L22 - Cardiovascular System PDF

L22- Cardiovascular System DR. PUGAZHANDHI BAKTHAVATCHALAM, ASSISTANT PROFESSOR OF ANATOMY AND PHYSIOLOGY, AUACAS, AUA  Heart Physiology: Sequence of Excitation Define Starlings law of the heart, Describe the venous pressure and peripheral resistance. Blood pre...

L22- Cardiovascular System DR. PUGAZHANDHI BAKTHAVATCHALAM, ASSISTANT PROFESSOR OF ANATOMY AND PHYSIOLOGY, AUACAS, AUA  Heart Physiology: Sequence of Excitation Define Starlings law of the heart, Describe the venous pressure and peripheral resistance. Blood pressure: definition , components, determinants, effects and management. 2  Cardiac Output (CO) and Reserve 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) 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 3  Cardiac Output: Example CO (ml/min) = HR (75 beats/min) x SV (70 ml/beat) CO = 5250 ml/min (5.25 L/min) 4  Regulation of Stroke Volume SV = end diastolic volume (EDV) minus end systolic volume (ESV) SV = EDV-ESV EDV = amount of blood collected in a ventricle during diastole ESV = amount of blood remaining in a ventricle after contraction 5  Factors Affecting Stroke Volume Preload – amount ventricles are stretched by contained blood Contractility – cardiac cell contractile force due to factors other than EDV Afterload – back pressure exerted by blood in the large arteries leaving the heart 6  Frank-Starling Law of the Heart Preload, or degree of stretch, of cardiac muscle cells before they contract is the critical factor controlling stroke volume Slow heartbeat and exercise increase venous return to the heart, increasing SV Blood loss and extremely rapid heartbeat decrease SV 7  Preload and Afterload Figure 19.21 8  Extrinsic Factors Influencing Stroke Volume Contractility is the increase in contractile strength, independent of stretch and EDV Increase in contractility comes from: Increased sympathetic stimuli Certain hormones Ca2+ and some drugs Agents/factors that decrease contractility include: Acidosis Increased extracellular potassium Calcium channel blockers 9  VENOUS PRESSURE PERIPHERAL RESISTANCE Venous Pressure generally refers to Peripheral vascular resistance the average pressure within venous (systemic vascular resistance, SVR) is compartment of circulation Blood the resistance in the circulatory from all the systemic veins flows into system that is used to create blood the right atrium of the heart, pressure, the flow of blood and is also therefore the pressure in the Right a component of cardiac function. atrium called Central Venous pressure Jugular Venous Pulse (JVP) There is no When blood vessels constrict valves between the Rt atrium and the (vasoconstriction) this leads to an increase in SVR. When blood vessels Internal Jugular Vein. So the degree dilate (vasodilation), this leads to a of distension of this vein is dictated by decrease in SVR. the Rt atrium pressure. increased jugular venous pressure If referring to resistance within the hypotension diminished heart sounds pulmonary vasculature, this is called pulmonary vascular resistance (PVR).  Contractility and Norepinephrine Sympathetic stimulation releases norepinephrine and initiates a cyclic AMP second-messenger system Figure 19.22 11  Regulation of Heart Rate: Autonomic Nervous System Sympathetic nervous system (SNS) stimulation is activated by stress, anxiety, excitement, or exercise (FIGHT or FLIGHT) Parasympathetic nervous system (PNS) stimulation is mediated by acetylcholine and opposes the SNS (HOUSEKEEPING & MAINTENANCE) PNS dominates the autonomic stimulation, slowing heart rate and causing vagal tone 12  Extrinsic Innervation of the Heart Heart is stimulated by the sympathetic cardioacceleratory center Heart is inhibited by the parasympathetic cardioinhibitory center Figure 19.15 13  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 14  Homeostatic Imbalances Hypocalcemia – reduced ionic calcium depresses the heart Hypercalcemia – dramatically increases heart irritability and leads to spastic contractions Hypernatremia (Na ??!!)– blocks heart contraction by inhibiting ionic calcium transport Hyperkalemia (K) – leads to heart block and cardiac arrest 15  Homeostatic Imbalances Tachycardia – heart rate over 100 beats/min Bradycardia – heart rate less than 60 beats/min Pericarditis inflammation of the pericardium Reduces cardiac output Antibiotics, anti-inflammatory 16  Circulatory Shock Circulatory shock – any condition in which blood vessels are inadequately filled and blood cannot circulate normally Results in inadequate blood flow to meet tissue needs Three types include: Hypovolemic shock – results from large-scale blood loss Vascular shock – poor circulation resulting from extreme vasodilation Cardiogenic shock – the heart cannot sustain adequate circulation 17  Alterations in Blood Pressure Hypotension – low BP in which systolic pressure is below 100 mm Hg Hypertension – condition of sustained elevated arterial pressure of 140/90 or higher Transient elevations are normal and can be caused by fever, physical exertion, and emotional upset Chronic elevation is a major cause of heart failure, vascular disease, renal failure, and stroke (cerebrovascular accident) 18  Hypotension Orthostatic hypotension – temporary low BP and dizziness when suddenly rising from a sitting or reclining position Chronic hypotension – hint of poor nutrition and warning sign for Addison’s disease Acute hypotension – important sign of circulatory shock Threat to patients undergoing surgery and those in intensive care units 19  Hypertension Primary or essential hypertension – risk factors in primary hypertension include diet, obesity, age, race, heredity, stress, and smoking Secondary hypertension – due to identifiable disorders, including excessive renin secretion, arteriosclerosis, and endocrine disorders 20  Aneurysm A weakening of the arteries and subsequent bursting Due to hypertension or arteriosclerosis Generally affect cerebral arteries, aorta, and renal arteries 21