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
Difference between action potentials in myocardium vs neurons and skeletal muscle
They are very similar but the overall potential and refractory period lasts longer (plateau phase). This allows the heart chambers to fill with blood adequately.
Describe the depolarization phase in cardiac muscle.
- Fast-gated Na+ channels open allowing rapid inward movement of Na+ ions into the cell.
- Membrane potential from -90mV to +30mV
- Gap junctions spread excitation
Describe the early repolarization phase in cardiac muscle.
- Trickle of K+ ions out of cell
- Slightly changes membrane potential charge in the negative direction
Describe the plateau phase in cardiac muscle.
- Unable to respond to a stimulus during this time.
- Ca2+ ions from the sarcoplasmic reticulum enter the cell, maintaining the membrane potential around +10mV.
- plateau phase lasts around 200msec.
- latter part of depolarization phase.
Explain the Ca++ channels during the plateau phase.
Ca2+ channels open slowly allowing ions into the cell and begins the process of coupling the electrical and mechanical response within muscle.
- Ca2+ ions supplied by the sarcoplasmic reticulum and diffusion across the cell membrane during the action potential increases its concentration within the cytoplasm.
- Ca2+ combines with troponin, removing tropomyosin’s inhibition of cross-bridge formation between the actin and myosin myofilaments.
- Cross-bridge formation allows for muscle contraction.
- During repolarization, Ca2+ concentration decreases within the cytoplasm via active transport.
Describe the Repolarization phase in cardiac muscle.
- Ca2+ channels close
- K+ channels open to allow outflow of ions
- Membrane more negative and returns to -90mV.
Describe the resting potential phase in cardiac muscle.
- Membrane potential restored to -90mV
- Now primed and ready for next action potential
What are the 5 phases of Action potential in cardiac muscle?
1) Depolarization
2) Early repolarization
3) Plateau
4) Repolarization
5) Resting potential
What is the pathway of conduction of an electrical signal in the heart?
1) SA node
2) Both atria
3) both AV nodes
4) Bundle of His (AV bundle)
5) Right and left bundle branches
6) Purkinje fibers
7) Ventricular myocardium (ventricles)
Describe an Electrocardiogram (ECG). What does it measure? What kind of medical problems could it detect?
- Evaluates electrical activity within the heart
- Measures currents in the extracellular fluid surrounding heart cells
- Could detect enlarged heart chambers, myocardial infarctions, or arrhythmias
On an ECG, how many times does the cycle normally repeat per minute when at normal resting rate?
75 beats per minute
What do deflections represent on an ECG?
- Represents timing and strength of the signal for atrial and ventricular contraction (systole) and relaxation (diastole)
What does the P wave represent?
-Atrial depolarization as action potential spreads from SA node to the atrial myocardium and AV node.
Contraction time for atria
0.1 seconds
What does the P-Q interval represent?
- Time from atrial to ventricular excitation.
- Pulse travels from AV node down bundle of His, right/left bundles, Purkinje cells and, finally ventricular myocardium.
What does the QRS complex represent?
- Ventricular depolarization
- Ventricular cardiac muscle cells contract (ventricular systole = at 0.3 sec)
What is signal is masked in an ECG? Why?
Atrial repolarization
It occurs at the same time as the QRS complex. Since the QRS complex has such a large signal, it masks the atrial repolarization signal.
What does the T wave represent?
- Ventricular repolarization
- Ventricular diastole at 0.5 seconds
What does the Q-T interval represent?
Time from start of ventricular depolarization to repolarization.
About 0.36 to 0.44 seconds.
