Chap 18 Study guide
In cardiac muscle, the fast depolarization phase of the action potential is the result of what event?
- Due to Na+ influx
The long plateau phase of the cardiac muscle action potential is due to what event?
- Due to Ca2+ influx
Where is the normal pacemaker of the heart located?
- The sinoatrial (SA) node is located in the myocardium of the right atrium, lateral to the entrance of superior vena cava
What are autorhythmic cells?
- Depolarize spontaneously because of leaking Na+ channels
Learn the sequence in which excitation would move through the conducting system of the heart
- Sinoatrial (SA) node → 2. Atrioventricular (AV) node → 3. Atrioventricular (AV) bundle → 4.Bundle branches → 5. Purkinje fibers
What is a heart block? Damage of what structure of the heart can cause a heart block?
- Few or no impulse from SA node reach the ventricles
- Defective AV node
What part of the brain regulates heart activity?
- Medulla oblongata
What electrocardiogram can be used for?
- Electrical activity of the heart
What electrical event happens during a P wave?
- Depolarization of SA node
What electrical event happens during a QRS complex?
- Ventricular depolarization
What electrical event happens during a T wave?
- Ventricular repolarization
What mechanical events are responsible for the heart sounds?
- Closing of heart valves
The first heart sound is heard when?
- AV valves close
The second heart sound is heard when?
- SL valves close
What is a cardiac cycle? At a heart rate of 70 beats/minute, a cardiac cycle lasts?
- Cardiac cycle: all events associated with blood flow through the heart during one complete heartbeat
- 0.8 Seconds
What is systole and what is diastole?
- Systole = contraction
- Diastole = relaxation
Learn the events that happen during the ventricular filling?
- AV valves open → Blood passively flows into ventricles → Atrial systole occurs
Learn the events that happen during the ventricular systole
- Atria relax → AV valves close → isovolumetric contraction → in ejection phase, ventricular pressure exceeds pressure in the large arteries, forcing the SL valves open → first heart sound
Learn the events that happen during the isovolumetric relaxation of the ventricles
- Ventricles relax → SL valves close → second heart sound
What is CO? How can CO be calculated?
- Cardiac output (CO) = volume of blood pumped by each ventricle in one minute.
- CO = heart rate (HR) x stroke volume (SV)
What factors can increase cardiac output?
- ⇧ venous return. ⇧ contractility (force of contraction). ⇧ sympathetic activity. ⇧ stroke volume. ⇧ heart rate.
What is stroke volume?
- Volume of blood pumped by one ventricle with each beat (during one contraction)
What factors can affect stroke volume?
- 1) venous return. 2) 3) EDV. 4) ESV.
What division(s) of the NS innervate the heart?
- Both sympathetic and parasympathetic
Which response would be characteristic of the parasympathetic nervous system?
- Lowers rate of heart contraction
What is the atrial (Bainbridge) reflex? How does it work?
- Atrial (Brainbridge) reflex = a sympathetic reflex initiated by increased venous return
- Atrial walls are stretched which stimulates the SA nodes and atrial stretch receptors. Stretch receptor activation activates sympathetic reflexes and leads to increased heart rate.
What are positive and negative chronotropic factors?
- Temporary stressors that influence heart rate.
- Positive chronotropic factors increase heart rate. Negative chronotropic factors decrease heart rate.
What are bradycardia and tachycardia?
- Bradycardia = heart rate slower than 60 bpm
- Tachycardia = abnormally fast heart rate (faster than 100 bpm)
What is congestive heart failure?
- Low CO because of weakened heart. Blood is backing up in the veins.