Cardivascular System - Lec 2-3 Flashcards
What’s the myocardium and what’s its relevance to the hearts phases?
Heart is a muscle and it’s made out of myocardium
The heart functions in phases of relaxation and contraction to carrry out its function
Relaxed phase = known as diastole (diastolic function of heart commences here)
Contraction phase = known as systole (systolic function occurs here)
Explain how blood is supplied to the HEART USING CORONARY arteries
Coronary circulation supplies myocardium, which is achieved by the left and right coronary artery (both originate from base of ascending aorta)
LCA
- anterior descending (interventricular) branch (LAD) = IV sulcus
- circumflex branch = AV sulcus
RCA
- Posterior descending (interventicular) branch (PDA) =
- right marginal branch (RM)
But BLOOD VESSELS TRAVEL IN THE SULCI OF HEART
Name the regions of the heart that the LCA supplies blood to
Left ventricle
Left atrium
IV septum
Name the regions of the heart that the RCA supplies blood to
Right atrium
Party if both ventricles
Parts of the conducting system
Name the cardiac veins and their positioning
Great cardiac vein
Middle cardiac vein
Small cardiac vein
Coronary sinus
Veins travel with arteries
What’s the function f the coronary sinus
Collects blood from the cardiac veins and returns them to the right atrium
Why do we image the coronary arteries usually
To identify the dominant artery
Tends to be the RCA as it gives rise to the post descending artery (in 80% of people)
What’re the characteristics of the cardiac muscle (myocardium)?
Similar to skeletal muscles in a sense
- contracts when it is depolarised
- force of contraction depends on resting length of the muscle
Different to skeletal muscles in some ways
- not under voluntary control
- once one cell has polarised, all cells will also (THE HEART FUNCTIONS LIKE A SINGKE CELL - A SYNCYTIUM)
Name the features of the electrical conduction system of the heart and their location
Sinoatrial node (SA) = bass of heart (above right atrium) Atrioventricular node (AV) = right atrium
(These 3 form a special conduction unit to get the ventricles depolarised because the ventricles are insulated from the atrium)
Atrioventricular bundle = right ventricle
Right and left bundle branches = interventricular septum
Purkinje fibres = apex of heart
Where does depolarisation of the heart originate?
PACEMAKER - The area of the heart that depolarises spontaneously first
This is usually the sinoatrial node, so if the SA is damaged, other areas may take over as the pacemaker
If this happens, the pattern of contraction may be disrupted or the heart may fail entirely. This can occur when a heart muscle is damaged due to a heart attack.
How is depolarisation of the heart controlled?
Te rate of depolarisation is controlled by the balance between the sympathetic and parasympathetic nervous systems
They are the subdivisions of the autonomic nervous system (ie. automatic actions). Therefore, with no conscious control
How exactly does electrical conduction of the heart occur?
So once the SA node has depolarised, the electrical activity spreads out across the entire muscle (cause the heart is one big cell) using the other different conduction features
So if the whole conduction system is not working properly, THE HEART WILL NOT CONTRACT PROPERLY
This may cause arrhythmia (detected using EEG)
Explain the sounds caused by the heart in relevance to anatomical functions
1st heart thump sound = closure of AV valves (they close when the pressure in v build up, so this builds up when v starts to contract)
Beginning of ventricular contraction (ventricular systole)
2nd thump sound = closers of semilunar valve
Happening at the beginning of ventricular relaxation ie. ventricular diastole
(when pressure in v becomes greater than the artery we’ll get blood travelling from region of low to high pressure
What phase is the heart in during the between stages of the waves on the ECG?
P - QRS = atrial systole
QRS - T = ventricular systole
QRS - P = atrial diastole
T - QRS = ventricular diastole
Explain the significance of different wave formations on a ECG of the heart
P wave = atrial contraction/depolarisation
QRS complex = ventricular contraction (atrial relaxation therefore repolerisation of atrium is also occurring here)
T wave = ventricular relaxation/repolerisation
Much bigger wave for QRS than P wave, because the muscle in the atrium is much smaller than the muscle in the ventricle THEREFORE, YOU GET LESS ELECTRICAL ACTIVTY IN ATRIUM
also you find that the wave formed for depolarisation is smaller than for repolerisation
How do you oBTAIN AN ECG
Adding electrodes on the patient skin in specific locations
On ECG we can record between each electrode, this helps us get a different views across the heart.
All of the differnt electrode positions give us a view of differnt directions of the heart, and provides us 12 views of the heart.
How is the pump function of the heart controlled?
2 factors affect the pumping function per min
- amount of blood pumped each time the heart contract
- number of times the heart beats each min (heart rate)
What is the cardiac output and how is it calculated
Cardiac output (Q) is relevant to the pumping function of the heart in that it is the amount of blood pumped each minute into either the systemic or pulmonary circulation)
It is obtained by: Q = HR x SV
SV (stroke vol) = The volume of blood pumped by the contracting ventricle on each beat
HR = heart rate which is regulated by a balance between symp and parasympathetic
What affects the stroke volume
Preload = AMOUNT OF BLOOD COMING BACK.
Contractibility = HOW STRONG IS HEART CONTRACTING
Afterload = RESISTANCE, PUMPING INTO ARTERIES.
What’s the contractibility?
Intrinsic strength of contraction of the ventricular muscle (not affected by venous return). Dependent on the muscle solely, in terms of how much calcium is being released into the muscle cells. SNS activity increased, increases calcium
INCREASED SV
The measure of contractibility determined by activity of sympathetic nervous system (increase SNS = increase contractile force)
Increased stress = increased HR = contracting greater force
What’s preload?
Amount of blood in the ventricle at the end of a diastole. HOW FULL IS THE VENTRICLE?
INCREASED SV
The end diastolic volume is determined by the amount of blood returning to the heart in the veins (the venous return)
The venous return determines the amount of stretch in the ventricular muscle. Therefore,
Increased preload = Increased stretch of muscle = greater force of heart contraction
What’s the reason for using a ECG signal of the heart
It’s used as a reference for image collection
Can do;
Prospective gating = image required at specific point in ECG cycle ie. during ventricular systole
Retrospective gating = imaging performed continuously with ECG signal stored
Beta blockers are frequently used to reduce heart rate to improve imaging
- adrenaline relaxed by sympathetic NS, high symp act. = more adrenaline and increases heart rate.
- so when you want image someone you want to drop the heart rate, and thus, we can use beta blockers to reduce adrenaline release and thus allow for better imaging
When the sympathetic nervous system activity is increased, we can presume that the following factors are also affected
Preload increases Contractibility increases Afterload decreases Stroke volume increases Heart rate increases CARDIAC OUTPUT INCREASES
SO If parasympathetic activty increases, then your CARDIAC OUTPUT DECREASES
What affects the venous return?
Sympathetic activation
- some muscle in the walls of the veins that contract, pressure increases which pushes more blood back into the heart. THUS INCREASING VENOUS RETURN
Muscle and thoracic pumping
- pressure in veins is normally low so when you do extraneous physical activity like excercing, muscles contract where they squeeze on the veins and increase pressure in them causing greater venous return
Changes in pressure within thorax
- breathing causes pressure changes in thorax
- this change causes changes in pressure within veins
- small breaths causes small change in venous pressure, and vice versa
What’s afterload
Afterload is the resistance against which the heart has to pump
DECREASED SV
For this, the ventricular pressure must exceed arterial blood pressure for blood to flow into the arteries. So when arterial pressure rises there is more resistance, thus harder to pump blood out of the heart (out flow)
Unlike preload and contractibility, the SNS is lowered in activity
