Cardiac Physiology Flashcards
How many heart chambers do fish have?
Two
How many heart chambers do reptiles and amphibians have?
Three
How do valves open and close?
forwards flow opens them and backwards flow closes them
How is eversion of the hart valves prevented?
chordae tendinae, attached to papillary muscles of the ventricles
Describe the characteristics of Myocardial cells
- excitable, striated, branches, mononucleated with abundant mitochondria.
How are myocardial cells joined together?
gap junctions (allows passage of ions)
How are action potentials able to spread quickly between cells?
intercalated discs allow myocardium to contract as a coordinated unit
What are the two types of cardiac muscle cells?
- Contractile cells (99%)
2. Autorhythmic cells/ pacemaker cells
Why are Autorhythmic cells important in the heart?
heart does not rely on nervous input to generate an action potential.
Where are Autorhythmic cells found in the heart?
found in SA and AV nodes, as well as conduction pathways
What happens in Phase 4 (Pre-potential) of the action potential at the SA Node?
- i(f) channels open
- inward Na current
- Depolarisation
- Opening of transient Ca++ channels (i(Ca))
- more depolarisation
What happens in Phase 0 (Rapid depolarisation)
opening of long lasting voltage gated Ca channels at threshold potential (-40mV)
What happens at Phase 3 (Repolarisation)
- Opening of K+ channels and closure of Ca channels
2. as membrane reaches -65mV, i(f)Na channels start to open again for Phase 4
In what order are the conducting centres (in order of speed)
- SA node
- AV node
- AV bundle
- Purkinje fibres
What affect does Acetylcholine have on the SA node?
- released from parasympathetic nerves
- Causes slow rate of rise of pacemaker potential (prolongs Phase 4).
- decreases HR
What affect does Catecholamine have on the SA node?
- released from sympathetic nerves and adrenal medulla
- act via beta-1 receptors on heart muscle to increase rate of polarisation in phase 4
- increase HR
What is the significance of the AV node?
delays the signal from the SA node and allows time for ventricular filling
What are the 5 phases of Contractile Cell action Potential
- Phase 0 (Rapid Depolarisation)
- Phase 1 (initial rapid repolarisation)
- Phase 2 (Plateau phase)
- Phase 3 (rapid repolarisation)
- Phase 4 (rest phase)
What happens in Phase 0 of Contractile Cell action Potential?
opening of voltage gated Na channels (i(f))
What happens in Phase 1 of Contractile Cell action Potential?
opening of transient K+ channels (i(k)(t))
What happens in Phase 2 of Contractile Cell action Potential?
Opening of long lasting Ca channels (L-Type) (iCaL)
What happens in Phase 3 of Contractile Cell action Potential?
K+ efflux due to opening of voltage gated K+ channels (i(k)
What is a refractory period?
occurs after initiation of action potential in an excited membrane and lasts until the action potential ends
What is the significance of the length of a refractory period?
a shorter period allows the muscle to maintain sustained contraction (e.g. skeletal muscle)
What is the sequence of events in contraction coupling in cardiac muscle?
- action potential enters from adjacent cell
- voltage gated Ca++ channels open, letting Ca++ in.
- Ca++ causes release of CA++ from SR via ryanodine receptor channels
- local release of Ca++ causes Ca++ spark
- Ca++ sparks create Ca++ signal
- Ca++ binds to troponin causing contraction of muscle
- relaxation when Ca++ unbinds from troponin
- Ca++ pumped back into SR for storage
- Ca++ exchanged for Na in ECF
- Na+ gradient is maintained by Na+-K+-ATPase
What physiological process is interrupted by foxglove poisoning?
Contraction of cardiac muscle
What affect does sympathetic activity have on the heart?
increases activity by increasing Ca++ influx
What is represented by the P wave?
Atrial depolarisation
What is represented by the QRS complex?
ventricular depolarisation
What is represented by the T wave?
ventricular repolarisation
Why is atrial repolarisation not seen on an ECG?
- slow process
- obscured by the QRS complex
- a much smaller muscle, so only makes a very small wave
What is shown by the PR interval?
duration of impulse from SA node to ventricles
What is shown by the QT interval?
ventricular depolarisation and repolarisation
What is shown by the RR interval?
one full cardiac cycle
List the main types of Arrhythmias
- sinus arrest
- sinus brady
- sinus tachy
- conduction block (1st, 2nd, 3rd degree block)
What is 1st degree AV block?
longer PR interval
What are the two types of 2nd degree AV Block?
Mobitz Type 1 and Mobitz Type 2
What is Mobitz Type 1?
PR intervals increase until AV node fails and no QRS wave is seen
What is Mobitz Type 2?
No QRS complex. requires a pacemaker
What is 3rd degree AV Block?
- complete conduction block
- no impulse goes through AV node, atrium and ventricle are in complete isolation and beat at their own intrinsic rate
What factors can cause ectopic pacemaker activity?
- toxins
- electrolyte imbalance
- ischemia
What is ectopic pacemaker activity?
frequency of action potentials is too high and coordinated contraction of myocardial cells isnt possible
What is Atrial Fibrilation?
- continuous random passage of action potentials through the atria
- ## irregular RR, no P wave
What is a complication of Atrial Fibrillation?
blood pools in atrium, causing clots
What is Ventricular Fibrillation?
- continuous random passage of action potentials through the ventricles (electrical chaos)
- emergency, requires CPR and defibrillation
What is Systole?
period of contraction/ ejection
What is Diastole?
period of relaxation/ filling
What can be seen on a Wigger’s diagram?
ECG, Heart sounds, pressure lines, ventricular volume, positions of valves, phase of cardiac cycle
