Cardio-Vascular system Flashcards
Why is it called a double circulatory system?
There’s a systemic circulatory system (to the body)
And a pulmonary one (to the lungs)
Why is the cardiac impulse of the heart described as myogenic?
The muscle generates its own electrical signal, causes its own contraction.
Where is the cardiac impulse generated?
In the SA node in the right atrium
How does the cardiac impulse travel from the SA node to the AV node?
Passes through the right and left atria walls causing both atria to contract
What is it called when both atria contract?
Atrial systole
What does the AV node do?
Conducts the impulse down through the Bundle of His and down left and right branches via the septum to the apex of the heart.
What happens to the cardiac signal at the apex of the heart?
Impulse travels up and around the ventricle walls via the purkinje fibres
What is the effect of the cardiac signal travelling up and around the ventricle walls?
Both ventricles contract from the bottom (ventricular systole) forcing blood up and out of the heart
After the ventricles contract what happens?
The heart relaxes (diastole) allowing the atria to fill before the next cardiac impulse is generated.
What is the cardiac cycle?
The events of one heart beat
What are the 2 phases of the cardiac cycle?
Diastole
Systole (atrial and ventricular)
How long does the cardiac cycle last?
0.8 seconds
How long is diastole?
0.5 seconds
How long is systole?
0.3 seconds
Describe what happens in diastole
Relaxation phase of the cardiac cycle
0.5 seconds
Both atria fill with blood, increasing atrial pressure.
70% of blood is forced past AV valves into ventricles
What are the 2 AV valves?
Bicuspid (left)
Tricuspid (right)
Describe atrial systole
Aortic and pulmonary valves are closed.
Both atria contract forcing remaining blood past AV valves into ventricles
AV valves then close.
Describe ventricular systole
Both ventricles contract forcing blood up past the aortic and pulmonary valves.
Aortic and pulmonary valves then close again as diastole starts the cycle again.
What is the definition of stroke volume?
Volume of blood ejected from the heart ventricles per beat
What is the definition of heart rate?
Number of heartbeats per minute
What is the definition of cardiac output?
Volume of blood ejected from the heart ventricles per minute
What is the normal resting value for stroke volume?
70ml
What is the trained value for stroke volume?
85ml
What is the normal resting value for heart rate?
70bpm
What is the trained value for heart rate?
Less than 60 bpm (bradycardia)
What is the cardiac output for both untrained and trained people?
5 Lmin (litres per minute)
What 2 things indicate high aerobic fitness based on heart rate
A low resting heart rate
Quick heart rate recovery after exercise
What causes bradycardia?
Hypertrophy of the heart muscle walls increases stroke volume as there are stronger contractions
What is stroke volume dependent on?
Venous return (mainly) High altitude (increases SV) High temperature (Increases SV) Gravity can also affect it
What is the definition of maximum heart rate?
The highest heart rate value one can achieve in an all-out effort to the point of exhaustion.
When will heart rate plateau?
During constant rate of sub-maximal work.
Aerobic work where oxygen supply = muscular demand
What is it called where the heart rate plateaus?
Steady state heart rate
What is the steady state heart rate?
The optimal heart rate for meeting the circulatory needs at that rate of work
How do you use steady state heart rate to know if a heart is efficient?
The lower the steady state heart rate the more efficient the heart
What is the normal value for SV at submaximal work?
100ml
What is the normal value for SV at maximal work?
120ml
What is the trained value for SV at submaximal work?
180ml
What is the trained value for SV at maximal work?
200ml
What is the value for cardiac output at submaximal work?
10 Lmin
What is the Max heart rate?
220-age
untrained lower/trained higher
What is the max cardiac output?
20/40 Lmin
What is Starling’s law?
Primary factor controlling SV/Q is the extent of ventricular stretch which is dependent upon venous return
Therefore, SV/Q is dependent on venous return.
How do you work out stroke volume?
Volume of blood at the end of diastole - Volume of blood at the end of systole
(EDV-ESV)
What happens to stroke volume during exercise?
Increases linearly with exercise but then plateaus/falls after 40/60% of max work rate
reserve ESV is used to increase SV so can only increase up to a certain amount afterwards only HR can increase.
When are maximal SV values reached?
Submaximal work
What happens to cardiac output during exercise?
Increases initially due to increase in SV and HR.
After 40-60% of max work increases in Q are due to HR more than SV
Describe starlings law
SV dependent on venous return (VR)
VR increases during exercise, more blood returns to heart, greater EDV stretches ventricles so they recoil with greater force, increasing ventricular contractility, almost completely emptying EDV/increasing SV.
Why does heart rate increase before exercise?
There’s an anticipatory rise as adrenaline directly stimulates the SA node which increases heart rate.
What 3 receptors rapidly increase heart rate?
Proprioceptors (motor movement)
Chemoreceptors (change in pH)
Baroreceptors (Increase in blood pressure)
What extra thing at maximal work increases heart rate?
Continued release of adrenaline
What is different between max and submax HR graphs?
Sub max plateaus whilst max has a slower rise to the max.
What causes a rapid drop in HR after exercise stops?
Decrease stimulation from
Proprioceptors (motor movement)
Chemoreceptors (change in pH)
Baroreceptors (Increase in blood pressure)
Why isn’t there a rapid decrease in heart rate after exercise has stopped all the way back to resting heart rate?
There is a slower decrease to resting heart rate whilst repaying the oxygen debt.
What causes there to be a longer recovery time for HR to get back to resting values?
Greater the work intensity, longer recovery as greater oxygen debt.
Need more oxygen to speed up removal of lactic acid produced in anaerobic work.
Where/ what is the cardiac control centre?
The medulla oblongata
Where heart rate is controlled.
What are the neural controls of cardiac output?
Proprioceptors (motor movement)
Chemoreceptors (change in pH)
Baroreceptors (Increase in blood pressure)
What is hormonal control of cardiac output?
Adrenaline (directly stimulates SA node to increase heart rate)
What is the intrinsic control of cardiac output?
Starlings law
increase VR and temp increase SV
What nervous system/nerve increases heart rate?
All the reasons that increase heart rate are sympathetic nervous system (cardiac nerve) stimulating the SA node to increase HR/SV.
What nervous system/nerve decreases heart rate?
All the reasons that decrease heart rate are parasympathetic nervous system (vagus nerve) stimulating the SA node to decrease HR/SV
What is the vascular shunt mechanism? Precapillary sphincters (PCS)
During exercise, cardiac output is redistributed. Arterioles and PCS of muscles vasodilate, of organs vasoconstrict.
So 80% of Q to muscles, 20% to organs.
At rest how much of cardiac output goes to muscles/organs?
80% to organs
20 to muscles
Arterioles/PCS of organs vasodilate, of muscles vasoconstrict
What is the structure of arterioles?
Thick middle layer of smooth muscle
What is the function of arterioles?
Vasoconstrict/vasodilate to either increase or decrease the distribution of cardiac output going to the muscles/organs
What is the structure of precapillary sphincters?
Ring of smooth muscle at the entry into muscle capillary networks
What is the function of precapillary sphincters?
Constrict/dilate to either increase or decrease the distribution of cardiac output going to the muscles/organs
What is the definition of venous return?
Venous/deoxygenated blood returning to the heart.
What are the 5 mechanisms that aid venous return?
Skeletal muscle pump Respiratory pump Pocket valves Gravity Smooth muscle
How does the skeletal muscle pump aid venous return?
Squeeze veins between muscles, opening valves
How does the respiratory pump aid venous return?
High to low pressure in thoracic cavity aids venous return
How do pocket valves aid venous return?
Prevent backflow of blood
How does gravity aid venous return?
All bod parts above heart aid venous return
How does smooth muscles aid venous return?
Venoconstriction venodilation aids venous return
How does an increase in venous return aid performance?
Increase SV so increase Q, which increases oxygen muscle transport which increases intensity they can work at or decreases anaerobic fatigue.
What does venous return need in order to push blood back towards the heart?
Pressure
If blood has insufficient pressure what will happen?
Blood will sit/pool within the pocket valves of veins.
Describe blood pooling
The feeling of ‘heavy legs’
Increased Q sent to muscles in legs without sufficient pressure to return it to the heart.
When are pocket valves, gravity and smooth muscle enough to maintain venous return?
At rest
Not during/immediately after exercise
When are the skeletal muscle and respiratory pumps needed?
During exercise to make sure venous return is maintained.
Where is the vasomotor control centre?
Medulla oblongata
What does the vasomotor control centre do?`
Stimulates arterioles and precapillary sphincters supplying
Organs to vasoconstrict (decrease Q)
Muscles to vasodilate (increase Q)
What is maintained during an active cool down?
HR/respiration, this maintains muscular/ respiratory pumps, which maintains venous return, and blood flow (SV/Q) to supply oxygen to maintain blood pressure and capillary dilation
What is capillary dilation?
Flushing muscles with oxygen to remove lactic acid
What does an active cool down remove?
Lactic acid
What does an active cool down prevent?
Blood pooling
