The cardiac pressure and volume cycle with ions and action potentials

Question 1

What is important about cerebral circulation?

Answer 1

Brain maintains all vital functions
Constancy of flow & pressure
Autoregulation

Question 2

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

Answer 2

Circle of willis

Question 3

Describe how renal circulation is an example of a portal system

Answer 3

Glomerular capillaries to peritubular capillaries

Question 4

Which compounds are produced by the kidneys?

Answer 4

ACE and Renin

Question 5

Give the function of ACE and Renin

Answer 5

Endocrine functions
Controlling blood volume
Responding to renal blood pressure

Question 6

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

Answer 6

80%

Question 7

How does skeletal muscle respond to adrenaline?

Answer 7

By causing vasodilatation

Question 8

Describe some special aspects of skin circulation

Answer 8

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

Question 9

Give the four sequential events of the cardiac cycle

Answer 9

Ventricular filling
Isovolumic* ventricular contraction
Ejection
Isovolumic ventricular relaxation

Question 10

When does the aortic valve close?

Answer 10

Left ventricular pressure < aortic pressure

Question 11

Describe the PV loop of mitral stenosis

Answer 11

Decrease preload

Decrease afterload

Question 12

Describe the PV loop of aortic stenosis

Answer 12

Increased afterload

Question 13

Describe the PV loop of mitral reguirgitation

Answer 13

Increase preload

Decrease afterload

Question 14

Describe the PV loop of aortic reguirgitation

Answer 14

Increase in preload

Question 15

What is S1?

Answer 15

Lub- first heart sound

AV valves close, normally loudest

Question 16

What is S2?

Answer 16

Dub- Second heart sound

Semilunar valves close

Question 17

Describe systolic murmur

Answer 17

Fluid leaves ventricle

AV regurgitation or SL stenosis

Question 18

Describe diastolic murmur

Answer 18

Fluid enters ventricle

AV stenosis or SL regurgitation

Question 19

What causes myocytes to contract?

Answer 19

The Cardiac Action Potential

Question 20

When do voltage gated channels open?

Answer 20

When voltage becomes positive

Question 21

List the two types of K+ channels

Answer 21

Delayed rectifier

Inward rectifier

Question 22

Describe the action of delayed rectifier K+ channels

Answer 22

Open when membrane depolarises

But all gating takes place with a delay

Question 23

Describe the action of inward rectifier K+channels

Answer 23

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

Question 24

Describe the sequence of initial depolarisation of an action potential

Answer 24

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

Question 25

Describe the sequence of repolarisation

Answer 25

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

Question 26

What is the refractory period?

Answer 26

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

Question 27

What is After-hyperpolarization?

Answer 27

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

Question 28

Describe the sequence of action potentials in a ventricular myocyte

Answer 28

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

Question 29

How do cardiac action potentials differ to skeletal action potentials?

Answer 29

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

Question 30

Describe the plateau phase

Answer 30

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+

Question 31

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

Answer 31

The timing of the different cardiac APs determines the ECG

Question 32

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

Answer 32

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

Question 33

Describe the sequence of a ventricular myocyte action potential

Answer 33

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)

Question 34

Describe the automaticity of the SAN

Answer 34

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

Question 35

What is pacemaker potential otherwise known as?

Answer 35

Diastolic potential

Question 36

What does the pacemaker potential relate to?

Answer 36

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

Question 37

Describe the If (funny current) and its actions

Answer 37

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

Question 38

What does blocking the Na+ channels do?

Answer 38

Decreases conduction velocity and can prevent arrythmias

Question 39

What does blocking the Ca 2+ channels do?

Answer 39

Decreases heart rate and contractile force