• Path of Blood Through the Heart OH Path of Blood Through the Heart

• Low O₂ and high CO₂ bloodvena cava and coronary sinusright atriunright atrium contractsright atrioventricular orificeright ventricleright ventricle contracts and tricuspid valve closes the right atrioventricular orificepulmonary trunkpulmonary arteries capillaries in the lungsgas exchange in the alveolipulmonary veinsleft atriumleft atrium contractsblood moves through the left atrioventricular orificeleft ventricleleft ventricle contractsbicuspid (mitral) valve closes the left atrioventricular orificeaorta and its branches (systemic circuit
• Blood Supply to the Heart OH-Coronary Circulation

• Blood is supplied to the tissues of the heart by the first two branches of the aorta--right and left coronary arteries.14015-14016

• One branch of the left coronary artery, the circumflex artery, follows the coronary sulcus between the right and left ventricle.
  • Branches supply blood to the walls of the left atrium and left ventricle.
• Another branch of the left coronary artery, the anterior interventriculary artery (left anterior descending artery) travels to the anterior interventricular sulcus and its branches supply the walls of both ventricles.
• The right coronary artery passes along the atrioventricular sulcus between the right atrium and right ventricles.
  • Gives off two major branches:

• Posterior interventricular artery--supplies walls of both ventricles.
• Marginal artery--supplies the walls of the right atrium and right ventricle
  • Because of the heart's activity, cardiac muscle must have a continuous supply of oxygenated blood.
  • Blood flow to the ventricles is poorest during contraction.
    • Muscle action of the fibers of the myocardium compress nearby vessels.
    • Openings of the coronary arteries are closed during contraction.
  • Blood that has passed through the myocardial capillaries is drained by branches of the cardiac veins which join the coronary sinus.

• Coronary artery disease. Plaque 14061, 14062

• Heart Sounds OH-Heart Sounds

• Lub-dup sounds are due to vibrations in the heart tissues that are created as the blood flow is suddenly increased or slowed with the contraction and relaxation of the heart chambers and with the opening and closing of the valves.
• Lub sound
  • Occurs during the ventricular contraction when the A-V valves are closing.
• Dup sound
  • Occurs during ventricular relaxation when the semilunar valves are closing.

• Cardiac Conduction System OH-T98 and ADAM Interactive:Conduction System of the Heart

• Throughout the heart are clumps of specialized cardiac muscle tissue whose fibers contain only a few myofibrils.
  • Initiate and distribute cardiac impulses throughout the myocardium.
  • Comprise the cardiac conduction system which coordinates the events of the cardiac cycle.
• Sinoatrial (S-A) Node
  • Consists of a small enlongated mass of specialized muscle tissue just beneath the epicardium.
  • Fibers are continuous with those of the atrial muscle fibers.
  • Membranes of the nodal cells are in contact with each other and have the ability to excite themselves.
    • Without being stimulated by nerve fibers or any other outside agents, the nodal cells initiate impulses that spread into the surrounding myocardiumand stimulate the cardiac muscle fibers to contract.
    • Activity is rhythmic.
  • Initiates 70-80 impulses/minute and is responsible for the rhythmic contractions of the heart and is often called the pacemaker.
• As a cardiac impulse travels from the S-A node into the atrial myocardium, the right and left atria contract almost simultaneously.
• Cardiac impulses passes along fibers to the atrioventricular node (A-V node)
  • Located in the floor of the right atrium just beneath the endocardium.
• Fibers that conduct the cardiac impulse into the A-V node have very small diameters and conduct impulses slowly and cause the impulse to be delayed.
  • Impulse is delayed still more as it travels through the A-V node.
    • This delay allows time for the atria to empty and the ventricles to fill with blood.
• Impulse now passes into a group of large fibers that make up the A-V bundle (Bundle of His) and the impulse moves rapidly through them.
• A-V bundle divides into the right and left bundle branches.
  • About 1/2 way down, the branches give rise to enlarged Purkinje fibers.
• Purkinje fibers spread from the interventricular septum into the papillary muscles and then continue downward to the apex of the heart.

9. Stimulated by the impulses on the Purkinje fibers, the ventricular walls contract with a twisting motion which squeezes or wrings blood out of the ventricular chambers and forces it into arteries.

• Electrocardiogram (ECG or EKG) OH-Electrocardiogram ADAM Interactive

• Impulse transmission through the conduction system generated electrical currents that can be detected on the body's surface.
• Three types of EKGs
  • Resting
  • Stress
  • Ambulatory
• In a typical record, three clearly recognizable waves accompany each cardiac cycle.
• P-Wave
  • Small upward wave.
  • Indicates atrial depolarization.
    • The spread of the impulse from the S-A node through the two atria.
    • A fraction of a second after the P-wave begins, the atria contract.
• QRS-Wave or Complex
  • Begins as a downward deflection, continues as a large, upright, triangular wave and ends as a downward wave at its base.
  • Represents ventricular depolarization-the spread of the electrical impulse through the ventricles.
  • Shortly after the QRS wave begins, the ventricles undergo contraction.
• T-Wave
  • Dome-shaped upward wave.
  • Indicates ventricular repolarization
• In reading the EKG, it is important to note the size of the deflection waves at certain time intervals.
  • Enlargement of the P wave
    • Indicates enlargement of the atria--atrial stenosis--mitral valve narrows, blood backs into the left atrium and there is an expansion of the atrial wall.
  • P-R Interval
    • Is measured from the beginning of the P-wave to the beginning of the QRS wave (complex).
    • Lengthening of this interval as in atherosclerotic disease and rheumatic fever occurs because the heart tissue, covered by the P-Q interval, namely the atria and A-V node is scarred or inflamed.
      • Impulse, as a result, travels at a slower rate and the interval is lengthened.
  • Enlarged Q-wave may indicate a myocardial infarction. Acute 14065, Old 14066
  • Enlarged R wave generally indicates enlarged ventricles.
  • S-T Segment
    • Represents the time between the end of the spread of the impulse through the ventricles and repolarization of the ventricles.
    • S-T segment is elevated in acute myocardial infarction.
    • S-T segment is depressed when the heart muscle receives insufficient oxygen.
  • T-Wave
    • Represents ventricular repolarization.
    • It is flat when the heart muscle is receiving insufficient oxygen.
    • May be elevated during hyperkalemia.
  • Fibrillation 16827 Play
  • Defibrillation 17233 Play

• Cardiac Cycle OH-126 and ADAM Interactive

• The heart can be viewed as two (2) separate pumps represented by the right and left halves of the heart.
  • Each pump consists of a primer pump (the atrium) and a power pump (the ventricle).
• Both atrial primer pumps complete the filling of the ventricles with blood and both ventricular power pumps produce the major force that causes blood to flow through the pulmonary and systemic arteries.
• The cardiac cycle refers to the repetitive pumping process that begins with the onset of cardiac muscle contraction and ends with the beginning of the next contraction.
• The duration of the cardiac cycle varies among people and also varies during an individual's lifetime.
  • May be as short as 0.25-0.30 seconds in a newborn infant to as long as 1 or more seconds in a well-trained athlete.
• The normal cardiac cycle (0.7-0.8 sec.) depends on two (2) factors:
  • Capability of cardiac muscle to contract.
  • Functional integrity of the conducting system.
• Abnormalities of cardiac muscle, the valves, or the conducting system of the heart may alter the cardiac cycle and compromise the pumping effectiveness of the heart.
• In cases of severe dysfunction, repair is necessary.
  • Angioplasty 14057-14059
  • Coronary artery bypass. Model and 14056
  • Artificial pacemaker implantation. 14025-14026
  • Valve replacement.
    • Excised for replacement 14000
    • Artificial valve 14004
  • Heart transplant. Artificial 14079-14080
• Cardiac Cycle Animation 16248 Play

• Systole and Diastole

• Systole means "to contract" and diastole means "to dilate".
  • Atrial systole--contraction of the atrial myocardium.
  • Atrial diastole--relaxation of the atrial myocardium.
  • Ventricle systole--contraction of the ventricular myocardium.
  • Ventricle diastole--relaxation of the ventricular myocardium.
  • When systole and diastole are used without reference to specific chambers, they mean ventricular systole and diastole.
• Atrial systole and diastole
  • Contraction of the atria is responsible for 30% of the ventricular filling.
  • Pressure changes in the atria include:
    • a wave--caused by atrial contraction.
    • c wave--caused by ventricular contraction.
    • v wave--caused by blood flowing into the atria.
• Ventricular systole and diastole
  • Contraction of the ventricles causes blood to move to the lungs and to the body.
    • Pressure generated by the right ventricle (blood to the lungs) is lower than than pressure generated by the left ventricle (blood to the body).
  • During the period of isometric contraction, ventricular contraction causes an increase in pressure within the ventricles but no movement of blood out of the ventricles.
  • Blood flows out of the ventricles during the period of ejection.
  • Semilunar valves close, ventricles relax, and pressure drops to 0 during the early stages of diastole and the ventricles begin to fill with blood.
  • Stroke volume is the difference between the end diastolic volume and end systolic volume. (the amount of blood pumped by the heart per beat)
  • Cardiac Output = Stroke Volume x Heart Rate
    • Resting college student
      • mL/beat x 72 beats/min. = 5040 mL/min or 5 L/min.
    • Exercising college student
      • mL/beat x 120 beats/min = 24000 mL/min or 24 L/min.
  • Cardiac output and peripheral resistance determine blood pressure.
    • Adequate blood pressure is necessary to ensure delivery of blood to tissues.
      • Healthy young adult 120 mm Hg/ 80 mm Hg.
• Aortic Pressure Curve
  • Contraction of the ventricles forces blood into the aorta, thus producing the peak systolic pressure.
  • Blood pressure falls to the diastolic level as blood flows out of the aorta.
• Regulation of the Heart

• Intrinsic Regulation
  • Venous return is the amount of blood that returns to the heart during each cardiac cycle.
    • An increase in venous return causes an increase in cardiac output.
  • Starling's Law of the Heart--Cardiac Output Venous Return
  • Venous return stretches the S-A node and increases the heart rate.
• Extrinsic Regulation
  • The cardioregulatory center in the medulla oblongata regulates the parasympathetic and sympathetic nervous control of the heart.
  • Parasympathetic Control
    • Parasympathetic stimulation is supplied by the vagus nerve.
    • Parasympathetic stimulation decreases heart rate and can cause a small decrease in the force of contraction (stroke volume).
    • Postganglionic neurons secrete acetylcholine which increases membrane permeability to K⁺, producing hyperpolarization of the membrane.
  • Sympathetic Control
    • Sympathetic stimulation is supplied by the cardiac nerves which are projections of the cervical sympathetic chain ganglia (spinal nerve).
    • Sympathetic stimulation increases heart rate and force of contraction (stroke volume).
    • Postganglionic neurons secrete norepinephrine which causes membrane permeability to Na⁺ and Ca²⁺ producing hyperpolarization of the membrane.
    • Epinephrine and norepinephrine are releases into the blood from the adrenal medulla as a result of sympathetic stimulation.
      • Effects of epinephrine and norepinephrine on the heart are long lasting compared to the effect of neural stimulation.
      • Both increase the rate and force of heart contraction

• Heart and Homeostasis

• Effect of Blood Pressure
  • Baroreceptors (sensory receptors are in the walls of certain large arteries i.e.Internal carotids and the aorta)--function to measure blood pressure.
  • In response to an increase in blood pressure, the baroreceptor reflexes decrease sympathetic stimulation and increase parasympathetic stimulation.
  • An increase in right atrial pressure also causes the cardioregulatory center to increase the heart rate through a reflex called the Bainbridge Reflex.
• Effect of pH, CO₂ and O₂
  • Chemoreceptors in the brain and carotids monitor blood CO₂, O₂, and pH levels.
  • In response to increased CO₂, decreased pH, or decreased O₂, autonomic nervous system reflexes increase sympathetic stimulation and decrease parasympathetic stimulation.
• Effect of Extracellular Ion Concentration
  • An increase or decrease in extracellular K⁺ decreases heart rate.
  • Increased extracellular Ca²⁺ increases the force of contraction of the heart and decreases the heart rate.
  • Decreased Ca²⁺ levels produce the opposite effect.
• Effect of Body Temperature
  • Heart rate increases when body temperature increases and decreases when bodytemperature decreases.

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