Unit 3 - Cardiac Physiology

Question 1

end diastolic volume (EDV)

Answer 1

amount of blood in ventricles after filling

normal = 135 ml

Question 2

end systolic volume (ESV)

Answer 2

amount of blood left in ventricles after ejection
ESV = EDV - SV
normal = 65 ml

Question 3

stroke volume (SV)

Answer 3

volume of blood pumped by each ventricle in one contraction

normal SV = 70 ml

Question 4

cardiac output (CO) & formula

Answer 4

• amount of blood pumped by each side of the heart in one minute
  CO = HR x SV
  normal CO = 70 (HR) x 70 ml (SV) = about 5 L/min

Question 5

ejection fraction (EF)

Answer 5

ratio of stroke volume to EDV
SV / EDV
Normal EF is about 50%
Ventricles only eject about half of blood they receive

Question 6

Determinants of Stroke Volume

Answer 6

1. preload
2. contractibility
3. afterload

Question 7

preload

Answer 7

• stretch of the heart prior to contraction
• blood available for pumping
• the more blood that comes back to the heart, the stronger the ventricle contraction

Question 8

contractibility

Answer 8

force of contraction

Question 9

afterload

Answer 9

• resistance (pressure) against which heart needs to pump

Question 10

intrinsic control of stroke volume

Answer 10

the heart’s inherent ability to vary stroke volume

Question 11

vagal tone

Answer 11

effect the parasympathetic NS has on HR.

- decreases the intrinsic rate of SA node to maintain normal HR at rest

Question 12

what is RMP of auto rhythmic cells?

Answer 12

-60 mv

Question 13

what is RMP of contractile cells?

Answer 13

-90 mv

Question 14

AP of auto rhythmic cells

Answer 14

RMP = -60 mv
TP = -40 mv
maximum = 0

Question 15

AP of contractile cells

Answer 15

RMP = -90 mv
TP = -70 mv
max = +30 mv

Question 16

What do the following waves represent on an ECG?

1. P wave
2. QRS wave
3. T wave

Answer 16

1. P wave - atrial depolarization
2. QRS wave - ventricular depolarization
3. T wave - ventricular depolarization

Question 17

What comprises the slow drift to threshold (aka PACEMAKER POTENTIAL)?

Answer 17

1. Decreased permeability for K+
2. Increased permeability of Na+ (flow inward) = FUNNY CHANNELS = voltage gated channels that open in hyperpolarized state
3. Increased permeability (inward) of Ca2+ = TRANSIENT Ca2+ channels

Question 18

Na+ FUNNY channels

Answer 18

Open at hyperpolarization

Aid in slow depolarization toward Threshold Potential

Close halfway to Threshold Potential

Question 19

Transient t-type Ca2+ channels

Answer 19

Open at hyperpolarization

Aid in pacemaker potential (slow depolarization)

Close at Threshold Potential

Question 20

What happens at TP in an autorythmic cell?

Answer 20

Ca2+ L-type (long lasting) channels open

Lead to large influx of positively charged ions = rising phase of action potential

Question 21

What make the 2 phases of Pacemaker Potential?

Answer 21

1. INITIAL PHASE - Takes off from RMP (-60 -> -40)
   - K+ stays in cell
   - Na+ funny channels open - Na+ enters cell
2. SECOND PHASE - takes it to TP
   - Transient (T-type) Ca2+ channels open

Question 22

Rising phase of AP

Answer 22

T-type ca2+ channels close

L-type CA2+ channels open

Takes it all the way to too

Question 23

Falling Phase

Answer 23

VG K+ channels open - begin leaving cell

Ca2+ L-type channels close

Cell becomes more negative;
After AP, slow closure of K+ cause hyperpolarization

Question 24

imaginary triangle used in determining the positions of ECG leads?

Answer 24

Einthoven’s triangle