The heart Flashcards
what are the 2 atrioventricular valves? where are they?
Mitral and tricuspid
They are between ventricles and atria
what are the 2 semilunar valves? where are they?
Aortic and pulmonary
They separate ventricles from the arteries
aortic- aorta
pulmonary- pulmonary artery
How are valves connected to the cardiac wall?
tendinous cords and papillary muscles
Why is the left side of the heart under more pressure?
pumps blood all around the body
what is the cardiac cycle?
flow of blood through the heart to meet the needs of the body
what is the function of valves?
they control unidirectional blood flow in the cardiac cycle
BLOOD FLOWS IN 1 DIRECTION ONLY
what is the largest vein and artery?
vein- vena cava
artery- aorta
what are the 3 layers of the heart wall?
*all cells are electrically active
Epicardium- outside layer
Myocardium- heart muscle
Endocardium- inner lining
what are the 2 types of cells within the myocardium?
conducting cells- rapidly spread action potentials
contractile cells- action potentials lead to contraction–>generation of force/pressure
where is the SAN located?
top of the right atrium
what is the link between the electrical signals and contraction of the myocytes?
extracellular calcium
myocardium are extensively branched muscle fibre cells, what are they connected by?
Intercalated discs (ID)
What structure are intercalated discs a part of?
Sarcolemma
We now know that myocardium are connected by ID. What else is found within these ID?
Gap junctions- channels between cells that allow depolarising current to flow from cell to cell
What does syncytium mean in myocardial cell structure?
When cells act together in a wave like formation
What gives the myocardium structural integrity?
Desmosomes- anchor fibres together
What are the 2 main phases of the cardiac cycle?
Diastole- relaxation
Systole- contraction
Explain the cardiac cycle- depolarisation sequence
Electrical signal starts from SAN (primary pacemaker) where cells depolarise spontaneously
Action potentials can EITHER move from cell to cell via gap junctions from right to left atria
OR
through conducting pathways
It takes 0.1s to reach the AVN (because there is a non conducting layer of tissue between atria and ventricles). This allows optimal atrial emptying
Action potential has reached AVN (secondary pacemaker) which is linked to His purkinje fibre system
Action potential is then carried to the ventricular muscles via left+right branches of conducting cells
Action potential propagates cells to cell allowing SYNCHRONISED ventricular contraction
Optimal ejection of blood
What are the 3 pacemakers? Outline the differences
1- SAN (60-100bpm)
2- AVN (40bpm)
3- Purkinje fibres (20bpm)
Explain the first part of the cardiac cycle sequence(wiggers diagram)
1- Atria depolarise due to SAN stimulation
2- Due to atria contracting, ATRIAL PRESSURE INCREASES
Ventricles are relaxed + mitral/tricuspid valves open (ventricles further fill with blood)
3- Ventricles contract leading to INCREASED VENTRICULAR PRESSURE
4- However, ventricular volume stays the same
5- Mitral + tricuspid valves close
Explain the second part of the cardiac cycle sequence(wiggers diagram)
1- Semilunar valves open- rapid blood ejection so DECREASED VENTRICULAR VOLUME
2- As the ventricular volume decreases, blood moves through to the aorta so ARTERIAL PRESSURE INCREASES
3-Ventricles are repolarising so pressure decreases as ventricles are no longer contacting
4- Arterial volume decreases due to elastic recoil
Explain the last part of the cardiac cycle sequence(wiggers diagram)
Isovolumetric ventricular relaxation:
1- Happens after ventricles fully repolarise
2- ventricles relaxed so pressure decreases
3- SLV close - ventricular pressure is below arterial pressure (S2)
4 - All valves closed + ventricular volume is constant
What causes heart sounds?
S1- mistrial and tricuspid valve closure
S2- aortic and pulmonary valve closure
S3- ventricles filling from atria
What Varys in myocytes?
They vary anatomy and channels. They have time dependent + voltage gated currents during cardiac cycle
Describe what the waves of an ECG show
P wave- depolarisation of atria
PR interval- time between atrial depolarisation and ventricular depolarisation
QRS complex- depolarisation of ventricles
ST segment- region between en of V depolarisation and V repolarisation
T wave- repolarisation of ventricles
