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Human Systems Physiology > Cardiovascular Lecture 3 > Flashcards

Cardiovascular Lecture 3 Flashcards

1
Q

What structure of cardiac muscle causes the striated appearance?

A

The regular arrangement of actin and myosin that generate force by the sliding filament mechanism. This arrangement is the sacromere.

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2
Q

What are the main structural features of a sacromere?

A

Z line, M line, I band, A band, Myofibril, Titin

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3
Q

What is the Z line?

A

Site of actin attachment

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4
Q

What is the M line?

A

Site of myosin attachment

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5
Q

What is the I band?

A

Actin filaments

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6
Q

What is the A band?

A

Myosin filaments

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7
Q

What is myofibril?

A

Filament bundles

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8
Q

What is titin?

A

Protein that tethers myosin to the Z line

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9
Q

How is tropomyosin removed, and what does this do?

A

Tropomyosin is removed by Ca2+ binding to troponin C, allowing myosin binding and cross-bridge formation

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10
Q

Describe the location of sacroplasmic reticulum with respect to other structures

A

The SR surrounds the myofibrils, and is closely associared with T-tubules.

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11
Q

What is in the sacroplasmic reticulum?

A

An abundance of mitochondria and internal Ca2+ stores

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12
Q

What are T-tubules?

A

Sacrolemmal invaginations positioned at the Z bands

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13
Q

What molecular ion is necessary for cardiac contraction?

A

Extracellular free Ca2+

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14
Q

What happens during the action potential plateau on the molecular level?

A

Ca2+ enters the cell through voltage gated L-type Ca2+ channels, localized in T-tubules. The amount entering is small, but causes a large release of Ca2+ from the adjacent junctional SR (Ca2+-induced Ca2+ release). This CICR occurs through ryanodine receptors (RyR), a Ca2+ gated Ca2+ channel in the SR membrane.

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15
Q

What happens when intracellular Ca2+ concentration is elevated?

A

Actin-myosin interaction can occur, causing cardiac contraction.

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16
Q

How does relaxation after contraction occur?

A

Removal of Ca2+ from the cytosol by:

  1. Re-accumulation in the SR by the SR Ca2+-ATPase (SERCA)
  2. Extrusion from the cell by the sacrolemmal Na+-Ca2+ antiporter (3:1 Na+:Ca2+) and ATP-driven Ca2+ pump
17
Q

Why can’t more muscle cells be recruited to increase contractile force?

A

All cardiac muscle cells contract during the heart beat.

18
Q

How is the contractile force increased?

A

Sympathetic stimulation and stretch

19
Q

Describe sympathetic stimulation

A

a. increases size of intracellular Ca2+ transient, resulting in a more forceful contraction (positive intropy)
b. increases rate of relaxation, resulting in shorter contraction (positive lusitropy)
c. Increases frequency of contractions (positive chronotopy)

20
Q

Describe strech

A

a. Occurs by the Frank-Starling mechanism, with increased venous return of blood to the heart, allowing the heart to pump whatever volume it recieves
b. Involves increases in myosin-actin interactions
c. Myosin-actin interactions are not increased by greater overlap of thick and thin filaments, but rather increased sensitivity to Ca2+ and reduced interfilament spacing, mediated by titin

21
Q

What represents the muscle force-length relationship?

A

Pressure-volume (PV)

22
Q

Describe PV during relaxation/filling (diastole)

A

Ventricular PV curve is relatively flat, indicating increased volume is accommodated with small increases in pressure -compliant (inverse of stiff)

23
Q

Describe PV with greater filling

A

Ventricle becomes much less distensible, reflecting the abundance of connective tissue

24
Q

What mechanism does developed pressure follow?

A

The Frank-Starling mechanism

25
Q

What is preload?

A

Force that stretches relaxed muscle (blood filling)

26
Q

What is afterload?

A

Force against which muscle must contract (pressure in artery against which ventricle ejects)

27
Q

What cardiac and vascular factors are affected by preload and afterload?

A
  1. venous tone
  2. peripheral resistance
  3. rate
  4. stroke volume
28
Q

What is contractility?

A

It defines performance at a given preload and afterload, which will determine the peak isometric force (isovolumic pressure) at a given initial fibre length (end-diastolic volume)

29
Q

Is cardiac muscle voluntary?

A

No, it is involuntary.

30
Q

What makes cardiac muscle different from skeletal muscle?

A

An influx of extracellular Ca2+ is required for contraction.
Force of contraction is increased by stretch (Frank-starling mechanism) and sympathetic stimulation, unlike skeletal muscle, which recruits muscle fires and undergoes tetanny

Human Systems Physiology (29 decks)

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