Heart actions 2

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Heart actions 2

  1. 1. Heart Actions Chapter 13: Cardiovascular System Unit 4: Transport
  2. 2. Cardiac Cycle <ul><li>A coordinated series of events occuring in the heart to ensure proper flow of blood in the CV system </li></ul><ul><ul><li>If interrupted or compromised, results in poor perfusion </li></ul></ul><ul><li>Blood moves between chambers based on differences in pressure </li></ul><ul><ul><li>Blood always moves from high pressure area to low pressure area </li></ul></ul>
  3. 3. Cardiac Cycle <ul><li>Some important terminology: </li></ul><ul><ul><li>Systole  When a chamber is contracting </li></ul></ul><ul><ul><ul><li>Contraction makes the chamber smaller </li></ul></ul></ul><ul><ul><ul><li>As chamber shrinks, pressure goes up </li></ul></ul></ul><ul><ul><li>Diastole  When a chamber is relaxing </li></ul></ul><ul><ul><ul><li>Relaxing chambers get bigger </li></ul></ul></ul><ul><ul><ul><li>Pressure goes down </li></ul></ul></ul>
  4. 4. Cardiac Cycle <ul><li>The atria contract while the ventricles relax. </li></ul><ul><li>The ventricles contract while the atria relax. </li></ul><ul><li>Pressure within the chambers rises and falls in repeated cycles. </li></ul>
  5. 5. Steps of the Cycle <ul><li>1. Atrial Systole/Ventricular Diastole </li></ul><ul><ul><li>Let’s start with blood flowing into both the left and right atria </li></ul></ul><ul><ul><ul><li>Atria swell with blood returning to the heart via large veins ( vena cava & pulmonary veins ) </li></ul></ul></ul><ul><ul><ul><li>Atria have a determined volume (they can only hold a certain amount of blood) </li></ul></ul></ul><ul><ul><ul><li>Pressure in atria increases due to increased volume pushing on the inside walls </li></ul></ul></ul><ul><ul><li>As ventricles relax, pressure drops below the pressure in atria </li></ul></ul><ul><ul><ul><li>Lower pressure in ventricles opens the A-V valves </li></ul></ul></ul><ul><ul><ul><li>Blood pours into ventricles </li></ul></ul></ul>
  6. 6. Steps of the Cycle <ul><li>1. Atrial Systole/Ventricular Diastole </li></ul><ul><ul><li>As muscles of ventricles relax, pressure drops below the pressure in atria </li></ul></ul><ul><ul><ul><li>Lower pressure in ventricles opens the A-V valves </li></ul></ul></ul><ul><ul><ul><li>Blood pours into ventricles </li></ul></ul></ul>
  7. 7. Steps of the Cycle <ul><li>1. Atrial Systole/Ventricular Diastole </li></ul><ul><ul><li>Blood flows into ventricles, filling them and increasing the pressure. </li></ul></ul><ul><ul><li>70% of blood in atria pour into vent’s passively </li></ul></ul><ul><ul><li>Finally, atria contract (systole), forcing the other 30% of blood into ventricles </li></ul></ul>
  8. 8. Steps of the Cycle <ul><li>2. Ventricular Systole/Atrial Diastole </li></ul><ul><ul><li>Ventricles swell with blood, increasing pressure </li></ul></ul><ul><ul><li>Ventricles contract, increasing the pressure (high press) as atria relax (low press), closing the A-V valves </li></ul></ul><ul><ul><ul><li>Prevents backflow of blood into the atria </li></ul></ul></ul><ul><ul><li>As ventricle contracts… </li></ul></ul><ul><ul><ul><li>Pressure increases to a point greater than the aorta and pulmonary trunk </li></ul></ul></ul><ul><ul><ul><li>Blood is forced into aorta/pulm trunk & through systemic circuit </li></ul></ul></ul>
  9. 9. Steps of the Cycle <ul><li>3. Atrial Systole/Ventricular Diastole </li></ul><ul><ul><li>After pumping blood out, ventricles begin to relax (low pressure) as atria begin filling with more blood. </li></ul></ul><ul><ul><li>When pressure in ventricle drops below that in the aorta/pulm trunk, semilunar valves close </li></ul></ul><ul><ul><li>Cycle repeats </li></ul></ul>
  10. 11. Heart Sounds <ul><li>Heart sounds are due to the vibrations that valve movements produce. </li></ul><ul><ul><li>The heart sound is a lubb-dubb. </li></ul></ul><ul><ul><ul><li>Lubb  occurs during ventricular contractions, when the A-V valves are closing </li></ul></ul></ul><ul><ul><ul><li>Dubb  occurs during ventricular relaxation, when the pulmonary and aortic valves are closing. </li></ul></ul></ul><ul><ul><ul><li>Heart Sounds </li></ul></ul></ul>
  11. 12. Heart Sounds <ul><li>Heart sounds are due to the vibrations that valve movements produce. </li></ul><ul><ul><li>A heart murmur is the result of one or more valves that do not close properly </li></ul></ul><ul><ul><li>Results in blood leaking backwards in the heart </li></ul></ul><ul><ul><li>Heart Murmurs </li></ul></ul>
  12. 13. Cardiac Muscle Fibers <ul><li>Cardiac muscle functions similarly to skeletal muscle </li></ul><ul><ul><li>Striated </li></ul></ul><ul><ul><li>Myosin and actin slide past each other in a contraction cycle similar to skeletal muscle </li></ul></ul><ul><ul><li>Require ATP produced by cellular respiration </li></ul></ul>
  13. 14. Cardiac Muscle Fibers <ul><li>Major difference: The fibers connect in a branching fashion, allowing electrical signals to pass easily from one cardiac mucle cell to another. </li></ul><ul><ul><li>Stimulation to any part of the network sends impulses throughout the heart, which contracts as a unit. </li></ul></ul><ul><ul><ul><li>There are two networks in the heart, each called a Functional Syncytium </li></ul></ul></ul><ul><ul><ul><li>One syncytium operates the atria, the second operates the ventricles. </li></ul></ul></ul>
  14. 16. Cardiac Conduction System <ul><li>Made of two functional syncytia </li></ul><ul><li>Coordinates the heart beat ( Cardiac Cycle ). </li></ul><ul><li>Made of special cells that themselves do not contract. </li></ul><ul><li>Performs two functions: </li></ul><ul><ul><li>Initiates electrical signal </li></ul></ul><ul><ul><li>Conducts the signal to heart muscle </li></ul></ul>
  15. 18. Sinoatrial Node <ul><li>The Sinoatrial Node (S-A node) is a small mass of specialized cardiac muscle tissue found in the wall of the right atrium. </li></ul><ul><ul><li>These cells reach threshold on their own , producing a muscle impulse (No CNS input needed) </li></ul></ul><ul><ul><li>Surrounding myocardial cells contract in response to the impulse from the S-A node. </li></ul></ul><ul><ul><li>Only the Atria contract due to the S-A node’s action </li></ul></ul><ul><ul><ul><li>*S-A node activity is rhythmic, and initiates one impulse after another (70 to 80 times a minute in an adult) </li></ul></ul></ul><ul><ul><ul><ul><li>*Pacemaker* </li></ul></ul></ul></ul>
  16. 20. Atrioventricular Node <ul><li>Cardiac impulse travels from the S-A node into the atrial syncytium , causing the right and left atria to contract almost simultaneously. </li></ul><ul><ul><li>Impulse from S-A node passes through myocardium to the Atrioventricular node , found near the top of the septum . </li></ul></ul><ul><ul><ul><li>The A-V node slows down the impulse </li></ul></ul></ul><ul><ul><ul><li>Impulse is sent down Purkinje Fibers into the inferior walls of the ventricles </li></ul></ul></ul><ul><ul><ul><li>Ventricular walls contract, squeezing from inferior toward superior due to Purkinje fibers taking electrical signal to the bottom of heart first </li></ul></ul></ul>
  17. 23. Electrocardiogram (ECG) <ul><li>An ECG ( EKG ) records electrical changes in the myocardium during a cardiac cycle. </li></ul><ul><ul><li>Super-sensitive electrodes are placed on the skin near the heart. </li></ul></ul><ul><ul><li>Changes in electrical activity caused by cardiac muscle contractions are detected </li></ul></ul><ul><ul><li>A graph is produced </li></ul></ul><ul><ul><li>The pattern contains several waves. </li></ul></ul><ul><ul><ul><li>1. The P wave represents atrial depolarization. </li></ul></ul></ul><ul><ul><ul><li>2. The QRS complex represents ventricular depolarization (contraction). </li></ul></ul></ul><ul><ul><ul><li>3. The T wave represents ventricular repolarization (relaxation). </li></ul></ul></ul>
  18. 24. Electrocardiogram (ECG) <ul><li>The graph pattern contains several waves. </li></ul><ul><ul><ul><li>1. The P wave represents atrial depolarization (contraction). </li></ul></ul></ul><ul><ul><ul><li>2. The QRS complex represents ventricular depolarization. </li></ul></ul></ul><ul><ul><ul><li>3. The T wave represents ventricular repolarization (relaxation). </li></ul></ul></ul>
  19. 27. Regulation of the Cardiac Cycle <ul><li>Physical exercise, body temperature, and the concentration of various ions affect heartbeat. </li></ul><ul><ul><li>Branches of sympathetic and parasympathetic nerve fibers innervate the S-A node and controls its pace </li></ul></ul><ul><ul><ul><li>What effect does the parasympathetic NS have on heart rate and blood pressure? </li></ul></ul></ul><ul><ul><ul><li>What effect does the sympathetic NS have on heart rate and blood pressure? </li></ul></ul></ul><ul><ul><li>Most people at rest have a HR lower than the S-A’s pace. Nervous system has a “brake” on the heart </li></ul></ul>
  20. 28. Regulation of the Cardiac Cycle <ul><li>Physical exercise, body temperature, and the concentration of various ions affect heartbeat. </li></ul><ul><ul><li>Most people at rest have a HR lower than the S-A’s pace. Parasympathetic nervous system has a “brake” on the heart </li></ul></ul><ul><ul><ul><li>S-A node has a “typical” cycle of 100 beats per minute </li></ul></ul></ul><ul><ul><ul><li>Parasymthpathetic nervous system slows down heart rate. </li></ul></ul></ul><ul><ul><ul><li>When a faster rate is required, the nervous system “brake” is removed, and sympathetic innervation may also increase HR more. </li></ul></ul></ul>

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