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case two > cardiac physiology > Flashcards

cardiac physiology Flashcards

1
Q

define systole

A

contraction

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2
Q

define diastole

A

relaxtion

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3
Q

describe sequence of mechanical events in the cardiac cycle

A
  1. ventricular filling
  2. atrial contraction
  3. isovolumetric ventricular contraction
  4. ventricular ejection
  5. isovolumetric ventricular relaxation
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4
Q

what happens during ventricular filling?

A

low pressure due to ventricular diastole so blood flows in from venous systems

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5
Q

what happens during artial contraction?

A

extra small volume of blood pushed into ventricle

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6
Q

what happens during isovolumetric ventricular contraction?

A
  • ventricles are electrically stimulated to contract
  • pressure in ventricles increases but volume stays the same
  • very brief period
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7
Q

what happens during ventricular ejection?

A

pressure in the ventricles is greater than in the arteries, so blood moves out of ventricles and into arteries

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8
Q

what happens during isovolumetric ventricular relaxation?

A

pressure drops but volume stays the same for a brief period

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9
Q

what causes heart sounds?

A

valves snapping shut

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10
Q

how can valves cause an altered sound?

A

valvular diseases

  • stenosis - narrowing
  • incompetence or regurgitation
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11
Q

what do intercalculated disks do?

A

dock and form direct contact with another muscle

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12
Q

identify where to listen to the heart sounds for different valves

A
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13
Q

describe process of atrial and ventricular contraction

A
  1. action potential from adjacent cell enters, triggering opening of calcium ion channels
  2. calcium ion influx triggers release of calcium ions from sarcoplasmic reticulum
  3. calcium ions bind to troponin to initiate contraction
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14
Q

describe process of atrial and ventricular relaxation

A
  1. calcium ions unbind from troponin
  2. calcium is pumped back into sarcoplasmic reticulum for storage
  3. some calcium is exchanged for sodium at the cell membrane
  4. sodium ion gradient is maintained by Na+/K+ ATPase
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15
Q

what does the SAN do?

A

sets heart rate and initiates cardiac cycle

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16
Q

what are HCN channels and where are they located?

A

hyperpolarisation-activated, cyclic nucleotide-dependent nonspecific channel

located in pacemaker cells

17
Q

describe phases 0, 3 and 4 on this graph

A

phase 0

  • upstroke of slow pacemaker a.p.
  • triggered at threshold potential (-55mV)
  • calcium ion influx (depolarisation)

phase 3

  • calcium ion channels inactivate
  • increase in potassium ion efflux
  • membrane hyperpolarises

phase 4

  • membrane potential never levels off and starts to drift back up
  • opening of sodium ion channels
  • reactivation of calcium ion channels
  • when m.p. is reset, cardiac cycle restarts
18
Q

describe phase 4: prepotential

A
  • permits automaticity (ability for heart cells to spontaneously depolarise and generate an action potential)
19
Q

describe what happens at each number on this graph showing ventricular myocyte action potential

A

0 - Na channels open

1 - Na channels close; fast K channels open

2 - Ca channels open; fast K channels close

3 - Ca channels close; slow K channels open

4 - resting potential

20
Q

how does the sympathetic nervous system affect heart rate?

A
  • activation causes releease of noradrenaline
  • bind to B1 adrenoceptor on cardiac pacemaker and myocyte cell membranes
  • increases opening of HCN channels in pacemaker cells, increasing Na influx
  • opens Ca channels, increasing Ca influx
  • increase in slope of prepotential
  • heart rate increases
    *
21
Q

how does the parasympathetic nervous system affect heart rate?

A
  • activation causes release of acetylcholine
  • binds to muscarinic cholinergic receptors
  • decreases opening of HCN channels, decreasing Na influx
  • slows opening of Ca channels, decreasing Ca influx
  • opens additional K channels, increasing K efflux
  • hyperpolarises membrane and reduces slope of prepotential
  • heart rate decreases
22
Q

how is an a.p. initiated and spread in the heart?

A
  1. Electrical activity initiated in SAN and spreads across SAN cells
  2. Rapidly moves across atria to AV node
  3. AV node fires, causing waves of depolarisation down the interventricular septum
  4. Move down Bundle of His and apex via Purkinje fibers
  5. Move from apex to top of hear, wave of depolarisation which apreads across the ventricular muscle
23
Q

define annulus fibrosis

A

non-conducting layer between atria and ventricles which electrically insulates the chambers from each other

24
Q

define stroke volume

A

vol of blood pumped by one ventricle (~75mL)

25
Q

define cardiac output

A

vol pumped per ventricle per min (~5mL)

26
Q

define venous return

A

vol of blood returning to the heart

27
Q

how is pulmonary circulation different to systemic circulation?

A
  • lower pressure
  • more pulsatile flow
  • uneven blood distribution
28
Q

define iontrope

A

an agent that alters the force or energy of muscular contractions

29
Q

define chronotrope

A

effects that change heart rate

case two (10 decks)

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