Cardiovascular System Flashcards
What are the different sections of the wall of the heart?
endocardium - inner wall, smooth endothelium, covers the valves
myocardium - muscular component
epicardium/visceral pericardium - inner wall of the pericardial sac
pericardial cavity - space
parietal layer of the pericardium
fibrous pericardium
What is the cardiac cycle?
systole
systole = contraction and emptying of blood
isovolumic contraction - valves are all closed, ventricles contract but there is no change in volume, when ventricular pressure exceeds aortic pressure the aortic valve opens
ventricular ejection
What is the cardiac cycle?
diastole
diastole = relaxation and filling of blood
isovolumic relaxation - starts when ventricular pressure drops below atrial pressure, aortic valve closes and the mitral/tricuspid valves open
passive ventricular filling
active ventricular filling
How can the heart beat be described?
myogenic
- does not need nervous stimulation as the signal for contraction arises from within the heart itself
- heart beat is initiated by cardiomyocytes
What is the rate of conduction in each section for the heart?
fastest to slowest
Sinoatrial node = 70-80ms
Atrioventricular node = 50-60ms
Bundle of His and Purkinje Fibres = 20-40ms
Where does conduction start and travel through?
Sinoatrial node - in the upper part of the right atria, initiates the electrical signal
Atria
Atrioventricular node - delays to the SA node, allows the atrium to empty completely and ventricles to fill
Bundle of His - branch of fibres that extend to the AVN, runs down the septum to send signals to the PK
Purkinje Fibres - specialised nerve cells that send signals to the left and right ventricle
Ventricles
Bachmanns Bundle - preferential path of conduction of the left atrium, connects the SAN to the left atrium
What are the different sections of an ECG complex?
electrocardiogram complex
P wave
QRS complex
T wave
U wave
PR interval
QRS interval
ST segment
QT interval
What is the P wave? What are the factors affecting it?
atrial contraction (left and right) - depolarisation spreads from the sinoatrial node throughout the atria
P wave morphology depends on
- size of atria
- origin of depolarisation
What is the PR interval?
period of time from the onset of the P wave to the onset of the QRS complex
- time taken for atrial contraction = atrial depolarisation to AVN initiation
Short PR interval = arrhythmia, fast heart beat
Long PR interval = heart failure, heart block
What is the QRS complex?
ventricular depolarisation/contraction
- impulse moves from the SAN (atria), AVN, Bundle of His to the Purkinje Fibres (ventricles)
What is the QT interval?
period of time from the onset of the QRS complex to the end of the T wave
- action potential duration = depolarisation and repolarisation of the ventricles
Long QT interval = rapid heart beat, seizure, blackout
What is the T wave?
repolarisation of the ventricles
- return to resting membrane potential
What is the ST segment?
not an interval
is the isoelectric/flat segment between the end of QRS and start of T wave
Depression of ST = ischaemia
Elevated ST = myocardial infarct
What is sinus rhythm? How can it be identified?
rhythm of the heart when the electrical stimuli is initiated by the SAN
Positive P wave = sinus rhythm
Negative P wave = unlikely to originate from the SAN
