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Chapter 13 Cardiovascular System. 13.3. 13.3. Heart Actions. Heart Actions. Systole = when a heart chamber contracts Diastole = when a heart chamber relaxes Cardiac Cycle = constitutes a complete heartbeat Atrial systole and ventricular diastole

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Heart Actions

heart actions
Heart Actions
  • Systole = when a heart chamber contracts
  • Diastole= when a heart chamber relaxes
  • Cardiac Cycle = constitutes a complete heartbeat
    • Atrial systole and ventricular diastole
    • Ventricular systole and atrial diastole
    • Both the atrial and ventricular diastole
cardiac cycle
Cardiac Cycle
  • Important: fluids always move from high to low pressure
  • A-V valves open and blood moves through the heart mostly due to pressure changes
    • 70% of blood moves from the right atria to the right ventricle before atrial contraction
    • 30% is pushed through by contraction of the atria
cardiac cycle1
Cardiac Cycle
  • Pressure rises in the ventricle as it contracts
    • Causes the A-V valves to close
    • Contraction of papillary muscles attached to cordaetendineae prevent the cusps from going back into atria
  • Now, low pressure in the atria causes it to fill with blood from veins
cardiac cycle2
Cardiac Cycle
  • Pressure builds as the ventricle contracts, causing the semilunarvalves to open
    • Blood flows from the ventricle to the arteries
    • Pressure drops in the ventricle as blood leaves and it begins to relax
  • The semilunar valves close when the pressure in the arteries is greater than that in the ventricles
heart sounds
Heart Sounds
  • Lubb-dupp due to the vibrations in heart tissues associated with the closing of valves
    • Lubb – A-V valves closing
    • Dupp – Pulmonary and aortic valves closing
cardiac muscle fibers
Cardiac Muscle Fibers
  • Functions like skeletal muscle fibers, except they connect in branching networks
    • Stimulation to any part of the network sends impulses through the heart
    • Causes the heart to contract as a unit
cardiac muscle fibers1
Cardiac Muscle Fibers
  • Functional syncytium – a mass of merging cells that function as a unit
  • 2 in the heart
    • In atrial walls
    • In ventricular walls
    • They are separated by the heart’s fibrous skeleton, except for a small area in the right atrial floor (connected by fibers of the cardiac conduction system)
cardiac conduction system
Cardiac Conduction System
  • Cardiac conduction system – Special muscle fibers that initiate and distribute impulses throughout the myocardium,
    • Coordinates the events of the cardiac cycle
cardiac conduction system1
Cardiac Conduction System
  • Sinoatrial (S-A) node – specialized tissue in the wall of the right atrium that initiates the cardiac cycle
    • Pacemaker (can reach threshold 70-80 times per min)
    • Needs no stimulation from nerve fibers
  • Travels to atrialsyncytium (causes atria to contract)
  • Then to junctional fibers (delay impulse transmission)
cardiac conduction system2
Cardiac Conduction System
  • Atrioventricular (A-V) node – Specialized mass of cardiac muscle fibers in the interatrial septum of heart
    • Transmits impulses from the S-A node to the A-V bundle
  • A-V bundle (bundle of His) – specialized fibers that conduct impulses from the A-V node to the ventricular muscle of the heart
    • Divides to form the right and left bundle branches
cardiac conduction system3
Cardiac Conduction System
  • Purkinje fibers – conduct impulses from the bundle branches to the ventricular syncytium
  • The ventricle contacts with a twisting motion, squeezing blood out of its chambers and into the aorta and pulmonary trunk
    • Muscle fibers form irregular whorls
  • Electrocardiogram (ECG) – a recording of the electrical activity associated with the heartbeat
    • Changes can be detected on the surface of the body because electrical currents can conduct through body fluids
  • Waves are created on the electrocardiogram which correspond to electrical changes
    • P wave – depolarization of the atrial fibers and contraction of the atria
    • QRS complex – depolarization of the ventricular fibers
    • T wave – ventricular muscle fibers repolarize
    • Between cycles, it stays along the baseline
  • Repolarization of the atrial fibers is obscured by the QRS complex
regulation of the cardiac cycle
Regulation of the Cardiac Cycle
  • Volume of blood pumped changes to accommodate cellular requirements
    • Strenuous exercise = requires more blood
  • S-A node changes rate as a response to sympathetic and parasympathetic nerve fibers
regulation of the cardiac cycle1
Regulation of the Cardiac Cycle
    • Parasympathetic stimulation = heart rate decreases
    • Continuously “braking” heart action
    • Can change heart rate by either increasing or decreasing impulses
  • Sympathetic stimulation = increases heart rate and force of myocardial contractions
regulation of the cardiac cycle2
Regulation of the Cardiac Cycle
  • Baroreceptor reflexes involving the cardiac control center of the medulla oblongata maintain the balance between sympathetic and parasympathetic stimulation
  • Baroreceptors detect blood pressure and sends that info to the brain which sends a message to the heart
regulation of the cardiac cycle3
Regulation of the Cardiac Cycle
  • The cerebrum and hypothalamus can also influence it
    • Causes fainting following emotional upset
    • Increases heart rate during anxiety
  • Temperature
    • Increased temperature increases heart rate
    • Colder temperatures decrease heart rate
regulation of the cardiac cycle4
Regulation of the Cardiac Cycle
  • Concentration of ions
    • Hyperkalemia (too much K+) decreases the rate and force of contractions
    • Hypokalemia (too little K+) produces a potentially life-threatening abnormal heart rhythm
    • Hypercalcemia (too much Ca+) increases heart actions, posing the danger that the heart will contract for an abnormally long time
    • Hypocalcemia (to little Ca+) depresses heart action