The cardiac pressure and volume cycle with ions and action potentials Flashcards

1
Q

What is important about cerebral circulation?

A

Brain maintains all vital functions
Constancy of flow & pressure
Autoregulation

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2
Q

Give the name of the circle of arteries found on the brains inferior surface

A

Circle of willis

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3
Q

Describe how renal circulation is an example of a portal system

A

Glomerular capillaries to peritubular capillaries

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4
Q

Which compounds are produced by the kidneys?

A

ACE and Renin

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5
Q

Give the function of ACE and Renin

A

Endocrine functions
Controlling blood volume
Responding to renal blood pressure

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6
Q

Which percentage of cardiac output does skeletal muscle use during strenuous exercise?

A

80%

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7
Q

How does skeletal muscle respond to adrenaline?

A

By causing vasodilatation

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8
Q

Describe some special aspects of skin circulation

A

Role in Thermo–Regulation
Perfusion can increase 100X
Arteriovenous Anastomoses- Primary role in thermoreg
Sweat Glands- Role in thermoregulation and Plasma ultrafiltrate
Response to Trauma- Red reaction, flare, wheal

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9
Q

Give the four sequential events of the cardiac cycle

A

Ventricular filling
Isovolumic* ventricular contraction
Ejection
Isovolumic ventricular relaxation

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10
Q

When does the aortic valve close?

A

Left ventricular pressure < aortic pressure

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11
Q

Describe the PV loop of mitral stenosis

A

Decrease preload

Decrease afterload

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12
Q

Describe the PV loop of aortic stenosis

A

Increased afterload

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13
Q

Describe the PV loop of mitral reguirgitation

A

Increase preload

Decrease afterload

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14
Q

Describe the PV loop of aortic reguirgitation

A

Increase in preload

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15
Q

What is S1?

A

Lub- first heart sound

AV valves close, normally loudest

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16
Q

What is S2?

A

Dub- Second heart sound

Semilunar valves close

17
Q

Describe systolic murmur

A

Fluid leaves ventricle

AV regurgitation or SL stenosis

18
Q

Describe diastolic murmur

A

Fluid enters ventricle

AV stenosis or SL regurgitation

19
Q

What causes myocytes to contract?

A

The Cardiac Action Potential

20
Q

When do voltage gated channels open?

A

When voltage becomes positive

21
Q

List the two types of K+ channels

A

Delayed rectifier

Inward rectifier

22
Q

Describe the action of delayed rectifier K+ channels

A

Open when membrane depolarises

But all gating takes place with a delay

23
Q

Describe the action of inward rectifier K+channels

A

Open when Vm goes below -60 mV
Very unusual! More open when cells are at rest
Functions: to clamp membrane firmly at rest
K+ channel lets K+ out of cell, repolarising it

24
Q

Describe the sequence of initial depolarisation of an action potential

A

The cell starts at rest (-70 mV)
Inward rectifier K+ channels are open, K+ flowing out is the dominant current
Resting membrane potential is near EK
Something causes the cell to become less negative
Depolarisation: inside the cell the voltage becomes less negative (or more positive)
Could be a nearby cell depolarising
Could be synaptic transmission where a neurotransmitter opens a ligand-gated channel

25
Q

Describe the sequence of repolarisation

A

Due to the passage of time, 2 delayed-action events occur
Na+ channel inactivation causes ↓ Na+ current going in
Delayed rectifier K+ channels open causing ↑ K+ going out
These cause the membrane to be less positive and more negative inside

26
Q

What is the refractory period?

A

Period of time during which neuron is incapable of reinitiating an AP,
The amount of time it takes for neuron’s membrane to be ready for a second stimulus once it returns to its resting state following an excitation

27
Q

What is After-hyperpolarization?

A

at the end of an AP the voltage inside temporarily goes slightly more negative than at rest, followed by a return to the resting membrane potential

When the voltage goes below -60 mV, the inward rectifier K+ channels open again; they stay open until next depolarisation
These normally clamp the voltage toward EK, and are responsible for maintaining the resting membrane potential
During AHP: the ↑ K+ permeability and ↓ Na+ permeability, the membrane potential moves closer to EK

28
Q

Describe the sequence of action potentials in a ventricular myocyte

A

Depolarisation: Na+ gates open in response to wave of excitation from pacemaker
Transient Outward Current: tiny amount of K+ leaves cell
Plateau phase: Inflow of Ca2+ just about balances outflow of K+
Rapid repolarization phase: Vm falls as K+ leaves cell
Back to resting potential

29
Q

How do cardiac action potentials differ to skeletal action potentials?

A

Much longer: up to 500 ms
Varies in duration and size
long refractory period, no tetany

30
Q

Describe the plateau phase

A
Dynamic equilibrium
Ca2+ current in
K+ current out
Decreased Vm decreases the Ca2+ current
Also for K+, but much less
So decreased Ca2+ current leads to positive feedback:
repolarisation by K+
31
Q

The cardiac action potential varies in different parts of the heart. How does this relate to the ECG?

A

The timing of the different cardiac APs determines the ECG

32
Q

List which parts of the cardiac action potential relate to the ECG

A

QT interval aligns with ventricular AP
QRS = ventricular depolarisation
T = ventricular repolarisation

33
Q

Describe the sequence of a ventricular myocyte action potential

A

At rest, the inward rectifier K+ channel  outward current stabilising membrane (phase 4)
The rapid rising phase (or upstroke) of the action potential is, exactly as in nerve and skeletal muscle, due to a transient increase in inward Na current (with positive feedback – phase 0)
Depolarization also leads to transient opening of time- and voltage-dependent Ca channels (phase 2)
The total K conductance decreases rather than increases upon depolarization
Repolarization is greatly delayed due to b) and c)

34
Q

Describe the automaticity of the SAN

A

Sinoatrial (SA) node cells are autorhythmic
resting potential is unstable
resting potential is close to threshold
Cells independently beat @ 100 bpm
Increased by symp activity
Decreased by parasymp activity
SA node is normally the pacemaker
Other cardiomyocytes can be too
SA (pacemaker) nodal cells responsible for the initiation of a heart beat in the healthy heart because they have fastest rate

35
Q

What is pacemaker potential otherwise known as?

A

Diastolic potential

36
Q

What does the pacemaker potential relate to?

A

Voltage drifts positive between nodal beats
Instead of resting potential
Because cells lack inward rectifiers
In myocytes of SA node, AV node, conduction system only
Slope of PP determines rate of firing

37
Q

Describe the If (funny current) and its actions

A

If makes the SA node cells spontaneously active - (HCN channel and autorhythmicity during the Pacemaker Potential)
If increases upon hyperpolarization
rather than depolarization
If leads to a net inward current
If —> a lot of Na+ current inward and a tiny K+ current outward
Depolarises cell toward 0 mV

38
Q

What does blocking the Na+ channels do?

A

Decreases conduction velocity and can prevent arrythmias

39
Q

What does blocking the Ca 2+ channels do?

A

Decreases heart rate and contractile force