Midterm 1: Cardiovascular System Flashcards
Explain End Diastolic Volume (EDV). What occurs during this process?
EDV is the volume of blood that fills the ventricle during diastole.
- Atria/ventricles are relaxed
- Blood enters atria, then passes through tricuspid valve to ventricles.
- Ventricle pressure increases
- SA node discharges (P wave), atria contract (atrial kick)
- End ventricle diastole or end-diastolic volume of 130 mL.
Diastole definition
Phase of the heartbeat when the heart muscle relaxes and allows the chambers to fill with blood.
Explain End Systolic Volume (ESV). What occurs in order to get this?
End systolic volume is the amount of blood left over in the ventricles after contraction.
- From the AV node, depolarization passes to ventricular tissues (QRS complex)
- Ventricles contract
- AV valves close to prevent backflow
- Briefly, all valves are closed
- Blood flows out of ventricles
- End ventricular systole or end-systolic volume (60 ml)
Systole definition
Phase of the heartbeat when the heart muscle contracts and pumps blood out of the heart.
What is Stroke Volume? What is a typical value? How is it measured?
Stroke Volume is the amount of blood that is pumped per beat. Normal is around 75 mL or 0.075 L
It is measured by taking the difference between End Diastolic Volume (EDV) and End Systolic Volume (ESV).
Stroke Volume (SV) = EDV - ESV
What is Cardiac Output? How is it measured?
Cardiac output is the total output of blood from the heart per minute.
It is measured by taking the number of beats per minute and multiplying it by the amount that is ejected per beat (stroke volume).
Cardiac Output (CO) = Heart Rate x Stroke Volume
What are the 4 stages of the Heart Cycle?
1) Isovolumetric Ventricular Contraction
2) Ventricular Ejection
3) Isovolumetric Ventricular Relaxation
4) Rapid Ventricular Filling
What is the first stage of the heart cycle? Describe this stage.
Isovolumetric ventricular contraction.
- Atrioventricular valves close and pressure increases making the first soft-sounding “lub” heart sound.
- This marks the beginning of systole and is associated with the peak of R wave in QRS complex.
- Semilunar valves open which is the start of ventricular ejection
What is the second stage of the heart cycle? Describe what happens in this stage.
Ventricular Ejection
- Rapid ejection of the blood (stroke volume)
- Ventricles begin to relax (T wave)
- Some blood remains in the ventricles (end-systolic volume)
What is the third stage of the heart cycle? Describe this stage.
Isovolumetric ventricular relaxation
- Marks the beginning of ventricular diastole as rapid decrease in pressure from 100 mmHg to around 0 mmHg.
- Semilunar valves close making the second, louder, “dub” sound.
What is the fourth stage of the heart cycle? Describe this stage.
Rapid Ventricular Filling
- As volume in ventricles is increased due to ventricular diastole, pressure is decreased further.
- AV valves open as ventricular pressure now less than atrial pressure and blood flows into ventricles (end-diastolic volume)
What does Starling-Frank Law state?
- The more the ventricles are filled during diastole, the more blood that will be ejected upon systole. AKA…. More EDV = More SV
- The heart takes in and pumps out the same amount of blood.
What is stroke volume regulated by?
Regulated by the force of the contraction. Harder contraction pumps more blood out (higher SV)
Which affects cardiac output and stroke volume the most? EDV or ESV?
End-Diastolic Volume (EDV)
Factors that can affect the cardiac output
- Heart rate
- Parasympathetic and Sympathetic nervous system
Bradycardia definition
Slower than normal heart rate
Tachycardia definition
Faster than normal heart rate
How does the parasympathetic nervous system affect cardiac output? What controls this process?
Parasympathetic nervous system slows conduction velocities and slows heart rate. It is under the control of the Vagus nerve (CN 10)
How does the sympathetic nervous system affect cardiac output? What controls this process?
It speeds up conduction velocity and heart rate. It is controlled by postganglionic fibers projecting from the uppermost part of the sympathetic trunk.
Describe the sinoatrial node (SA node) location, its firing rate, excitation time, and what its controlled by.
- Located in the right atrium near the entry of the superior vena cava.
- Fires 90-100 times per minute.
- 50 millisecond excitation time
- Controlled by autonomic nervous system
Describe the atrioventricular node (AV node) function, location, and its firing rate.
- Propagates signal to AV bundle (bundle of His)
- Located within septum near tricuspid valve.
- Fires 40-50 times per minute
Why is there a delay of signal between the SA node and AV node? How long is that delay?
There is a delay in order to allow the atria to completely contract which allows more filling of the ventricles.
The delay is 200 milliseconds.
Describe the Purkinje fibers, their location, firing rate, and what happens when they fire too slow.
- Specialized cardiac muscle fibers
- Run just below the endocardium before penetrating deeper into the myocardium.
- Fire 20-40 times per minute
- When they fire too slow, a pacemaker is possibly needed.
Describe cardiac muscle function and response time to the AV node.
- Functions as a single unit in response to electrical stimulation by containing gap junctions through intercalated disks.
- 50 millisecond time from AV node to ventricular myocardium
