Week 6 The cardiovascular system (control of contraction) Flashcards

1
Q

Vertebrate hearts are neurogenic/myogenic?

A

Myogenic

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2
Q

Define Myogenic.

A

ability to generate spontaneous rhymical depolarisations

the rate of depolarisation varies

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3
Q

What are pacemaker cells?

A

specialized cardiac muscle cells which are more excitable than the others and therefore contract first (Cardiac muscle contracts without neural stimulation)

  • fast intrinsic rhythm of firing - determunes contraction rate
  • Fish - sinus venosus
  • Other vertebrates - sinoatrial node (SAN)
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4
Q

What type of cell is this?

A

rod shapped cardiac myocyte.

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5
Q

How does cardic muscle vary from skeletal muscles or others?

A

How they are joined together through intercalated discs containing desosomes enables cells to be myogenic and communicate very well with eachother (unobstructedly - no walls that take time to pass) - fluid like movement, depolisation moves uninterrupedly.

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6
Q

Cardiac muscle: What is the role of desosomes and gap junctions?

A
  • desosomes: transfer the force from cell to cell
  • gap junctions: allow passage of electrical signals
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7
Q

Cardiac muscle: how are intercalated discs formed?

A
  • formed from plasma membrane of 3 adjacent cells which are intertwined and bounded together by gap junctions and desosomes
  • cells binding together mechanically, chemically and electrically results in their acting together
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8
Q
A
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9
Q

How does sacromeres of cardiac muscle differ from skeletal muscle?

A
  • have the same banding patters
  • but cardiac sarcomeres have branching fibrillar networks which are continuous in three dimesion throughout the cytoplasm
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10
Q

How does the sacroplasmic reticulum and the T system function?

A
  • The plasma membrane invaginates traversely forming tubular system (T tubules) between cisternae.
  • contain voltage-sensor proteins which activate when membranes depolarize
  • induced sarcoplasmic reticulum to release Ca2+
  • T tubules and adjacent cisternae form a diad
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11
Q

Uses of Energy (ATP) in the heart:

A
  • enormous energy demand is related primarily to ATP-dependent processes driving Excitation Contraction coupling (movement of ions)
  • about 70–75% of total intracellular ATP is used for force generation powering work output
  • remaining 25–30% is used for basal metabolism
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12
Q

What is the key regulator of EC in the heart?

A

Sodium-Potassium Pump, maintains sodium levels with a careful change.’

permiability of sodium increase/decreases the action potencial in heart , meaning the distribution of these ions across the cardic cell membrane to maintain an electrochemical gradient.

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13
Q

What does Cardiac Na/K ATPase play a role in?

A

Na/K ATPase controls the Na/K pump.

  • trans-membrane transport
  • ion homeostasis
  • electrical excitability
  • control of cell volume and contractility
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14
Q

What are the properties of the pacemaker cells?

A
  • small, few myofibrils, mitochondira & other organelles
  • do NOT contract
  • unstable resting membrane potencial (RMP) –> pacemaker potencial
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15
Q

What is the hierarchy of pacemakers?

A

different action potencials for the pacemakers

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16
Q

How does the cardiac conduction system work?

A

reliant on the desmosomes and gap junctions.

  • conduction from SA to AV node via atrial muscle is slow
  • contraction through AV node is slow - AV pause
    • allows ventrivular filling to occur before passing on the electrical impulse
    • prevents transmission of high rates from the atria
  • conduction through the V is fast
    • allows for apex to contract before base.
17
Q

What is excitation - contraction coupling?

A

action potencial resulting in contraction

  • action potencial generation (electrical activity based on ion movement) occurs first, resulting in the intracellular Ca2+ concentration altering, then resulting in the tension of cardiac muscle
18
Q

EC coupling in cardiac muscles: detail with T-Tubules:

A
  • AP enters from adjacent cells opening the Ca gates voltage channels, Ca2+ enters incuding local release of Ca.
  • Ca2+ binds to troponin to initiate contraction
  • relaxation occurs when Ca2+ unbinds
  • Ca2+ pumped back into sarcoplasmic reticulum to be sotres ready for next contraction
19
Q

Pacemaker Cell Action Potential: What occurs during pacemakerpotencial?

A

action potencial is the transient depolization of the cell

  • unstable RMP ( resting metabolic potencial)
  • ‘funny’ (pacemaker channels) channel opens, resuling in the:
    • ↑permiability to Na+
    • ↓K+ efflux (to balance charges)
    • ↑membrane potencail
20
Q

Pacemaker Cell Action Potential: What occurs during the steap incline?

A
  • membrane near threshold
  • T-type Ca2+ channels open resulting in depolarization & AP
21
Q

Pacemaker Cell Action Potential: What occurs during action potencial?

A
  • T-type Ca2+ channels open
  • K+ channels open
  • repolarisation of cell
22
Q

What are the features of cardiac muscles that ensure a rapid spread of electrical activity?

A

Intercalated discs - link adjacent cells

  • gap junctions (pathway for electrical current to spread from cell-cell)
    • Electrotonic current speed
  • desosomes (mechanically hold cells together)
23
Q

What is the order of events for conduction?

A
  • starts at SNA
  • spreads through both A - internodal pathway
  • passes though AVN
  • spreads through V - bundles of His, Purkinje fibres
  • contraction begins at apex
24
Q

What is an AV nodal delay?

A

Delay = 0.1 s

  • ensures that A contraction precedes V contraction
  • allows complete centricular filling
25
Q

What sets the heart rate (HR)?

A

the rate of action potencial firing in pacemakers

26
Q

What are the hormones that control the HR?

A
  • norepinephrine (increases HR) - sympatheic neurons
  • epinephrine (increases HR) - adrenal medulla
  • acetylcholine (decreases HR) - parasympatheic neurons
27
Q

How do these hormones control the HR?

A