Cardiovascular System - Cardiac cycle, sounds and rhythms Flashcards
Systole
- Heart contaction
Diastole
Relaxation of heart
Atria contraction
- Diastole initial when the atrium is filling with blood
- then Atrium in systole when contracting and pushing blood to ventricle
Ventrical contraction
- Initially diastole when the ventricle is being filled with blood from atrium
- Systole when ventricle contracts until all blood enters either aorta or pulmonary vein then returns to diastole
Sino Atrial node
- Specialised electrically active Myocardial tissue of atrium
- Intrinsic unstable spontaneous depolarisation
- Generates electrical activity-Impulse
Atria ventricular node
- Specialised electrically active Myocardial tissue ventricular midline
- Intrinsic unstable spontaneous depolarisation
- Generates electrical activity-Impulse
Inter nodal tracks
- Conduction pathways (Anterior, Middle & Posterior)
- Carry pulse, depolarise and contract atria (right and left)
- Converge at AV node
Fibrous mid-line
No electical conductivity
Bundle of HIS (AV bundle)
- Collect and carry to higher and lower part of the ventricles
Purkinge Fibres
Specialised myocardium for electrical conduction towards contractile myocytes
Vagus innervation
Suppress the heart rate
Sympathetic Innervention
-Stimulates the AV and SA node this increases the heart rate
Cardiac muscle
- Striated branched muscle fibre containing single nucleus with many mitochondria
- Gap junctions so depolarisation between cells
- Desmosomes hold the fibres close together in contractions
Properties of Cardiac muscle
Auto-rhythmicity
Ability to initiate heart rate consistent and continuous at regular pace without any external stimuli (autonomic)
Properties of Cardiac muscle
Excitability
- Ability to respond to stimuli of adequate strength and duration (threshold or more)
- Ability to generate and process action potential
Properties of Cardiac muscle
Conductivity
Ability to conduct and transmit impulse through the cardiac tissue
Properties of Cardiac muscle
Contractility
Ability to contract in response to stimulation (mechanical)
Exitation-Contraction Coupling in Contractile Myocytes
Step 1 - Action Potential arrival
Action Potential from adjacent cell excites myocytes and trigger membrane depolarisation in T-tubules
Exitation-Contraction Coupling in Contractile Myocytes
Step 2 - Calcium enters cell
Calcium enters the cell via voltage gated channel open the calcium enters cell
Exitation-Contraction Coupling in Contractile Myocytes
Step 3 - Calcium binding
Calcium binds to Ryanodine receptor (RYR) and induce Calcium release from SR
Exitation-Contraction Coupling in Contractile Myocytes
Step 4 - Trigger myosin
Calcium binds to troponin and triggers acting-myosin complex and contraction
Exitation-Contraction Coupling in Contractile Myocytes
Step 5 - Calcium unbind
Calcium unbind from troponin and pumped back into SR
Exitation-Contraction Coupling in Contractile Myocytes
Step 6 - Calcium causing relaxing
Calcium unbinding cause relaxation and excess Ca2+ exchanged with Na+
Exitation-Contraction Coupling in Contractile Myocytes
Step 7 - Maintainance of Na+ gradient
Na+ gradient is maintained by sodium-potassium- ATPase pump.
P wave
Atria depolarlisation contraction (systole)
QRS complex
- Isovolumetric contraction when ventricle is filling
- Ventricle depolarisation
T wave
Ventricle repolarisation
Atrial Systole
- Atrial myocardium contraction for 0.1 sec
Ventricle Systole
Ventricular myocardium contraction at 0.3s
Synus Rhythums
- Calculate by observing the R-R intervals
- Calculate if there is Sinus bradycardia less beats per minute
- Sinus tachycardia heart beat too fast
ECG readings
1mV = 10mm high
5 boxes across is 1s
Sinus bradycardia
- Rate is less than 60bpm
- Usually asymptomatic beta blockers and calcium channel blockers my be the cause
Sinus tachycardia
- rate greater than 100bpm
- Occours in exercise and stress
- Asymptomatic could by hypervolemea
