Cardiovascular system IV - cardiac cycle, sounds & rhythms Flashcards
Systole:
Heart contraction
Diastole:
Heart relaxation
Stages of cardiac cycle:
1) Ventricular filling
Atrial contraction [ventricular filling mid-t-late diastole]
2) Isovolumetric contraction phase
Ventricular ejection phase [Ventricular systole - atria in diastole]
3) Isovolumeric relaxation [early diastole]
Heart _______ Flow
Electrical
Sino Atrial (SA) Node Pace Maker
Right side
Atria Ventricular (AV) node
Left side
SA node [right]
Specialised electrically active Myocardial tissue-Atria
Intrinsic/electrical unstable-Physiological origin of contraction
Spontaneous depolarisation,
90-100 times/min
Generates electrical activity-Impulse
AV node [left]
Specialised electrically active Myocardial tissue- Atria-Ventricular mid line
Generates electrical activity-Impulse
Intrinsic/electrical unstable-
Spontaneous depolarisation,
Lower than SA (40-60 times/min)
Inter-nodal tracks
Conduction/Preferential pathways (Anterior, Middle & Posterior)
Carry pulse, depolarise and contract atria (right and left)
Converge at AV node
Fibrous mid line
No electrical conductivity
Bundle of HIS (AV bundle)
The border between the two ventricles
Collect and carry to higher and lower part of the ventricles (Apex); 20-40 times/min
Purkinge Fibres
Specialised myocardium for electrical conduction (not contraction) towards contractile myocytes (cardiac cells)
Vagus innervation
Para sympathetic
Slows down the SA & AV nodes
Supresses the heart rate
Sympathetic Innervation
Stimulate SA & AV nodes
Increases the heart rate
Cardiac muscle
99%- contractile; 1% Auto-rhythmic cells
Cardiac muscle structure:
Striated type, branched muscle fibers (myofibrils) contains single nucleus, many mitochondria and T-tubules
Connected by intercalated disks
Gap junctions- Depolarisation between cells
Desmosomes- Hold fibers together during contraction
What are the key properties of Cardiac muscle>
- Auto-rhythmicity = Ability to initiate heartbeat, consistent and continuous at regular pace without any external stimuli
- Excitability = Ability to respond to stimuli of adequate strength and duration (threshold or more)
Ability to generate and process action potential - Conductivity = Ability to conduct and transmit impulse through the cardiac tissue
- Contractility = Ability to contract in response to stimulation (mechanical)
Action p in the myocytes triggers the L type calcium to enable to bind to the RYR.
Excitation contraction
Where is calcium stored?
In the cytoplasmic reticulum
When is calcium released
Durning depolarization
Exhitation - Contraction Coupling in Contractile Myocytes
7 steps
Exhitation - Step 1 = AP
AP from adjacent cell excites myocytes and trigger membrane depolarisation in T-tubules
Excitation - Step 2 Calcium enters the cells
Calcium enter the cells via voltage gated channel opens and calcium enters the cells
Exhitation - Step 3 Calcium binding
Calcium binds to Ryanodine receptor (RYR) and induce Calcium release from SR
Exhitation - Step 4 triggers myosin
Calcium binds to troponin and triggers acting-myosin complex and contraction
Excitation - Step 5 calcium unbinds
Calcium unbind from troponin and pumped back into SR
Excitation - Step 6 relaxation
Calcium unbinding cause relaxation and excess Ca2+ exchanged with Na+
Excitation - Step 7 Na+ gradient maintained
Na+ gradient is maintained by sodium-potassium- ATPase pump.
Cardiac cells (Myocytes)
-90mV (polarised)»_space;> +20mV (depolarised)
A wave of depolarisation that begins in the SA node and spreads over the heart CAUSES…
Contraction
Between points P and Q there is a delay, why is this? There is a slight drop.
[see in graph - 17 lec slides]
So that the blood can flow from the vein to the the ATRIUM - FILL UP
1st wave - P-wave
Atria depolarisation
QRS complex - first 3 waves
Ventricle depolarisation
4th wave
Ventricle repolarisation
What does the graph showing SINUS rhythms show?
Isoelectric signal line
PQRST Regular- Right Order
70-100 BPM- Sinus Rhythm
< 70 BPM- Sinus Bradycardia
>100 BPM- Sinus Tachycardia
Sinus bradycardia
The rate is <60bpm
(not usually <40bpm)
Patients usually asymptomatic and no treatment is required
beta-blockers / calcium channel blockers
May also be seen in athletes and occur during sleep.
Sinus tachycardia
Rate is > 100bpm, but not usually > 130bpm at rest
Occurs normally in exercise / stress.
Patient is usually asymptomatic.
Hypovolaemia / underlying medical problems
Sinus Rhythms (ECG/EKG)
ECG - the wave
Sinus Arrythmia
“regularly irregular”
P-P intervals varies by more than 10%
Heart Block/Disease
Respiratory Disease
