CVR 2: Cardiovascular Flashcards
How do inotropes increase contractility?
Increase the plateau of action potential, increase Ca ingress and release from SR, therefore more Ca binds to TnC, increasing contractility of myofibrils.
What is excitation-contraction coupling?
Chemical reaction, using chemical energy derived from ATP, resulting in mechanical action (contraction).
Begins with depolarisation and ends when Ca binds to TnC.
“When the heart is relaxing it isn’t resting!”
What does this mean?
When the heart is relaxed, it is still working hard, using ATP to pump Ca ions out of the myocytes.
Why is the T-tubule important in myocytes?
To allow calcium into the cell closer to the SR and myofibrils.
How does the myocyte remove calcium from the cytoplasm during relaxation?
Using ATP, moves Ca into SR stores.
Sodium/calcium exchanger uses electrochemical potential to allow 3x sodium ions into the cell in exchange for 1x calcium ion to leave.
Sodium gradient is then maintained by Na+/K+ ATPase.
Why is titin important and where is it found?
Titin is important because it acts as a spring in the myofibrils.
Attaches the myosin to the actin at the Z discs.
What are the three troponins in the troponin complex and what are their individual functions?
TnI = inhibits any interaction between actin and myosin.
TnC = binds to calcium, moves TnI and TnT (hence tropomyosin) away from actin, exposes actin binding site to myosin heads.
TnT = binds to tropomyosin to anchor the troponin complex and helps position the tropomyosin on actin, to also prevent myosin binding to actin.
What is a sarcomere?
The functional unit of myofibril, the region between two Z-lines.
What is isovolumic contraction?
Part of the cardiac cycle where the ventricle contracts without causing any change in the volume of blood in the ventricle.
Occurs after mitral/tricuspid valves close and before aortic/pulmonary valves open.
What pressure does the LV need to reach to open the aortic valve?
Diastolic pressure.
What is the ejection fraction in females vs males (percentage of blood ejected with each beat)?
Females = 65%
Males = 55%
What do the 1st and 2nd heart sounds correspond to?
“Lub dub”
1st = closing of mitral valve “lub” This is just after the start of isovolumic contraction.
2nd = closing of aortic valve “dub” This is also the start of isovolumic relaxation.
What is the early phase of filling?
When pressure in the left atrium increases above pressure in the left ventricle, blood rushes into ventricle passively prior to any atrial contraction.
In a young healthy adult, what percentage of blood from the left atrium moves into the ventricle during early phase of filling, and which heart sound can this create in youth/athletes/pregnancy?
85%
3rd heart sound (gallop).
When is the 3rd heart sound pathological and what does it suggest?
In adults over middle age, suggestive of congestive heart failure.
When does diastasis occur in the cardiac cycle?
When pressure in left atrium and left ventricle becomes equalised due to early phase of filling equalising the pressure. Net flow of blood = 0.
What is atrial augmentation?
When left atrium contracts and squeezes out the last part of blood in the atria, happens milliseconds after P wave on ECG.
When might you hear the 4th heart sound?
Galloping sound of blood being forced into stiff or hypertrophic left ventricle during atrial augmentation. Pathological sign of failing left ventricle.
A patient with AF has developed a hypertrophic left ventricle. Would you hear a 4th heart sound?
No! Because they don’t have any atrial augmentation.
Does contraction of the left ventricle (systole) occur before or after the mitral valve closes?
Before! Isovolumic contraction starts just before mitral valve closes.
What does preload refer to?
The load/volume of blood present before left ventricular contraction has started/degree of stretch of the myocardium.
“Left ventricular end-diastolic pressure”.
What is afterload?
The load after the ventricle starts to contract. The amount of pressure the heart needs to exert against pressure caused by aorta and circulation.
How does titin relate to Starling’s law?
Titin in myofibril keeps the unit tight. If the heart is overfilled and go beyond the capacity and stretch/elasticity of the titin, the heart is unable to contract efficiently.
What is elasticity of the heart?
The ability of the myocardium to recover its normal resting shape after removal of systolic stress.
How is ejection fraction calculated?
Stroke volume/end-diastolic volume.
What do pressure-volume loop graphs demonstrate?
Changing relationship between LV pressure and LV volume during cardiac cycle.
In embryonic development, from which layer do the coronary arteries develop from?
Ectoderm; the cardiac neural crest.
In embryonic development, from which layer does the myocardium develop?
Mesoderm (all types of muscle develop from the mesoderm).
What is the heart like at day 15 of embryonic development?
Tube-like heart, similar to a fish. First heart field; which will develop into left ventricle & atria, and second heart field; which will develop into right ventricle.
By what day of embryonic development does the heart start to resemble a mammalian heart?
Day 50.
What is a transcription factor and how might this relate to embryonic development of the heart?
Type of protein which when expressed “turns on/off” many other gene expressions.
If someone has a genetic variant which alters/deletes code for particular transcription factors which regulate embryonic heart development, could cause a malformed heart; congenital heart condition in baby or miscarriage.
What are the three stages of cardiac formation in the embryo?
- Formation of the primitive heart tube.
- Cardiac looping.
- Cardiac septation.
Why is Nodal important in embryological development and what is it?
Family of proteins, responsible for signalling developing cells to either move away or towards it; determines positioning e.g. left/right positioning of the heart.
What is the atrioventricular canal?
The initial gap between the embryonic single atrium and ventricle, which separates into two openings - eventually becoming the openings which situate the mitral & tricuspid valves.
What are the three types of capillaries?
Continuous (most common)
Fenestrated (kidney, small intestine, endocrine glands)
Discontinuous/sinusoidal (liver sinusoids, have larger openings than fenestrated)
When do the precursors of blood vessels form in the embryo, what are they called, and where do they form?
Day 17
Blood islands
Form in the yolk sac
When does vasculogenesis commence in the embryo?
Briefly describe the process.
Day 18
1. Blood islands = core of haemoblasts surrounded by endothelial cells.
2. Develop into angioblasts.
3. Angioblasts coalesce to form angioblastic cords throughout embryonic disc.
When and how does angiogenesis take place in embryonic development?
Day 18 onwards.
Driven by angiogenic growth factors.
Takes place by proliferation and sprouting. Other mesodermal cells are recruited to develop into smooth muscle intima media.
In embryonic development, do the 1st and 2nd aortic arch become coronary vessels?
No, they become minor head vessels.
In embryonic development, which aortic arch becomes the carotid arteries?
3rd aortic arch.
