Week 4: Coronary Circulation Flashcards
What are autorhythmic cells and what do they do?
- specialised muscle cells
- self depolarising
- form the conduction system and carry impulses
What are contractile cells and what do they do?
- cells that contract in response to impulse
- branched fibres
- cells connected to one another by gap junctions
What is the sinoatrial node?
SA node, pacemakers, involved in the inter nodal pathway
What is the atrioventricular node?
AV node, gatekeeper, involved in the AV bundle (left and right branches) and purkinje fibres.
What sinus rhythm does the conduction system set?
60-100bpm
How does conduction occur through the heart?
- SA node begins depolarisation (contraction)
- the impulse travels through the atria by inter-nodal pathway
- impulse spreads to AV node
- impulse delayed at AV node for 0.1 sec
- impulse travels through AV bundle
- impulse distributed throughout the ventricles by purkinje fibres
What causes an increase in calcium action potential in the sarcoplasmic reticulum?
A cardiac action potential
In what phase do Ca2+ enter the myofibril?
During the plateau phase
What does a cardiac action potential maintain?
Contraction, aiding the heart function
Which nerve supplies the SA and AV nodes?
Vagus nerve (parasympathetic)
What are the three stages in the cardiac cycle?
- atrial systole
- ventricular systole
- ventricular diastole
Which chambers of the heart go through systole and diastole?
All chambers of the heart
What occurs in atrial systole?
SAN discharges and atria contract, ventricles relax, lasts 0.1 sec, responsible for 20% ventricular filling
What occurs in ventricular systole?
(0.3sec) ventricles contract, IV pressure rises, AV valves close, iso-volumetric contraction, ventricular pressure increases, SL valves open, blood enters aorta, end systolic vol = 60-70ml
What occurs in ventricular diastole?
(0.4sec) ventricles relax, blood starts flowing back from vessel, SL close, iso-voulmeric relaxation, rapid filling of ventricle (80%), atrial systole (transfer remaining blood to ventricles 20%), end diastolic vol= 130-140ml
What are some factors that can affect heart rate?
Gender, autonomic nerve activity, age, circulating hormones, activity/exercise, temp, baroreceptor reflex, emotional states
What is cardiac output?
The amount of blood pumped by each ventricle per min
What is the equation for cardiac output?
CO=HR X SV
What are 3 main factors that can affect heart rate?
- autonomic innervation
- hormones
- parasympathetic stimulation
What are the 3 factors affecting stroke volume?
- preload
- contractility
- afterload
How does preload affect SV?
An increase end-diastolic vol increases stretching which increase SV
An increase in venous return increases preload, increasing SV
How does contractility increase SV?
An increase int he strength of contraction increases SV
Better tines heart has stronger contraction. Sympathetic stimulation, adrenaline and calcium ions increase cotractility
How does afterload decrease SV?
An increase in afterload decresases SV
High blood pressure, obesity, stress decrease SV
Exercise increases SV
What is a cardiac reserve?
The difference between resting and maximal cardiac output
Who may have an increased cardiac output by 7/8 X?
Trained athletes
What is cholesterol?
A type of lipid
How is cholesterol transported?
By transport proteins
What does too much cholesterol lead to?
Deposition in blood vessels, causing a reduced blood floe and causing tissue hypoxia, can potentially lead to a clot
What is atherosclerosis and what can it lead to?
The thickening of blood vessels due to cholesterol deposition.
Can reduce blood supply to vital heart muscle tissue, leading to hypoxia, causing the tissue to die, causing myocardial infarction which disturbs impulse conduction
