The heart Flashcards
What is the protective fluid filled sac around the heart ?
The pericardium
What does right atria receive?
Deoxygenated systemic venous return
Function of right ventricle
Pushes blood to pulmonary circulation for oxygenation
What does the left atrium receive?
Oxygenated blood from pulmonary circulation
Function of left ventricle
Pumps oxygenated blood under high pressure to brain and body
Name what attaches atrioventricular valves to the cardiac wall
Chordae tendinea
Papillary muscles
Structure of the heart wall
- epicardium
- myocardium
- endocardium
Function of epicardium
Reduces friction with pericardial fluid + coronary blood
Specialisation of myocardium
Encased in collagen fibres
Specialisation of endocardium
Smooth muscle
Function of a conducting cell
Rapidly spread action potentials
Name the heart conducting cells
Purkinje system
Sinoatrial node
AV node
Bundle of his
Atrial internodal tracts
Function of contractile cells
Ap leads to contraction causing generation of force or pressure
What is a myocyte?
Muscle cells in the heart
What are the 5 stages of a cardiac action potential?
0 - Upstroke of action potential
1- Rapid depolarisation
2- Plateau phase
3- Repolarisation
4- Electrical diastolic phase
What are the 4 time dependent and voltage gated currents?
Na+
Ca+
K+
Pacemaker current
Describe the Na+ current
Rapid depolarising phase
Ap in atrial and ventricular muscle and purkinje fibres
Which is the largest current in the heart?
Na+ current
Describe Ca+ current
Rapid depolarising phase
SAN, AVN
Triggers contraction in all cardiomyocytes
Describe K+ current
Repolarises all cardiomyocytes
Describe the pacemaker current
Pacemaker activity of SAN, AVN and purkinje fibres
How does an action potential propagate in cardiac cells?
Synchronised ventricular contraction
Depolarisation flows from one cell to another (syncytium) via gap junctions
What is a myocardium?
A branched muscle fibre cell connected by intercalated discs
Describe the cell structure of a myocardium
Intercalated disk is part of the sarcolemma
Gap junctions
Desmosomes anchor fibres together
What are t tubules formed from?
Deep invaginations in the sarcolemma
Describe the events after T tubule depolarisation
T tubule depolarisation triggers calcium release in the cell core (near z line)
Calcium is released from sr
Actin and myosin are able to interact and a large instantaneous force occurs
What is a dyad?
Sarcoplasmic reticulum and T tubules
What is coupled to an L type T tubule Ca2+ channel?
Ca2+ release in cardiomyocytes and VSMC
What is a T type Ca2+ channel coupled to ?
Pacemaker and conducting cells
What does Cytosolic calcium activate?
Activates a channel on the sarcoplasmic reticulum which causes calcium induced calcium release
What is the effect of a global increase in calcium concentration?
Calcium binds troponin C and releases troponin I which inhibits actin
What is the cardiac depolarisation sequence?
SAN depolarisation is spontaneous ->
AP propagates from left to right side of the heart (rate of 60-100/min) via gap junctions->
Reaches AVN ->
Fibrous AVN ring prevents the signals from propagating AVN tissue ->
AP is passed to ventricular muscle (via HIS purkinje fibre system)
What is the primary pacemaker in the cardiac depolarisation sequence?
SAN
What is the secondary pacemaker in the cardiac depolarisation sequence?
AVN
Where in the heart is the sinoatrial node?
In the right atrium
Where in the heart is the atrioventricular node?
In the right atrium
Describe the cardiac cycle
- Atrial systole
- Isovolumetric ventricular contraction
- Rapid ventricular ejection
- Reduced ventricular ejection
5 . Isovolumetric ventricular relaxation - Rapid ventricular filling
- Reduced ventricular filling
What happens in Atrial systole?
Atria are depolarised
Mitral and tricuspid valves open
Ventricles further fill
Contraction causes an increase in p
What happens in isovolumetric ventricular contraction?
Ventricular p > atrial p
Purkinje fibres electrical activation cause ventricular contraction causing large increase in p
Mitral/tricuspid valve closes
What happens in rapid ventricular ejection?
Ventricular p > aortic p
SLV opens
Stroke volume ejection
Ventricular volume decreases
Atrial p increases
What happens in reduced ventricular ejection?
Final blood ejection from ventricles due to contraction
Ventricular repolarisation as ventricular p decreases
Arterial volume decreases
What happens in isovolumetric ventricular relaxation?
Occurs when ventricles are fully repolarised Ventricles relax causing ventricular p decrease
Ventricular p > arteriole p
All valves are closed
Ventricular volume remains constant
Atrial p increases
Arteriole v decreases
What happens in rapid ventricular filling?
Atrial p > ventricular p
Mitral and tricuspid valves open
Blood enters the ventricles from atria
What happens in reduced ventricular filling?
Remaining blood enters the ventricle
What does an ECG measure?
The movement of external portion of ions
What does the P wave show?
Atrial depolarisation
What does the PR interval show?
AVN conduction as it reflects initial depolarisation of atria to ventricles
What does QRS show?
Depolarisation of ventricles
What does T wave show?
Repolarisation of ventricles
What does atrial tachycardia display on ECGs?
P wave masks T wave due to speed
What does atrial fibrillation display on ECGs?
P wave isn’t presented
How does ventricular fibrillation display on ECGs?
No sequenced filling of ventricles so no sequenced pattern
