cardiac contractile elements Flashcards
primary role of the cardiovascular system
distribution of dissolved gases and other molecules for nutrition growth and repair
secondary roles of the cardiovascular system
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
arteries
away from heart
veins
to the heart
what kind of pump is the heart
4 chamber pump
dual pum
left is main
right is boost
what are the two circulations
pulmonary and systematic
systemic circulation
left side (aorta)
aorta is high pressure, vena cava is low
oxygenated aterial blood
multiple parallel paths
pulmonary circulation
de-oxygenated arterial blood
3 functional parts of the heart
heart
blood
vessels
what is blood flow driven by
constant pressure across variable resistance
left side of the heart
constant pressure generator
maintains steady mean arterial pressure at its exits (aorta)
parallel circuits in heart
parallel blood flow
less resistance in the blood, same amount of O2 to all organs
valves
movement is passive
orientation is responsible for unidirectional flow
what are the atrioventricular valves
tricuspid and mitral/bicuspid
what are the semilunar valves
pulmonic and aortic
pulmonic valve
located between right ventricle and pulmonary artery
consists of 3 cusps (anterior, right and left)
aortic valve
located between right ventricle and aorta
consists of 3 cusps (left, right, anterior)
mitral (bicuspid) valve
two cusps (anterior and posterior)
chordae tendineae cordis
attached to free edges of the valves
strong ligaments
prevent valves from becoming everted during ventricular systole
heart strings
papillary muscles
provide tension for chordae tendinae
left ventricle
more muscular
pumping blood against more resistance
endocardium
layers of epithelial and purkinji fibers
myocardium
95 percent cardiomyocytes by mass
- most of weight
epicardium
outside, outer
sympathetic nerves
fat, ready supply
pressure overload in cardiacmyocytes
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
volume overload
ie/ valve failure or aerobic exercise
- increased cell length up to 10-20%
- stretching contractile units - longer power strokes
z-line
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
I band
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
A band
contains thick myosin filaments
does not change with contraction
defined by length of myosin
anisotropic to polarized light
H-zone/ band
center of A band (myosin)
no overlapping thin filaments
changes size during contraction
M line
attachment for myosin
intercalated disk
combination of mechanical junctions and electrical junctions
communicating force and sharing electrical signals
sarcoplasmic reticulum
where calcium is stores and lots of mitochondria
internal network of membranes
fasicles
a bundle of this forms a muscle like the bicep
myofibrils
smallest unit of skeletal muscle
bundle of myofilaments - run along axis of the cell
a bundle of aligned muscle fibers forms a fasicles
what are the cardiomyocytes structural elements
contractile elements
t-tubules
mitochondria
SR
nucleus
golgi
ribosomes
contractile elements
50 percent of cell volume
t-tubules
invaginations
align with z-lines
mitochondria
30-45 percent of cell volume
subsarcolemmal
intermyofibrillar
nucleus
mono or binucleated
myocyte branching
provides longitudinal and diagonal coupling
coupled at intercalated disks
macula adherens
also called desmosomes
holds adjacent cells together
cytoskeleton proteins
physical coupling
share force from one cell to another
gap junction
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
connexon
central pores
hexamers
6 connexins/connexon
no coupling
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
coupling
= 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
titin
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
nebulin
extends along length of thin filament
from z line to thin filament ends
aligns thin filament
regulates thin filament length
actin
thin filament
helical
13 molecules (monomers) per turn
tropomyosin
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
what are the different types of troponin
TnT
TnC
Tnl
troponin
present on each tropomyosin dimer
influences position of tropomyosin molecule on the actin filament
3 subunits
TnT
tropomyosin binding
pushes tropomyosin away from the myosin binding site on actin and into the actin groove
TnC
calcium binding
promotes movement of tropomyosin on the actin filament that exposes tropomyosin binding sites on actin
facilitates actin-myosin interaction and therefore contraction
TnI
inhibitatory
moves away from actin/tropomyosin filament - allowing tropomyosin filament to move
binds actin
increase in calcium in cross-bridge cycling
allows for it to continue
triggers contraction by removing inhibition of cross-bridge cycling
decrease of calcium in cross bridge cycling
is the signal to decrease/relax cross-bridge cycling
achieved by removing a transporting calcium from sarcoplasm
what does calcium bind to in cross bridge cycling
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
rigor mortis
no more ATP - therefore crossbridges remained locked in rigid conformation of ADP-bound actomyosin
steps of cross-bridge cycling
- 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 - 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 - 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 - Pi is released. Myosin heads change conformation, resulting in the power stroke. The filaments slide past each other. Pulls actin filament toward myosin tail
- ADP is released
- last step of cycle and then it is repeated again
- actin-myosin complex is left in rigid state
ATP in cross bridge cycling
gives NRG for cycling
if unregulated this cycling would continue until myocytes is depleted of ATP
troponin C calcium binding sites
site 1: dysfunctional in cardiac muscle
site 2: binds calcium - initiated contraction
site 3 and 4: high affinity, always occupied
explain the steps after calcium binding to TnC
Tnl and tropomyosin move
exposed myosin binding site
crossbridge cycling
contraction
calcium tension relationship
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
myosin
thick filament
intertwined complex or proteins like thin filaments
heavy chains
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
light chains
two pairs
- regulatory or phosphorylatable - regulates ATPase activity or myosin
- essential or alkali
- stabalize structure (myosin head stability
- no point of regulation
alpha to alpha contractions
V1 fastest
alpha beta contractions
V2 medium
beta beta contractions
V3 slowest
