4. O2 Demand Flashcards Preview

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Flashcards in 4. O2 Demand Deck (24):
1

How would an increase in the amount and rate of Ca2+ release affect the magnitude and rate contraction?

Faster, more forceful contraction

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2

What vasculature provides the heart w/ its own bloodflow?

Coronary arteries

3

When does the heart get blood flow from the coronary arteries? When does it cease?

  • Blood flow ceases during active contraction (systole) as arterioles and capillaries are compressed
  • Blood flow occurs during diastole when heart is relaxing

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4

Oxygen consumption in cardiac vs. skeletal muscle

Cardiac oxygen consumption at rest is 20x greater per gram of muscle than skeletal muscle

5

Oxygen extraction in cardiac vs. skeletal muscle

Oxygen extraction is maximal in resting heart

  • 80% of presented O2 is removed in heart
  • 25% of O2 is removed in a skeletal muscle

6

Cardiac capillary density in cardiac vs. skeletal muscle

  • Cardiac capillary density = 3,000-4,000/mm2
  • Skeletal muscle = 500-2000/mm2 

7

What is the most aerobic muscle in the body?

Heart

8

What is the only way to meet the increased demand for O2 in the heart?

Increase coronary blood flow

9

What determines the myocardial O2 supply?

O2 content supplied by coronary blood flow

10

What factors determine myocardial O2 demand?

  • Wall stress
  • HR
  • Contractililty (SBP)

11

What factors account for 90% of heart work?

  • HR
  • Contractility (SBP)

12

Law of LaPlace

Wall tension depends on radius of curvature

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13

What is wall stress?

Relation b/t ventricular volume and tension

14

Equation for wall tension of a thick-walled sphere

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15

What are the effects of cardiac geometry on energy demand?

Larger radius w/ same wall thickness —> high wall tension

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16

Explain excitation-contraction coupling during systole. (CICR)

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17

What is the relationship b/t Isometric Tension and pCa?

Increase Ca2+ --> greater force 

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18

Explain the relation b/t sarcomere length and Ca2+ sensitivity of tension.

  • Increased sarcomere length --> increased Ca2+ sensitivity of tension
  • More force for a given level of Ca2+

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19

What characterizes the relaxation phase of excitation-contraction coupling?

Removal of Ca2+ from cytosol

20

What are the mechanisms by which Ca2+ is pumped out of the cytosol? What % does each pump out?

  • Ca2+ ATPase pump (~5%)

  • Na+/Ca2+ Exchange (~15%)

  • SERCA Ca2+ ATPase pump (~80%)

21

What is the function fo the SERCA Ca2+ ATPase pump?

Replenishes SR Ca2+ load

22

What is the SERCA pump regualted by?

Phospholamban (PL)

23

How does phospholamban regulate the SERCA pump?

PL inhibits SERCA by delaying relaxation (diminishes lusitrophy) --> restricts speed at which SERCA pump can function at rest

24

Define lusitropy.

Ability of the contractile process to terminate rapidly --> relax faster