Physiology 3 - Cardiovascular Physiology Flashcards
What is the Main Function of the Heart?
To generate pressure to overcome resistance to drive flow
What is Cardiac Output?
- HR x SV
- “the performance of the heart”
How does the heart generate pressure?
- Electrical
- Electrical activation: heart rate
- SA node - stimulates atria to contract
- AV node - pause for atrial filling
- Purkinje fibers - ventricular contraction
- Mechanical
- Muscular activation: stroke volume
- Cardiac Myocytes
- Systole
- Diastole
What is Stroke Volume?
EDV-ESV
What are the events of Electrical Activation of the Heart?
- SA node depolarizes
- Action potential spreads throughout atria
- Action potential goes through AV node and into Purkinje fibers of bundle of His
- This deploarizes the septums and then the rest of the ventricle from apex to base via P fibers and gap junctions
What are the Mechanical Phases of the Cardiac Cycle?
What Ion is Responsible for Resting Membrane Potential?
Potassium
What Ion is responsible for depolarization of muscle cells?
Sodium
What Ion is responsible for deploarization of SA/AV nodes?
Calcium
What Ions are responsible for repolarization?
Potassium moving out of cell
What is the Shape of an Action Potential Seen in SA or AV node?
What is the Shape of an Action Potential Seen in Cardiac Muscle Cells?
What is the Extrinsic Control of the Heart?
ANS Regulation: SNS (beta 1 receptors) vs. PNS (muscarinic receptors)
What are the Effects of Sympathetic Stimulation on the heart?
- Increase in heart rate
- decrease in duration of diastole (mainly)
- decrease in duration of systole
- Increase in contractility
- increase in force of contraction
- increase in speed of contraction
- greater volume ejected in shorter time
- Both HR and SV increase, increasing CO
What are the Effects of Parasympathetic Stimulation on the Heart?
- Decrease in heart rate
- Increase in duration of diastole (mainly)
- Increase in duration of systole
- Modest decrease in contractility
- decrease in force of contraction
- decrease in speed of contraction
- slightly lesser volume ejected in longer time
- Both HR and SV decrease, decreasing CO
What is Preload?
Volume that comes back to the heart
What is Afterload?
Amount you have to contract against in order to push blood out of heart
What is the Effect of Preload on Stroke Volume?
- Usually, but not always, an increase in EDV (or preload) increases the calcium entry into the ventricles, which increases the force of contraction
- This results in an increase in the stroke volume
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What is the Starling Mechanism?
The tendency of the heart to alter contractile force to keep the ESV approximately constant
What is Starling’s Law of the Heart?
The principle that the heart varies its SV with changes in EDV so as to reach a roughly constant ESV
What determines Blood Pressure? (The equations)
What two things contribute to Mean Arterial Blood Pressure?
Cardiac Output (Q) and TPR
How do you obtain the MAP from a Blood Pressure reading?
