The heart Flashcards
Distinguish b/t the pulmonary + systemic circuits
Pulmonary circuit = carries blood to + from gas exchange surfaces of the lung
systemic circuit = carries blood to + from rest of body
Describe the structure of the pericardium
- fibrous network of collagen fibres enclosing the heart
- lined by serous membrane w/ 2 layers (parietal pericardium = outer, visceral pericardium = inner)
Why is the pericardial cavity filled with fluid
to reduce friction
Describe cardiac tamponade
Pericarditis leading to increased production of pericardial fluid -> pericardial effusion
Describe the 3 layers of the heart wall
- epicardium = visceral layer of serous membrane
- myocardium = cardiac muscle tissue / provides pumping action
- endocardium = continuous w/ endothelial lining of great vessels
Describe the structure + function of cardiomyocytes
Cardiac muscle cells / fibres
- contain single nucleus
- connected
Describe the structure + function of intercalated discs
- join cardiomyocytes via gap junctions + desmosomes
- maintain structures + enhance electrical connections by conducting action potentials
What separates the right and left atria
the interatrial septum
Differentiate between the structure + function of the ventricles
right ventricle = pumps blood to systemic circulation
-> thinner wall b/c less pressure required to pump blood than LV
left ventricle = pumps blood to systemic circulation
-> thicker wall
-> greater pressure
-> rounder in shape
Describe the passage of blood through the heart
Right atrium = receive blood from systemic circulation via:
- superior vena cava
- inferior vena cava
- coronary sinus
Right atrium -> right ventricle through AV (tricuspid) valve
Right ventricle -> pulmonary trunk + pulmonary arteries -> pulmonary circulation
Blood passes through lungs + returns to heart through 4 pulmonary veins
Pulmonary veins -> left atrium -> left ventricle through AV valve (bicuspid) -> systemic circulation via aorta
List the structure + function of the 4 valves of the heart
- direct blood flow through + out of heart
- prevent backflow of blood
- composed of dense connective tissue covered by endothelium
What determines if the AV valves open + close
Open = pressure in atria greater than pressure in ventricles
close = pressure in ventricles greater than pressure in atria
State the function of each of the semilunar valves + what they are located between
- prevent blood flowing back into heart / located b/t ventricles + major arteries
Pulmonary semilunar valve located at base of pulmonary arterial trunk
Aortic semilunar valve located at base of aorta -> enables blood to move into the systemic circuit
Describe the structure + function of coronary arteries
- branch from ascending aorta
- carry oxygenated blood to myocardium @ non-steady (pulsatile) rate
blood flow increases during exercise
Describe the structure + function of the coronary sinus
- carries deoxygenated blood back to the right atrium
- thin walled vein w/ no smooth muscle to alter diameter
What is myocardial infarction
Heart attack -> blockage of coronary artery therefore no blood supply to heart muscle
State when the atria + ventricles contract + relax
Atria contract + relax together
Ventricles contract + relax together
Define autorhythmic fibres
Specialised muscle fibres that initiate + conduct action potentials to form the conduction system
Define contractile fibres
provide the mechanical work to pump the heart via excitable tissue that rapidly spreads action potentials through gap junctions
Describe the function of the sinoatrial node (SA node)
Pacemaker
spontaneously depolarises 80-100 times/min
-> rate of depolarisation modified by neurotransmitters from the ANS
Describe the function of the atrioventricular (AV) node
- spontaneously depolarises 40-60 times/min
Describe why AV nodal delay occurs
Slowed conduction allows atria time to relax + fill ventricles
Describe the action potential of an autorhythmic cell
- excitable membrane leads to no stable resting membrane potential
- when pacemaker cell goes into depolarisation stage, membrane potential drifts towards threshold, causing spontaneous depolarisation
this causes a slow influx of Na+ w/out outflow of K+
Describe the phases of a cardiac action potential
- rapid depolarisation
- voltage gated sodium channels open
- rapid influx of Na+ - plateau
- Na+ channels close rapidly (+30mV) causing Na+ efflux
- voltage gated slow Ca2+ channels open causing ca influx - repolarisation
- voltage gated slow ca channels close
- voltage gated slow K channels open -> K+ efflux + relative refractory period
Describe tetany
whereby twitch summation occurs causing an elimination of the relaxation phase due to rapid + prolonged contraction -> no longer pump blood
List the sequence of electrical events at the heart
- SA node spontaneously generates an action potential
- stimulus spreads across atria + reaches AV node
- AV nodal delay occurs before contraction begins
- action potential spreads along AV bundle, bundle fibres + purkinje fibres
- action potential relayed across ventricles -> ventricles contract
What is the cardiac cycle
the period b/t the start of one heartbeat + the beginning of the next
includes:
- systole (contraction)
- diastole (relaxation)
Describe the function of an ECG
Detect summed electrical activity of all cardiac cells w/ each peak representing a different component of the cardiac cycle
What is atrial fibrillation
- uncoordinated atrial depolarisations
- up to 500bpm, atrial wall quivers
What are premature ventricular contractions
where ventricular myocardial cells depolarise + triggers premature contraction
What is ventricular tachycardia
4 PVC w/out intervening normal beats
What is ventricular fibrillation
whereby ventricles quiver + stop pumping -> cardiac arrest
