Cardiovascular Physiology 2019-1.ppsx

Cardiovascular System Chapter 14 Objectives Learn the structure & functions of the cardiovascular system Discuss divisions of the circulatory system and the differences between the two systems Describe the path of blood flow through the heart Define & discuss blood pressure Discuss the cardiac cyc...

Cardiovascular System Chapter 14 Objectives Learn the structure & functions of the cardiovascular system Discuss divisions of the circulatory system and the differences between the two systems Describe the path of blood flow through the heart Define & discuss blood pressure Discuss the cardiac cycle (systole and diastole) Discuss what generates a pulse Objectives Discuss the origin of the heartbeat Discuss the electrical system of the heart, the role it plays in myocardial contraction & how it’s evaluated Identify the sequence of the electrical impulses of the heart Define heart rate & discuss its regulation Discuss auscultation of the heart Functions of the Cardiovascular System Maintenance of normal blood pressure within the arteries Maintenance of blood flow to tissues Maintenance of normal blood pressure within the capillaries and veins Must be able to do this at rest and during physical activity Heart Structure & Function Cone shaped, hollow muscular structure Located between the third and sixth intercostal spaces in the dog Made up of a series of chambers and valves Its function is to pump blood through the body Tissues of the Heart The heart is surrounded by a fibroserous covering = pericardial sac = pericardium Outer surface of the heart = epicardium Muscle tissuse = myocardium Inner surface of the heart = endocardium -> lines the interior walls of the heart chambers and the luminal surface of blood vessels Heart Chambers and Valves 4 chambers = left & right atria & ventricles Left & right sides of heart are separated from one another by the interatrial and interventricular septa The ventricles are separated from the atria by the left & right atrioventricular valves (AV Valves) Aortic & pulmonic (semilunar) valves prevent backflow of blood back into the ventricles when the blood is pumped out (one way valves) Circulatory Systems Cardiovascular system is divided into two circulatory systems Systemic circulation (80% blood volume) Pulmonary circulation (15% blood volume) Each has venous and arterial systems Systemic venous Pulmonary arterial Pulmonary venous Systemic arterial Systemic Arterial Circulation High-pressure system Hydrostatic pressure is required to perfuse tissues with a high resistance to blood flow Heart Kidney Brain & other tissues above heart Pulmonary Arterial & Venous & Systemic Venous Circulations Low-pressure Low resistance to blood flow High-pressures in venous systems may cause fluid to leak from the vessels and to accumulate as edema Blood Pressure (BP) = force exerted by the blood against inner walls of the blood vessels Refers to systemic arterial blood pressure (although all vessels have this force) Maintenance of normal blood pressure (arteries) allows proper tissue perfusion & prevention of edema formation (capillaries & veins) Systemic arterial blood pressure rises and falls in coordination with the cardiac cycle Diastole – pressure falls Systole - pressure rises Cardiac Cycle Contraction & relaxation of the heart occurs in a cyclic pattern in response to electrical stimuli generated by the heart’s pacemakers Cycle is divide into two parts Systole Diastole Systole Atrial & Ventricular Contraction Generation of pressure w/in heart Ejection of blood into systemic & pulmonary circulations Blood pressure rises Diastole Relaxation of heart Filling with blood Blood pressure falls Pulse = difference between the systolic and diastolic pressures = pulse pressure Ventricles contract -> blood ejected into large arteries -> arterial walls stretch & recoil as the pressures, increase & decrease, respectively -> felt as a pulse The greater the pulse pressure the stronger the palpated pulse Peripheral (Systemic) Resistance Flow of blood is limited by the friction created between the blood & the arterial vessel wall In order for blood to flow forward, blood pressure must be greater than this resistance Changes in Peripheral Resistance & Blood Pressure Sympathetic NS -> vasoconstriction of arterioles > inc BP & resistance Predominates during exercise -> blood flow to muscles preferentially At rest, parasympathetic system is dominant -> blood flow directed towards digestive & other organs Cardiac Muscle Fibers Striated, involuntary, branched w/ single, central nuclei & intercalated discs Unlike skeletal muscle, impulses travel cell to cell, via intercalated discs, in a wave like fashion -> heart contracts as a unit or not at all Review cardiac muscle contraction on pg 370 and pg 229 (Chap 8). Origin of the Heartbeat Cardiac tissues have automaticity -> depolarization occurs w/out stimulation by a nerve ending -> intrinsic ability for spontaneous depolarization & repolarization results in rhythmic pumping action muscle fibers w/in the RA = Sinoatrial node (SA node) = pacemaker of the heart Impulses originate here, travel through the specialized cells of the conduction system & spread throughout the musculature of the atria and ventricles Sequence of Electrical Impulses Electrical impulses are conducted across specific pathways so specific parts of the heart are activated at the right time SA node spontaneously depolarizes -> wave of depolarization -> Atrioventricular (AV) node Impulse travels slowly to allow time for atria to fill before impulse conduction across the atrial myocardium -> stimulates atrial contraction & emptying of blood into ventricles Impulse continues through AV node to the the bundle of His in the interventricular (IV) septum -> travels w/in right & left bundle branches to ventricular apex & the Purkinje fibers -> ventricular contraction Cardiac Conduction System Heart Sounds Listening to the heart (cardiac auscultation) enables the listener to hear the sounds that accompany closure of the cardiac valves and, to a lesser extent, contraction of the heart muscle These are repeated for each cardiac cycle Lub-Dub 1st heart sound (Lub) = closure of AV valves 2nd sound (Dub) = closure of semilunar valves following ventricular ejection of blood Heart Rate = frequency of cardiac cycles = number of beat per minutes (bpm) Generally smaller animals have higher rates than larger -> smaller have higher metabolic rate due to their larger surface area per unit of body mass Heart Rate (HR ) Determined by the SA node = dominant pacemaker -> suppresses all other pacing sites AV node, Purkinje system If the SA node does not fire one of the others would pick up the cardiac rhythm but it would be slower Regulation of Heart Rate HR determined by various factors including body temperature Most important factor is Autonomic Nervous System Balance between sympathetic & parasympathetic NS determines rate of spontaneous depolarization of SA node Stimulation of SNS -> faster rate of spontaneous depolarization -> HR increases Activation of PNS -> HR slows Electrocardiogram (ECG) Graphic recording of the electrical activity of the heart showing the direction impulses are traveling which are reflected on the graph by a pattern of either positive (up) or negative (down) deflections (waves) representing depolarizations & repolarizations in the heart Heart Rate can be determined also Heart Rhythm Normal = sinus rhythm – determined by SA node w/in RA Arrhythmias = too fast or too slow Bradyarrhythmia = too slow – cannot pump enough blood to meet body’s needs Tachyarrhythmia = too fast – cannot fill heart adequately & will have abnormal pumping function Contractility of the Myocardium At molecular level it’s determined by interaction of calcium ions w/ contractile proteins (actin, myosin) Sympathetic NS greatly impacts level of contractility SNS -> norepinerphrine -> stimulation of cardiac beta-adrenergic receptors -> inc in rate & force of myocardial contraction by increasing the amount of calcium available Review Divisions of the circulatory system What are the differences between the two systems? What are the functions of the cardiovascular system? Define the cardiac cycle (systole and diastole) and discuss systolic and diastolic pressures Define blood pressure How is the pulse generated? Review What is the origin of the heartbeat? Explain the electrical system of the heart, the role it plays in myocardial contraction & how it’s evaluated Identify the sequence of the electrical impulses of the heart Define heart rate & discuss its regulation What is auscultation of the heart?