Transcript Slide 1
Cardiovascular Physiology 1) Blood Solution of Nutrients/Wastes 2) Heart Pump 3) Peripheral Circulation Tubes The primary function of the Cardiovascular system is to 1) deliver nutrients/oxygen and 2)remove wastes/CO2 from the cells in your body Cardiac Physiology The primary function of the HEART is to generate a Pressure gradient in the vascular system Pressure gradient allows blood to move by BULK FLOW through the body & the lungs Gradients A GRADIENT is a difference in any parameter over distance Molecules move “down” gradients from “Hi” to “Lo”, spontaneously e.g. Pressure, concentration, temperature, energy Bulk Flow Many molecules moving simultaneously in one direction, from an area of high P to low P PATMOS mm Hg Lo P Hi P Expiration Inspiration Hi P Lo P PLUNGS mm Hg Poiseulle’s Law of Bulk Flow: Its all about PRESSURE P1 P2 FB = kB(P1 - P2) L/min FB = Bulk Flow L/min kB = bulk flow constant ~ tube diameter If P1 > P2, flow goes from 1 to 2 If P1 < P2, flow goes from 2 to 1 If P1 = P2, no flow occurs Bulk Flow: Movement DOWN a Pressure Gradient Cardiac Cycle The cardiac cycle links 1) Electrical 2) Contractile 3) Pressure 4) Flow through the heart! The Heart is surround by cardiac muscle Pericardium Myocardium Endocardium Myocardial Fibers Myocardium Anatomy Myocardium is very similar to skeletal muscle Except • Intercalated discs form Gap junctions between adjacent myocardial fibers • Myocardial fibers branch • SR and T-tubules are weakly linked….Ca2+ is slowly released upon excitation Pacemaker Cells: Heart is Autorhythmic! How do pacemaker cells spontaneously produce action potentials? Pacemaker cells have an UNSTABLE resting membrane potential! 1) Prepotential: Few Na+ channels open, Na+ influx = funny current 2 3 2) Depolorization: VG Ca2+ channels open INFLUX of Ca2+ 1 3) Repolarization: K+ channels open EFFLUX of K+ Drugs to treat Arrhythmias sometimes work on Ca2+ channels! Myogenic signal propagates down Myocardium Electrical Properties of the Myocardium Plateau Skeletal muscle AP look and behave like neural cells Due to the SLOW CLOSING OF Ca2+, Myocardium REPOLARIZES VERY SLOWLY Excitation-Contraction Coupling of Cardiac Muscle 1 ECF 1) Action Potential Ca2+ Sacrolemna 2) VG Ca2+ channels open, CA 2+ Influx ICF RyR 2 3 SR Ca2+ 4 VG Ca2+ Channel T-tubule Ca2+ Spark 3) Ca2+ influx triggers RyR channels on SR to open Calcium Induced Calcium Release 4) Ca2+ pours out of SR Ca2+ Spark! 5) Sparks sum to create Ca2+ signal 5 Ca2+ Signal 6) Ca2+ binds Troponin, crossbridge formation, Contraction! Sarcomere 6 Contraction Calcium Sparks Video Myocardium contraction is GRADED! Amount of Ca2+ entering myocardium is proportional to contraction strength Ca2+ Force of Myocardium Ca2+ Ca2+ Spark Ca2+ Signal Contraction # of Cross bridges Formed Amount of Calcium INFLUX Amount of Calcium INFLUX Excitation-Contraction Coupling in Myocardium vs. Skeletal Muscle Skeletal Muscle Refractory Myocardium Ca2+ Plateau prolongs the refractory period…..summation cannot happen! Guarantees that Cardiac Muscle Contract-Relaxes Rhythmically!!!!! Don’t get CONFUSED! • Pacemaker Potentials • Cardiac Muscle Excitation Pacemaker EXCITATION >>>>>>>>>>>>>>>>>>>>.Cardiac Muscle Excitation- Contraction Heart’s Electrical Conducting System SA = 100 min-1 AV node = 40 min-1 AV bundle Bundle branches Purkinje Fibers 10-30 min-1 Why do the SA pacemaker cells beat a higher frequency than AV, Bundle Branches & Purkinje? SA NODE AV NODE SA Node has More Funny Current (Na+) channels What about Bundle Branches and Purkinje (10-30 min-1)? SA Node Atrial Muscle AV Node AV Bundle Bundle Branches Purkinje Fibers Ventricular Muscle No Plateau Phase Shorter Refractory Period Excitation involves Calcium PLATEAU Huge Refractory Period Ventricular Systole: Contraction Ventricular Diastole: Relaxation Atria have Systole and Diastole TOO! 1 Late diastole Atria & Ventricles START 5 Early Ventricular DIASTOLE. 2 Atrial systole S1 S2 4 Late Ventricular Systole 3 Early Ventricular SYSTOLE Cardiac Cycle The cardiac cycle links 1) Electrical 2) Contractile 3) Pressure 4) Flow through the heart! High Ventricular Pressure Forces AV Valves Shut Low Ventricular Pressure Forces Aortic/Pulmonary Valves Shut Valves respond to pressure! Guarantees One-Way Blood Flow Chordae Tendinae Papillary Muscle Relaxed ventricular muscle (diastole) Contracting ventricular muscle (systole) Low pressure in ventricle High pressure in ventricle AV valve flops open Aortic Valve Shuts AV valve forced shut Aortic Valve Opens Blood Flow through heart is driven by Pressure! Isovolumetric CONTRACTION Isovolumetric RELAXATION Blood Flow through Heart R. AV Valve L. AV Valve Cardiac Cycle The cardiac cycle links 1) Electrical 2) Contractile 3) Pressure 4) Flow through the heart! Wiggers Diagram 1 2 3 4 1) No electrical activity Atrial & Ventricular Diastole Pressure is low Volume is increasing 2) P-wave = Atrial Depol. Atrial Systole Atrial Pressure Rises Ventricular volume increases 5 3) QRS = Atrial Repol, Ventricular Depol. Ventricular Systole, Atrial Diastole Ventricular Pressure rises dramatically Atrial Pressure rises Ventricular Volume flat, then decreases as AV closes and Aortic and Pulmonary Valves Open 4) T-wave = Ventricular Repol. Ventricular Diastole Pressure drops dramatically in ventricle & rises in Atria Ventricular Volume decreases then is flat as aortic and pulmonary valves CLOSE 5) No electrical activity Atrial & Ventricular Diastole Pressure & Volume slowly rise as blood fills