Cardiovascular System Flashcards by Tracie K

The pulmonary circuit is supplied by the _____ side of the heart.

right

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The systemic circuit is supplied by the ______ side of the heart.

left

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What are the 3 layers of the heart wall?

Epicardium
Myocardium
Endocardium (endothelium)

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Pressure within chambers of the heart varies with …

heartbeat cycle

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How do pressure differences in the chambers of the heart drive blood flow?

High pressure to low pressure
Valves prevent backward flow of blood
All valves open passively based on pressure gradient

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What is autorhythmicity?

the ability to generate own rhythm

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What do autorhythmic cells do?

electrical signal passageway

- cells provide a pathway for spreading excitation through the heart

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What do pacemaker cells do?

Spontaneously depolarizing membrane potentials generate action potentials
Coordinate and provide rhythm to heartbeat

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What do conduction fibres do?

Rapidly conduct action potentials

- Initiated by pacemaker cells

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Spread of excitation between cells make the _____ contract then _______.

atria

- ventricles

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The coordination of the spread of excitation between cells is due to:

gap junctions

- conduction pahtways

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What is concentrated at the intercalated discs?

desmosomes

- gap junctions

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Intercalated discs are junctions between …

adjacent myocardial cells

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What do desmosomes do?

resist mechanical stress

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What do gap junctions do?

link cardiac cells

- electrical coupling

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Why doesn’t contraction of the heart doesn’t occur the same way we think of blood flow?

Both atria contract and then both ventricles contract

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Describe the path of the initiation and conduction of an impulse.

action potential initiated at SA node
interatrial pathway
AV node (some delay)
to ventricals

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Impulse travels to ventricals via…

bundle of His
right and left bundle branches
purkinje fibres

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Describe the intertribal pathway.

SA node → right atrium → left atrium
Rapid
Simultaneous contraction of right and left atria

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Describe the internodal pathway.

SA node → AV node

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Describe AV node transmission.

Only pathway from atria to ventricles
Slow conduction: AV nodal delay = 0.1 sec
Atria contract before ventricles

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How can heartbeat be controlled by pacemakers?

Autorhythmic cells (“pacemaker potentials”)

- Spontaneous depolarizations (Caused by channels opening/closing)

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Describe electrical activity in pacemaker cells.

no external stimulus required
no steady resting membrane potential
Changes in membrane permeability to: Na+, K+ and Ca++

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No steady resting membrane potential means…

Immediate depolarization

- “ramping” = pacemaker potential

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Name the 3 channels for changes in membrane permeability.

- K+ channels - Funny channels - T-type & L-type channels

What happens in the first part of pacemaker potential (slow depolarization)?

- K+ close | - funny channels open

What happens in the last part of pacemaker potential (slow depolarization)?

T-type open

What happens during rapid depolarization?

L-type open

What happens during repolarization?

- L-type close | - K+ open

What are the steps of cardiac action potential?

- depolarization - brief repolarization - plateau - repolorization - rest

What happens during depolarization?

Na+ in

What happens during brief repolarization?

Ca2+ in

What happens during depolarization?

K+ out

Cardiac contractile cells takes how long?

250-300 msec

Skeletal muscles take how long?

1-2 msec

How does excitation-contraction coupling in cardiac contractile cells have properties similar to skeletal muscles?

- t-tubules - troponin-tropomyosin regulation - SR and Ca2+

How does excitation-contraction coupling in cardiac contractile cells have properties similar to smooth muscles?

- Gap junctions | - Extracellular Ca2+

What are the steps of excitation-contraction coupling in the heart?

1. Depolarization of cardiac contractile cell (Gap junction) 2. Calcium channels (Plasma membrane) 3. T tubules 4. Calcium release from the SR 5. Calcium binds to filaments 6. binding sites exposed 7. cross bridge cycle

AP travels down _______.

t tubules

Extracellular Calcium influx induces (“tells”) ____ to release ______ as well as signaled from ___ travelling down _____.

- SR - calcium (CICR) - AP - t-tubules

Calcium binds to ______.

troponin

What is troponin?

- a protein on tropomyosin | - causes tropomyosin to “move” out of the way and expose binding sites on actin for myosin filaments *stays bound*

What happens in the cross bridge cycle?

myosin binding to actin- slide-release

How does relaxation of cardiac muscle occur?

- calcium removed from cytosol | - resting conditions reestablished

What are the 3 ways calcium is removed from cytosol in the heart?

- SR ATPase-pumped back into SR - Plasma membrane atpase-pumped out into extracellular matrix - Na+-Ca++ exchanger in plasma membrane

What happens during resting conditions?

Troponin and tropomyosin move back to their positions and cover binding sites

What does a electrocardiogram do?

- gives a look at the electrical activity of the heart on the surface of the skin - Using electrical leads and electrodes – detects synchronicity of electrical signal provides a picture of what is happening - Used clinically to detect abnormalities – collect HR data

How is your body a conductor?

Currents in body can spread to surface (ECG, EMG, EEG)

Distance and amplitude of spread depend on two factors:

- Size of potentials - Synchronicity of potentials from other cells (Heart electrical activity = synchronized)

What are the parts of the electrical activity of the heart?

- P wave - QRS complex - T wave

P wave signals:

atrial contraction

QRS complex signals:

ventricular contraction/systole

T wave signals:

ventricular relaxation/diastole

What is the P-Q interval?

time between conduction of signal through AV node

What is the Q-T interval?

time of ventricular systole (length of contraction phase)

What is the T-Q interval?

length of diastole or ventricular relaxation (when the heart is filling with blood

What is the R-R interval?

measure of HR, beginning of ventricular systole to the next contraction

What are the 2 main periods of the cardiac cycle?

- systole | - diastole

What happens during systole?

contraction of ventricles

What happens during diastole?

relaxation of ventricles

Valve opening is dependent on...

pressure differences

What are the 4 phases of cardiac cycle?

1. ventricular filling 2. isovolumetric ventricular contraction 3. ventricular ejection 4. isovolumetric ventricular relaxation

Describe the ventricular filling phase.

- venous return - AV valves open - blood fills atria - passive until atrial contraction

Describe the isovolumetric ventricular contraction phase.

- start of systole - no change in volume - all valves closed - pressure in ventricles starts to increase

Describe the ventricular ejection phase.

- end of systole - Ventricular pressure exceeds aortic- blood pumped out - AV valves closed - Semilunar open - Valves close when pressure is greater outside chambers (aortic)

Describe the isovolumetric ventricular relaxation phase.

- beginning of diastole - no change in volume - relaxation: no blood in or out - valves closed