Cardiac Cycle Flashcards
what makes up the cardiovascular system?
heart, blood vessels, blood
what is the function of the CVS?
transport of oxygen, nutrients to meet the metabolic demands of the body, transport of metabolic waste products for excretion, transport of hormones, maintains constant body temperature and transfers heat, aids response to infection and injury, assists regulation of fluid and pH within the body
what type of muscle tissue is the heart tissue?
cardiac muscle
what is cardiac muscle tissue?
specialised striated muscle, coordinated contraction to pump blood around the body to meet the metabolic demands
what are the heart muscle cells called?
cardiomyocytes
what is the myocardium in the left ventricle lke?
significantly thicker than the right
why is the myocardium in the left ventricle thicker?
generates a much greater pressure to overcome aortic resistance so blood can enter the systemic circulation
what is the myocardium of the right ventricle like?
thinner than left ventricle
how much volume does the right ventricle pump in comparison to the left ventricle
generally the same volume of blood
what are the atrioventricular valves?
tricuspid and mitral (bicuspid) valves
what are the semilunar valves?
pulmonary and aortic valves
what does the tricuspid valve do?
permits blood to flow between right atria and right ventricle
what does the bicuspid valve do?
permits blood to flow between left atrium and left ventricle
what does the pulmonary valve do?
permits blood to flow between right ventricle and pulmonary artery
what does the aortic valve do?
permits blood to flow between left ventricle and aorta
what type of process is the opening and closing of the heart valves?
passive
why do the valves open and close?
due to pressure differences across valves
what forces the atrioventricular valves open?
when the pressure in the atrium is greater than in the corresponding ventricle
what closes atrioventricular valves?
when the contacting ventricle achieves an internal pressure that is greater than the corresponding atrium
where does the blood go when the ventricles contract?
it is forced through the semilunar valves and into the pulmonary artery/aorta
what do semilunar valves do during systole (ventricle contraction)
allow blood to flow from ventricles into arteries
what do semilunar valves do during diastole (ventricle relaxation)
prevents backflow of blood from arteries into ventricles
what are atrioventricular valves joined to?
papillary muscles
what are papillary muscles?
muscular projections of the ventricular walls
what connects papillary muscles to valve cusps?
chordae tendineae
what is the function of papillary muscles?
prevent the backflow of blood by limiting the valves’ movements
what does the Lub sound of the heart signify?
the AV valves closing
what does the Dub sound of the heart signify?
the semilunar valves closing
when is a third heart sound heard?
oscillation of blood flow into ventricle or various disease states
what is valve regurgitation?
blood leaks back into chambers, occurs by a valve not closing tightly
what is valve stenosis?
thickening/stiffening of valve cusps, prevents heart valve from opening fully; not enough blood can flow through
what is congenital heart defects?
often pulmonary/aortic valves that do not form properly during development
what is end diastolic volume?
volume of blood in the ventricle prior to contraction
what is end systolic volume?
volume of blood remaining in ventricle after each ejection
during systole are the ventricles emptied of blood?
no
how you calculate stroke volume?
EDV-ESV
what is stroke volume?
volume of blood ejected per heart beat
what is heart rate determined by?
the rate which the cardiac pacemaker fires action potentials
what is resting heart rate?
60-100bpm
what part of the nervous system determines the rate of action potential firing and heart rate?
autonomic nervous system (ANS)
what do the sympathetic nerves do?
release noradrenaline, binds to beta 1 adrenoreceptors on SA node, activation of a G protein and production of cyclic adenosine monophosphate (cAMP), INCREASES HEART RATE
what do the parasympathetic nerves do (vagus nerve)
release acetylcholine (Ach), binds to M2 muscarinic receptors on SA node, activates inhibitory G protein, blocks cAMP pathway and allows K+ efflux from cell, DECREASES HEART RATE
what are alpha and beta adrenoreceptors?
subtypes of alpha and beta receptors
what type of adrenoreceptor does the heart have on nodal tissue, cardiac conduction systems and the myocardium?
beta-1 adrenoreceptors
what do alpha and beta adrenoreceptors do?
bind noradrenaline released by sympathetic nerves and bind circulating adrenaline
what are the effects of adrenoreceptors in the heart?
positive ionotropy, positive chronotropy, positive lusitropy, positive dromotrophy
what is positive ionotropy?
increased strength of myocardial contraction
what is positive chronotropy?
increased heart rate
what is positive lusitropy?
increased rate of myocardial relaxation
what is positive dromotrophy?
increased conduction speed in AV node
what triggers the heart to contract?
action potential spreads as a wave of depolarisation, from SA node from cell to cell through the cardiac conduction system
what is the first step of heart contraction?
depolarisation from SA node through myocytes of RA and LA initiating contraction
what is the second step of heart contraction?
propagation of depolarisation through RA to AV node
what does the slowness of the propagation of AP through the AV node allow?
completion of atrial contraction prior to initiation of ventricular excitation and contraction
what is the third step of heart contraction
AP then propagates from AV node along interventricular septum via the Bundle of His
what is the fourth step of heart contraction?
Bundle of His separates into the left and right bundle branches which innervate the walls of the myocardium
what is the fifth step of heart contraction?
rapid propagation of AP along purkinje fibres initiated coordinated contraction of the cardiac myocytes of the left and right ventricles
what is phase 0 of the SA node action potential?
voltage-gated calcium channels open and calcium enters the cell
what is phase 4 of the SA node action potential?
Na+ slowly enters through leaky Na+ channels
what is phase 3 of the SA node action potential?
voltage-gated K+ channels open and K+ leaves cell and Ca+ channels close
what is phase 4 of the cardiac action potential in the ventricle?
sodium, calcium channels closed and potassium channels open, membrane potential is -90mV
what is phase 0 of the cardiac AP in the ventricle?
rapid Na+ influx through open Na+ channels
what is phase 1 of the cardiac AP in the ventricle?
transient K+ channels open and K+ efflux returns TMP to 0mV
what is phase 2 of the cardiac AP in the ventricle?
influx of calcium through ligand calcium channels is electrically balanced by K+ efflux through delayed rectifier K+ channels
what is phase 3 of the cardiac AP in the ventricle?
calcium channels close but delayed rectifier K+ channels remain open and return TMP to -90mV
what is excitation-contraction coupling?
the coupling of the electric excitation brought by the action potential to the mechanical contraction of the cardiac myocytes
what does calcium bind to in excitation-contraction coupling?
troponin
what is the first step of the cardiomyocyte contractile cycle?
Ca binds to troponin C, leading to conformationl change that displaces tropomyosin from the actin binding sites
what is the second step in the cardiomyocyte contractile cycle?
crossbridge formation with ATP causing hydrolysation into ADP and Pi
what is the third step in the cardiomyocyte contracile cycle?
power stroke moves actin filament towards the centre of the sacromere. ADP and Pi are released from the myosin heads
what is the fourth step in the cardiomyocyte contractile cycle?
actin released with ATP binding to myosin. Myosin heads cocked back into firing position, ready to make crossbridges further downstream
what is the fifth step in the cardiomyocyte contractile cycle?
cycle continues until cellular Ca levels decrease allowing calcium to dissociate from troponin, Tropomyosin returns to its original conformation that blocks actin binding site
what does an ECG do?
detect phasic changes in potential difference between two electrodes
where are the electrodes of an ECG attached to?
limbs and surface of chest
what does the P wave signify?
atrial depolarisation
what does the QRS complex signify?
ventricular depolarisation
what is the P-R interval?
delay through the AV node
what is the S-T interval?
plateau phase of ventricular action potential
what is cardiac output?
volume of blood pumped by the heart per minute
how do you calculate cardiac output?
stroke volume x heart rate
what is starlings law?
the force of muscle contraction increases as the muscle is stretched in response to an increased filling of the hearts chambers
what does starlings law relate to?
end diastolic pressure and peak systolic pressure
what is cardiac preload?
initial stretching of cardiac myocytes prior to contraction
what is cardiac preload indicated by?
ventricular end-diastolic volume (pressure)
what is cardiac afterload?
pressure heart must eject blood against
what is the left ventricle afterload related to?
aortic pressure
