Presentation on theme: "Aims Introduction to the heart. Heart contraction and electrical conduction. Readings; Sherwood, Chapter 9."— Presentation transcript:
Aims Introduction to the heart. Heart contraction and electrical conduction. Readings; Sherwood, Chapter 9
Cardiovascular Physiology Cardiac Muscle –Myocytes (cardiac muscle cells) –Myocytes are connected to each other via __Intercalated Disks__ Composed of Desmosomes and Gap Junctions Allow waves of action potentials to spread from one cell to the next (Syncytium). Sherwood’s Human Physiology 9-8 (9-6 6th Edition)
Sherwood’s Human Physiology 9-5 (9-4 6th Edition) Human Heart Anatomy
Sherwood’s Human Physiology 9-4 (9-3 6th Edition) Valve Physiology Valves are mechanical devices and function in response to blood flow. They function on the principle that they stay open as long as the blood pressure is greater in the emptying chamber. They close as soon as the blood pressure is greater in the filling chamber, thus blood flow is unidirectional. P1P1 P2P2 P1P1 P2P2
Guyton’s Textbook of Medical Physiology 4-1 Ion Concentrations Inside a cell –K + Outside a cell –Na + –Ca + –Cl -
Guyton’s Textbook of Medical Physiology 4-2 Cell Membrane Transport Passive –Simple diffusion –Facilitated diffusion Active (needs energy)
Two Types of Cardiac Cells Autorhythmic Cells –__non-contractile_________ –Initiate and conduct action potentials responsible for contraction. –Located in the SA node, AV node, Bundle of His, Purkinje fibers. Contractile Cells –99% of the cardiac muscle cells
Sherwood’s Human Physiology 9-11 (9-8 6th Edition) Specialized Conduction System Sinoatrial (SA) node. _Pacemaker____ Cells exhibit autorhythmicity.
Sherwood’s Human Physiology 9-11 (9-8 6th Edition) Specialized Conduction System Atrioventricular (AV) node Delays electrical signal due to a decreased number of gap junctions.
Guyton’s Textbook of Medical Physiology 10-3 Conduction Delay Atrioventricular fibrous tissue –Acts as an insulator
Sherwood’s Human Physiology 9-11 (9-8 6th Edition) Specialized Conduction System Atrioventricular (AV) bundle or Bundle of His. Transmits electrical signal down to the ventricles. Purkinje fibers Send action potential through ventricles. Has increased number of gap junctions.
Sherwood’s Human Physiology 9-10 (9-7 6th Edition) Pacemaker Potential Decreased K + efflux and constant Na + influx via leak channels. –Resulting in a higher resting potential. Slow Ca ++ inward permeability via transient voltage- gated Ca ++ channel.
Pacemaker Potential Ca ++ inward permeability via longer lasting voltage-gated Ca ++ channel. Resulting in __faster depolarization___ Sherwood’s Human Physiology 9-10 (9-7 6th Edition)
Pacemaker Potential K + outward permeability via voltage-gated channel. Resulting in repolarization Sherwood’s Human Physiology 9-10 (9-7 6th Edition)
Pacemakers SA node (normal pacemaker) –70-80 action potentials per minute. Ectopic Pacemakers AV node –40-60 action potentials per minute. Bundle of His and purkinje fibers –20-40 action potentials per minute.
Pacemakers Sherwood’s Human Physiology 9-12 5 th Edition only
Abnormal Conduction Pathway Guyton’s Textbook of Medical Physiology 10-4Sherwood’s Human Physiology 9-15 1.Normal -SA node sets the pace 2.SA Node non-functional -AV node sets the pace at a slower rate 3.AV Node non-functional -Atria contract at SA node rate while ventricles contract at Purkinje fiber rate (much slower) -Complete heart block that requires an artificial pacemaker. 4.Purkinje fiber is hyper-excitable - Called an ectopic focus that causes a premature beat.
Abnormal Conduction Pathway Guyton’s Textbook of Medical Physiology 10-4Sherwood’s Human Physiology 9-15
Guyton’s Textbook of Medical Physiology 10-2 SA node potentials vs. cardiac cell potentials SA node has a higher resting potential than other cardiac muscle cells.
ECC in Cardiac Muscle The majority of Ca ++ required for contraction comes from the sarcoplasmic reticulum and not the ECF. Sherwood’s Human Physiology 9-16 (9-12 6th Edition)
Refractory Period Long refractory period important because it makes tetanus impossible. Sherwood’s Human Physiology 9-17 (9-12 6th Edition)
Requirements for Efficient Cardiac Contraction 1.Atrial excitation and contraction need to be complete before ventricular contraction occurs. 2.Excitation of cardiac muscle fibers should be coordinated so that each chamber contracts as a unit. 3.Pair of atria and pair of ventricles should be coordinated so that both members of the pair contract simultaneously.
What is an Electrocardiogram (ECG or EKG)? It is not a direct recording of the actual electrical activity of the heart. It measures the portion of the electrical activity of the heart that is transduced in the body fluids and reaches the body surface. It is a complex recording that represents the overall activity throughout the heart during depolarization and repolarization. –Not a single cell measurement
ECG 6 body & 6 chest leads for a total of 12 leads Sherwood’s Human Physiology 9-18 (9-14 6th Edition)
ECG P wave- atrial depolarization PR segment- AV nodal delay QRS complex- ventricular depolarization and atrial repolarization ST segment- ventricular contraction and emptying T wave- ventricular repolarization TP interval- ventricular filling Sherwood’s Human Physiology 9-19 (9-15 6th Edition)
Next Time Cardiac Cycle Cardiac regulation –Extrinsic vs. intrinsic Reading; Sherwood, Chapter 9
Objectives 1.Describe the structure and function of cardiac myocytes. 2.Describe the anatomy of the heart and how blood flows through it. 3.Describe cardiac contraction 1.Conduction (normal and abnormal) 2.Pacemakers 3.Action potentials 4.Refractory period 4.Describe the ECG. 1.P Wave, QRS Complex, T Wave, Abnormal ECG