1 Flashcards
Name the four coronary arteries
1) Right Coronary Artery
2) Left Main Coronary Artery
3) Left Anterior Descending Coronary Artery
4) Left Circumflex Coronary Artery
How does the heart get its blood supply?
What phase of the cardiac cycle does the heart get blood?
Cardiomyocytes supplied by Coronary arteries during diastole
Coronary ostia is located behind aortic valve leaflets so cannot flow while blocked during systole. Micro-vasculature is also compressed during systole which further reduces blood flow
Explain the automaticity of the SA node
Slow inward flow of Na “pacemaker current” results in spontaneous depolarization
What is the function of the intercalated discs
Allow ions to pass through cells, allowing for rapid transmission of AP
What are the main differences between cardiac myocyte and skeletal muscle
Cardiac has a longer duration: allowing for prolonged Ca entry and muscle contraction
Cardiac has a longer refractory period: allowing sufficient time for ventricles to empty
Cardiac has low resistant gap junctions - intercalated discs
What specific isoforms of regulatory proteins are used to diagnose a myocardial infarction
Troponin I and Troponin T are unique for cardiac muscle vs skeletal muscle
TnC is the same for cardiac and skeletal
Resting values of BP, HR, SV, Q, and VO2
BP: 120/80 mmHg HR: 60-80 bpm SV: 70mL/beat Q (cardiac output): 5L/min VO2: 250mL/min
Chronotropy
Rate of contraction
Ionotropy
Force of contraction
Dromotropy
Velocity of contraction
How does the autonomic nervous system decrease heart rate
Through the PNS:
acetylcholine acts on muscarinic receptors (M2) at the SA and AV nodes to decreasing chronotropy (rate of contraction)
Intrinsic Control (100bpm) + PNS = 60-80bpm resting HR
How does the autonomic nervous system increase heart rate
Through the SNS:
norepinephrine (NE) acts on beta receptors (mainly B2) to increase chronotropy
As well stimulates the adrenal cortex to release the catecholamine epinephrine (E) which also acts on beta 1 and beta 2 receptors to increase chronotropy
During Exercise: PNS withdrawal + SNS Activation = 110-220bpm
How does SNS and catecholamines affect ionotropy and chronotropy
SNS –> Epinephrine
Catecholamines –> Norepinephrine
Act on beta 2 receptors on SA and AV node to increase chronotropy (rate of contraction) - increasing HR
Act on beta 1 receptors on cardiomyocytes to increase inotropy (force of contraction) - increasing SV by decreasing ESV
At submaximal exercise, which has a bigger impact: increasing HR or increasing SV?
At sub-maximal exercise, largely influenced by increasing in SV since there is a more rapid increase initially and then plateaus
At maximal exercise, which has a larger impact on blood flow: increasing HR or increasing SV?
At maximal exercise, increase in blood flow is most influenced by an increase in HR as there is consistent linear increase
What intrinsic factors increase venous return
increasing blood volume
venoconstriction (mostly done by SNS (NE) and catecholamines (E))
skeletal muscle pump
respiratory pump
This increases the length-tension relationship described by Frank-Sterling mechanism which increases SV
What’s the passive force in Frank-Sterling mechanism?
Blood filling the ventricles causes a stretch in the sarcomeres, causing an increase in tension - increasing the force
What’s the active force in the Frank-Sterling mechanism?
Refers to the ability of the crossbridges to produce force. At the optimal sarcomere length (Lo) there is the maximal amount of thick and thin filament overlap producing the largest amount of force
How is ejection fraction calculated and what does it represent?
(SV/EDV) x 100
Represents the amount of blood ejected from the left ventricle as a percentage of the total blood in the l. ventricle prior to contraction
What is a typical EF of a healthy individual?
50-70%
What is a typical EF of a person with systolic dysfunction?
35-40%
What is the typical EF of a person with diastolic dysfunction?
50-70% - able to eject the available blood in the ventricle, but the amount of blood available is diminished (% the same, volume is lowered)
How does the automatic nervous system control blood pressure
PNS: release of Ach, acts on muscarinic M2 receptors to cause vasodilation
SNS: release of NE, acts on alpha 1 and alpha 2 receptors to cause vasoconstriction
How do hormones control blood pressure
Epinephrine: acts on alpha receptors to cause vasoconstriction, acts on beta 2 receptors to cause local vasodilation seen in active skeletal muscle
Angiotensin II: vasoconstrictor
Vasopressin: antidiuretic that increases blood volume through reabsorption at kidneys. Acts on alpha receptors to cause vasoconstriction
Atrial Natriuretic Factor: released in atria during stretch caused by the increase in blood volume. Acts to decrease blood volume by inhibiting renin. Causes vasodilation
