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