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Human physiology > Cardiac 2 (BP) > Flashcards

Cardiac 2 (BP) Flashcards

1
Q

What are skeletal muscles like?

A
  • Muscle cells made up of sarcomeres that cont thick filaments (composed of myosin) and thin filaments (composed of actin)
  • Shortening of sarcomere occurs via sliding filament mechanism, where actin filaments slide along adjacent myosin filaments
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2
Q

What are cardic muscles like?

A
  • Similar to skeletal muscle in terms of composition & function
  • DIFFERENT in terms of how cells interact
  • Cardiac muscle acts like a syncytium - a single, multinucleated cell formed from many fused cells
  • A wave of depolarisation is followed by atrial & ventricular contraction, push the blood the same time into other areas
  • Its purpose is to all work together - all muscles need to work at once
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3
Q

What are the parts of the heart involved in cardiac excitation?

A
  • Interatrial pathway
  • Sinoatrial (SA) node
  • Right branch of bundle of His
  • Atrioventricular (AV) node
  • Left branch of bundle of His
  • Purkinje fibres
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4
Q

How is the heart able to generate its own rhythm?

A
  • 1% cardiac cells - with pacemaker activity (set the pace of the heart) (auto-rhythmic cells)
  • 99% cardiac cells → contractile function
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5
Q

What is the “natural pacemaker” of the heart?

A

The Sinoatrial (SA) node

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6
Q

How big is the Sinoatrial (SA) node?

A

Approx 8mm long & 2mm thick

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7
Q

What is the Sinoatrial (SA) node?

A

It is a specialised region in the right atrial wall at the junction between the superior vena cava & the right atrium

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8
Q

What are cells within the SA node like?

A

They normally fire very FAST, generate heart beat

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9
Q

Do cells in the SA node have a resting potential?

A

Do not have resting potential (don’t rest, always moving); transmembrane potential ‘less negative’ than in ventricular cardiomyocytes

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10
Q

What are the phases of the SA node?

A
  • Phase 0 = upstroke of action potential is less steep than myocyte
  • Phase 3 = Plateau is not sustained
  • Phase 4 = Membrane potential deviates from K+ equilibrium potential
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11
Q

What are the stages of the action potential of SA node?

A
  • Slow depolarisation = Na+ influx (slow), Ca2+ influx; reduced K+ efflux
  • Rapid depolarisation = Ca2+influx
  • Repolarisation = K+ efflux
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12
Q

What is the potential of ventricular cells (the 99%)?

A

No pacemaker potential - cells remain essentially at rest (-90mV) until excited by electrical activity propagated from the pacemaker

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13
Q

What are the stages of an AP being made in the ventricular cells (the other 99%)?

A
  • Rapid depolarisation: Na+ influx
  • Plateau phase: Ca2+ influx
  • Repolarisation: K+ efflux
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14
Q

What happens between the upstroke & downstroke of the ventricular cell?

A

There is a refractory period –> cannot be constantly firing

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15
Q

What is needed for cardiac excitation?

A

Needs to be efficient & co-ordinated

  • Action potentials generated at SA node
  • Rapid excitation thru both atria
  • Excitation reaches AV node where conduction is SLOW
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16
Q

What does cardiac excitation allow for?

A

Allows atria to contract & empty blood into ventricles

17
Q

How is cardiac excitation an efficient & co-ordinated pump?

A

Excitation spreads rapidly down the bundle of His & Purkinje fibres to ensure almost simultaneous of ventricular cells → efficient, co-ordinated pump

18
Q

Why must cardiac exitation be efficient & co-ordianted?

A

Must be efficient & co-ordinated, if not blood will start to back up (e.g. into the lungs can cause difficulty breathing) can lead to heart failure

19
Q

How can caridac excitation be recorded?

A

Can be recorded from the surface of the body with an electrocardiogram (ECG)

20
Q

What is recorded in an ECG?

A

4 events but only 3 are visible

1 - Atrial depolarisation = P wave
2 - Ventricular depolarisation = QRS complex
a. Masks atrial repolarisation (lub-dub sound)
3 - Ventricular repolarisation (resetting & waiting to start again) = T wave

21
Q

What do systole & diastole mean?

A

Systole = contract
Diastole = relax

22
Q

What are the 3 key parts of cardiac contraction?

A

1 - Atrial systole

2 - Ventricular systole

3 - Ventricular diastole

23
Q

What happens in atrial systole?

(Cardiac contraction)

A

a) A-V valves open & atria empty blood into ventricles

b) Atrial excitation & contraction should be complete before onset of ventricular contraction

24
Q

What happens in ventricular systole?

(Cardiac contraction)

A

a) Part 1: ventricles contract → rise in pressure forces closed A-V valve (stops backflow of blood)

b) Part 2: Pressure in ventricle rises above aortic pressure → aortic valve opens & blood is ejected from heart

25
Q

What happens in ventricular diastole?

(Cardiac contraction)

A

a) Part 1: Pressure in ventricles falls below atrial pressure → aortic valve closes

b) Part 2: pressure in ventricles falls below atrial pressure → A-V valve opens & filling begins

26
Q

At rest what are the following like:

Cardiac Output = Heart Rate X Stroke Volume

A

Cardiac Output = Heart Rate X Stroke Volume

5 litres/min = ~70 beats/min X 70 ml/beat

27
Q

During exercise what are the following like:

Cardiac Output = Heart Rate X Stroke Volume

A

Cardiac Output = Heart Rate X Stroke Volume

22 litres/min = ~200 beats/min X 110 ml/beat

28
Q

What does the control of cardiac output depend on?

A
  • Factors affecting HEART RATE
  • Factors affecting STROKE VOLUME
29
Q

What are the 3 factors that influence stroke volume?

A

1 - End diastolic Volume (preload)

2 - Aortic pressure (afterload)

3 - Contractility

30
Q

What is end diastolic volume (preload)?

(Stroke volume)

A

This is the volume of blood that is coming back up to your heart and filling it

a) Resting cardiac muscle stretched prior to contraction

b) Venous tone, blood volume, posture, intrathoracic pressure

31
Q

What is aortic pressure (afterload)?

(Strove volume)

A

How hard does your heart have to work to get the blood out of my left ventricle into my body

a) Pressure against which the heart must work to eject blood during systole

b) Aortic stiffness, peripheral resistance, blood volume

32
Q

What is contractility?

(Stroke volume)

A

How well your heart can pump

a) Strength & vigour of the heart’s contraction (myocardial fibres) during systole, at a given preload and afterload

b) Inc by sympathetic nerve stimulation & circulating catecholamines, calcium, positive inotropic drugs (sympathetic → noradrenaline → beta adrenoreceptors)

c) Decrease by hypoxia, acidosis, infarction

33
Q

What is heart rate influenced by?

A

1 - Intrinsic rate

34
Q

Finish from the flashcard above

A

:)

Human physiology (43 decks)

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