Physiology 3 - Cardiac Contractility Flashcards Preview

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Flashcards in Physiology 3 - Cardiac Contractility Deck (34)
1

In cardiac muscle, what does troponin bind to?

Tropomyosin

2

With regard to calcium, how does muscle relaxation occur?

Calcium is repackaged away, either in the sarcoplasmic reticulum or exchanged for sodium, which is in turn pumped out via the sodium potassium pump

3

By implementing sympathetic innervation as opposed to parasympathetic innervation, what is the effect on the ventricles?

Tension (not volume) increases and quicker

4

During what period is it possible to depolarise the membrane again?

Relative Refractory Period

5

Look at slide 5

Look at slide 5!

6

Why does the volume of the ventricles never go down to 0?

Allows for room to move - by having a 50ml reserve of blood in the ventricle, it means relaxation and contraction is a lot smoother - not having to contest with suction

7

What occurs during (normal) systole?

Ventricular contraction

8

What occurs during (normal) diastole?

Ventricular relaxation

9

11:49

Isovolumetric

10

When will the aortic valve open?

When the pressure in the ventricle exceeds the pressure in the aorta

11

Why is there a small jump in the aortic pressure just as it starts to decrease?

As the aortic valve closes, there is a slight rebound of blood against the valve, briefly pushing the pressure up

12

How is the stroke volume (SV) measured/calculated?

End diastolic volume - End systolic volume

13

How is the cardiac output (CO) calculated (L/min)

Stroke Volume x Heart Rate

14

During cardiac contraction, what type of ion channels does an action potential cause to open?

L type DHP channels

15

What is the result of L type DHP channels opening?

Large Ca2+ influx

16

Which type of T-tubule (cardiac or skeletal muscle) is larger and by how much?

Cardiac is larger - 5x greater in diameter and 25x greater in volume

17

What does DHPR activation cause?

Release of Ca2+ from SR via RyR channels

18

What is the preload?

How much blood is in the heart before it contracts

19

What increase the preload?

Increased venous return

20

What is responsible for the cardiac muscle refractory period?

Inactivation of Na+ channels

21

How does cardiac muscle's period of contraction differ to skeletal muscle's period of contraction?

250ms long, as opposed to 200ms long

22

Name the three 'periods' of cardiac contraction.

Absolute refractory period
Relative refractory period
Period of supranormal excitability

23

What is the average duration of the ARP?

245ms

24

At each of these contraction periods, can the cardiac muscle cells be stimulated to depolarise again and if so, how easily is this depolarisation achieved?

ARP - cannot be stimulated
RRP - may be stimulated, but stimulus would have to be larger than the original
SNP - smaller than normal stimulus will result in depolarisation

25

What is the period of isovolumetric contraction?

Brief period when aortic and mitral valves are both closed, but ventricle is contracting, allowing pressure to build up to that of the aortic pressure

26

What is the period of isovolumetric relaxation?

Period when the aortic and mitral valves are both closed and the ventricular pressure is falling, but not below that of the pressure in the atria

27

What are the 4 stages of ventricular contraction/pumping?

1. Isovolumetric contraction
2. Period of rapid ejection (1/3rd of the time) - 70% of ejection fraction
3. Period of slow ejection (2/3rds of the time) - 30% of ejection fraction
4. Isovolumetric relaxation

28

What is the average/normal aortic pressure?

120/80mmHg

29

What is the average/normal pulmonary pressure?

30/12mmHg

30

What is the End Systolic Volume?

Volume in ventricle at the end of systole (80% + 20%)

31

What is the End Diastolic Volume?

Volume in ventricle at the end of diastole

32

What is the Stroke Volume?

The quantity of blood expelled per beat. EDV – ESV.

33

What is the Cardiac Output?

The volume of blood pumped by the heart over a given time period (L/min). HR x SV.

34

What is normal, resting CO?

5L/min

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