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Phase 1 Medicine (JA) > Cardiac physiology > Flashcards

Cardiac physiology Flashcards

1
Q

Define membrane potential

A

The potential difference across a cell membrane generated by the differential ion concentrations

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2
Q

Name 3 ways in which ion movement is dictated

A
  1. Ion ratio (ECF vs ICF)
  2. Membrane permeability
  3. Membrane voltage
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3
Q

Define the Nernst equation?

A

Otherwise known as the equilibrium potential. A voltage that directly opposes the net diffusion of a particular ion through a membrane.

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4
Q

What is the Nernst equation?

A

E=+/-61.5Log(10).[ionE/ionI]

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5
Q

What are the intracellular and extracellular concs of K+?

A

Intra = 140mmol/l

Extra=4mmol/l

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6
Q

Which equation is used to measure the membrane potential?

A

Goldman-Hodgkin-Kats equation

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7
Q

What is the membrane potential of a large nerve?

A

-90 mV

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8
Q

Diffusion potentials of Na+ and K+ bring the membrane potential to -86mV. What pushes the potential to -90mV?

A

Na+/K+ ATPase

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9
Q

Name the 2 types of cardiac conducting cell?

A

Nodal and conducting

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10
Q

Name 2 things that nodal cells do?

A

Establish the rate of contraction and spontaneously depolarise

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11
Q

What is the resting membrane potential of nodal cells (e.g. in the SA node)

A

-60mV

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12
Q

What is a positive inotrope?

A

An agent which increased the force of contraction

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13
Q

What is a negative chronotrope?

A

An agent which decreases the rate of contraction

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14
Q

What is a dromotropic agent?

A

Something which alters the conducting speed of the AV node

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15
Q

Name the phases of nodal action potential and what happens in each phase.

A

Phase 4 - spontaneous depolarisation. Leaky Na+ channels allow Na+ into the cell, bringing the membrane potential towards threshold.
Phase 0 - -40mV threshold met. L-type Ca2+ channels open. Further depolarisation of the cell.
Phase 3 - Voltage gated K+ channels open and repolarise the cell

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16
Q

How is the action potential of the SAN regulated?

A
  1. Spontaneous depolarisation
  2. Sympathetic innervation (+ve inotrope, +ve chronotrope)
  3. Parasympathetic innervation (-ve chronotrope, -ve inotrope)
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17
Q

describe the cardiac action potential.

A

Phase 0 - Depolarisation of the cell through influx of Na+ (up to +20mV)
Phase 1 - Partial repolarisation. Leaky K+ channels release K+
Phase 2 - Plateau and contraction. Slow Ca2+ channels are open, no permeability of K+
Phase 3 - Rapid repolarisation of cell through K+ efflux

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18
Q

What do conducting cells do?

A
  1. Carry stimulus from atria to ventricles
  2. Only in a single direction
    They are specialised cardiac cells. Not neural tissue
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19
Q

On an ECG, what do the P, QRS, and T waves represent?

A 
P = atrial depolaration
QRS = Ventricular depolarisation
T = Ventricular repolarisation
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20
Q

On ECG paper, what does 5mm represent on the x and y axis?

A 
X = Time = 0.2s
Y = Voltage = 0.5mv
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21
Q

How long are PR, ST, QT and QRS waves?

A

PR = 120-200
ST = 270-300
QT=350-420
QRS=80-110

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22
Q

What do the QTcB and QTcF formulas do?

A

Bazett’s and fridericia’s formulas account for increased heart rate and shortened QT interval. Allows good comparison when heart rate is high

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23
Q

Which wave represents septal depolarisation?

A

Q wave

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24
Q

What is an isoelectric line?

A

The flat line on the ECG

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25
Q

What are the names of the limb leads of a 12-lead ECG and which view do they give of the heart?

A

3 x bipolar limb leads (I, II, III)
3 x Augmented unipolar (AVR, AVL, AVF)
Look at conduction in the coronal plane (anterior, posterior)

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26
Q

What are the leads which aren’t limb leads in a 12-lead ECG? How are these denoted and what view do they give of the heart?

A

Precordial/chest leads (V1 > V6)

Give a transverse section of the heart

27
Q

Where do the electrodes go to generate the bipolar limb leads?

A

(-/-) RA
(+/+) LL
(+/-) LA

28
Q

What is Einthoven’s law?

A

Lead II potential = Lead III + lead I

29
Q

What views do the unipolar limb leads give of the heart?

A 
AVF = "foot" inferior view
AVL = Left side of the heart
AVR = Right side of the heart
30
Q

What are the names of the unipolar precordial (chest leads) and what view do they give of the heart?

A

V1 - V6, horizontal transverse section of the heart

31
Q

What does ischaemia do to the cardiac action potential?

A

Less negative resting membrane potential (-55mV)
Fast Na+ channels inhibited
Shortened endocardial action
ECG T wave has a negative deflection

32
Q

What is end diastolic volume?

A

The volume of blood in the ventricles after relaxation

33
Q

What is end systolic volume?

A

The volume of blood in the ventricles after contraction

34
Q

What is stroke volume?

A

The volume of blood ejected from the ventricles after contraction

35
Q

What is cardiac output?

A

CO = HR x SV

36
Q

What is Starling’s law?

A

Increased EDV = increased preload on muscle fibres = increased stroke volume

37
Q

What is preload?

A

Preload is the amount of sarcomere stretch experienced by cardiac muscle cells. This is directly proportional to EDV or the volume of blood in the ventricles when after relaxation.

38
Q

What is afterload?

A

Afterload is the pressure which the cardiac myocytes need to overcome to eject the blood from the ventricles. This is directly proportional to the pressure within the aorta and pulmonary vessels for the left an right ventricles respectively.

39
Q

What is the Bainbridge reflex?

A

Increase in venous pressure (increased venous return) leads to increased force and rate of heart contraction.

  1. Increased venous return
  2. Atrial baroreceptor stretch and SAN
  3. Afferent signal via vagus to medulla
  4. Efferent sympathetic response
  5. Increased force and rate of contraction
40
Q

What is the most abundant solute in the ECF?

A

Na+. Determines the osmotic pressure and blood volume. ECF=150mmol/L ICF=15mmol/L

41
Q

Name 3 acute methods of regulating blood pressure

A

1) Baroreceptors
2) Chemoreceptors
3) Atrial (Bainbridge reflex)

42
Q

Name the four stages of the cardiac cycle.

A

1) Mid to late ventricular diastole
2) Isovolumetric contraction
3) Mid to late ventricular systole
4) Isovolumetric relaxation

43
Q

What is isovolumetric contraction?

A

Event occuring in early systole whereby the ventricles have started to contract, but there is no change in blood volume. No blood is ejected yet. All valves are closed.

44
Q

Where does the first heart sound come from?

A

S1 (lub). During isovolumetric contraction, when the pressure in the ventricles exceeds atrial pressure, causing the AV valves to snap shut.

45
Q

Where does the second heart sound come from?

A

S2 (dub). During isovolumetric relaxation, when the pressure in the arteries exceeds the pressure in the ventricles causing the semilunar valves to snap shut.

46
Q

What is stroke volume?

A

Volume of blood ejected from the ventricles per beat (ml/beat). End diastolic volume (130 ml) - end systolic volume (50 ml) = 80 ml/beat

47
Q

Define cardiac output.

A

CO=HRxSV (80x60=4,800ml/min)

48
Q

Name 6 things that affects heart rate.

A

1) ANS
2) Hormones (T3, T4)
3) Body temperature
4) Ions (K+, Ca++)
5) Chemoreceptors (PO2, pCO2, H+)
6) Age

49
Q

Name 3 things that influence stroke volume.

A

1) preload (remember starlings law)
2) contractility
3) afterload

50
Q

Name 3 things that will increase afterload. What is the effect on stroke volume?

A

1) Aortic valve dysfunction
2) Atherosclerosis
3) Hypertension
All decrease stroke volume.

51
Q

Name 3 things that positively influence the contractility of the heart (force of contraction).

A

1) SNS - Noradrenaline - beta1 adrenergic receptors
2) Hormones (T3, T4) increase number of b1 adrenergic receptors
3) Drugs - Dopamine, digitalis, adrenaline

52
Q

Write an equation for BP.

A

BP = CO x total peripheral resistance

53
Q

Name 2 places where peripheral baroreceptors can be found.

A

1) Aortic sinus (CNX)

2) Carotid sinus (CNIX)

54
Q

Which four areas of the medulla are important for baroreceptor afferent reception?

A

1) Solitary tract nucleus
2) Cardiac acceleratory centre
3) Vasomotor centre
4) Cardiac inhibitory centre (Dorsal nucleus of vagus)

55
Q

What is poiseulles law?

A

Resistance = 8nl/Pi r 4 (as you decrease the radius of a blood vessel, you increase the resistance. As you increase resistance, you increase BP.

56
Q

How does the cardiac accelatory centre respond to hypotension from the baroreceptors?

A

Sympathetic stimulation (T1-L2).

1) positive chronotrope for SA node and AV node (increases HR)
2) Increases contractility of the myocardium of the heart (increased SV, increased BP)

57
Q

How does the vasomotor centre respond to hypertension from the baroreceptors?

A

Sympathetic stimulation (T1-L2)

1) Binds Alpha1 adrenergic receptors
2) Contracts smooth muscle
3) Decreases radius
4) Increases resistance

58
Q

What do juxtaglomerular cells release in response to low BP?

A

Renin

59
Q

Write the steps of the renin-angiotensin system up to angiotensin II.

A

1) JG cells secrete Renin in response to low BP
2) Angiotensinogen secreted by the liver
3) Renin catalyses angiotensinogen into angiotensin I
4) Angiotensin I moves to lungs
5) ACE converts angiotensin I into angiotensin II

60
Q

Name 3 areas that angiotensin II acts on.

A

1) Adrenal gland (Zona glomerulosa > aldosterone)
2) Hypothalamus (Supraoptic nucleus > Anti-diuretic hormone [Vasopressin])
3) Thirst centres (Increase intake of fluids, Increases EDV, increases SV, increases CO, increases BP)

61
Q

Where does ADH (vasopressin) work to increase BP?

A

Collecting duct of the nephron. Acts to reabsorb water from the collecting duct to increase blood volume, increase EDV, Increase SV, increase CO, increase BP.

62
Q

How does aldosterone act on the distal convoluted tubule?

A

1) Steroid hormone, binds to intracellular receptors
2) Increases NA+ and K+ channels to remove Na+ and K+ from the filtrate into the cell
3) Na+/K+ ATPase pumps 3Na+ into the blood
4) H20 follows Na+ into the blood increasing Blood volume, increasing EDV, increase SV, increasing CO, increasing BP

63
Q

How does aldosterone act on the proximal convoluted tubule?

A

Increases Na+, Cl- and H20 reabsorption into the blood. Increases blood volume.

64
Q

What is the relationship between low BP and urine output?

A

Low BP = Low GFR = Low urine output (Oliguria)

Phase 1 Medicine (JA) (8 decks)

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