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Cardiovascular > Heart physiology > Flashcards

Heart physiology Flashcards

1
Q

how is cardiac muscle arranged?

A

cardiac muscle cells of myocardium arranged in tightly bound layers encircling chambers

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2
Q

what does cardiac muscle do when the walls of the chamber contract?

A

exerts pressure on blood

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3
Q

contrast with skeletal muscle cells

A

skeletal muscle cells can be rested for prolonged periods and only a fraction are activated in a muscle per contraction

every heart cell contracts with every beat

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4
Q

1% of cardiac cells name and function

A

conducting system

electrical contact with cardiac muscle cells via gap junctions

initiates heartbeat and rapidly spreads action potentials

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5
Q

types of innervation received by heart

A

sympathetic and parasympathetic (in vagus nerves) nerve fibres

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6
Q

sympathetic innervation

A

sympathetic postganglionic fibres innervate entire heart adn release norepinephrine

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7
Q

parasympathetic innervation

A

fibres terminate ~ cells in atria

release acetylcholine

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8
Q

receptors for norepinephrine on cardiac muscle

A

beta-adrenergic

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9
Q

epinephrine - origin, effect

A

adrenal medulla

binds to same receptors as norepinephrine, exerts same actions

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10
Q

receptors for acetylcholine

A

muscarinic type

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11
Q

where does initial depolarisation arise?

A

sinoatrial node (SA node)

small group of conducting system cells

located in RA near entrance of SVC

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12
Q

sequence of excitation

A

SA node
internodal pathways/Bachmann’s bundle to RA/LA
AV node
(slight delay to prevent simultaneous contraction)
Bundle of His (down interventricular septum)
RBB & LBB
Purkinje fibres

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13
Q

purkinje fibres and their function

A

large diameter conductor cells

rapidly distribute impulse through most of ventricles

make contact with myocardial cells, which then pass on the impulse

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14
Q

what are the 2 main forces driving ions across cell membranes?

A

chemical potential and electrical potential

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15
Q

what is chemical potential?

A

ion moves down its concentration gradient

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16
Q

what is electrical potential?

A

ion moves away from ions/molecules of like charge

17
Q

what is the transmembrane potential (TMP)?

A

electrical potential difference (voltage) between the inside and outside of cell

18
Q

changes in TMP

A

net movement of +ve ions into cell -> TMP more +ve

TMP more -ve when movement of +ve ions out of cell

19
Q

what do ion channels do?

A

maintain ionic concentration gradients and charge differentials between inside and outside

20
Q

what are the properties of cardiac ion channels?

A

selectivity, voltage-sensitive gating, time-dependence

21
Q

what is selectivity?

A

only permeable to single type of ion based on physical configuration

22
Q

what is voltage-sensitive gating?

A

specific TMP range required for particular channel to be in open configuration

specific channels open and close as the TMP changes during cell depolarisation and repolarisation

23
Q

what is time dependence?

A

some ion channels are configured to close a fraction of a second after opening - can’t open until TMP back to resting levels

24
Q

what is an action potential?

A

electrical stimulation created by a sequence of ion fluxes through specialised channels in the membrane of cardiomyocytes. leads to contraction

25
Q

what is the sarcolemma?

A

membrane of cardiomyocytes

26
Q

what occurs in phase 4?

A

resting phase

resting potential is -90mV due to a constant outward leak of K+ through inward rectifier channels

Na+ and Ca2+ are closed at resting TMP

27
Q

what occurs in phase 0?

A

depolarisation

action potential triggered in a neighbouring cardiomyocyte/pacemaker cell -> TMP above -90mV

fast Na+ channels open, Na+ leaks in, further raises TMP

reaches -70mV (threshold potential - self sustaining inward Na+ current)

large Na+ current depolarises TMP to 0mV - above for overshoot. fast Na+ channels close (time dependent)

L-type Ca2+ open when TMP is greater than -40mV - small but steady influx of Ca2+ down its concentration gradient

28
Q

what happens in phase 1?

A

early repolarisation

TMP slightly positive

some K+ channels open briefly and an outward flow of K+ returns to TMP to ~ 0mV.

29
Q

what happens in phase 2?

A

plateau phase

L type Ca2+ channel are still open and there is a small constant inward current of Ca2+.

K+ leaks out down its conc gradient through delayed rectifier K+ channels

2 countercurrents electrically balanced, TMP maintained at plateau below 0mV

30
Q

what happens in phase 3?

A

repolarisation

Ca2+ channels gradually inactivated

persistent outflow of K+, now exceeding Ca2+ inflow, brings TMP towards -90mV.

Cardiovascular (11 decks)

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