cvs physiology Flashcards
the cardiovascular system is a bulk flow system supplying what?
- O2 and CO2
- nutrients
- metabolites
- hormones
- and heat
are pumps in series or parallel
pumps are in series meaning output must be equal
are vascular beds in series or parallel
most vascular beds are in parallel meaning all tissues get oxygenated blood which allows regional redirection of blood
sequence of events during excitation-contraction coupling in cardiac muscle
- cardiac muscle forms a functional syncytiu
- cardiac muscle has a long action potential
- long action potential = long refractory period
- some cells have unstable resting membrane potential and act as pacemaker
resting membrane potential in non-pacemaker tissue
-90mV
resting membrane potential in pacemaker tissue
no resting potential
describe initiation and spread of electrical activity throughout the heart
- pacemaker cells in sinoatrial node spontaneously depolarise to threshold
- threshold then spreads gradually through the atria causing it to contract, pushing blood into the ventricles
- depolarisation spreads to atrioventrucular node, slowly as it gives time for depolarisation
- depolarisation spreads rapidly through bundle of His and Perkunje fibres causing ventricular contraction
- the ventricles then relax
what does the p wave correspond to
atrial depolarisation
what does the QRS complex correspond to
ventricular depolarisation
what does the T wave correspond to
ventricular repolarisation
what is the RR interval
QRS to QRS
what is the PR interval
time from atrial depolarisation to ventricular depolarisation, due to transmission through the AV node
what is the normal time for PR interval
0.12-0.2s
what is the normal QRS time
0.08s
what is the QT interval
time taken for ventricles to depolarise and repolarise
what is the normal time for QT interval
0.42s at 60bpm (varies with heart rate)
how do you measure the heart rate from an ECG
measure the amount of R waves in 30 large squares (6s) and multiply by 10 to get bpm
what is bradycardia
slow heart rate below 60bpm
what is tachycardia
high heart rate above 100pbm
what is normal heart rate
60-100bpm
characteristics of normal sinus rhythm ECG
regular rhythm rate
each QRS complex is followed by a normal P wave
PR interval is constant
characteristics of sinus tachycardia ECG
heart rate over 100bpm
P waves are hidden within each preceding T wave
characteristics of sinus bradycardia ECG
heart rate under 60bpm
prominent U waves in precordial leads is a common finding
what is a STEMI
ST-segment elevation - myocardial infarction
what is a non-stemi
non-ST segment elevation myocardial infarction
describe late diastole in the cardiac cycle
both sets of chambers are relaxed and ventricles fill passively
describe atrial systole in the cardiac cycle
atrial contraction forces a small amount of additional blood into ventricles
describe isovolumic ventricular contraction in cardiac cycle
first phase of ventricular contraction pushes AV valves closed but does not create enough pressure to open semilunar valves.
describe ventricular ejection in the cardiac cycle
as ventricular pressure rises and exceeds pressure in the arteries, the semilunar valves open and blood is ejected
describe isovolumic ventricular relaxation
as ventricles relax, pressure in ventricles falls, blood flows back into cusps of semilunar valves and snaps them closed
what is the 1st heart sound
closure of the AV (mitral and tricuspid) valves
what is the 2nd heart sound
closure of the semilunar (aortic and pulmonary) valves
what is the 3rd heart sound
rapid passive filling phase
what is the 4th heart sound
active filling phase
what is a systolic murmur
stenosis of aortic/pulomary valves or regurgitation of mitral/tricuspid valves
what is a diastolic murmur
stenosis of mitral/tricuspid valves or regurgitation through aortic/pulmonary valves
what would a continuous murmur be a sign of
ductus arteriosus
effects of the sympathetic nervous system on heart rate
- sympathetic nerves release noradrenaline
- plus circulating adrenaline from adrenal medulla
- both act of B1 receptors on the sinoatrial node
- slope of the pacemaker potential is increased
- heart rate is increase (tachycardia)
effect of parasympathetic nervous system on heart rate
- vagus nerve releases acetylcholine
- this acts of muscarinic receptors on the sinoatrial node
- this hyperolarises cells and decreases slope of pacemaker potential
- heart rate is decreased (bradycardia)
effect of sympathetic nervous system on stroke volume
- sympathetic nerves release noradrenaline
- plus circulating adrenaline from adrenal medulla
- both act on B1 receptors on the myocytes
- this increases contractility (an inotropic effect)
- which gives stronger but shorter contraction
- stroke volume is increase
effect of parasympathetic nervous system on stroke volume
- little effect
- probably due to vagus nerve not innervating ventricular muscle
effects of preload on stroke volume
- increased venous return causes increased EDV and therefore increased stroke volume
- decreased venous return causes decreased EDV and therefore decreased stroke volume
effects of afterload on stroke volume
- he ventricle will have to work harder to push open the aortic valve and it will have less energy left to eject blood
- stroke volume will decrease
what is systolic pressure
the pressure when your heart pushes blood out
what is diastolic pressure
the pressure when your heart rests between beats
what is pulse pressure
the difference between systolic and diastolic blood pressures
what are korotkoff sounds
resonant motion of the arterial wall, which begins after the artery transitions from a buckled state to an expanding state
what are korotkoff sounds used for
usedto define systolic and diastolic pressures inside the arterial system
what happens to the aortic pressure wave as it passes through the vascular tree
pressure falls throughout the vascular tree
effect of Gravity on pressure and flow in veins
decreased EDV, preload, SV, CO, and MAP
effect of skeletal muscle pump on pressure and flow in veins
rhythmic contraction increases venous return and EDV
what is EDV
end-diastolic volume
effect of respiratory pump on pressure and flow in veins
increased respiratory rate and depth increase venous return and EDV
effect of venomotor tone on pressure and flow in veins
mobilisis capacitance and increases EDV
clotting process
- formation of a platelet plug
- formation of a fibrin clot
anti-clotting mechanisms
- stops blood contacting collagen
- produces prostacyclin and NO
- produces tissue factor pathway inhibitor TFPI -
- expresses thrombodulin
- expresses heparin
- secretes tissue plasminogen activator t-PA
types of capillary structure
continuous = no clefts or pores
fenestrated = clefts and pores
discontinuous = clefts and massive pores
significance of the blood-brain barrier
it shields the brain from toxic substances in the blood, supplies brain tissues with nutrients, and filters harmful compounds from the brain back to the bloodstream
what is oedema
the accumulation of excess fluid
what causes oedema
- raised CVP
- lymphatic obstruction
- hypoproteinaemia
- increased capillary permeability
what is active hyperaemia
an adaption to match blood supply to the metabolic needs of that tissue
what triggers active hyperaemia
triggered by an increase in local metabolism
what results from active hyperaemia
- increased concentration of metabolites
- triggers release of paracrine signal (EDRF/NO)
- causes arteriolar dilation
- increases flow to wash out metabolites
what is pressure autoregulation
an adaptation to ensure that tissue maintains its blood supply despite changes in MAP
what triggers pressure autoregulation
a decrease in perfusion pressure
what results from pressure autoregulation
- increased metabolic activity causes a decrease in flow
- metabolites accumulate
- triggers release of paracrine signal (EDRF/NO)
- causes arteriolar dilation causing flow to be restored to normal
what is reactive hyperaemia
an extreme version of pressure autoregulation
what triggers reactive hyperaemia
occlusion of blood supply
what results from reactive hyperaemia
a subsequent increase in blood flow
sympathetic nerves effect on arteriolar tone
- release noradrenaline
- binds to a1 receptors
- causes arteriolar constriction
- therefore there is decreased blood flow through that tissue and tends to increase TPR and MAP
parasympathetic nerves effect on arteriolar tone
- usually no effect
- genitalia and salivary glands are exception, increasing flow
adrenaline effect on arteriolar tone
- released from adrenal medulla
- binds to a1 receptors
- causes arteriolar constriction
- decreased flow through that tissue and tends to increase TPR and MAP
what is MAP
- mean arterial pressure
- the driving force pushing blood through the circulation
what happens with too low a MAP
fainting (syncope)
what happens with too high MAP
hypertension
components of the arterial baroreceptor reflex
- vagus nerve
- glossopharyngeal nerve
- medullary cardiovascular centres
- parasympathetic vagus nerve
- sympathetic nerve
- adrenal medulla
- internal carotid arteries
- common carotid arteries
- carotid sinus baroreceptors
- aortic arch baroreceptors
function of the arterial baroreceptor reflex
to inform the autonomic nervous system of beat-to-beat changes in blood pressure within the arterial system
what effect does the upright position have on the cardiovascular system
induces cardiovascular stressors on the body due to the shifting of fluid
upright position causes the greatest translocation of blood from the thoracic region to the lower limbs
receptors involved in sensing plasma volume
osmo-sodium receptors
