Cardiac System Flashcards
Describe the conduction system of the heart.
Specialised tissue conducts nerve impulses, SA & AV node, bundle of His, bundle branches & Purkinje fibres.
Describe the hearts nerve supply.
Nerve branches from sympathetic & parasympathetic divisions of autonomic NS.
State the functions of the pericardium.
- protects & anchors heart
- prevents overfilling w blood
- serous fluid reduces friction
Pulmonary circuit
blood to & from lungs (vena cava & pulmonary artery)
Systemic circuit
Blood to & from body (pulmonary vein & aorta)
arteries are ___ vessels
pressure
veins are ___ vessels which can ___ to match blood volume
capacitance, distend
Diastolic Phase
myocardium relaxes
Systolic phase
myocardium contracts
State the phases of cardiac cycle.
State the valves involved.
1. Atrial diastole & systole AV valves open. 2. Ventricular filling: mid-to-late diastole 3. Ventricular systole AV valves close (lubb) 4. Ventricular diastole semilunar valves close (dubb)
Ventricular systole:
Atria ___ , rising ventricular pressure closes __ valves. -___ sound.
_____ _____ phase
relax, AV, lubb
Isovolumetric contraction
Ventricular diastole:
Ventricles ___ , closes ___ valves.
___ sound.
relax, semilunar.
dubb
State the AV valves
mitral (bicuspid) & tricuspid
State the semilunar valves
Aortic & pulmonic
Tachycardia
High resting heart rate
Bradycardia
Low resting heart rate.
Pulse
Surge in arterial pressure.
Cardiac Output (CO)
Vol. of blood pumped by each ventricle per min
CO (mL/min) = HR (bpm) x SV (mL/b)
What is cardiac reserve?
Compare that of an athlete to an average person.
difference between resting & max. CO.
Athlete CR is GREATER.
What factors determine heart rate?
Autonomic innervation & hormones
What factors determine stroke vol.?
End-diastolic & systolic vol.
Stroke Volume (SV)
Vol. of blood pumped LEFT by ventricle per beat.
SV = EDV - ESV
end diastolic/systolic vol.
Blood pressure
Force exerted by blood against blood vessel walls
Function of baroreceptors
Detect change in BP.
What does BP 120/80 show
PUMP (peak) pressure / FILL (minimum) pressure
PRELOAD
Degree of stretch before contraction.
= EDV
AFTERLOAD
Pressure required to eject blood from ventricles.
Frank-Starling Mechanism
The change of hearts force of contraction in response to a change in venous return.
Increased venous return increases EDV hence preload.
Myocyte stretching increases force generation.
__ afterload –> «_space;CO
Cardiac Output (CO)
Increased
__ contractility –>»_space;CO
Increased
> > CO = __HR X SV
> >
State the 5 features of the cardiac conduction system
SA node, AV node, Bundle of His, bundle branches, purkinje fibres.
SA node
Pacemaker
- generate spontaneous action potentials.
AV node
Controls heart rate. Delays impulse (~0.1s) from SA node before it passes down ventricles - allows atrial emptying.
Purkinje fibres
DISTRIBUTE IMPULSE across ventricular myocardium
Where does depolarisation occur in heart.
From SA node across atria.
-
Describe impulse conduction through heart.
DEPOLARISATION across SA node & atria. ~0.1s delay at AV node. Atrial contraction. Impulse travels along interventricular septum within AV bundle & purkinje fibres to right ventricle. Impulse distributed by Purkinje fibres. Ventricular contraction occurs.
Speed of action potential propagation in cardiomyocytes is ____ due to ___________________
Slow, gap junctions & small diameter of fibres.
Speed of action potential propagation in skeletal muscle is ____ due to
Fast, larger diameter of fibres.
Describe the characeristics of cardiomyocytes.
Striated, mono-nucleated, branched, connected by intercalated discs w desmosomes.
Describe the Sliding Filament Theory.
- Ca2+ binds to TN-C on thin filaments
- Exposed actin binding site for myosin head
- ATP hydrolysis -> actin-myosin conformational change
- RATCHET actin-myosin complex & sarcomere shortens
- Ca2+ dissociates from TN-C, myosin unbinds from actin
Describe cardiomyocyte contraction
- Ca2+ enters via L-type
- CICR (Ca2+»_space;>)
- Ca2+ interacts w TN-C
- Actin binding site freed
- Actin moves over myosin (contraction)
- IC Ca2+ reabsorbed into SR via SERCA pump, & removed from cell via Na+/Ca2+ exchanger & ATP-dependent Ca2+ pump.
- Ca2+ dissociates from TN-C & actins binding site inhibited.
Resting potential ~ __ equilibrium potential
K+
Resting potential = __mV
-85mV
Action potentials induce __ channel opening
Na+
State the phases of an Action Potential:
p0 Rapid DEPOLARISATION p1 Initial REPOLARISATION p2 Plateau p3 REPOLARISATION p4 Resting POTENTIAL
Outline the phases of an action potential
EXCITATION:
p0 :»_space;> Na+ permeability, membrane potential»_space;>
p1 : K+ permeability»_space;>, CICR (L type open)
p2 : K+ balances Ca2+ flow. Cardiomyocyte contraction.
p3 : K+ channels remain open. Membrane potential falls ~E(k)
p4 : resting potential = -85mV
Excitation depolarisation threshold potential = __mV
-65mV
What is pacemaker tissue?
Areas of unstable resting potential
Rhythmic ____ -> rhythmic ____
Depolarisation, contraction
Automaticity =
Ability to spontaneously depolarise & trigger AP
Where is automaticity active in the heart?
SA & AV nodes & Bundle of His.
____ node is the primary pacemaker of the heart, determining __ __ .
1 depolarisation = __ heartbeat(s)
Sinoatrial
Heart rate
1
Characteristics of sinoatrial node pacemaker cells
No true resting potential
Generate regular spontaneous action potentials.
How is the cardiac cycle regulated?
Sympathetic & parasympathetic NS.
Cardiac centres in medulla oblongata receive input from hypothalamus.
How does the parasympathetic system regulate the cardiac cycle?
Cardioinhibitory centre - vagus nerve
SA & AV nodes
ACh secreted - hyperpolarises
«< HR
How does the sympathetic system regulate the cardiac cycle?
Cardioaccelerator centre activates cardiac nerves.
Norepinephrine secreted
» contractility
Electrocardiogram: P wave
atrial depolarisation
Electrocardiogram: QRS complex
ventricular depolarisation
Electrocardiogram: T wave
ventricles repolarised
Electrocardiogram: PR interval
contraction -> relaxtaion.
start of atrial to ventricular depolarisation
Electrocardiogram: Q-T interval
time for a single cycle of depolarisation & repolarisation.
State the 3 groups of pacemaker cells
SA node
AV node,
Bundle of His & Purkinje fibres