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pharmacology > Cardiovascular System Physiology > Flashcards

Cardiovascular System Physiology Flashcards

1
Q

Describe the sinoatrial node.

A
  • The pacemaker
  • Specialised cardiac muscle cells, continuous with atrial syncytium
  • Generate spontaneous action potentials
  • Action potentials pass to atrial muscle cells and to the AV node
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2
Q

Describe atrioventricular node.

A
  • Action potentials conducted more slowly here
  • Ensures ventricles receive signal to contract after atria have contracted
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3
Q

Describe the AV bundle

A
  • Passes through hole in cardiac skeleton to reach interventricular septum
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4
Q

Describe right and left bundle branches.

A
  • Extend beneath endocardium to apices of right and left ventricles
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5
Q

Describe the purkinje fibres

A

– Large diameter cardiac muscle cells with few myofibrils.
– Many gap junctions.
– Conduct action potential to ventricular muscle cells (myocardium)

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6
Q

Describe the conducting system of the heart. (8)

A
  • Depolarisation from SA node across atria.
  • Three tracts within atria conduct
    depolarisation to AV node.
  • Conduction slows in AV node; allows atria
    to empty into ventricles before vent.
    systole.
  • Atrioventricular bundle (bundle of His)
    connects AV to bundle branches
  • Purkinje Fibres = terminal bundle branches
  • SA node generates impulses about 75x/min
  • AV node delays the impulse approx. 0.1 secs
  • Impulse passes from atria to ventricles via
    bundle of His to the Purkinje fibres and finally
    to the myocardial fibres
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7
Q

Describe cardiac muscle.

A
  • Faintly striated
  • Branched, mono-nucleated cells
  • Connected by intercalated disc
  • High conductance gap junctions
    (connexons)
  • Desmosomes: cadherin
  • Functional syncytium
  • Continuous action potential
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8
Q

Compare cardiac muscle to skeletal muscle.

A

Cardiac: Action propagated from cell to
cell.
Skeletal: Action along length of single fibre
* Slow propagation in cardiac muscle
because of gap junctions and small
diameter of fibres.
* Faster in skeletal muscle due to larger
diameter fibres.

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9
Q

Describe the sliding filament theory (cardiomyocyte contraction)

A
  • Ca2+ binds to TN-C on thin filaments
  • Exposes site on actin which can bind to myosin head
  • ATP hydrolysis supplies energy for actin-myosin conformational change
  • ‘Ratcheting’ of actin-myosin and shortening of the sarcomere occurs
  • Ca2+ dissociates from TN-C and myosin unbinds from actin with energy from ATP
  • Cycle ends when ATP binds to myosin and the sarcomere returns to original length.
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10
Q

Describe cardiomyocyte contraction.

A
  • Ca2+ enters through L-type channel
  • Ca2+ -induced calcium release (CICR) occurs
  • Stimulates Ca2+ release from SR
  • Intracellular Ca2+ rises ~ 0.5-2μM
  • Ca2+ interacts with troponin-C
  • Myosin binding site on actin freed
  • Actin moves over myosin causing myocyte contraction
  • Intracellular Ca2+ reabsorbed into SR via the sarco-endoplasmic reticulum Ca
    ATPase (SERCA) pump and removed from the cell via Na+/ Ca 2+ exchanger and
    ATP-dependent Ca 2+ pump.
  • Ca2+ dissociates from TN-C and the binding site on actin is inhibited.
  • ATP required to unbind myosin from actin and reset the sarcomere to normal length.
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11
Q

When does an action potential occur?

A
  • When excitation depolarisation exceeds threshold of -70mV
  • Na+ gates open
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12
Q

Describe Phase 0: rapid depolarisation.

A
  • Na + permeability&raquo_space; x100 fold
  • Membrane potential rises to +20 to +30mV
  • Na + gates ‘inactivated’; Na + permeability falls
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13
Q

Describe Phase 1: initial repolariastion

A
  • K + permeability&raquo_space; by conc. & elec. gradient
  • Simultaneous opening of L-type voltage-gated Ca 2+ channels; inward flow Ca 2+
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14
Q

Describe Phase 2: Plateau phase

A
  • K + balances Ca 2+ flow = plateau phase
  • Generates cardiomyocyte contraction
  • Ca 2+ channels inactivated
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15
Q

Describe Phase 3: Repolarisation

A
  • K + channels remain open
  • Membrane potential falls to ~ E K
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16
Q

Describe Phase 4: Resting potential

A
  • Return to resting potential = -70mV
17
Q

What is the pacemaker potential?

A
  • After action potential - membrane potential depolarises until threshold potential reached
  • Na+ ion channels open; another AP triggered
18
Q

Give two characteristics of pacemaker tissue.

A
  • Rhythmic depolarisation results in rhythmic contraction
  • Ability to spontaneously depolarise and trigger AP = automaticity
19
Q

Where is the sinoatrial node location?

A

Right atrium (close to vena cava)

20
Q

Describe characteristics of the sinoatrial node.

A
  • K+ permeability lower than other regions
  • Resting potential = -60mV
  • Cells lack inward rectifier channel
21
Q

What is the role of the sinoatrial node?

A

Serves as cardiac primary pacemaker - determines heart rate

22
Q

Describe action potentials of sinoatrial node pacemaker cells.

A
  • No true resting potential
  • Generate regular, spontaneous action potentials
23
Q

Describe phase 4: spontaneous depolarisation (SA pacemaker cells)

A
  • Inward movement of Na +, outward movement of K +
  • K+ movement decays with time
  • Pacemaker potential depolarises to -55mV
  • Ca2+ inward current accelerates to threshold potential -55 to -40mV
24
Q

Describe phase 0: Depolarised of SA pacemaker cells.

A
  • Ca2+ increases due to L-type Ca++ channels.
25
Q

Describe phase 3: repolarisation of SA pacemaker cells

A
  • Voltage controlled K+ channels open and help repolarise cell as Ca 2+ channels inactivate
26
Q

Describe the regulation of the cardiac cycle.

A
  • Sympathetic and parasympathetic nervous systems
  • Cardiac centres in medulla oblongata receive input
    from hypothalamus, monitoring blood pressure and
    dissolved gas concentrations
27
Q

Describe the parasympathetic nervous system.

A
  • Cardioinhibitory centre (vagus nerve)
  • Nerve branches to SA and AV nodes;
  • Secrete acetylcholine; hyperpolarises heart;
  • Decreased HR (Dominant effect)
28
Q

Describe the sympathetic nervous system.

A
  • Cardioaccelerator centre activates sympathetic
    neurons (cardiac nerves);
  • Secretes norepinephrine (Minor effect on Rate);
  • Increases force of contractions; increases heart
    contractility
29
Q

Describe the role of beta blockers.

A
  • Slows heart rate and lowers blood pressure
  • Blocks adrenaline and noradrenaline
  • Affects receptors in the heart and blood vessels
  • Slows SA-node which initiates heart beat
30
Q

What does a slow heart rate allow? (beta blockers and calcium channel blockers)

A
  • Allows left ventricle to fill completely and lowers the heart workload
31
Q

What is the benefit of dilated arteries? (beta blockers and calcium channel blockers)

A
  • Lowers blood pressure
32
Q

What is the role of calcium channels blockers?

A
  • Slow heart rate and lowers blood pressure
  • Affects the heart and blood vessels
  • Slows SA-node which initiates heart beat with electrical impulses
33
Q

State the differences between cardiac arrest and a heart attack.

A
  • Cardiac arrest is an electrical problem whereas a heart attack is a circulation problem
  • Cardiac arrest the person is unconscious whereas heart attack the person will probably be conscious
34
Q

Describe the cardiac polarisation or depolarisation events
represented by the P-wave, the QRS complex and the T-wave.

A

P wave = depolarisation of the atrial myocardium
QRS complex = ventricular depolarisation and atrial repolarisation
T wave = repolarisation of ventricles

35
Q

What does lub and dub sounds represent?

A
  • Lub indicates closure of the AV valves - bicuspid and tricuspid - mitral L before tricuspid R
  • Dub indicates closure of semilunar valves aortic and pulmonary with a split sound to represent aortic before pulmonary

pharmacology (40 decks)

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