cardiac output and blood pressure Flashcards
what is cardiac output?
- volume of blood ejected by the heart per minute
- measured in ml-min-3
how do you work out cardiac output?
cardiac output = stroke volume x heart rate
what is stroke volume?
- volume of blood ejected per beat
what is heart rate?
- beats per minute
describe parasympathetic nervous system
- vagus nerve releases acetylcholine which slows down HR
- stimulation concentrated to SA and AV nodes
- causes cell membranes to become more hyperpolarised causing SA node rhythm to slow
describe sympathetic nervous system
- releases norepinephrine which increase heart rate
- supplies SA and AV nodes so causes cell membrane to depolarise faster
- shortens AV node delay and speeds up relaxation
what does circulating epinephrine trigger?
- increase in heart rate but lags behind neural stimulation
what opposing factors is stroke volume controlled by?
- force of muscle cell contraction
- arterial pressure against which they eject blood
what is force of contraction regulated by?
- length- tension properties of cardiac muscle cells
- effects of hormonal influence on contractility of cardiac muscle
describe length tension properties
- relationship between end diastolic volume and stroke volume
what can length tension properties be known as?
- Starling’s law of the heart
- more blood returned= more blood pumped out
how can end diastolic volume be increased?
- by greater filling of the heart (venous return) so greater stroke volume because stretching muscle fibres cause them to contract more forcefully
how does training affect the equation?
increased stroke volume means increased cardiac output
- increased 02 delivery
describe cardiac hypertrophy
increased stroke volume = decreased resting heart rate
what is the effect of diastole?
- greater SV because the cardiac muscle fibres stretching cause them to contract more forcefully
what does sympathetic nerve activity and circulating epinephrine cause?
- increases force of contraction so cardiac muscle will contract more forcefully for a given amount of stretch
when does heart rate and stoke volume increase?
- when vagus nerve activity decreases (removal of parasympathetic)
- increased sympathetic nerve activity, increased epinephrine and end diastolic volume
what is blood pressure?
- pressure exerted by blood upon walls of blood vessels
on average, what is the normal blood pressure value?
120-180 mmHg
what three factors affect blood pressure?
- arteries become stiffer with age due to loss of elasticity
- pressure is higher in foot and lower in head due to hydrostatic pressure
- on average women have lower BP than ,men
where is blood pressure highest?
- close to heart
- declines as blood moves further away
what ensures that blood moves forwards even when heart is relaxed?
- elastic properties of the walls of major arteries
what is blood pressure for ventricles, arteries and arterioles? why?
- pulsatile due to rhythmic contraction of the heart
describe blood pressure in relation to cardiovascular system
- driving force for flow
- pressure gradient between arteries and veins
- must be maintained at all times