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Cardiovascular System > The Cardiac Cycle > Flashcards

The Cardiac Cycle Flashcards

1
Q

What is convection?

A

The mass movement of fluid caused by pressure difference

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2
Q

Why is diffusion not used for whole body transport?

A

Diffusion is a very slow process for distances > 1 mm which is why it’s useless for whole body transport

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3
Q

What is the Sino Atrial Node?

A

Group of cells located in the right atrium wall

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4
Q

What is the function of the SAN?

A

The SAN has the ability to spontaneously produce an action potential that travels through the heart via the electrical conduction system
SAN sets rhythm of the heart - natural pacemaker

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5
Q

What is the AV node?

A

Part of the electrical conduction system of the heart, coordinating the top of the heart

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6
Q

What is the role of the AV node?

A

The AV node electrically connects the right atrium and right ventricle, delaying impulses, so that the atria have time to empty their blood into ventricles, before ventricular contractions.

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7
Q

How is the resting potential maintained?

A

The cell interior has a negative resting potential compared to the exterior. Normally there’s a high [K+] inside and high [Na+] and {Cl-] outside
The Na+/K+ ATP pump transports 3 Na+ out for every 2 K+ in

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8
Q

Outline how SAN pacemaker potential occurs?

A
  1. Resting membrane potential
    • Funny channel - If threshold
    • membrane repolarises below If threshold - unstable
    • At -50 mV Na+ channel activated causing slow Na+
      influx
  2. Rapid depolarisation
    • Cell depolarises, reaching threshold which activates
      Ca2+ channels causing rapid depolarisation
  3. Repolarisation
    • Ca2+ channels are switched off and Voltage K+
      channels are opened causing an efflux of K+
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9
Q

Describe how atrial & ventricle muscle action potentials occur

A
  1. Rapid depolarisation
    • Depolarisation signal received from SAN, opening
      Na+ channels leading to Na+ influx
    • Voltage gated Ca2+ channels open slowly
  2. Early repolarisation
    • Na+ channels close
    • Cells begin repolarising
  3. Plateau phase
    • VGCC fully open causing an influx of Ca2+
    • Halts repolarisation and voltage gated K+ channels
      slowly open
  4. Rapid depolarisation
    • Ca2+ channels close and K+ channels fully open
      causing an efflux of K+
  5. Resting membrane potential
    • Stable Na+/K+ ATP pump in 3:2 ratio
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10
Q

Outline how electrical conduction occurs in the heart

A
  1. Electrical activity generated in SAN spreads out via gap
    junctions into atria
  2. At AV node, conduction is delayed to allow correct
    filling of ventricles
  3. Conduction occurs rapidly through Bundle of HIs into
    the ventricles
  4. Conduction through Purkinje fibres spreads quickly
    throughout ventricles
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11
Q

Where is electrical activity generated in the heart?

A

Electrical activity is generated at the SAN node and conducted throughout the heart
Electrical activity is converted to myocardial contraction, creating pressure changes within chambers

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12
Q

Which direction does blood flow in the heart?

A

Blood flows from areas of high to low pressures, unless blocked by a valve

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13
Q

How do valves function?

A

Valves open and close depending on chamber pressure changes

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14
Q

How do the events in the heart differ between the right & left sides?

A

Cardiac events are the same on the right & left sides, but the right has a lower pressure than the left

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15
Q

Outline the route of blood flow through the heart

A

Systemic circulation
vena cava -> right atrium -> tricupsid valve (AV) -> right ventricle -> pulmonary valves (SL) -> pulmonary arteries

Lung circulation
pulmonary veins -> left atrium -> bicupsid (mitral AV) valve -> left ventricle -> aortic (SL) valve -> aorta

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16
Q

Describe the events that take place during the cardiac cycle

A
  1. Ventricular filling / atrial contraction - diastole
    Blood enters atria then into ventricles
    pressure in atria > ventricles
    mitral / tricupsid valves open aided by atrial contraction
  2. Isovolumetric contraction - systole
    Pressure in full ventricles > atria
    mitral / tricupsid valves close
    Closed ventricle contracts increasing pressure
  3. Ejection - systole
    Pressure in ventricles > aorta / pulmonary artery
    valves open and blood is ejected into atria
  4. Isovolumetric relaxation
    aorta / pulmonary artery pressure > ventricles
    aortic / pulmonary valves close
    closed ventricle relaxes ready to receive blood
17
Q

Describe the left ventricular pressure changes that occur during the cardiac cycle

A
  1. Ventricular diastole (left atrium contraction)
    slight rise in ventricular pressure
    mitral valves close
    ventral pressure > atrial pressure
  2. Isovolumetric contraction causes pressure rise
  3. Ejection occurs when ventricle pressure > aorta as
    aortic valves open
  4. Isovolumetric relaxation causes large pressure drops
    Ventricles empties as ventricular pressure > atria
    aortic valves close and mitral valves open
18
Q

Outline the left ventricular volume changes

A
  1. filling of ventricles due to atrial contraction
    EDV = 120 ml
  2. Full ventricles have higher pressure so mitral valves
    close initiating systole but no change in volume yet
  3. Ventricular pressure > aortic valve pressure causing
    ejection of blood
  4. Isovolumetric relaxation occurs when ventricular
    pressure falls as aortic valves close due to high aortic
    pressure
19
Q

How is Stroke volume calculated using Ventricular volumes?

A

SV = EDV - ESV

SV - stroke volume
EDV - end diastolic volume
ESV - end systolic volume

20
Q

Summarise the cardiac cycle using the Ventricular pressure - volume loop

A

Mitral valves open
Mitral valves close
Aortic valves open
Aortic valves close

The ventricle pressure - volume loop relates to the amount of energy consumed during the cardiac cycle

21
Q

Outline the equation used to calculate Work Done by the heart

A

Work = Change in ventricle pressure x Change in volume

area inside the ventricle pressure - volume loop is the amount of stroke work done

22
Q

Describe the cardiac events occurring in the right atria and jugular veins

A

a wave

  • atrium contract
  • blood moves out of atrium into ventricles

x descent

  • atrium releasing blood
  • tricupsid valves closed, refilling of atria begins

v wave

  • atrium full and tense
  • tricupsid valves closed and atria start to empty

y descent
- atrium emptying and tricupsid valves opened

23
Q

What are the noises heard from the heart?

A

The noises heard from the heart are vibrations induced by the closure of cardiac valves, ventricular chamber vibrations and turbulent blood flow through valves

24
Q

Describe the noises occurring during cardiac cycle

A

S1 - ‘lub’
closure of tricupsid / mitral valves at beginning of ventricular systole

S2 - ‘dub’
closure of aortic / pulmonary valves (SL) at end of ventricular systole

S3 - occasional
turbulent blood flow into ventricles, detected near end of first 1/3 diastole, especially in older people

S4 - pathological in adults
Forceful atrial contraction against a stiff ventricle - less prominent in young people

Cardiovascular System (16 decks)

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