Popular in Human Anatomy and Physiology II
Popular in Biological Sciences
This 9 page Class Notes was uploaded by Jess Graff on Saturday February 20, 2016. The Class Notes belongs to BMS 508 at University of New Hampshire taught by Mary Katherine Lockwood, PhD in Spring 2016. Since its upload, it has received 17 views. For similar materials see Human Anatomy and Physiology II in Biological Sciences at University of New Hampshire.
Reviews for BMS 508
Report this Material
What is Karma?
Karma is the currency of StudySoup.
You can buy or earn more Karma at anytime and redeem it for class notes, study guides, flashcards, and more!
Date Created: 02/20/16
BMS 508.03 2/17/2016 Chapter 20 (cont) The Cardiovascular System (cont) The Conducting System • Cardiac Physiology • 2 types of cardiac muscle cells 1. Conducting system • Controls and coordinates heartbeat 2. Contractile cells • Produce contractions that propel blood • The Cardiac Cycle • Begins with action potential at SA node 1. Transmitted through conducting system 2. Produces action potentials in cardiac muscle cells (contractile cells) • Electrocardiogram (ECG or EKG) 1. Electrical events in the cardiac cycle can be recorded on an electrocardiogram • The Conducting System • A system of specialized cardiac muscle cells 1. Initiates and distributes electrical impulses that stimulate contraction • Automaticity 1. Cardiac muscle tissue contracts automatically • Structures of the Conducting System • Sinoatrial (SA) node – wall of right atrium • Atrioventricular (AV) node – junction between atria and ventricles • Conducting cells – throughout myocardium • Conducting Cells • Interconnect SA and AV nodes • Distribute stimulus through myocardium • In the atria 1. Internodal pathways • In the ventricles 1. AV bundle and the bundle branches • Prepotential • Also called pacemaker potential • Resting potential of conducting cells 1. Gradually depolarizes toward threshold • SA node depolarizes first, establishing heart rate • Heart Rate • SA node generates 80–100 action potentials per minute • Parasympathetic stimulation slows heart rate • AV node generates 40–60 action potentials per minute • The Sinoatrial (SA) Node • In posterior wall of right atrium • Contains pacemaker cells • Connected to AV node by internodal pathways • Begins atrial activation (Step 1) • The Atrioventricular (AV) Node • In floor of right atrium • Receives impulse from SA node (Step 2) • Delays impulse (Step 3) • Atrial contraction begins • The AV Bundle • In the septum • Carries impulse to left and right bundle branches 1. Which conduct to Purkinje fibers (Step 4) • And to the moderator band 1. Which conducts to papillary muscles • Purkinje Fibers • Distribute impulse through ventricles (Step 5) • Atrial contraction is completed • Ventricular contraction begins • Abnormal Pacemaker Function • Bradycardia – abnormally slow heart rate • Tachycardia – abnormally fast heart rate • Ectopic pacemaker 1. Abnormal cells 2. Generate high rate of action potentials 3. Bypass conducting system 4. Disrupt ventricular contractions • The Electrocardiogram (ECG or EKG) • A recording of electrical events in the heart • Obtained by electrodes at specific body locations • Abnormal patterns diagnose damage • Features of an ECG • P wave 1. Atria depolarize • QRS complex 1. Ventricles depolarize • T wave 1. Ventricles repolarize • Time Intervals between ECG Waves • P–R interval 1. From start of atrial depolarization 2. To start of QRS complex • Q–T interval 1. From ventricular depolarization 2. To ventricular repolarization • Contractile Cells • Purkinje fibers distribute the stimulus to the contractile cells, which make up most of the muscle cells in the heart • Resting potential 1. Of a ventricular cell about –90 mV 2. Of an atrial cell about –80 mV • Refractory Period • Absolute refractory period 1. Long 2. Cardiac muscle cells cannot respond • Relative refractory period 1. Short 2. Response depends on degree of stimulus • Timing of Refractory Periods • Length of cardiac action potential in ventricular cell 1. 250–300 msec • 30 times longer than skeletal muscle fiber • Long refractory period prevents summation and tetany • The Role of Calcium Ions in Cardiac Contractions • Contraction of a cardiac muscle cell 1. Is produced by an increase in calcium ion concentration around myofibrils • 20% of calcium ions required for a contraction 1. Calcium ions enter plasma membrane during plateau phase 2+ • Arrival of extracellular Ca 1. Triggers release of calcium ion reserves from sarcoplasmic reticulum (SR) • As slow calcium channels close 1. Intracellular Ca 2+ is absorbed by the SR 2. Or pumped out of cell • Cardiac muscle tissue 1. Very sensitive to extracellular Ca 2+concentrations • The Energy for Cardiac Contractions • Aerobic energy of heart 1. From mitochondrial breakdown of fatty acids and glucose 2. Oxygen from circulating hemoglobin 3. Cardiac muscles store oxygen in myoglobin The Cardiac Cycle • The Cardiac Cycle • Is the period between the start of one heartbeat and the beginning of the next • Includes both contraction and relaxation • Two Phases of the Cardiac Cycle • Within any one chamber • Systole (contraction) • Diastole (relaxation) • Blood Pressure • In any chamber • Rises during systole • Falls during diastole • Blood flows from high to low pressure • Controlled by timing of contractions • Directed by one-way valves • Cardiac Cycle and Heart Rate • At 75 beats per minute (bpm) • Cardiac cycle lasts about 800 msec • When heart rate increases • All phases of cardiac cycle shorten, particularly diastole • Phases of the Cardiac Cycle • Atrial systole • Atrial diastole • Ventricular systole • Ventricular diastole • Atrial Systole • Atrial systole • Atrial contraction begins • Right and left AV valves are open • Atria eject blood into ventricles • Filling ventricles • Atrial systole ends • AV valves close • Ventricles contain maximum blood volume • Known as end-diastolic volume (EDV) • Ventricular Systole • Ventricles contract and build pressure • AV valves close causing isovolumetric contraction • Ventricular ejection • Ventricular pressure exceeds vessel pressure opening the semilunar valves and allowing blood to leave the ventricle • Amount of blood ejected is called the stroke volume (SV) • Ventricular pressure falls • Semilunar valves close • Ventricles contain end-systolic volume (ESV), about 40% of end- diastolic volume • Ventricular Diastole • Ventricular diastole • Ventricular pressure is higher than atrial pressure • All heart valves are closed • Ventricles relax (isovolumetric relaxation) • Atrial pressure is higher than ventricular pressure • AV valves open • Passive atrial filling • Passive ventricular filling • Heart Sounds • S 1 • Loud sounds • Produced by AV valves • S2 • Loud sounds • Produced by semilunar valves • S3, S4 • Soft sounds • Blood flow into ventricles and atrial contraction • Heart Murmur • Sounds produced by regurgitation through valves Cardiodynamics • Cardiodynamics • The movement and force generated by cardiac contractions • End-diastolic volume (EDV) • End-systolic volume (ESV) • Stroke volume (SV) • SV = EDV – ESV • Ejection fraction • The percentage of EDV represented by SV • Cardiac Output (CO) • The volume pumped by left ventricle in one minute • CO = HR SV • CO = cardiac output (mL/min) • HR = heart rate (beats/min) • SV = stroke volume (mL/beat) • Factors Affecting Cardiac Output • Cardiac output • Adjusted by changes in heart rate or stroke volume • Heart rate • Adjusted by autonomic nervous system or hormones • Stroke volume • Adjusted by changing EDV or ESV • Autonomic Innervation • Cardiac plexuses innervate heart • Vagus nerves (N X) carry parasympathetic preganglionic fibers to small ganglia in cardiac plexus • Cardiac centers of medulla oblongata • Cardioacceleratory center controls sympathetic neurons (increases heart rate) • Cardioinhibitory center controls parasympathetic neurons (slows heart rate) • Cardiac reflexes • Cardiac centers monitor: • Blood pressure (baroreceptors) • Arterial oxygen and carbon dioxide levels (chemoreceptors) • Cardiac centers adjust cardiac activity • Autonomic tone • Dual innervation maintains resting tone by releasing ACh and NE • Fine adjustments meet needs of other systems • Effects on the SA Node • Membrane potential of pacemaker cells • Lower than other cardiac cells • Rate of spontaneous depolarization depends on: • Resting membrane potential • Rate of depolarization
Are you sure you want to buy this material for
You're already Subscribed!
Looks like you've already subscribed to StudySoup, you won't need to purchase another subscription to get this material. To access this material simply click 'View Full Document'