Regulation of the cardiovascular system 1 Flashcards
What is the cardiac output?
- The volume of blood pumped into the aorta per unit of time
What is stroke volume?
- is the volume of blood pumped out (or ejected) by each ventricle each time the heart beats
What is end diastolic volume (EDV)?
- the amount of blood that will maximally fill the heart at the end of contraction
What is end systolic volume (ESV)?
- where not all blood has been ejected from the heart so a little amount if left after contraction
How do you work out ejection fraction?
= stoke volume (ml) /end diastolic volume (ml)
What is venous return?
= volume of blood returned to the right atrium/or heart per unit time
In a normal functioning heart what is venous return like in comparison with cardiac output ?
- venous return is equal to cardiac output
In a normal functioning heart what is right cardiac output like in comparison with left cardiac output?
- right cardiac output is equal to left cardiac output
What is heart failure?
- where the heart cannot maintain normal cardiac output at normal filling pressures
What is the equation for cardiac output?
Cardiac output (ml/min) = stroke volume (ml/beat) x heart rate (BPM)
What is cardiac output a measure of?
- a measure of cardiac work
What is the cardiac output of a normal animal proportional to?
- cardiac output is proportional to the overall metabolism of its whole body
Cardiac output varies under different physiological and pathological factors - what are the major determinants for stroke volume?
- contractility
- preload
- afterload
What is the determinant for heart rate?
- change heart rate
What is the heart and its factors regulated by?
- regulated by the ANS
What does the mammalian heart rate depend on?
- depends on pacemaker cells (SA node)
The ANS can alter heart rate - how does the parasympathetic NS alter the heart rate?
- by the vagus nerve and it innervates the SA and AV nodes with small amounts to atria
How does the sympathetic NS alter the heart rate?
- by adrenergic fibres that innervate SA and AV nodes, atria and ventricles
When the heart is at rest what branch of the ANS dominates?
- At rest, parasympathetic effects dominate
What can heart rate be increased by?
- increased sympathetic tone
- decreased parasympathetic tone
What is heart rate set by?
- set by rate of action potential generation at the SA node (primary pacemaker)
What does sympathetic innervation release?
- noradrenaline
How does noradrenaline aid in action potentials in the SA node?
- binds to beta 1 adrenoreceptors
- opens more “f” channels (leaky sodium channels) = faster funny current
- this increases the rate of depolarisation and therefore this are more APs per unit of time
What does the parasympathetic NS release?
- acetylcholine
How does acetylcholine affect action potentials in the SA node?
- binds to muscarinic (M2) receptors
- opens fewer f channels so there is slower funny current and decreased depolarisation
- therefore fewer APs per unit time
What is the AV node and what control is it under?
- The AV node is the secondary pacemaker and it is also under automimic control
What is the effect of noradrenaline on the AV node?
- binds to beta 1 adrenoreceptors
- decreases AV refractory period and increases AV conduction
What is the effect of acetylcholine on the AV node?
- binds to muscarinic (M2) receptors
- increases AV refractory period (decreases AV conduction)
What is myocardial contractility?
- it is a measure of the force generated by the cardiac myocytes
Contractility of the heart is influenced by automimic innervation - what receptors do Atrial myocytes have and what receptors do ventricular myocytes have?
- atrial myocytes have B1 and some M2 receptors
- ventricular myocytes have b1 receptors
Sympathetic innervation increases contractility ultimately through what effects?
- through ca2 + effects
What does parasympathetic innervation do to contractility of the heart and how?
- decreases contractility
- indirectly via presynaptic inhibition of noradrenaline release
For the heart to function effectively as a pump what does it need?
- co-ordinated transmission of excitation
- co-ordinated coupling of excitation-contraction in different regions
- sequential diastole and systole of the atria and ventricles
- precise regulation of input and output
What are the consequences of an imbalance in outputs from the RV and LV?
- pulmonary oedema in lung tissue
What allows the study of intrinsic mechanisms regulating cardiac output?
- an isolated heart-lung preparation
what is preload?
- the filling of the heart and the stretch blood places on the ventricle walls when the heart is maximally filled
- determined in vivo by venous volume rate of venous return
What two things are directly related to preload?
- venous return (or pressure) and stroke volume
What happens when we raise the reservoir level?
- increases filling pressure AKA preload
Increasing filling pressure increases what?
- increases stroke volume
preload is an important determinant of what?
- of stroke volume
What is the Frank-Starling law of the heart?
- the energy of contraction of a cardiac muscle fibre is proportional to the initial fibre length at rest
What does increasing venous return do?
- increases the volume of blood entering the heart during diastole and therefore increases end diastolic volume
What does increasing end diastolic volume increase?
- increases strength of subsequent systolic contraction
Flow rate into and out of the heart is equalised how?
- venous return is equal to cardiac output
What can increase without the heart rate increasing?
- stroke volume and cardiac output
Describe the relationship between EDV and SV:
- reservoir raised
- pressure causing ventricular filling increases
- more blood enters ventricle
- ventricular muscle stretches
- ventricular muscle responds with a stronger contraction
Blood principally returns due to what?
- due to driving force of ventricular contraction
What other factors can also affect venous return?
- displacement of blood from veins (sympathetic vasoconstrictor fibres)
- skeletal muscle contractions massage blood through veins
- changes in intra-thoracic pressure when breathing (thoracic pump)
What is afterload?
- resistance to ejection of blood from the heart
- determined in vivo by peripheral resistance which is proportional to arterial pressure
What is afterload indicated by in live animals?
- indicated by arterial pressure
Increased resistance (afterload) directly opposes what and causes what impact?
- opposes ejection and therefore decreases SV and CO
To maintain CO, heart must keep what up?
- must keep stroke volume up via increased contractility
Sympathetic stimulation of myocytes increases what?
- increases contractility (inotropy = measure of contractility)
- increased stoke volume at same filling pressure
What can preload determine?
- central venous pressure (CVP)
= pressure in the right atrium - CVP is low but positive to keep veins inflated
