Ventricle and Left Ventricle) separated by interventricular septum. Ventricular walls are thicker than atrial walls; pump blood further. RV: pumps blood into the pulmonary circulation (low pressure, short circulation). LV: plumbs blood into the systematic circulation (high pressure, long circulation) LV wall is 2-4 times as thicker than the wall of RV. Chambers of the Heart (2 Ventricles = Discharging) Walls are ridged by trabeculae carneae (are rounded or irregular muscular columns which project from the inner surface of the right and left ventricles of the heart) Vessel leaving the right ventricle: Pulmonary trunk → lung Vessel leaving the left ventricle: Aorta → all body Note that the wall of the left ventricle is much thicker than that of the right ventricle – WHY?  Chambers of the Heart (Atria & Ventricles) Walls and grooves that separate heart chambers are; ✓ Two atria: Separated internally by the interatrial septum The coronary sulcus (atrioventricular groove) encircles the junction of the atria and ventricles Auricles increase the atrial volume ✓ Two ventricles: Separated by the interventricular septum Anterior and posterior interventricular sulci mark the position of the septum externally Heart Valves Valves are made of dense connective tissue, covered by endothelium Valves prevent the back flow of the blood into the heart (one-way blood flow) 1. Atrioventricular valves (AV): - Tricuspid valve: Between RA & LV (3 “flaps” or cusps) - Bicuspid valve (mitral valve): Between LA & LV ( 2 cusps) 2. Semilunar valves (SV) (3 “flaps” or cusps): - Pulmonary semilunar valve: Between RV & pulmonary trunk - Aortic semilunar valve: Between LV & aorta  Heart Valves How dose the valves open and close to direct the blood flow? 1. Chordae Tendineae: tiny “tendons” which keep the “flaps” of these valves pointing in the direction of the blood flow. 2. Papillary Muscles: “PULL” on the chordae tendinea when the ventricle contract Relax when the ventricular pressure is low (empty ventricle) How do Heart Valves work? https://youtu.be/UbmI2Yo4NIo?si=GlRoohS7cEXutTbT Blood Flow: Systemic Circulation The heart is two side-by-side pumps: Right side is the pump for the pulmonary circuit Vessels that carry blood to and from the heart Superior & Inferior vena cava, pulmonary arteries Left side is the pump for the systemic circuit Vessels that carry the blood from heart to all body tissues Pulmonary veins, Aorta Blood Flow: Pulmonary Circulation “Equal volumes of blood are pumped to the pulmonary and systemic circuits” Pulmonary circuit is a short, low-pressure circulation Systemic circuit blood encounters high pressure circulation and long pathways Anatomy of the ventricles reflects these differences (Left side is thicker than the Right side) Overview of Blood Flow Systemic and Pulmonary Circulation Heart Blood Supply (Coronary Circulation) The heart itself requires nutrients, oxygen & waste removal Right & left arteries and their branches Branched off from ascending aorta Carry oxygenated blood to heart’s myocardium Coronary sinus (veins) Drains deoxygenated blood drains into the RA Coronary Circulation The right and left coronary arteries arise from the base of the aorta. The left coronary artery divides into two branches: 1. The anterior interventricular (know as left anterior descending artery) – (wall of both ventricles) 2. The circumflex artery (left ventricle and left atrium) The right coronary artery divides into: 1. The right marginal artery (right ventricle) 2. The posterior interventricular artery, anastomose with the anterior interventricular artery Coronary Circulation Venous blood is collected by the coronary veins join to form the coronary sinus (empties into the right atrium) The sinus has 3 large tributaries: 1. The great cardiac vein (anterior interventricular sulcus) 2. The middle cardiac vein (post. interventricular sulcus) 3. The small cardiac vein (right inferior margin) Histology of the Cardiac Muscle Tissue  Cardiac muscle cells are striated, short, fat, branched, and interconnected  Intercalated discs: junctions between cells anchor cardiac cells : 1. Desmosomes 2. Gap junctions  The intercalated discs connect cardiac muscle fibers into a functional syncytium Attachment between cardiac cells Holds fibers together Coordinate contraction: Allow muscles Aps to conduct from one fiber to the next Autorhythmic Fibers (The Conduction System) The activity of the heart is independent but coordinated – this results from: 1. The presence of gap junctions 2. The heart’s “in-house” conducting system. The intrinsic cardiac conduction system is the noncontractile cardiac cells specialized that make the atria & ventricles contract in appropriate sequence (forming 1% of the cardiac fibers) Components of the conduction system: 1. Sinoatrial node (SA): Pacemaker 2. Atrioventricular node (AV) 3. Atrioventricular (AV) bundle: bundle of His 4. R & L bundle branches 5. Purkinje fibers (subendocardial) : conduction myofibers  Autorhythmic Fibers: The Conduction System Action potential initiation by pacemaker cells that are found in the sinoatrial and atrioventricular nodes FT  Action Potential and Contraction of Contractile Fibers Action potential initiation by contractile cardio myofiber cells.  Electrocardiogram (ECG) Electrocardiogram (ECG or EKG): a composite of all the action potentials generated by nodal and contractile cells at a given time Normal EKG has 3 waves: 1. P wave: atrial depolarization of SA node (0.1 sec) → atria contract 2. QRS complex: ventricular depolarization → ventricles contract 3. T wave: ventricular repolarization → ventricles relax Atrial repolarization record is masked by the larger QRS complex Action Potential Propagation Through the Heart Modifying the Basic Rhythm: Extrinsic Innervation of the Heart Sympathetic: all parts of the heart including SA and AV nodes, conducting system, and the ventricles. Acts to: Increase heart rate and conduction. Increase the force of contraction. Parasympathetic (via vagus) restricted to atria (SA and AV nodes). Decreased HR and conduction The Cardiac Cycle (the mechanical events) Systole - contraction Diastole - relaxation Cardiac Cycle = Single heartbeat Systole of atria occurs simulants with diastole of ventricles Diastole of atria occurs simultaneously with systole of ventricles  The Cardiac Cycle (the mechanical events) EDV (End diastolic volume) amount of blood that collects in a ventricle during diastole “relax”. ESV (End systolic volume) is the volume of blood remaining in the ventricle after it has contracted. FT The Cardiac Cycle (the mechanical events) Now that you understand the pressure changes, let’s look at how they correspond to the electrical events and volume changes in the heart. Heart Sounds Two sounds (lub-dup) associated with closing of heart valves ✓1st heart sound = Lub Closing of AV valves (end of ventricular filling) ✓2nd heart sound = Dup Closing of SL valves (begging of ventricular diastole) Heart murmurs: abnormal heart sounds most often indicative of valve problems What is Cardiac Output (CO)? CO is the volume of blood ejected from the left or right ventricle into the aorta or pulmonary trunk per minute CO = heart rate (HR) x stroke volume (SV) Must know HR = number of beats per minute SV = volume of blood pumped out by one ventricle with each beat (measure of contractility) Example CO (ml/min) = HR (75 beats/min) x SV (70 ml/beat) CO = 5250 ml/min (5.25 L/min) Regulation of Stroke Volume SV = EDV – ESV Must know Factors affecting SV (by altering EDV or ESV): EDV is determined by: 1. Preload: degree of stretch of heart muscle before it contracts 1. How long ventricular diastole last 2. Contractility: the contractile strength 2. Venous pressure achieved at a given muscle length ESV is determined by: 3. Afterload: Back pressure exerted by Arterial blood pressure arterial blood Force of ventricular contraction Example (at rest): SV = EDV – ESV = EDV (End diastolic volume) amount of blood that collects in a ventricle during diastole “relax”. 120 ml/beat – 50 ml/beat = 70 ml/beat ESV (End systolic volume) is the volume of blood remaining in the ventricle after it has contracted. PRELOAD: “Frank-Starling Law” The relationship between stroke volume and preload is called: Frank-Starling law of the heart Increased venous return distends (stretches) the ventricles and increases contraction ---- increase Stroke Volume Thus, maintaining the equality of right and left cardiac outputs Exercise and the Heart Regulation of Heart Rate Autonomic Nervous System (ANS) Regulation of the heart originates in the cardiovascular (CV) center. Inputs from Proprioceptors, Chemoreceptors, Baroreceptors Chemical Regulation Hormones – Epinephrine, Norepinephrine, and Thyroid hormones Cations like Na+, K+, and Ca2+ (hyper, hypocalcemia and hyper and hypokalemia) have a large effect n the heart Other factors age, gender, exercise and body temperature influence HR