Cardiovascular System PDF

The Cardiovascular System  THE CARDIOVASCULAR CIRCUIT Mosby items and derived items © 2006 by Mosby, Inc. MAIN FUNCTIONS OF THE CIRCULATORY SYSTEM - Transport and distribute essential substances to the tissues - Remove metabolic byproducts - Adjustment of oxygen and nutrie...

The Cardiovascular System  THE CARDIOVASCULAR CIRCUIT Mosby items and derived items © 2006 by Mosby, Inc. MAIN FUNCTIONS OF THE CIRCULATORY SYSTEM - Transport and distribute essential substances to the tissues - Remove metabolic byproducts - Adjustment of oxygen and nutrient supply in different physiologic states - Regulation of body temperature - Humoral communication Mosby items and derived items © 2006 by Mosby, Inc.  THE CIRCULATORY SYSTEM The circulatory system is a closed circuit containing a pump (the heart) that serves to maintain a pressure gradient sufficient to sustain an effective blood flow from the distributing ducts or arteries to the thin vessels or capillaries and back through the collecting ducts or veins. Mosby items and derived items © 2006 by Mosby, Inc.  FUNCTIONS OF THE HEART - Generating blood pressure - Routing blood: separates pulmonary and systemic circulations - Ensuring one-way blood flow: valves - Regulating blood supply Changes in contraction rate and force match blood delivery to changing metabolic needs Mosby items and derived items © 2006 by Mosby, Inc.  CIRCUITS OF THE HEART Pulmonary circuit blood to and from the lungs Systemic circuit blood to and from the rest of the body Vessels carry the blood through the circuits Arteries carry blood away from the heart Veins carry blood to the heart Capillaries permit exchange Mosby items and derived items © 2006 by Mosby, Inc. Mosby items and derived items © 2006 by Mosby, Inc.  CARDIAC MUSCLE Elongated, branching cells containing 1-2 centrally located nuclei Contains actin and myosin myofilaments Intercalated disks: specialized cell-cell contacts.  Gap junctions allow action potentials to move from one cell to the next Electrically, cardiac muscle of the atria and of the ventricles behaves as single unit Mitochondria comprise 30% of volume of the cell vs. 2% in skeletal Mosby items and derived items © 2006 by Mosby, Inc.  CARDIAC MUSCLE Mosby items and derived items © 2006 by Mosby, Inc.  THE CHAMBERS OF THE HEART Right atrium – receiving chamber for blood from systemic side. No valve between vena Cava and R atrium Left atrium – receiving deoxgenated blood from lungs Right ventricle – pumps blood to lungs via pulmonary arteries Left ventricle – pumps blood to systemic circuit via aorta The left side of the heart is more muscular than the right side Mosby items and derived items © 2006 by Mosby, Inc.  THE CHAMBERS OF THE HEART Mosby items and derived items © 2006 by Mosby, Inc.  THE HEART VALVES  Atrioventricular valves between A & V  Tricuspid valve – Right side  Bicuspid valve – left side  Semilunar valves  Pulmonic semilunar valve  Aortic semilunar valve  Functions of valves  AV valves prevent backflow of blood from the ventricles to the atria  Semilunar valves prevent backflow into the ventricles  Valves and other connective tissue do not conduct electrical impulses and make up heart skeleton Mosby items and derived items © 2006 by Mosby, Inc.  THE HEART VALVES Mosby items and derived items © 2006 by Mosby, Inc.  DIASTOLE AND SYSTOLE Cardiac cycle – the electrical and physical events of an entire heart beat(0.8 seconds), during which 2 events occur: 1. Diastole – resting phase – no active contraction 2. Systole – active muscle contraction and electrical impulses Mosby items and derived items © 2006 by Mosby, Inc. CARDIAC CYCLE Diastole Systole Mosby items and derived items © 2006 by Mosby, Inc.  THE CARDIAC CYCLE Cardiac cycle refers to all events associated with blood flow through the heart from the start of one heartbeat to the beginning of the next During a cardiac cycle  Each heart chamber goes through systole and diastole  Correct pressure relationships are dependent on careful timing of contractions Mosby items and derived items © 2006 by Mosby, Inc.  PHASES OF THE CARDIAC CYCLE Atrial diastole and systole -  Blood flows into and passively out of atria (85% of total)  AV valves open  Atrial systole pumps only about 15% of blood into ventricles Ventricular filling: mid-to-late diastole  Heart blood pressure is low as blood enters atria and flows into ventricles  85% of blood enters ventricles passively  AV valves are open, then atrial systole occurs  Atrial systole pumps remaining 15% of blood into ventricles Mosby items and derived items © 2006 by Mosby, Inc.  PHASES OF THE CARDIAC CYCLE Ventricular systole  Atria relax  Rising ventricular pressure results in closing of AV valves (1st heart sound - ‘lubb’)  Isometric (Isovolumetric) contraction phase  Ventricles are contracting but no blood is leaving  Ventricular pressure not great enough to open semilunar valves  Ventricular ejection (Isotonic contraction) phase opens semilunar valves  Ventricular pressure now greater than pressure in arteries (aorta and pulmonary trunk) Mosby items and derived items © 2006 by Mosby, Inc.  PHASES OF THE CARDIAC CYCLE Ventricular diastole Ventricles relax Backflow of blood in aorta and pulmonary trunk closes semilunar valves (2nd hear sound - “dub) Blood once again flowing into relaxed atria and passively into ventricles Mosby items and derived items © 2006 by Mosby, Inc.  CHARACTERISTICS OF THE HEART excitability: cells can respond to an electrical stimulus contractility: the specialized ability of the cardiac muscle cells to contract, thus converting chemical energy into mechanical energy rhythmicity: ability of cardiac muscle to contract and relax regularly. automaticity: cells can depolarize without any impulse from outside source (self- excitation) conductivity: cells can propagate the electrical impulse from cell to another Mosby items and derived items © 2006 by Mosby, Inc.  ACTION POTENTIAL IN SKELETAL AND CARDIAC MUSCLE Mosby items and derived items © 2006 by Mosby, Inc.  ACTION POTENTIAL IN CARDIAC MUSCLE 1. Rising phase of action potential Due to opening of fast Na + channels 2. Plateau phase Closure of sodium channels Opening of calcium channels Slight increase in K + permeability Prevents summation and thus tetanus of cardiac muscle 3. Repolarization phase Calcium channels closed Increased K+ permeability Mosby items and derived items © 2006 by Mosby, Inc. REFRACTORY PERIODS Relative refractory period cell will respond to a second action potential but the action potential must be stronger than usual Absolute refractory period cell will not respond to a repeated action potential regardless of how strong it is, and it occupies the whole period of systole and part of diastole Mosby items and derived items © 2006 by Mosby, Inc.  CONTRACTILITY Frank-Starling law of the heart – self regulating mechanism that controls stroke volume and force. The greater the stretch of the heart muscle the stronger the force of contraction up to a maximum End-diastolic volume – measure of the return flow of blood and stretch of the ventricles Mosby items and derived items © 2006 by Mosby, Inc.  CONTRACTILITY Frank-Starling mechanism means that the greater the heart muscle is stretched during filling, the greater is the force of contraction and the greater the quantity of blood pumped into the aorta. Or, stated another way: Within physiologic limits, the heart pumps all the blood that returns to it by the way of the veins. Mosby items and derived items © 2006 by Mosby, Inc.  CONTRACTILITY Heart muscle: Is stimulated by nerves and is self-excitable (automaticity) Contracts as a unit; no motor units Has a long (250 ms) absolute refractory period Cardiac muscle contraction is similar to skeletal muscle contraction, i.e., sliding-filaments Mosby items and derived items © 2006 by Mosby, Inc.  RHYTHMICITY Factors affecting Rhythmicity Autonomic innervation Electrolytes  Allow for electrical and mechanical function of heart  Sodium: major extracellular cation, role in depolarization  Potassium: major intracellular cation, role in repolarization  Calcium: intracellular cation, role in depolarization and myocardial contraction Temperature Blood pH Mosby items and derived items © 2006 by Mosby, Inc.  CONDUCTING SYSTEM OF HEART Mosby items and derived items © 2006 by Mosby, Inc.  CONDUCTION SYSTEM OF THE HEART SA node: sinoatrial node. The pacemaker.  Specialized cardiac muscle cells.  Generate spontaneous action potentials (autorhythmic tissue).  Action potentials pass to atrial muscle cells and to the AV node AV node: atrioventricular node.  Action potentials conducted more slowly here than in any other part of system.  Ensures ventricles receive signal to contract after atria have contracted AV bundle: passes through hole in cardiac skeleton to reach interventricular septum Right and left bundle branches: extend beneath endocardium to apices of right and left ventricles Purkinje fibers:  Large diameter cardiac muscle cells with few myofibrils.  Many gap junctions.  Conduct action potential to ventricular muscle cells (myocardium) Mosby items and derived items © 2006 by Mosby, Inc.  HEART PHYSIOLOGY: INTRINSIC CONDUCTION SYSTEM Auto-rhythmic cells: Initiate action potentials Have unstable resting potentials called pacemaker potentials Use calcium influx (rather than sodium) for rising phase of the action potential Mosby items and derived items © 2006 by Mosby, Inc.  EXTRINSIC INNERVATION OF THE HEART Vital centers of medulla 1. Cardiac Center  Cardioaccelerator center  Activates sympathetic neurons that increase HR  Cardioinhibitory center  Activates parasympathetic neurons that decrease HR Cardiac center receives input from higher centers (hypotha-lamus), monitoring blood pressure and dissolved gas concentrations Mosby items and derived items © 2006 by Mosby, Inc.  REGULATION OF THE HEART Neural regulation Sympathetic stimulation - a positive chronotropic factor  Supplied by cardiac nerves.  Innervate the SA and AV nodes, and the atrial and ventricular myocardium.  Increases heart rate and force of contraction.  Epinephrine and norepinephrine released.  Increased heart beat causes increased cardiac output. Increased force of contraction causes a lower end- systolic volume; heart empties to a greater extent. Limitations: heart has to have time to fill. Mosby items and derived items © 2006 by Mosby, Inc.  REGULATION OF THE HEART Parasympathetic stimulation - a negative chronotropic factor  Supplied by vagus nerve, decreases heart rate, acetylcholine is secreted and hyperpolarizes the heart  greater extent. Limitations: heart has to have time to fill. Hormonal regulation  Epinephrine and norepinephrine from the adrenal medulla.  Occurs in response to increased physical activity, emotional excitement, stress Mosby items and derived items © 2006 by Mosby, Inc.  CHEMICAL REGULATION OF THE HEART The hormones epinephrine and thyroxine increase heart rate Intra- and extracellular ion concentrations must be maintained for normal heart function Mosby items and derived items © 2006 by Mosby, Inc.  HEART RATE Pulse = surge of pressure in artery  infants have HR of 120 bpm or more young adult females avg. 72 - 80 bpm young adult males avg. 64 to 72 bpm HR rises again in the elderly Tachycardia: resting adult HR above 100 stress, anxiety, drugs, heart disease or  body temp. Bradycardia: resting adult HR < 60 in sleep and endurance trained athletes Mosby items and derived items © 2006 by Mosby, Inc.  REGULATION OF HEART RATE  Chronotropism: an influence on the heart rate. - +ve chronotropic factors: factors that increase heart rate - -ve chronotropic factors: factors that decrease heart rate  Ionotropism: an influence on contractility - +ve inotropic factors: factors that increase contractility - -ve chronotropic factors: factors that decrease contractility Mosby items and derived items © 2006 by Mosby, Inc.  FACTORS AFFECTING HEART RATE Heart rate  Cardiovascular control center – in medulla  Cardioexcitatory and cardioinhibitory centers (ANS)  Neural reflexes  Atrial stretch receptors reflex  Proprioceptor reflex  Chemoreceptor reflex  Baroreceptor reflex  Nociceptor reflex  Cerebral Cortex Mosby items and derived items © 2006 by Mosby, Inc. BARORECEPTOR AND CHEMORECEPTORS Mosby items and derived items © 2006 by Mosby, Inc.  FACTORS AFFECTING HEART RATE Venous Return Skeletal muscle pump Muscular contraction squeezes adjacent veins causing a milking action Valves prevent opposite flow Mosby items and derived items © 2006 by Mosby, Inc.  FACTORS AFFECTING HEART RATE Venous Return Constriction of veins Sympathetic stimulation causes contraction of the smooth muscle walls of veins Gravity Mosby items and derived items © 2006 by Mosby, Inc.  PRELOAD Preload is the diastolic volume load present before contraction has started at the end of diastole. It reflects the venous filling pressure that fills the left atrium, which in turn fills the left ventricle during diastole When the preload increases, the left ventricle distends during diastole and the volume rises Mosby items and derived items © 2006 by Mosby, Inc.  AFTERLOAD Afterload is the systolic load on the left ventricle after it has started to contract  resistance against which left ventricle must pump Mosby items and derived items © 2006 by Mosby, Inc.  PRELOAD AND AFTERLOAD The importance of the concepts of preload and afterload is that in many abnormal functional states of the heart or circulation, the pressure during filling of the ventricle (preload), the arterial pressure against which the ventricle must contract (afterload), or both are severely altered from normal. Mosby items and derived items © 2006 by Mosby, Inc.  CARDIAC OUTPUT (CO)  CO is the amount of blood pumped by each ventricle in one minute  CO is the product of heart rate (HR) and stroke volume (SV) CO = HR x SV (ml/min) = (beats/min) x ml/beat  HR is the number of heart beats per minute  SV is the amount of blood pumped out by a ventricle with each beat  Cardiac reserve is the difference between resting and maximal CO  SV = EDV - ESV Mosby items and derived items © 2006 by Mosby, Inc.  EJECTION FRACTION In cardiovascular physiology, ejection fraction (EF) is the fraction of blood pumped out (forward) from the right ventricle of the heart to the pulmonary circulation (lungs) and left ventricle of the heart to the systemic circulation (brain and body) with each heart beat or cardiac cycle. Mosby items and derived items © 2006 by Mosby, Inc.  EJECTION FRACTION However, because the left ventricle is the heart's main pumping chamber, ejection fraction is usually measured only in the left ventricle (LV). Mosby items and derived items © 2006 by Mosby, Inc.  EJECTION FRACTION Healthy individuals typically have ejection fractions between 55% and 70%. Damage to the muscle of the heart (myocardium), such as that sustained during myocardial infarction or in cardiomyopathy (chronic disorder of the heart muscle), impairs the heart's ability to eject blood and therefore reduces ejection fraction. This reduction in the ejection fraction can manifest itself clinically as heart failure. Mosby items and derived items © 2006 by Mosby, Inc.  EJECTION FRACTION The ejection fraction may decrease if: 1- You have weakness of your heart muscle 2- A heart attack has damaged your heart 3- You have problems with your heart's valves 4- You have had long-standing, uncontrolled high blood pressure Mosby items and derived items © 2006 by Mosby, Inc.  ARTERIAL BLOOD PRESSURE CURVE Mosby items and derived items © 2006 by Mosby, Inc.  ARTERIAL BLOOD PRESSURE CURVE By expanding under pressure, the aorta absorbs some of the force of the blood surge from the heart during a heartbeat. The loss of arterial compliance that occurs with aging explains the elevated pulse pressures found in elderly patients Mosby items and derived items © 2006 by Mosby, Inc.  JUGULAR WAVE FORM Mosby items and derived items © 2006 by Mosby, Inc.  JUGULAR WAVE FORM The " a " wave corresponds to right Atrial contraction. The " c " wave corresponds to right ventricular Contraction causing the triCuspid valve to bulge towards the right atrium. The " x " descent follows the 'a' wave and corresponds to atrial relaXation and rapid atrial filling due to low pressure. The " x' " (x prime) descent follows the 'c' wave and occurs as a result of the right ventricle pulling the tricuspid valve downward during ventricular systole. Mosby items and derived items © 2006 by Mosby, Inc.  JUGULAR WAVE FORM The " v " wave corresponds to Venous filling when the tricuspid valve is closed and venous pressure increases from venous return - this occurs during and following the carotid pulse. The " y " descent corresponds to the rapid emptYing of the atrium into the ventricle following the opening of the tricuspid valve Mosby items and derived items © 2006 by Mosby, Inc.  LAMINAR VS. TURBULENT FLOW Mosby items and derived items © 2006 by Mosby, Inc.  ARTERIAL BLOOD PRESSURE (BP) Is the lateral pressure generated by the pumping action of the heart on the wall of aorta & arterial blood vessels per unit area. OR = Pressure inside big arteries (aorta & big vessels). Of two components:  systolic … (= max press reached) = 90-145 mmHg.  diastolic … (= min press reached) = 60-90 mmHg. In normal adult  120/80 mmHg. Mosby items and derived items © 2006 by Mosby, Inc.  FACTORS AFFECTING ABP Sex … M > F …due to hormones/ equal at menopause. Age … Elderly > children …due to atherosclerosis. Emotions … due to secretion of adrenaline & noradrenaline. Exercise … due to  venous return. Hormones … (e.g. Adrenaline, noradrenaline, thyroid H). Gravity …  Lower limbs > upper limbs. Race … Orientals > Westerns … ? dietry factors, or weather. Sleep …  due to  venous return. Pregnancy … due to  metabolism. Mosby items and derived items © 2006 by Mosby, Inc.  RENIN-ANGIOTENSIN SYSTEM Most important mechanism for Na+ retention in order to maintain the blood volume. Any drop of renal blood flow &/or  Na+, will stimulate volume receptors found in juxtaglomerular apparatus of the kidneys to secrete Renin which will act on the Angiotensin System leading to the production of aldosterone. Mosby items and derived items © 2006 by Mosby, Inc.  ANTI-DIURETIC HORMONE (ADH) Hypovolemia & dehydration will stimulate the osmoreceptors in the hypothalamus, which will lead to release of ADH from posterior pituitary gland. ADH will cause water reabsorption at kidney tubules. Mosby items and derived items © 2006 by Mosby, Inc.  LOW-PRESSURE VOLUME RECEPTORS Atrial natriuritic peptide (ANP) hormone, is secreted from the wall of right atrium to regulate Na+ excretion in order to maintain blood volume. Mosby items and derived items © 2006 by Mosby, Inc.  AN ELECTROCARDIOGRAM Mosby items and derived items © 2006 by Mosby, Inc.  ELECTROCARDIOGRAM Record of electrical events in the myocardium that can be correlated with mechanical events P wave: depolarization of atrial myocardium.  Signals onset of atrial contraction QRS complex: ventricular depolarization  Signals onset of ventricular contraction.. T wave: repolarization of ventricles PR interval or PQ interval: 0.16 sec  Extends from start of atrial depolarization to start of ventricular depolarization (QRS complex) contract and begin to relax  Can indicate damage to conducting pathway or AV node if greater than 0.20 sec (200 msec) Q-T interval: time required for ventricles to undergo a single cycle of depolarization and repolarization  Can be lengthened by electrolyte disturbances, conduction problems, coronary ischemia, myocardial damage Mosby items and derived items © 2006 by Mosby, Inc.