D4 The Heart Flashcards
what is cardiac muscle contraction?
myogenic
what are the features of cardiac muscle cells which aid with their function? 3
- muscle cells are branched to allow for faster signal propagation and contraction in 3D
- muscle cell are not fused together but connected by gap junctions at intercalated discs
- lots of mitochondria (more that skeletal) more reliant on skeletal muscle
what are unique functional properties of cardiac muscle? (3)
- longer periods of contraction and refraction (to maintain viable heart beat)
- heart tissue does not become fatigued (continuous, life-long contraction)
- interconnected network of cells is separated between atria and ventricles (contract separately)
what valves ensure one-wy circulation of blood? (2)
- atrioventricular valves (tricuspid and bicuspid) prevent blood flowing back into atria
- semilunar valves prevent blood in arteries from flowing back into ventricles
what causes heart sounds? (2)
- 1sy heart sound is caused by closure of atrioventricular valves at start of ventricular systole
- 2nd heart sound caused by closure of semilunar valves at start of ventricular diastole
what is the cardiac cycle mapped by?
electrocardiograph
what is the cardiac cycle? (9)
- sinoatrial (SA) node (pacemaker) starts the cardiac cycle
- SA node sends an ‘action potential’ through the cardiac muscle to the left and right atrial walls.
atria contract (depolarise) - this causes the P wave in an ECG. - AV node receives the ‘action potential’ signal to from the SA node
- AV node holds signal for 0.1 seconds
- AV node sends ‘depolarisation’ signal to bottom of left and right ventricles;
- conducting fibres in the heart’s central septum carry the signal rapidly
- ventricles contract - this causes the QRS spike in the ECG.
- The ventricles repolarise - causing the T wave.
- the heart is ready to beat again. (The atria repolarise during the ventricle contraction QRS)
describe stages of cardiac cycle (bioninja) (4)
- P wave represents depolarisation of the atria in response to signalling from the sinoatrial node (i.e. atrial contraction)
- QRS complex represents depolarisation of the ventricles (i.e. ventricular contraction), triggered by signals from the AV node
- T wave represents repolarisation of the ventricles (i.e. ventricular relaxation) and the completion of a standard heart beat
- Between these periods of electrical activity are intervals allowing for blood flow (PR interval and ST segment)
what are 3 examples of heart conditions?
tahycardia - elavates reasting heart rat (>120bpm)
bradycardia - depressed heart rate <40bpm
arrhythmias - irregular heartbeat common
fibrillations - unsynchronised contraction of atra or ventricles leading to dangerous spasmodic heat activity
what is an artificial pacemaker used for?
to treat
- abnormally slow heart rates (bradycardia)
- arrhythmias from blockages within heart’s electrical conduction system
what is fibrillation?
rapid, irregular and unsynchronised contraction of heart muscle fibres
how is fibrillation treated?
- by defibrillator
- it depolarises the heart tissue to terminate unsynchronized contractions
- when heart is depolarised normal sinus rhythm should re-establish by sinoatrial node
