cardiac cycle and output (6b) Flashcards
apart from the intrinsic conduction system what regulates heart activity
the autonomic nervous system inhibit or stimulate heart activity
what is the cardiac cycle
one complete heartbeat
usually 0.8 seconds long
what is systole
contraction
what is diastole
relaxation
what are the five steps of a cardiac cycle
atrial diastole
atrial systole
isovolumetric contraction
ventricular systole
isovolumetric relaxation
what happens during atrial diastole
heart is relaxed and has low pressure
AV valves are open
blood flows from veins to atria to ventricles
semilunar valves are closed
what happens during atrial systole
ventricles are is diastole/relaxed
atria contract
blood is forced into the ventricles to complete ventricular filling
what happens during isovolumetric contraction
atria stop contracting
ventricles contract causing the intraventricular pressure to rise
AV valves close
for a moment ventricles are closed chambers
what happens during ventricular systole
ventricles are contracting
intraventricular pressure is higher than major arteries = semilunar valves open
blood is ejected
atria are relaxed and filling with blood
what happens in isovolumetric relaxation
ventricles relax
pressure falls = semilunar valves close
ventricles are closed chambers for a moment
once atrial pressure is higher than intraventricular pressure = AV valves open
what is cardiac output
amount of blood pumped by the heart in one minute
CO = stroke volume x HR
usually around 5.25L/min (almost all the blood in an adult)
in an ECG what do the letters refer to
P: impulse to atrial muscle from SA node activation
Q: AV node activates
QRS: AV node activation sending impulses to ventricular muscle
T: relaxing/recovery wave
what is stroke volume
volume of blood discharged from one ventricle with each contraction
usually about 60% of the blood present in one ventricle
what is starlings law
states that the more stretched the walls of the ventricle are gives a higher stroke volume because it creates a stronger contraction
what is venous return
amount/flow of blood from peripheral veins into the R atrium
what is the result of increased venous return to the heart
it increases the blood volume during relaxation = more forceful contraction = increased stroke volume = increased cardiac output
does a slow heart beat increase stroke volume
yes because the ventricles have more time to fill with blood
how does exercise increase venous return
contraction of skeletal muscle squeeze the veins which pushes the blood towards the heart
how is the medulla involved in HR
it contains cardiac control center
baroreceptors (stretch) in the carotid sinus and aorta send it information
chemoreceptors send information regarding O2, CO2 and H+ blood levels
hypothalamus and cerebrum send it information
also receives information from hormones and blood borne chemicals
mechanism of how the sympathetic system regulates HR
sympathetic cardioacceleratory center sends impulses to SA and AV nodes and ventricular myocardium
the resting potential of the SA and AV nodes becomes more positive = increasing the probability of impulses
myocardium is stimulated to increase contractility = increasing force and contraction volume
overall increases amount of blood reaching cells to increase O2 and glucose transport
this occurs during physical/emotional stress
mechanism of how the parasympathetic system regulates HR
parasympathetic cardioinhibitory center sends impulses using the vagus nerve to the SA and AV nodes and atrial myocardium
vagus nerve releases acetylcholine on the heart, making the resting membrane potential negative = decreasing impulse probability
keeps heart at rest, at normal vagal tone
how is the hypothalamus related to HR
is stimulates responses associated with exercise, emotion and fight/flight so increasing HR
which hormones and ions affect HR and what do they do
epinephrine: increases HR
thyroxin (TH): increases HR by acting of cardiac muscle
calcium: high concentration = contractions stop, low concentrations = contractions are prolonged (heart could stop)
potassium: low concentrations = irregular rhythm
sodium levels are also monitored
what is the cardiac reserve
hearts ability to quickly adjust to immediate demands
maximum % that the cardiac output can increase above normal (young adult 300-400%)
