Chapter 18 - The Cardiovascular System: The Heart

1. Chapter 18 - The Cardiovascular System: The Heart I. Heart Anatomy A. General 1. Inverted cone 2. Apex: inferior tip that points down and to the left 3. Between lungs

4. Cardiac Muscle as a Syncytium Intercalated disks: membranes that separate cardiac muscle cells from one another; have gap junctions that allow free diffusion of ions. A Syncytium of many heart muscle cells that are interconnected so that when one cell is excited, AP spreads to all cells. Heart has 2 syncytiums: atrial (walls of 2 atria) and ventricular (walls of 2 ventricles). AP are conducted by A-V bundle of nerve fibers

9. Chordae tendineae: attached to AV flaps are tiny white collagen cords that anchor the valve cusps to the papillary muscles.Prevent valve from bulging too far backward toward the atria during ventricular contraction

10. Valves Valves close passively when a backward pressure gradient pushes blood backward, and they open when a forward pressure gradient forces blood in the forward direction.

11. II. Coronary Circulation: blood supply of the heart A. Coronary Arteries 1. Left coronary artery 2. Right coronary artery - arise from the base of the aorta, encircle the heart, and provide a functional heart blood supply.

14. III. Cardiac Muscle A. Microscopic Anatomy 1. The walls of the heart are cardiac muscle. 2. cells are called myocardial cells; are striated, but branched and connect with other myocardial cells. 3. The site where one myocardial cell joins with another is the intercalated disc. Gap junctions allow ions to pass from cell to cell so the entire myocardium behaves as a functional unit

16. Intercalated disks: membranes that separate cardiac muscle cells from one another; have gap junctions that allow free diffusion of ions.

19. Neural Regulation of Heart Activity Autonomic Nervous System Regulation: Increases heartbeat Decreases heartbeat Intrinsic Conduction System: Cardiac cells initiate & distribute impulses Sequential manner from atria to ventricles The sympathetic nervous system increases both the rate and force of heartbeat Parasympathetic a ctivation slows the heart Cardiac center in medulla sympathetic - motor neurons synapse with gnaglionic neurons In the sympathetic chain ganglia, then to SA and AV nodes, heart muscle, and coronary arteries Parasympathetic -dorsal vagus nucleus in medulla, then, which in turn sends inhibitory impulses to the SA and AV noses via the Vaagus nerve The heart has a special neural system, specialized muscle fibers that generate rhythmic impulses to cause contraction of hear muscle.The sympathetic nervous system increases both the rate and force of heartbeat Parasympathetic a ctivation slows the heart Cardiac center in medulla sympathetic - motor neurons synapse with gnaglionic neurons In the sympathetic chain ganglia, then to SA and AV nodes, heart muscle, and coronary arteries Parasympathetic -dorsal vagus nucleus in medulla, then, which in turn sends inhibitory impulses to the SA and AV noses via the Vaagus nerve The heart has a special neural system, specialized muscle fibers that generate rhythmic impulses to cause contraction of hear muscle.

20. Impulses originate in the sinus node or SA node which is a strip of specialized cells in the right atrium. Sinus nodal fibers attach to the atrial fibers and the impluses that initiate in the SA node go through the atrial muscle wall The internodal pathways carry impulses from the SA node to the AV node in the lower part of the right atrium The AV node delays the impulse and then passes the impulse to the AV bundle and left and right bundles of Purkinje fibers The muscle fibers in the right atrium and upper portions of both right and left ventricles receive impulses from the AV bundle, and the lower portions of the ventricles receive impulses from the respective bundles of pUrkinje fibersImpulses originate in the sinus node or SA node which is a strip of specialized cells in the right atrium. Sinus nodal fibers attach to the atrial fibers and the impluses that initiate in the SA node go through the atrial muscle wall The internodal pathways carry impulses from the SA node to the AV node in the lower part of the right atrium The AV node delays the impulse and then passes the impulse to the AV bundle and left and right bundles of Purkinje fibers The muscle fibers in the right atrium and upper portions of both right and left ventricles receive impulses from the AV bundle, and the lower portions of the ventricles receive impulses from the respective bundles of pUrkinje fibers

21. SA nodal fibers are connected to surrounding atrial muscle fibers and also the three internodal pathways. The purpose is to initiate contractions in the right atrium and to conduct impulses to the AV node The AV node and AV bundle delays the impulse about 0.13 seconds. This delay allows time for the atria to fill the ventricles before they contract. Without influence from the SA node, the AV nodal fivers discharge at an intrinsic rate of 40-60 times per minute. Purkinje fibers at 15-40 times per minute. As long as the SA node discharges at a rate higher than the AV node and Purkinje fibers, the SA nose is the pacemaker of the heart.SA nodal fibers are connected to surrounding atrial muscle fibers and also the three internodal pathways. The purpose is to initiate contractions in the right atrium and to conduct impulses to the AV node The AV node and AV bundle delays the impulse about 0.13 seconds. This delay allows time for the atria to fill the ventricles before they contract. Without influence from the SA node, the AV nodal fivers discharge at an intrinsic rate of 40-60 times per minute. Purkinje fibers at 15-40 times per minute. As long as the SA node discharges at a rate higher than the AV node and Purkinje fibers, the SA nose is the pacemaker of the heart.

22. IV. Heart Physiology A. Electrical Events 1. Intrinsic Conduction System: cardiac cells initiate & distribute impulses in a sequential manner from atria to ventricles 2. Action Potentials of Autorhythmic Cells a. Fast sodium channels and slow calcium channels that are slower to open and remain open (responsible for the plateau). Decreased K permeability b. Pacemaker potentials: spontaneously changing membrane potentials that cause contraction c. Fast Ca2+ channels when threshold is reached causes depolarization d. K+ leaving causes repolarization

25. Sequence of Excitation

26. AA block - impulse does not enter the atrial muscle so no contraction of the atria and no P wave. Ventricles contract in response to the impulse from the AV nose. Heart is slowAA block - impulse does not enter the atrial muscle so no contraction of the atria and no P wave. Ventricles contract in response to the impulse from the AV nose. Heart is slow

27. Long PR interval = first degree heart block Two p waves per QRS complex = No clearly identifiable QRS or p waves - irwgular waveform Firillation occurs from impulses that travel abnormally in the heart muscle to stimulate one area, then another and another� Conductio speed is lsow, the impulse can then re-stimulate the first areas again. Athe ventricles pump little or no blood so brain damage, and death will occur if fibrillations are not stopped. Fibrillation causes ischemia of heart muscle Can be stopped by electrical shock (1000 volts frol a few ms). This depolarizes the heart muscle and it all becomes refractory at once. If fibrillation has occurred for over a minute, the heart will be weakened by lavk of coronary blood flow. Long PR interval = first degree heart block Two p waves per QRS complex = No clearly identifiable QRS or p waves - irwgular waveform Firillation occurs from impulses that travel abnormally in the heart muscle to stimulate one area, then another and another� Conductio speed is lsow, the impulse can then re-stimulate the first areas again. Athe ventricles pump little or no blood so brain damage, and death will occur if fibrillations are not stopped. Fibrillation causes ischemia of heart muscle Can be stopped by electrical shock (1000 volts frol a few ms). This depolarizes the heart muscle and it all becomes refractory at once. If fibrillation has occurred for over a minute, the heart will be weakened by lavk of coronary blood flow.

28. Conditions Decreased voltage of QRS because of old myocardial artery infarctions with diminished muscle mass. . Abnormal rhythms of pacemaker Blocks at different points in spread of the impulse Tachycardia; increased body temp., SNSystem stimulation Bradycardia; athletes stronger heart

31. Cardiac Output CO = HR x SV: measure of cardiac performance  CO = Amount of blood pumped by each ventricle in 1 minute; controlled by the flow of blood into the heart or venous return. Product of Heart Rate ( beats/minute) and Stroke Volume Stroke volume: volume of blood pumped by one ventricle during a contraction (force or ventricular contraction). CO= 72beats/min X 70mL/beat = 5040mL/min. or 5L/min. Average CO is 5 liters, so the heart pumps all the blood in the body through it in 1 minute!! EXERCISE: 30-50L/min.

32. 2. Stroke Volume Regulation SV related to the force generated by cardiac muscle during a contraction: > force > stroke volume. Force is effected by 2 parameters length of the muscle fiber at the beginning of contraction ability of muscle to contract. 3. Starlings Law: The heart pumps all the blood that returns to it. As additional blood enters the heart, the heart contracts more forcefully. The increased blood stretches the walls of the heart chambers, so: 4. As sarcomere length increases, the force increases and the Stroke Volume increases.

33. 3. Regulation of Heart Rate a. ANS: target heart muscle and blood vessels 1) Parasympathetic: reduces heart rate, constricts vessels 2) Sympathetic: exercise, fright - NE & E bind to heart receptors causing the pacemakers to fire more rapidly and increases heart rate. b. Chemical Regulation 1) Hormones: epinephrine liberated by adrenal medulla 2) Ions: intra and extracellular relationships are maintained by normal heart function c. Other factors: age, gender, exercise

34. Exercise 1. Mass discharge of SNS system with stimulatory effect heart is stimulated Arterioles contracted, except active muscles dilated 2. Increase in arterial pressure Increased blood flow required by the muscles (except coronary and cerebral systems) Can be 2L/minute 3. Increase in cardiac output 4. Athletes heart is stronger so stroke volume is large per beat; this in turn results in bradycardia