control of cardia output I Flashcards
cardiac output =
heart rate x stroke volume
what is cardiac output CO
the volume of blood ejected bty each ventricle per minute
what is heart rate HR
the number of contractions (beats) per minute
what is stroke volume SV
the volume of blood ejected by each ventricle per beat
compare the cardiac output of an athlete to a non athlete
a non athlete has a greater resting cardiac output, a lower resting heart rate and produces a greater cardiac output when exercising
three pathways of innervaton of the heart
blood volume reflexes
autonomic
sympathetic via adrenal glands
describe blood volume reflexes
baroreceptors in the wall of carotid artery and carotid body chemoreceptor travel along sensory nerve fibers to the cardioregulatory center and chemoreceptors in the medulla oblongata
describe autonomic innervation of the heart
involuntary
parasympathetic nerve fibers end at the SAN. acetylcholine from vagus nerve
sympathetic nerve fibres hit the SAN and travel across the ehart. noradrenaline
describe innervation of the heart via the adrenal glands
sympathetic
signal comes out cns to adrenal medulla, produces adrenaline and noradrenaline
what is meant by chronotropic
increases the heart rate, cuts donwn the time that the SAN rests
what does an increase in heart rate do to cardiac output
increases it
what effect do noradrenaline and adrenaline have on the heart
positive chronotropic
stimulates the hyperpolarisation of ion channels at the SAN so more action potentials
(there is reduced repolarisation so the peak goes back up faster)
what effecr does acetylcholine have on heart rate
slows it, ie negative chronotropic
shifts the threshold for an action potential to more hyperpolarise potentials via activated K+ channels to hyperpolarise.
why do trained atheltes have lower heart rates
increased vagal tone
vagus nerve releases acetylcholine
tachycardia
fast heart rate
bradycardia
slow heart rate
what is the end diastolic volume
the volume of blood in the ventricle at the end of loading or filling
what is end systolic volume
the volume of blood at the end of a contraction and beginning of a filling
is the lowest volume of blood in the ventricle at any point in cardiac cycle
what is the formula for stroke volume
EDV-ESV
end diastolic volume - end systolic volume
what factors affect the end diastolic volume
preload- the amount of blood returned to the atria
contractility- the processes that control contraction of the heart
afterload- the resistance the blood faces as it leaves the ventricle
what does preload depend on
the filling of the ventricles depends on the atrial filling which is determined by central venous pressure or venous return
what does an increase in end diastolic volume lead to
an increase in the initial length of the cardiac muscle fibres (they become stretched) and this increases stroke volume and therefore cardiac output
what is starlings law of the heart
the energy of contraction is proportional to the initial length of the cardiac muscle fibre
what three factors affect venous return/ central venous pressure
posture
muscle pump-constriction of veins by skeletal muscle
respiratory pump- inspiration creates an internal pressure difference . moves blood back to heart
