Cardiac Cycle Flashcards
What is the cardiovascular system made up of?
heart, blood vessels, blood (circulation)
What does the blood transport?
hormones, waste products, nutrients
Where are the pacemaker cells of the heart?
sinoatrial node
What are the entering and exiting vessels?
Pulmonary veins (-> left atrium)
superior and inferior vena cava veins (-> right atrium)
aorta artery (left ventricle ->)
pulmonary arteries (left/right) (right ventricle ->)
What are the valves?
T -tricuspid (AV)
P -pulmonary (SL)
M - bicuspid mitral (AV)
A - aortic (SL)
What is the classification of valves?
atrioventricular
semilunar
What type of process is opening and closing the valves, passive or active?
passive
What are the ventricles?
large thick-walled chambers that forcefully pump blood out of the heart. (left/right)
What are atria?
two upper chambers in the heart, are smaller than the ventricles
What is diastole?
heart relaxation
What is systole?
heart contraction
What happens in the filling phase of the cardiac cycle?
during diastole, blood from the pulmonary and vena cava flows into the right/left atria then into the ventricles
the ventricles fill with blood, until the ventricles’ pressure is equal to that in the veins.
at the end of diastole, the atria contract, squirting a small amount of extra blood into the ventricles. This increases the ventricles’ pressure so that it is now higher than that in the atria, causing the atrioventricular valves (mitral/tricuspid) to close.
Where does the tricuspid valve permit blood flow?
blood flow between right atria and right ventricle
Where does the bicuspid (mitral) valve permit blood flow?
blood flow between left atria and left ventricle
Where does the pulmonary valve permit blood flow?
blood flow between right ventricle and pulmonary artery (outflow tract)
Where does the aortic valve permit blood flow?
blood flow between left ventricle and aorta
What happens in the isovolumetric contraction stage?
As contraction begins both sets of valves are closed, meaning that no blood can escape from the ventricles. Therefore, the start of systole increases the pressure within the ventricles, ready to eject blood into the aorta and pulmonary trunk. The stage of isovolumetric contraction lasts for approximately 50ms, while the pressure builds up.
What happens in the outflow stage?
Once the ventricles’ pressure exceeds the pressure in the aorta/pulmonary arteries, the outflow valves (semilunar) open, and blood is pumped from the heart into the great vessels.
At the end of systole, around 330ms later, the ventricles begin to relax, decreasing the ventricular’s pressure compared to the aorta. The decrease in pressure causes the valves to close.
What happens in the isovolumetric relaxation stage?
At the end of the outflow phase, both sets of valves are closed once again. The ventricles begin to relax, reducing the pressure in the ventricles so that the atrioventricular valves open. The ventricles then begin to fill with blood, and the cycle begins once again
What are atrioventricular valves fastened to and what is their function?
papillary muscle which are projections of the ventricular walls. they function to prevent back flow of blood into atria. made from chordae tendineae (connective tissue)
Where does the superior vena cava vein deliver from?
It delivers blood to the right atrium from the head, neck, upper limbs, and chest.
Where does the inferior vena cava vein deliver from?
It carries blood to the right atrium from the rest of the trunk, the viscera, and the lower limbs.
What could affect the mitral valve to cause it to malfunction?
untreated bacterial or viral infection that infiltrates the valve cusps.
What is a sign of faulty valves?
heart murmur
What are the heart sounds
1st - Lub sound from AV valves closing
2nd - Dub sound from SL valves closing
What does a 3rd heart sound indicate?
heart valve defect
What is the pulmonary circulation?
Pulmonary circulation transports de-oxygenated blood from the heart to the lungs to be re-saturated with oxygen before being dispersed into the systemic circulation.
What is the systemic circulation?
Systemic circulation carries oxygenated blood from the left ventricle, through the aorta, through the arteries, to the capillaries in the tissues of the body. From the tissue capillaries, the deoxygenated blood returns through a system of veins to the right atrium of the heart.
What are the differences between the right and left ventricle?
Right - thinner myocardium, same volume of blood as left ventricle
Left - thicker myocardium, greater pressure to overcome aortic pressure
What is the stroke volume (SV)?
volume of blood ejected during ventricular systole
What is the end diastolic volume?
the volume of blood in ventricle prior to ventricular contraction
What is the end systolic volume?
volume of blood remaining in ventricle after contraction (not all blood emptied)
How can the stroke volume be calculated?
EDV - ESV = SV
What is heart rate determined by?
rate which pacemaker cells (sinoatrial node) fires action potentials
What is resting heart rate range?
60-100 bpm
What sympathetic receptors does the heart mostly contain?
Beta 1 receptors
What are the sympathetic effects on the heart?
increased heart rate
increased contraction
increased rate of relaxation
increased conduction speed in AV node
Describe action of sympathetic nerves on heart
Noradrenaline binds to β1 – adrenoceptors on SA Node
Activation of Gs-protein (stimulatory G-protein)
Adenylyl Cyclase activation Increase (cAMP)
cAMP activates protein kinase – A (PK-A)
PK-A phosphorylates and activates receptors and calcium-ion channels in cardiomyocytes
What cranial nerve is the parasympathetic response derived from?
vagus nerve
Where does the parasympathetic neurotransmitter bind?
Binds to M2 muscarinic receptors in cardiac muscle, particularly at the SA & AV nodes
Describe action of parasympathetic nerves on heart
Activates inhibitory G-protein
Blocking cAMP pathway and allows K+ out from cell
What are the parasympathetic effects on the heart?
decreased heart rate
decreased contraction
decreased rate of relaxation
decreased conduction speed in AV node
What triggers the heart to contract?
A wave of depolarisation, initiated at the cardiac pacemaker, the SA Node travels through the Cardiac Conduction System innervating the myocardium and travels cell to cell within the myocardium.
Describe events of excitation-contraction coupling in cardiac muscle
Electrical signal is sent by pacemaker cells in sinoatrial node
Travels across myocytes of both atrium initiating contraction
After a pause, allowing for completion of atrial contraction, the signal travels to the AV node
Then travels to the bundle of His where it separates into both left and right bundle branches to innervate the walls of the myocardium
Action potential reaches Purkinje fibres which initiate contraction of cardiac myocytes in left/right ventricles
Describe the action potential at the sinoatrial node
Phase 4 - slow depolarisation from -60mV is caused by funny currents that trigger action potential, leaky Na+ channels allow Na+ into the cell,
Phase 0 - depolarisation stage of action potential when a threshold of -40mV is reached. Ca+ channels open allowing calcium into the cell
Phase 3 - repolarisation occurs, voltage gated K+ ion channels open and Ca+ channels close
Describe the action potential at ventricular cells
Phase 0 - rapid Na+ influx through Na+ channels caused by arriving AP
Phase 1 - threshold reached at 30mV, K+ channels open trying to return membrane potential to 0mV
Phase 2 - slow release of Ca2+ from L type channels that triggers release of calcium in sarcoplasmic reticulum, K+ channels are open
Phase 3 - Ca2+ channels close but delayed K+ channels remain open and return membrane potential to -90mV
Phase 4 - Na+, Ca+ channels closed, only K+ channels open to keep membrane stable
Describe contraction of cardiomyocyte
- action potential travels to T-tubules resulting in the release of calcium
- calcium enters sarcoplasm and binds to troponin C
- once calcium is bound to troponin-C and tropomyosin is displaced from actin binding sites, myosin heads can bind to actin.
- following this ADP and inorganic phosphate released from the myosin head so the power stroke can occur. In this the myosin head pivots and bends, pulling on the actin and moving it, causing muscle contraction.
- after this occurs a new molecule of ATP binds to the myosin head, causing it to detach from the actin.
- finally, the ATP is hydrolysed into ADP and inorganic phosphate.
- following this, the cycle can begin again and further contraction can occur.
What is an echocardiogram and what is it is used for?
type of ultrasound scan
can be used to aid detection in
Impaired function due to myocardial infarction (heart attack)
Congenital heart disease; birth defects that impact cardiac function
Cardiomyopathy: enlargement (thickening) of ventricular walls
Endocarditis: infection of endocardium that damages heart valves
Heart Failure: Heart is unable to adequately pump blood to meet metabolic demands of body
What is tachycardia?
fast heart-beat
What is bradycardia?
slow heart-beat
What is atrial fibrillation?
irregular and fast heart-beat
What is STEMI?
ST segment elevation myocardial infarction
-long interruption of blood supply to heart, most serious heart attack
What is ECG?
It is an electrogram of the heart which is a graph of voltage versus time of the electrical activity of the heart using electrodes placed on the skin.
What is the cardiac output (CO)?
volume of blood pumped by the heart per minute
How to calculate the CO?
Stroke Volume (SV) x Heartrate (HR)
What is starlings law?
The force of muscle contraction increases as the muscle is stretched in response to an increased filling of the heart’s chambers.
Heart muscle must respond to stretching in this way otherwise circulation of blood would fail.
This response is intrinsic to the heart
What nervous system is control of the cardiac output?
sympathetic
What are chordae tendinae?
The chordae tendinae are thin strands of connective tissue that anchor the leaflets of each AV valve so that they cannot open into the atrium (thus allowing backflow of blood into the atrium).
What is the QRS complex?
ventricular depolarisation
What is the P wave?
atrial depolarisation
What is the S-T interval?
interval between depolarisation of ventricles and repolarisation of ventricles
plateau phase where contraction happens
What is the P-Q interval?
transmission of action potential to AV node from SA node
What is the affect of after load on stroke volume?
an increase of after load generally causes a decrease in stroke volume
How does opening and closing of the valves occur?
pressure difference across valves
When do the AV valves open?
when the atrial pressure is higher than the ventricular pressure
When do the AV valves close?
when the ventricular pressure is higher than the atrial pressure
