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BPK 305 > cardiac contractile elements > Flashcards

cardiac contractile elements Flashcards

1
Q

primary role of the cardiovascular system

A

distribution of dissolved gases and other molecules for nutrition growth and repair

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2
Q

secondary roles of the cardiovascular system

A

fast signaling to cells through hormones or NTs

delivers heat from core of body to surface (dissipation)

mediation of inflammation and host defence responses against invading microorganisms

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3
Q

arteries

A

away from heart

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4
Q

veins

A

to the heart

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5
Q

what kind of pump is the heart

A

4 chamber pump
dual pum
left is main
right is boost

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6
Q

what are the two circulations

A

pulmonary and systematic

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7
Q

systemic circulation

A

left side (aorta)

aorta is high pressure, vena cava is low

oxygenated aterial blood

multiple parallel paths

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8
Q

pulmonary circulation

A

de-oxygenated arterial blood

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9
Q

3 functional parts of the heart

A

heart
blood
vessels

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10
Q

what is blood flow driven by

A

constant pressure across variable resistance

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11
Q

left side of the heart

A

constant pressure generator

maintains steady mean arterial pressure at its exits (aorta)

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12
Q

parallel circuits in heart

A

parallel blood flow

less resistance in the blood, same amount of O2 to all organs

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13
Q

valves

A

movement is passive

orientation is responsible for unidirectional flow

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14
Q

what are the atrioventricular valves

A

tricuspid and mitral/bicuspid

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15
Q

what are the semilunar valves

A

pulmonic and aortic

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16
Q

pulmonic valve

A

located between right ventricle and pulmonary artery

consists of 3 cusps (anterior, right and left)

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17
Q

aortic valve

A

located between right ventricle and aorta

consists of 3 cusps (left, right, anterior)

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18
Q

mitral (bicuspid) valve

A

two cusps (anterior and posterior)

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19
Q

chordae tendineae cordis

A

attached to free edges of the valves

strong ligaments

prevent valves from becoming everted during ventricular systole

heart strings

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20
Q

papillary muscles

A

provide tension for chordae tendinae

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21
Q

left ventricle

A

more muscular

pumping blood against more resistance

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22
Q

endocardium

A

layers of epithelial and purkinji fibers

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23
Q

myocardium

A

95 percent cardiomyocytes by mass
- most of weight

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24
Q

epicardium

A

outside, outer

sympathetic nerves

fat, ready supply

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25
Q

pressure overload in cardiacmyocytes

A

ie/ hypertension or weightlifting

increased cell width 2-3 fold

  • high blood pressure - heart is working hard (not really good) - heart gets big
  • more parallel contractile units
  • stronger contractions
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26
Q

volume overload

A

ie/ valve failure or aerobic exercise

  • increased cell length up to 10-20%
  • stretching contractile units - longer power strokes
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27
Q

z-line

A

connections tether each myofibril to its neighbour and align the sarcomere

forms sarcomere boundary

thin actin filaments run through (project from both faces)

contains a-actinin

perpendicular to the axis of myofibrils - and has its diameter

in center of I band

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28
Q

I band

A

decreases (shortens) with contraction

increases with relaxation

contains actin filaments

regions of thin filaments that do not overlap with the thick filament

isotropic to polarized light

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29
Q

A band

A

contains thick myosin filaments

does not change with contraction

defined by length of myosin

anisotropic to polarized light

30
Q

H-zone/ band

A

center of A band (myosin)

no overlapping thin filaments

changes size during contraction

31
Q

M line

A

attachment for myosin

32
Q

intercalated disk

A

combination of mechanical junctions and electrical junctions

communicating force and sharing electrical signals

33
Q

sarcoplasmic reticulum

A

where calcium is stores and lots of mitochondria

internal network of membranes

34
Q

fasicles

A

a bundle of this forms a muscle like the bicep

35
Q

myofibrils

A

smallest unit of skeletal muscle

bundle of myofilaments - run along axis of the cell

a bundle of aligned muscle fibers forms a fasicles

36
Q

what are the cardiomyocytes structural elements

A

contractile elements

t-tubules

mitochondria

SR

nucleus

golgi

ribosomes

37
Q

contractile elements

A

50 percent of cell volume

38
Q

t-tubules

A

invaginations

align with z-lines

39
Q

mitochondria

A

30-45 percent of cell volume

subsarcolemmal

intermyofibrillar

40
Q

nucleus

A

mono or binucleated

41
Q

myocyte branching

A

provides longitudinal and diagonal coupling

coupled at intercalated disks

42
Q

macula adherens

A

also called desmosomes

holds adjacent cells together

cytoskeleton proteins

physical coupling

share force from one cell to another

43
Q

gap junction

A

also called nexus

connexins (2 connexins/gap junction)

links cells electrically

cells that communicated through this are electrically coupled

interconnect cytosols of neighbouring cells

allow some small molecules to diffuse freely between cells

electrical coupling

create a functional syncytium (electrically coupled tissue)

regulated permeability

almost touching

parallel to myofilaments

44
Q

connexon

A

central pores

hexamers

6 connexins/connexon

45
Q

no coupling

A

do their own thing, contract randomly, tissue will not contract

cells cannot communicate and coordinate with each other

occurs if their is a disruption in gap junctions if cells are physically seperated

could cause less effeciency - arrhythmias, ineffective pumping

used in: localized contractions, maintain rhythm (preventing overactivity, differentiations, pathologically a protective mechanism

46
Q

coupling

A

= functional syncytium

occurs when cells within syncytium are connected allowing for coordinated electrical signals and mechanical contractions

usually in gap junctions

leads to synchronized contraction - essential for efficient heart function - ensures heart beats in a single unit

47
Q

titin

A

protein that tethers to the z-line

extends from the z-line to center of sarcomere

the largest known protein: around 30,000 a.a

from m line to z line

acts like a spring (elastic)

stabilizes position of contractile elements

returns stretched muscle to resting length

important for alignment of thick filament in the sarcomere

some forms of muscular dystrophy have been attributed to defects in titin

48
Q

nebulin

A

extends along length of thin filament

from z line to thin filament ends

aligns thin filament

regulates thin filament length

49
Q

actin

A

thin filament

helical

13 molecules (monomers) per turn

50
Q

tropomyosin

A

lies near actin groove

interferes with myosin binding

length = around 1/2 helical turn of actin

2 filaments/actin

dimers of tropomyosin extend over entire actin filament and cover myosin binding sites on actin molecules

each dimer extends over the entire actin actin molecule

dimers arranged in head-tail formation

51
Q

what are the different types of troponin

A

TnT

TnC

Tnl

52
Q

troponin

A

present on each tropomyosin dimer

influences position of tropomyosin molecule on the actin filament

3 subunits

53
Q

TnT

A

tropomyosin binding

pushes tropomyosin away from the myosin binding site on actin and into the actin groove

54
Q

TnC

A

calcium binding

promotes movement of tropomyosin on the actin filament that exposes tropomyosin binding sites on actin

facilitates actin-myosin interaction and therefore contraction

55
Q

TnI

A

inhibitatory

moves away from actin/tropomyosin filament - allowing tropomyosin filament to move

binds actin

56
Q

increase in calcium in cross-bridge cycling

A

allows for it to continue

triggers contraction by removing inhibition of cross-bridge cycling

57
Q

decrease of calcium in cross bridge cycling

A

is the signal to decrease/relax cross-bridge cycling

achieved by removing a transporting calcium from sarcoplasm

58
Q

what does calcium bind to in cross bridge cycling

A

binds to regulatory proteins

in absense of calcium they will inhibit actin-myosin interactions = no contraction

conformational change occurs when calcium binds to one or more of these proteins - releases inhibition

59
Q

rigor mortis

A

no more ATP - therefore crossbridges remained locked in rigid conformation of ADP-bound actomyosin

60
Q

steps of cross-bridge cycling

A
  1. ATP (initiates another cycle) binds to myosin head, causes the dissociation of the actin-myosin complex
    - reduces affinity of myosin to actin - in this state muscles are relaxed
    - myosin head is attached to actin filament after the power stroke from the previous cycle
    - released state
  2. ATP is hydrolyzed (to ADP + Pi) causing myosin heads to return to their resting conformation
    - rate limiting step - gives us a different form of myosin
    - myosin head pivots into cocked position - muscle is completely relaxed
  3. a cross-bridge forms and the myosin head binds to a new position on actin
    - the binding increases the affinity of the myosins - ADP - Pi complex for actin
  4. Pi is released. Myosin heads change conformation, resulting in the power stroke. The filaments slide past each other. Pulls actin filament toward myosin tail
  5. ADP is released
    - last step of cycle and then it is repeated again
    - actin-myosin complex is left in rigid state
61
Q

ATP in cross bridge cycling

A

gives NRG for cycling

if unregulated this cycling would continue until myocytes is depleted of ATP

62
Q

troponin C calcium binding sites

A

site 1: dysfunctional in cardiac muscle
site 2: binds calcium - initiated contraction
site 3 and 4: high affinity, always occupied

63
Q

explain the steps after calcium binding to TnC

A

Tnl and tropomyosin move
exposed myosin binding site
crossbridge cycling
contraction

64
Q

calcium tension relationship

A

occupancy of site 2 on Tn C

change in troponin complex conformation

myosin binding site on actin is exposed

cross- bridge formation

tension or force

65
Q

myosin

A

thick filament

intertwined complex or proteins like thin filaments

66
Q

heavy chains

A

2 chains form coiled helix

tail and 2 heads (1 rod, 1 hinge and a head)
- cross bridges between thin and thick filaments

heads= S1 - each possess a site for binding actin and a site for binding and hydrolyzing ATP

binding sites: actin and ATP

alpha or beta isoforms
- different rates of ATP breakdown
- different rates of contraction

isoform expression can change physiologically
- thyroxine (hyperthyroid) - increase alpha expression

67
Q

light chains

A

two pairs

  1. regulatory or phosphorylatable - regulates ATPase activity or myosin
  2. essential or alkali
    - stabalize structure (myosin head stability
    - no point of regulation
68
Q

alpha to alpha contractions

A

V1 fastest

69
Q

alpha beta contractions

A

V2 medium

70
Q

beta beta contractions

A

V3 slowest

BPK 305 (5 decks)

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