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Bpk 305 > Cardiac Contractile Elements > Flashcards

Cardiac Contractile Elements Flashcards

1
Q

What is the mitral (bicuspid) valve between?

A

Left atrium and left ventricle

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2
Q

Where is the tricuspid valve located

A

Between the right atrium and right ventricle

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3
Q

What are the layers of the ventricular wall

A

Ventricular cavity—> endocardium (thinnest)—>myocardium (thick)—>epicardium (outer)

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4
Q

What layer of cells makes up most of the cardiomyocytes

A

Myocardium. 95% of mass

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5
Q

What is the shape of adult cardiomyocyte (and size)

A

Rectangular
120-150 micro m long. 10-20 micro m wide

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6
Q

What are the ways cardiomyocytes can be overloaded

A

Pressure overload
Volume overload

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7
Q

How does pressure overload effect the cardiomyocytes

A

Increase cell width 2-3 fold. Causes more parallel contractile units
think wider = more in line

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8
Q

How does volume overload effect cardiomyocytes

A

Increase cell length up to 10-20%. Causes stretching of contractile units to make them longer

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9
Q

Which sarcomere sections shorten during contraction

A

I band (actin) and H zone (myosin)

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10
Q

Which section doesn’t change during sarcomere contraction

A

A band

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11
Q

What is between cardiac cells

A

A cleft that allows blood flow through capillaries

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12
Q

What are the 7 structural elements of a cardiomyocyte?

A

-Contractile elements- 50% of cell volume
-T-tubules- align with Z lines
-Mitochondria- two types= subsarcolemmal (help pump calcium out of cell) and intermyofibrillar (used for atp energy used directly in contraction) overall 30-35% volume.
-Sarcoplasmic reticulum- repository for Ca2+
-Nucleus- mono or binucleated skeletal is polynucleated
-Golgi
-Ribosomes

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13
Q

What are the types of coupling between cardiomyocytes

A

Physical coupling- desmosomes aka macula adherens. Have cytoskeletal proteins.
Electrical coupling- gap junctions aka nexus. Have connexins (protein)

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14
Q

Where are neighbouring cardiomyocytes coupled?

A

Intercalated disks

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15
Q

What is a functional syncytium

A

cardiomyocytes work together to performed coordinated contraction. This is possible because they have both physical and electrical coupling no coupling = no functional syncytium

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16
Q

What makes up a gap junction

A

2 connexons per gap junction
1 connexon is a hexamer of six connexins

17
Q

Do gap junctions regulate what can go through

A

Yes. Regulated permeability. Ex- by acidosis

18
Q

Function of Titin

A

-Stabilizes position of contractile elements
-Returns stretched muscle to resting length

19
Q

Is titin paired with thin or thick filaments? Where else is it connected?

A

Myosin
From M line to Z line (half of sarcomere)

20
Q

Function of nebulin

A

Aligns thin filament

21
Q

Is nebulin paired with thin or thick filament? What else is it connected to?

A

Actin
Z line to thin filament ends

22
Q

What are the components of the thin filament

A

Actin filaments- helical, 13 mcs per turn
Tropomyosin- lies near actin groove
Troponin complex (Tn)
- TnT: tropomyosin binding
- TnC: Ca2+ binding
- TnI: inhibitory

23
Q

Cross-bridge cycling: what stage is ATP added, ATP hydrolyzed, Pi released, ADP released

A

ATP added- release myosin head from actin
ATP hydrolyzed- cock myosin head
Pi released- power stroke
ADP released- myosin attached to actin

24
Q

How much Ca is needed for 50% force generation

A

1 microM

25
Q

Where does Ca bind on the thin filament

A

Troponin C (known as the calcium sensor)

26
Q

How many binding sites does troponin C have? And name their role

A
  1. Site I- dysfunctional in cardiac muscle
    Site II- initiates contraction
    Site III and IV- high affinity so always occupied
27
Q

Role of tropomyosin

A

Block myosin from binding to actin

28
Q

Name troponin complex parts and their roles

A

TnT- binds tropomyosin
TnC- binds calcium
TnI- binds actin

29
Q

How many calcium molecules bind to troponin complex in cardiac vs skeletal

A

Cardiac- 1
Skeletal- 2

30
Q

What are the components of myosin

A

2 heavy chains- one tail (coiled helix), 2 heads, binding sites for actin and ATP
4 light chains- in two pairs, regulatory (phosphorylatable) + alkali (essential (structural role))

31
Q

What are the three isoforms of the thick filament heavy chains

A

Alpha-alpha (fastest) -mouse
Alpha-beta
Beta-beta (slowest) -elephant
humans have more beta
Thyroxine promotes alpha expression

Bpk 305 (10 decks)

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