L1 Introduction To Cardiac Physiology PDF

Introduction By Prof. Amr Medhat Abbas Professor of Medical Physiology  Learning outcomes: At the end of the lecture, you will be able to: 1. Describe the structure of the circulatory system. 2. Describe the systemic and pulmonary circulations. 3. Describe the physiolog...

Introduction By Prof. Amr Medhat Abbas Professor of Medical Physiology  Learning outcomes: At the end of the lecture, you will be able to: 1. Describe the structure of the circulatory system. 2. Describe the systemic and pulmonary circulations. 3. Describe the physiological anatomy of the heart. 4. Describe the types of cardiac muscle fibers and explain their functions. 5. Describe the types of cardiac valves and explain their functions. 6. Describe the functional histology of cardiac muscle.  The circulatory system includes: (I) Heart: - It is a hollow muscular organ which pumps blood into the blood vessels. (II) Blood vessels: 1. Elastic vessels: (Arteries): Transport blood to tissues. 2. Resistant vessels (Arterioles):  Last small branches of arterial system.  offers high resistance to blood flow to the capillaries. 3. Exchange vessels (capillaries):  They have very thin and permeable wall.  So, they allow for exchange of substances between the blood and the interstitial fluid. 4. Capacitance vessels (veins): i.Transport blood from tissues to heart. ii.Reservoir of blood.  Divisions of the circulation (1) Systemic circulation (General circulation): Left ventricle  Aorta  Arteries  arterioles  capillaries  veins  large veins (superior and inferior venae cavae)  right atrium (2) Pulmonary circulation (lesser circulation): Right ventricle  pulmonary artery  two pulmonary arteries  one supplying the right lung and the other to the left  capillaries venules  veins  four pulmonary veins  left atrium  The heart Physiological anatomy of the heart: Heart: hollow muscular organ. Site: in left side of thoracic cavity, partly behind the sternum. Size: approximately the size of a man's fist. Weight: - 320gm. - 250gm. Heart: is enclosed in a sac called pericardium.  Pericardium: Formed of two layers: 1.Parietal layer: lines the thoracic cavity. 2.Visceral layer: (epicardium). Pericardial space Present between the visceral and parietal layers. Contains small amount of fluid  lubrication for the continuous movement of the enclosed heart. Importance of pericardium: 1- prevention of sudden over distension of the heart. 2- It gives support to the heart. Layers of the cardiac muscle: 1- Endocardium: the most inner layer. 2- Myocardium: an intermediate thick muscular layer. 3- Epicardium: the most outer layer (visceral pericardium).  Types of cardiac muscle fibers: (I) Nodal fibers: 1.Sinoatrial node (SAN): - Located in: Posterior wall of right atrium, immediately beneath & medial to opening of SVC. 2.Atrioventricular node (AVN) - Located in: Right side of inter atrial septum at junction of atria and ventricles, close to opening of coronary sinus. (II) Specialized conducting fibers: The AV bundle (Bundle of His): AVN  AV bundle  divides into two branches: right and left, that run down the right & left sides of interventricular septum to apex of the heart  reflected upward along the lateral walls of ventricles to base of heart. It is the only connection between atria and ventricles. Purkinje network (Fibers): These are terminal fine branches of the bundle system. They pass through the whole thickness of both ventricles towards the epicardium. (III) contractile muscle fibers: A. Atrial muscle (Right and left atria) B. Ventricular muscle (Right and left ventricles) A. Atrial muscle (Right and left atria) Thin RA wall is thinner than LA. Right and left atria are separated by interatrial septum. Functions: a.Blood reservoirs. b.Pumping 30% of venous return into ventricles during their diastole. The remaining 70% passes from atria to ventricles without pumping.  c. Contain SAN & AVN (important for initiation & propagation of action potential). d. Contain receptors of many cardiac reflexes. e. Secrete atrial natriuretic peptide (ANP)  important in regulating ABP B. Vemtricular muscle (Right and left atria) Wall of LV is three times as thick as the RV. RV and LV are separated by interventricular septum. Function: Act as pump which ejects the blood into arteries.  Cardiac valves: Types: (1) Atria ventricular valves (AV valves): (Separate atria from ventricles). * Tricuspid valve: It communicates RA with RV. * Mitral valve (left AV valve): It communicates LA with LV (2) Semilunar valves: *Aortic valve: it communicate LV with Aorta *Pulmonary valve: It communicates RV with pulmonary artery Function of cardiac valves: (1)AV valves prevent backflow of blood from ventricles to atria during ventricular systole. (2)Semilunar valves prevent backflow of blood from aorta and pulmonary arteries to ventricles during ventricular diastole. (3)Valves allow passage of blood only in one direction inside the heart  Functional histology of cardiac muscle: - Cardiac muscle as a syncitium: There are cell membranes that separate individual muscle cells from one another. These membranes form gap junctions which allow free diffusion of ions. Action potentials travel from one cardiac muscle to another with only slight resistance. So, when one of these cells become excited, the action potential spread to all of them. Heart is composed of two syncytia: i. Atrial syncytium: the wall of the two atria. ii. Ventricular syncytium: the wall of the two ventricles. Normally, action potentials can be conducted from atrial into ventricular syncitium only by AV bundle.  References 1. Costanzo, Linda S. "BRS Physiology (Board Review Series)." (2018). 2. Ganong, William F. "Review of medical physiology." (2020).