Myocardial Adaptations/Failure & Metabolism

Question 1

Is the heart a post-mitotic organ?

Answer 1

No, it has small regeneration properties

Question 2

What percent of the volume do each of the organelles in the myocyte take up?

Answer 2

Myofibrils 60
Mitochondria 23
Sarcoplasmic reticulum 2
TT-system 1

Question 3

What three subcellular biochemical systems are central to muscle function?

Answer 3

Metabolism
Calcium-regulating
Contractile unit

Question 4

What is a physiological response?

Answer 4

If the heart is completely able to compensate to an overload condition

Question 5

What is a pathological response?

Answer 5

If the heart is not adequately able to completely adapt to an overload response

Question 6

When does compensatory cardiac hypertrophy take place?

Answer 6

In response to an increase in cardiac afterload

Question 7

What is afterload?

Answer 7

The pressure which the left ventricle must pump against to eject the blood

Question 8

Why does hypertrophy occur?

Answer 8

In an attempt to normalize wall stress

Question 9

LaPlace’s Law:

Answer 9

T (wall stress) = (pressure x radius)/(2 x wall thickness)

Question 10

What signals for concentric hypertrophy?

Answer 10

Tension

Question 11

What signals for eccentric (longitudinal) hypertrophy?

Answer 11

Stretch

Question 12

What does a pressure overload cause?

Answer 12

Myocytes to become greater in diameter not in length

Question 13

What does a volume overload cause?

Answer 13

Myocytes to become elongated with and increase in mitochondria

Question 14

How do myofibrils change with concentric hypertrophy?

Answer 14

Myofibrils increase in number added in parallel but not in diameter

Question 15

How do myofibrils change with eccentric hypertrophy?

Answer 15

Increase in diameter and are added in series and some parallel

Question 16

Does hypertrophy cause a lack of oxygen supply due to decreased capillary density?

Answer 16

No

Question 17

In endurance sports what type of stress is placed on the left ventricle?

Answer 17

An increase in volume so sarcomeres are added in series

Question 18

In strength training what type of stress is placed on the heart?

Answer 18

Increased afterload = increased wall stress; concentric hypertrophy thus sarcomeres are added in parallel

Question 19

How can exercise stop maladaptive heart growth?

Answer 19

By promoting miRNA-222 which stops cardiac maladaptions and promotes healthy remodeling

Question 20

What inhibits SERCA2 and how?

Answer 20

PLB (phospholamban) when it is not phosphorylated

Question 21

Which channels are affect in a failing heart?

Answer 21

SERCA2 pumps are reduced

NCX activity is enhanced

Question 22

What is the Bowditch effect?

Answer 22

Increases in HR increases in the force of contractions in normal heart due to increased concentrations of Ca2+ intracellularly

Question 23

Why do failing hearts not respond with a Bowditch effect?

Answer 23

Either sarcoplasmic Ca2+ levels are not increased or filament activation is defective

Question 24

What are earlier signs of cardiac failure when looking at autonomics?

Answer 24

Increased sympathetic tone and decreased parasympathetic tone

Question 25

What occurs to beta receptors in heart failure?

Answer 25

Beta-adrenergic receptors are down-regulated decreasing the response to inotropic stimuli

Question 26

What occurs to NE stores in heart failure?

Answer 26

It becomes depleted leading to the heart being functionally denervated and contractile dysfunction

Question 27

What are V1, V2, V3 myosin isoforms respectively?

Answer 27

alpha/alpha (fast)
alpha/beta (intermediate)
beta/beta (slow)

Question 28

What is the shift in myosin isoforms during pressure overload?

Answer 28

V1 shifts to V3

Question 29

What does the heart prefer as an energy source?

Answer 29

Free fatty acids

Question 30

During exercise what does the heart prefer as an energy source?

Answer 30

Lactate

Question 31

In failing hearts substrate utilization changes from lipids to what?

Answer 31

Carbohydrates