Cardiovascular I

Question 1

Describe the pulmonary and systemic circuits of the mammalian cardiovascular system.

Answer 1

Pulmonary Circulatory System: circuit that delivers deoxygenated blood to the lungs for gas exchange and returns oxygenated blood back to the heart.
Systemic Circulatory System: circuit that delivers oxygenated blood to all organ systems/body tissues for cellular respirations and returns deoxygenated blood to the heart.

Question 2

Identify major vessels of the heart including: aorta, pulmonary trunk, pulmonary arteries, pulmonary veins, superior vena cava, and inferior vena cava.

Question 3

Identify chambers and areas of the heart including: atria, ventricles, anterior interventricular sulcus, interventricular septum, interatrial septum.

Question 4

Identify major valves and valve components including: mitral, left and right atrioventricular, bicuspid, tricuspid, aortic valve, pulmonary valve, chordae tendineae, papillary muscle.

Question 5

Describe the blood flow through the left and right side of the heart and associated vessels.

Answer 5

1. Deoxygenated blood is returned to right side of the heart from systemic cirulation via superior and inferior vena cava, into right atrium.
2. Blood flows from right artium to right ventricle through tricuspid valve.
3. Right ventricle contracts, forcing pulmonary/semilunar valve to open, and blood flows to lungs via pulmonary trunk and arteries.
4. Pulmonary veins return oxygenated blood.
5. Blood flows from left atrium into left ventricle via bicuspid valve.
6. Left ventricle contracts, forcing aortic valve to open, and blood is pumped through aorta where it enters systemic circulation.

Question 6

Define: venous return, diastole, systole, end diastolic volume, end systolic volume.

Answer 6

Venous Return: volume of blood returning to the heart.
Diastole: phase of relaxation, and ventricles fill with blood.
Systole: phase of contraction of ventricles, causes the ejection of blood into the aorta and pulmonary trunk.
End Diastolic Volume: total volume of blood in the ventricles at the end of diastole.
End Systolic Volume: volume of blood that remain in the ventricles following ventricular contraction.

Question 7

State the proportion of blood flow due to the ventricles and atria.

Answer 7

25% due to the contraction of the atria.
75% due to the venous return.

Question 8

Indicate the major driving forces of blood throughout the body.

Answer 8

-Contraction of ventricles
-Venous return
-Elasticity of arteries, which absorbs pressure from ejection phase and gradually returns into arterial system to maintain blood flow

Question 9

Describe the functional syncytium of the heart and indicate its importance in cardiac physiology.

Answer 9

Functional Syncytium: myocardial cells are electrically interconnected by gap junctions, allowing rapid, coordinated contractions.
-Heart contracts as one unit which enables pumping of blood

Question 10

Discuss the functional significance of the gap junctions in myocardial cells.

Answer 10

Gap junctions electrically conduct myocardial cells together allowing action potentials to rapidly spread, triggering contractions of entire heart at almost same time.

Question 11

Describe the steps in a full cardiac cycle.

Answer 11

Cardiac Cycle: repeating patterns of systole and diastole.
Systole
1. Isovolumetric Contraction: when ventricles are fully packed with blood and pressure is higher in the ventricle than atria causing AV valves to be closed.
a. Pressure in ventricles isn’t high enough to push semilunar valves open.
b. Period between contraction of atria and beginning of ventricular contraction (0.1-0.2s time lag in electrical conduction)
2. Ejection/Ventricular Contraction: phase oh contraction of ventricles due to propagation of action potential.
a. Increases pressure within ventricles and forces semilunar valves open.
b. Blood flows out of heart via aorta and distributed through body by atrial system.
Diastole
3. Isovolumetric Relaxation: as blood pressure is transferred to arteries, pressure within ventricles drop, causing semilunar valves to close.
a. Pressure in atria and ventricles is low and AV valves are closed.
b. Period where both atria and ventricles relaxed and waiting for venous return to atria.
4. Rapid Filling: as venous blood returns and fills atria.
a. Pressure within atria rises and pushes AV valves open, allowing blood to flow into ventricles.
5. Atrial Contraction: contraction of atria triggered by action potential by SA node.
a. Pushes final volume of blood from atria to ventricles.

Question 12

Define: end-diastolic volume, stroke volume, end-systolic volume, ejection fraction, isovolumetric contraction, isovolumetric relaxation.

Answer 12

End-Diastolic Volume: volume of blood in ventricles at end of diastole
Stroke Volume: volume of blood pumped by one ventricle per heartbeat
End-Systolic Volume: volume of blood that remains in the ventricles following ventricular contraction
Ejection Fraction: volume of blood that’s ejected by left and right ventricle per heartbeat
Isovolumetric Contraction: period between contraction of the atria and beginning of ventricular contraction; when ventricles are filling with blood
Isovolumetric Relaxation: period where atria and ventricles are both relaxed prior to venous return

Question 13

Relate volume and pressure changes over the cardiac cycle and indicate: isovolumetric contraction, isovolumetric relaxation, ejection, rapid filling.

Answer 13

Cycle Phase Volume (ventricle)
Pressure (ventricle)
1. Isovolumetric Contraction: increases to max. volume, increases pressure
2. Ejection: decreases in volume increase, followed by decrease in pressure
3. Isovolumetric Relaxation: decreases to lowest volume, low pressure (no change)
4. Rapid Filling: increases in volume, low pressure
5. Atrial Contraction: increases in volume, increase pressure

Question 14

Discuss what produces the heart sounds and when over the cardiac cycle.

Answer 14

Lub-dub sound corresponds to closing of heart valves during cardiac cycle.
Lub: closing of AV valves (isovolumetric contraction)
Dub: closing of semilunar valve (isovolumetric relaxation)

Question 15

Identify tissues that are capable of automaticity in the heart.

Answer 15

Automaticity: automatic nature of heart, determined by regions that can spontaneously generate action potentials.
SA Node, AV Node, Purkinje Fibres

Question 16

Define: automaticity, conductivity, rhythmicity, excitability, contractility.

Answer 16

Automaticity: self-generated, automatic
Conductivity: ability to transmit electrical signal
Rhythmicity: ability to spontaneously depolarize/repolarize in repetitive and stable method
Excitability: ability to be excited when stimulated
Contractility: ability to contract

Question 17

Describe the pacemaker of the mammalian heart.

Answer 17

Pacemaker of the heart is the SA node, located near the superior vena cava in the right atrium. It spontaneously generates an action potential every 0.8s.

Question 18

Indicate RMP and threshold potentials of the sinoatrial node.

Answer 18

RMP: Resting membrane potential of SA node = -60mV
Threshold potential of SA node = -40 mV

Question 19

Describe the intrinsic rate of the sinoatrial (SA) and atrioventricular (AV) nodes and factors which can increase and decrease the rate.

Answer 19

SA node spontaneously generates action potential every 0.8s = Resting Heart Rate of 60-100 bpm.
-AV node can also generate action potential but at slower rate
-If SA node doesn’t fire, AV node generates action potential = 40-50 bpm
-Stimulation of SNS would increase rate of action potential generation
-Stimulation of PNS would decrease rate

Question 20

Identify the channel and movement of ions which result in a pacemaker potential of the SA node.

Answer 20

HCM Channels: unique to pacemaker cells
-Cells respond to hyperpolarization, allowing Na+ into the cell and produce depolarization, K+ out
-Cyclic nucleotide, channels also respond to cAMP

Question 21

Identify the channel and movement of ions which results in depolarization of SA node.

Answer 21

-Voltage-gated Ca2+ channels open once it reaches -40mv
-Causes diffusion of Ca2+ into cell, producing upward action potential

Question 22

Identify the channel and movement of ions which results in repolarization of the SA node

Answer 22

-Voltage-gated K+ channels open once reaches over 0mV
-Causes diffusion of K+ ions out of the cell (interior of PM is negative)

Question 23

Define chronotropic, inotropic, dromotropic

Answer 23

Chronotropic: mechanisms that affect the cardiac rate (positive increase, negative decrease)
Inotropic: modifying the force or speed of contraction of muscles (positive strengthen, negative weaken)
Dromotropic: affects conduction speed in AV node, thus rate of electrical impulses (positive increase conduction speed, negative decrease conductive speed)

Question 24

Discuss how the autonomic nervous system can alter pacemaker potentials of the SA node

Answer 24

-Autonomic nervous system release epinephrine and norepinephrine; increases rate of depolarization by stimulating β1-adrenergic receptors and production of cAMP within the cells
-Causes opening of HCN channels; influx of Na+ and leads to reaching threshold faster, increasing heart rate
-Release of acetylcholine causes opening of K+ channels, increasing efflux of K+ cells out of pacemaker cells
-Slows down depolarization, takes longer to reach threshold; decreases in heart rate

Question 25

Predict changes in inotrophy, chronotrophy, and dromotrophy after sympathetic and parasympathetic stimulation of the heart.

Answer 25

-SNS increases heart rate; increase in chronotropic, inotropic, and dromotropic effects
-PNS decreases heart rate; decrease in chronotropic, inotropic and dromotropic effects

Question 26

Describe the HCN channels and how they are influenced by the sympathetic nervous system.

Answer 26

-HCN channels or hyperpolarization activated cyclic nucleotide-gated channels and open in presence of cAMP
-Catecholamines released by SNS will cause production of cAMP in pacemaker cells by stimulating β1-adrenergic receptors, thus opening more HCN channels

Question 27

Describe how the potassium channels are influences by the parasympathetic nervous system.

Answer 27

PNS releases acetylcholine causing K+ channels to open

Question 28

Define ectopic pacemaker

Answer 28

Ectopic Pacemaker: pacemaker other than SA node, produces slower than normal sinus rhythm

Question 29

Describe the myocardial resting membrane potential, depolarization, and repolarization

Answer 29

-Resting membrane potential: of myocardial cells is -85mV
-Depolarization: will depolarize upon stimulation from action potential generated by SA node
-Stimulates opening of Na+ channels; positive
feedback to open more Na+ channels
-Increase membrane potential to -15mV; Na+
channels quickly close
-Membrane potential is maintained at 200-300ms
(plateau phase) prior to repolarization
-Voltage gated K+ and Ca2+ channels being opened
at the same time, causing the simultaneous diffusion
of K+ out of and Ca2+ into the cell
-Repolarization: takes place following closure of Ca2+ channels and opening of voltage-gated K+ channels; movement of K+ channels out of cell
-Returns membrane potential to -85mV

Question 30

Identify the channel(s) and movement of ions which result in myocardial depolarization

Answer 30

-Voltage-gated Na+ channel (fast Na+ channel)
-Fast diffusion of Na+ channel into cell

Question 31

Identify the channel(s) and movement of ions which results in the plateau phase of the myocardial action potential

Answer 31

-Slow voltage-gated Ca2+ channels and voltage-gated K+ channels
-Slow diffusion of Ca2+ into cell, K+ out of cell

Question 32

Identify the significance of the plateau phase of the myocardial action potential

Answer 32

-Plateau phase allows for sustained contraction of myocardial cells, allowing for powerful contraction to pump blood against pressure in arterial system
-Maintaining depolarization and prolonging the action potential

Question 33

Identify the channel(s) and movement of ions which results in repolarization of the myocardial action potential

Answer 33

-voltage-gated K+ channels
-diffusion of K+ out of cell

Question 34

Define the absolute refractory and relative refractory periods of myocardial action potentials and when they occur

Answer 34

Absolute Refractory Period: period during an action potential when a new action potential can’t be stimulated under any circumstances
-takes place from the beginning of the action potential until midway through repolarization (-50mV) and lasts 250 ms
Relative Refractory Period: period during an action potential when a new action can be stimulated under specific conditions
-can take place midway through repolarization until the end of repolarization (-50 to -90mV) just before relaxation phase

Question 35

Describe path of an action potential through the conduction system

Answer 35

-electrical activity is transmitted through heart via specialized myocardial cells; from atria to ventricles
-action potential spontaneously generated via SA node; travels rapidly to Bachmann’s bundle causing contraction of atrium
-same action potential transmitted to AV node; conduction rate slows down (allow ventricles to fill)
-then action potential passes through Bundle of His and conducted rapidly to apex of heart via right and left bundle branches and action potential continues along Purkinje Fibres within ventricular wall
-action potential spreads from inside of heart towards outside; causing ventricles to contract at same time

Question 36

Identify anatomically: SA node, Bachmann’s bundles, AV node, Bundle of His, bundle branches, Purkinje fibres

Answer 36

SA Node: located in upper quadrant of right atrium, near superior vena cava
Bachmann’s Bundle: conductive tissues that passes action potentials from right to left atria
AV Node: located on inferior portion of interatrial septum
Bundle of His: conductive tissue located at top of interventricular septum
-splits into right and left bundle branches that run down interventricular septum
Bundle Branches: fibres that run along the interventricular septum to the apex of the heart
Purkinje Fibres: fibres within wall of ventricles; continue from left and right bundle branches and run through left and right ventricles

Question 37

Describe myocardial excitation-contraction coupling

Answer 37

-myocardial excitation-contraction triggers the contraction of cardiac muscles and depends on the Ca2+-induced-Ca2+ release
-calcium released from the sarcoplasmic reticulum will bind to troponin on the sarcomere fibre; formation to tropomyosin; triggering contraction of the cardiac muscle

Question 38

Discuss calcium induced-calcium release

Answer 38

-once AP depolarized the myocardial cell and T-tubule membranes voltage-gated Ca2+ channels and Ca2+ moves down its concentration gradient into the cell
-when in sarcoplasm, Ca2+ binds to ryanodine receptors and opens these Ca2+ channels, large amounts of Ca2+ leaves sarcoplasmic reticulum and interact with troponin to initiate contraction
-Ca2+ acts as secondary messenger to induce its own release

Question 39

Discuss the role of the sarcoplasmic reticulum in myocardial excitation-contraction coupling

Answer 39

-sarcoplasmic reticulum has a large storage of calcium, which is released during the ‘calcium-induced-calcium release’ and triggers contraction of the cardiac muscle by binding to troponin
-90-98% of the Ca2+ needed for myocardial contraction originated from the sarcoplasmic reticulum

Question 40

Describe how relaxation occurs after contraction in cardiomyocytes

Answer 40

Relaxation of cardiomyocytes is achieved by removing calcium from the cytoplasm after contraction, by 2 methods:
1. Ca2+ is transported to the extracellular fluid by Na+/Ca2+ exchange pumps
2. Ca2+ is transported back to sarcoplasmic reticulum via Ca2+/ATPase

Question 41

Discuss the importance of ECGs

Answer 41

ECP is important non-invasive procedure to assess cardiac function and identify possible cardiac pathologies
-captures the electrical activity of the heart to monitor cardiac function

Question 42

Describe what makes the waveforms on an ECG

Answer 42

Differences in electrical potential between the sensors is recorded and plotted against time to produce the characteristic waves we see on an ECG
-ECG doesn’t record an action potential but results from production of action potential

Question 43

Correlate the P, QRS, and T wave to phases of the cardiac cycle

Answer 43

P Wave: depolarization/contraction of atria
QRS Wave: depolarization/contraction of ventricles
-atrial repolarization also occurs but is masked in waves by ventricular contraction
T Wave: repolarization of ventricles

Question 44

Identify the morphology of the P, QRS, and T waves

Answer 44

P Wave: small positive wave
QRS Wave: sharp upward wave, followed by sharp downward wave
T Wave: small positive wave

Question 45

Identify the PR and ST interval and indicate their significance to the cardiac cycle

Answer 45

PR Interval: represents the time it takes for the action potential to pass through the AV node (ex. delay in ventricular contraction)
ST Interval: represents the time between ventricular depolarization and repolarization when the heart is in its relaxed state