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VET YEAR ONE > FORM & FUNCTION (Cardiac Muscle) > Flashcards

FORM & FUNCTION (Cardiac Muscle) Flashcards

1
Q

Cardiac muscle function:

A

-generates waves of contraction responsible for squeezing the heart to pump blood throughout the body

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2
Q

Cardiac muscle connected to:

A

-pulmonary circulation (lungs)
-systemic circulation (rest of the body)

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3
Q

Four chambers:

A

-right atrium (RA), right ventricle (RV) to the lungs
-left atrium (LA), left ventricle (LV) to systemic organs
*left: oxygenated (red)
*right: deoxygenated (left)

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4
Q

Cardiac muscle fibers:

A

-contractile fibers (striated and like skeletal fiber)
-conduction fibers (ex. pacemakers)

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5
Q

Contractile fibers:

A

-cardiomyocytes form complex junctions between extended processes
-only 1-2 centrally located nuclei
-dark-staining lines
-junctions at intercalated discs: desmosomes and fascia adherents
-gap junctions

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6
Q

Desmosomes:

A

-joins the intermediate filaments in one cell to the neighbouring (lateral side)
-mechanical strength

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7
Q

Adherents:

A

-join an actin bundle in one cell to a similar bundle in a neighbouring cell (lateral side)
-mechanical strength

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8
Q

Dark-staining lines (contractile fibers):

A

-intercalated discs
>interface between cells
*need to contract together!

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9
Q

Gap junctions: (contractile fibers)

A

-between cells longitudinally
=electrical synapses
-allow Aps to pass in wave from one cell to the next cardiac cells
-all cells contract as a single unit
*functional syncytium

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10
Q

Functional syncytium:

A

-simultaneous contraction of all cardiac muscle fibers

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11
Q

Conducting fibers: specialized cells

A

-nodes (SA and AV node)
-bundles of His
-bundle branches
-Purkinje fibers

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12
Q

Nodes: conducting fibers

A

-generate and relay electrical impulses
-SA node cells: primary pacemakers of the heart

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13
Q

Bundle of His, Bundle branches and Purkinje fibers: conducting fibers

A

-transmit impulses to the ventricular myocardium

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14
Q

Conducting fibers: structural characteristics:

A

-few myofibrils: optimized for rapid conduction
-highly branched: allow for quick signal propagation

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15
Q

How does the duration of cardiac muscle AP compare to that of skeletal muscle?

A

-last longer and has a plateau
*lasts as long as the contraction

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16
Q

Sequential propagation of the AP:

A
  1. Initiation in SA (SinoAtrial node)
  2. Propagates through the atria
  3. Through the AV (AtrioVentricular) node
  4. Through the Purkinje fibers
  5. Through the ventricles
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17
Q

AP phases in cardiomyocytes:

A
  1. Phase 0: rapid depolarization
  2. Phase 1: initial repolarization
  3. Phase 2: plateau phase
  4. Phase 3: rapid repolarization
  5. Phase 4: resting membrane potential
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18
Q

Phase 0:

A

-rapid depolarization
-triggered by the opening of voltage-gated Na+ channels
-rapid influx of Na+ ions

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19
Q

Phase 1:

A

-initial repolarization
-closure of Na+ channels and opening of K+ channels
-outward flow of K+ ions

20
Q

Phase 2:

A

-plateau phase
-sustained depolarization
-opening of slow L-type calcium channels (voltage gated) allowing Ca2+ influx
*unique to cardiomyocytes

21
Q

Phase 3:

A

-rapid repolarization
-closure of Ca2+ channels
-rapid outflow of K+ ions

22
Q

Phase 4:

A

-Na/K pump and a Na/Ca exchanger to re-establish ion balance

23
Q

Regulation of L-type Ca channel:

A
  1. Sympathetic: E binds to beta-adrenergic receptor (GPCR) leading to activation of adenylyl cyclase=increased cAMP
  2. Parasympathetic: ACh binds to muscarinic cholinergic receptor leading to inactivation of adenylyl cyclase=decreased cAMP
    *cAMP activates PKA that phosphorylates L-type Ca2+ channels
24
Q

Phosphorylated L-type Ca2+ channel:

A

-more likely to open

25
Q

T-tubules and SR in cardiac muscle:

A

-larger T-tubules and less developed SR=’dyads’ rather than ‘triad’
-DHPR does NOT mechanically affect RyR opening
-rise in intracellular Ca2+ comes form extracellular space through DHPR from the t-tubules
>more Ca2+ released by Ca-induced Ca release mechanism through RyRs
*cross-bridge cycling is the same as skeletal muscle

26
Q

Contrast between skeletal and cardiac muscle AP:

A

-AP of cardiac has a plateau phase and a long refractory period: overlaps the time scale of force generation
*prolonged refractory period until the end of contraction means no summation occurs in cardiac muscle

27
Q

Length-tension relationship: skeletal vs. cardiac muscle

A

-skeletal: wider range of length over which tension is near optimum
-cardiac myocyte: narrower and steeper curve

28
Q

Skeletal and cardiac muscle at 75% sarcomere length

A

-skeletal: 84% force
-cardiac: 0% force

29
Q

Cardiac myocyte length-tension: increase from 75 to 90% sarcomere length

A

-increases tension from 0-70% of the maximum
-tension that develops during contraction increases with increased length: Frank Starling Relationship

30
Q

Frank Starling Relationship

A

*when change of cardiac muscle it will produce more force
-more blood volume=stretch cardiac muscle more=need more force to pump it around the body

31
Q

Force-velocity relationship: skeletal vs. cardiac muscle

A

-skeletal: Vmax=0 force (different for different fiber types)
-cardiac muscle: if increase preload or contractibility you get more force and increased Vmax

32
Q

Increase preload: cardiac muscle:

A

-stretching of cardiac cells before contraction
*increases force

33
Q

Increased contractility:

A

-heart’s inherent capacity to contract

34
Q

Preload:

A

-volume of blood in the ventricle prior to contraction

35
Q

Inotrophy:

A

-contractility refers to how powerful the heart can contract

36
Q

Energy sources for cardiac muscles:

A

*oxidative phosphorylation
-60% of ATP from FFA
-30% of ATP from glucose and other CHO
-glycogen granules and lipid droplets are abundant
-lactate, ketone bodies and AA can be used for energy
-ATP creatine phosphate system

37
Q

ATP Creatine phosphate system:

A

-creatine kinase-MB (isoforms in heart muscle) is a biomarker for myocardial infraction (heart attack
>now clinicians use troponin

38
Q

Oxygen demand for cardiac muscles:

A

*required
-almost entirely aerobic
-depends heavily on oxygen supply
-relies on myoglobin to store and release oxygen within cells
-limited capacity to use glycolysis

39
Q

Fatigue of cardiac muscles:

A

-high resistance due to constant demand for ATP and rich blood supply
>lots of mitochondria to make sure they don’t fatigue

40
Q

Mitochondrial density of cardiac muscles:

A

-make up 25-30% of cell volume
(skeletal: only 2% of cell volume)

41
Q

Cardiac muscle: innervation receptors

A

-ACh receptors: muscarinic cholinergic (slow GPCR)
-E/NE receptors: beta-adrenergic receptor

42
Q

Cardiac muscle innervation divisions:

A

-autonomic system
-sympathetic and parasympathetic stimulation

43
Q

Sympathetic stimulation:

A

-NT: NE
-increases heart rate and contractility
-beta-adrenergic receptor activates the cAMP second-messenger system

44
Q

Parasympathetic stimulation:

A

-NT: ACh
-decreases heart rate
-muscarinic receptors

45
Q

Cardiac muscle adaptation:

A

-hypertrophy
-hyperplasia: NOT
>if myocardial fibers die, they are replaced by fibrous noncontractile scar tissues

VET YEAR ONE (108 decks)

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