Flashcards in CVS Session 2 Deck (108):
What is the function of capacitance vessels?
Allow a store of blood so cardiac output is variable
Which are the two outflow valves of the heart?
Which are the inflow valves of the heart?
Describe the specialised form of cardiac muscle.
How is force generated in cardiac muscle cells?
Electrical event in cell membrane --> increase calcium --> actin and myosin sliding filaments interact
What is the unique feature of electrical signals in cardiac muscle cells?
1 electrical signal = 1 contraction
How long is the contraction of a cardiac muscle cell?
What does a cell in systole do to its neighbour?
Trigger it to enter systole
What produces a coordinated contraction across the whole heart?
An AP generated in a small group of pacemaker cells
Describe the generation of action potentials by pacemaker cells.
Spontaneous at regular intervals
Briefly describe the spread of excitation across the heart.
SAN --> atrial systole --> AVN 120 ms delay --> Bundle of His --> endocardial to epicardial --> apex up to ventricle
What prevents tearing of the cardiac muscle during pumping?
Relaxation takes place outside to inside (opp. direction to excitation)
Why is the SAN not overridden as the 'master node' of the heart?
It is quick and powerful to fire
In a normal heart what is the only route for atrial to ventricular excitation spread?
Via the AVN
How is the arrangement of muscle in the ventricle used to maximise expulsion?
Figure of 8 arrangement
In which direction does the spread of excitation from the apex upwards force the blood to flow?
Towards the outflow valves
What is the Bundle of His?
Specialised cardiac tissue to accelerate AP conduction
What allows the heart to work as a reciprocating pump?
Regular alternating systole and diastole
Inflow and outflow valves
What occurs during diastole?
Ventricles fill from the veins
What occurs during systole?
Ventricles pump blood into arteries
What allows blood into the left ventricle from the atrium?
Mitral inflow valve
What closes the mitral valve?
Ventricular pressure > atrial pressure
What allows blood to flow from the left ventricle to the aorta?
Aortic outflow valve
What opens the aortic valve?
Intra-ventricular pressure > aortic pressure
How are cardiac valves arranged?
Flaps lying over each other or against wall
What is needed to close cardiac valves?
Regurgitation to lift valve flaps
How do inflow and outflow valves differ?
They are configured in opposite directions
At rest, how often does the SAN generate and AP?
About once a second
Is the length of ventricular systole variable?
Not really, always ~280 ms
How long is diastole at rest?
What is the variable portion of HR?
Length of diastole
Describe the end of ventricular systole.
IV pressure high
Outflow valves open
p(ventricular) > p(atrial)
Atrioventricular valves closed
What happens as the ventricles start to relax after ventricular systole?
p(IV) < p(atrial)
Brief backflow closes outflow valves
All valves closed
What occurs in atrial systole?
Small amount of blood is pumped into ventricle to limit loss of regurgitation
Is limiting loss of regurgitation during atrial systole necessary?
What happens in ventricular systole?
p(IV) increases rapidly
After brief backflow A/V valve closes --> all valves closed
Isovolumetric contraction - blood trapped
What opens outflow valves?
p(IV) > p(atrial)
What halogens when the outflow valves open?
Rapid ejection phase
Blood moves to arteries
Arterial pressure rises rapidly
What happens during systole?
Blood returns to atria
Eventually p(atria) > p(IV)
A/V valves are open
What is the rapid filling phase?
A/V valves are open so ventricles fill rapidly with most filling occurring in the 200-300 ms it lasts
When does ventricular filling stop?
When p(IV) = p(atrial)
What is diastasis?
Occurs halfway through diastole
Ventricular filling decreases as the ventricles are already full when the atria contract
What happens at the end of systole?
Rate of ejection decreases due to elastic walls of arteries
Arterial and intra ventricular pressure peak
Outflow ceases w/ blood in ventricle
What causes the first heart sound?
Closure of the A/V valves
When is the first heart sound heard?
Onset of ventricular systole
What causes the second heart sound?
Closure of outflow valves
When is the second heart sound heard?
End of ventricular systole
What is the time interval of the first and second heart sounds at rest?
280 ms (systole)
What is the time interval of the second and first heart sounds at rest?
700 ms (diastole)
What might alter the quality of heart sounds?
Altered valves e.g. calcification
What might cause splitting of heart sounds?
If left and right heart valves do not close at the same time
What causes a 3rd heart sound?
Rapid expansion of ventricle in early diastole during rapid filing phase
When is a 3rd heart sound more commonly heard?
In thinner people
What causes a 4th heart sound?
Atrial systole in children
What causes heart murmurs?
Turbulent blood flow
What may cause turbulent blood flow?
When do heart murmurs occur?
When blood flow is highest e.g. rapid ejection phase in aortic stenosis
What is the typical stroke volume ejected per beat in an adult?
How is cardiac output calculated?
Stroke volume x heart rate
At rest, what is the cardiac output for an average adult?
80 ml x 60 bpm = 5 l per minute
In the fourth week of development, what is just beginning to differentiate into primitive blood cells and capillaries?
Primary heart fields w/ blood islands
Is the cardiogenic field of the composite bilaminar and trilaminar embryo relatively differentiated?
What is the progenitor to cardiac tissues?
What forms the primitive heart tube?
Briefly outline the formation of the primitive heart tube by lateral folding.
2 large BV come together to form one large BV that has arisen from the cardiogenic area
Around which days does the CVS develop?
Why does the CVS develop so early?
It is needed by the foetus
What brings the primitive heart tube into the thoracic region?
How is the heart tube arranged after cephalocaudal folding?
It is suspended in the pericardial cavity by a membrane that subsequently degrades
What are the regions of the primitive heart tube from head to tail end?
Turn us arteriosus
Which end of the heart tube does blood from the embryonic body enter?
Which part of the primitive heart tube is the pulsatile structure?
Describe the movements of the cephalic and caudal portions of the heart tube during looping.
Cephalic: forward, down and right
Caudal: backwards, up and left
How does the pericardial cavity grow in relation to the heart tube?
It does not grow as much so it becomes filled by the heart tube
What are the results of looping of the primitive heart tube?
Arteries in front of veins
Transverse pericardial sinus forms
Primordium of right ventricle closest to outflow tract
Primordium of left ventricle closest to inflow tract
Atrium dorsal to bulbus cordis
What does repositioning of the ventricle primordiums optimise?
Septum formation b/w cavities of the heart
Do the primitive chambers of the heart develop symmetrically?
Nope - ventricle enlarges much more than the primitive atrium
How does the atrium communicate with the ventricle after looping?
Via atrioventricular canal
Briefly describe the development of the sinus venosus.
R+L sinus horns equal in size --> venous return shifts to RHS --> L sinus horn recedes so RHS dominant --> R sinus horn absorbed by enlarging R atrium
Where does the right atrium develop from?
Most of primitive atrium
What receives venous drainage from the body and heart?
Where does the left atrium develop from?
Small portion of primitive atrium
Where does the pulmonary vein arise?
What happens to the proximal parts of the pulmonary vein in the left atrium?
Absorbed so 4 drain into it
What receives oxygenated blood from the lungs?
How does the wall of the left atrium near the pulmonary vein compare to t he surrounding wall?
Trabeculated component in comparison to the surrounding smooth wall
What forms the oblique pericardial sinus?
Expansion and vein absorption of the left atrium
What are the lungs bypassed in the foetal circulation?
They are non-functional
How does the utero-placental circulation receive oxygenated blood from the mother?
Via placenta and umbilical vein
Why is the liver bypassed in foetal circulation?
So all of the oxygen being carried is not used up by the especially high activity of the liver in the foetus
What is needed in foetal circulation to transition after birth?
A series of shunts and diversions that can be shut off immediately
What is needed to flow through the right ventricle in the foetal circulation?
Small amount of blood so there is resistance for muscle to work against
How does the early arterial system begin?
Bilateral symmetrical system of arched vessels
What creates the major arteries leaving the heart?
Extensive remodelling of aortic arches resulting in loss and movement of different parts
What does the 4th aortic arch give rise to?
Right = proximal part of R subclavian artery
Left = arch of aorta
What does the 6th aortic arch (pulmonary arch) give rise to?
Right = R pulmonary artery
Left = L pulmonary artery and ductus arteriosus
What is the ductus arteriosus?
Foetal vessel needed to bypass lungs
What does the ductus arteriosus become in the neonate?
Which nerve corresponds with the 6th aortic arch?
Recurrent laryngeal nerve
Where do the left and right recurrent laryngeal nerves descend to?
Left: T4-T5 through mediastinum
What does the nerve corresponding to the 6th aortic arch innervate?
What influences the course of the L and R recurrent laryngeal nerves?
Caudal shift of developing heart
Expansion of developing neck
Need for foetal shunt b/w pulmonary trunk and aorta
Briefly describe the determination of the course of the L and R recurrent laryngeal nerves.
Aortic arches remodelled --> heart descends and nerve hooks on 6th aortic arch, turning back on itself --> L nerve hooked on ductus arteriosus, R nerve drops to T1 around R subclavian artery
Why does the R recurrent laryngeal nerve drop to T1?
More extensive remodelling on the right
What is the name of the pulmonary trunk-aorta shunt in the foetus?
What must happen after looping of the primitive heart tube?
Septation - primitive chambers must be divided
Which part of cardiac development is most prone to complications?