Cardiac Contractile Elements Flashcards
What is the mitral (bicuspid) valve between?
Left atrium and left ventricle
Where is the tricuspid valve located
Between the right atrium and right ventricle
What are the layers of the ventricular wall
Ventricular cavity—> endocardium (thinnest)—>myocardium (thick)—>epicardium (outer)
What layer of cells makes up most of the cardiomyocytes
Myocardium. 95% of mass
What is the shape of adult cardiomyocyte (and size)
Rectangular
120-150 micro m long. 10-20 micro m wide
What are the ways cardiomyocytes can be overloaded
Pressure overload
Volume overload
How does pressure overload effect the cardiomyocytes
Increase cell width 2-3 fold. Causes more parallel contractile units
think wider = more in line
How does volume overload effect cardiomyocytes
Increase cell length up to 10-20%. Causes stretching of contractile units to make them longer
Which sarcomere sections shorten during contraction
I band (actin) and H zone (myosin)
Which section doesn’t change during sarcomere contraction
A band
What is between cardiac cells
A cleft that allows blood flow through capillaries
What are the 7 structural elements of a cardiomyocyte?
-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
What are the types of coupling between cardiomyocytes
Physical coupling- desmosomes aka macula adherens. Have cytoskeletal proteins.
Electrical coupling- gap junctions aka nexus. Have connexins (protein)
Where are neighbouring cardiomyocytes coupled?
Intercalated disks
What is a functional syncytium
cardiomyocytes work together to performed coordinated contraction. This is possible because they have both physical and electrical coupling no coupling = no functional syncytium
What makes up a gap junction
2 connexons per gap junction
1 connexon is a hexamer of six connexins
Do gap junctions regulate what can go through
Yes. Regulated permeability. Ex- by acidosis
Function of Titin
-Stabilizes position of contractile elements
-Returns stretched muscle to resting length
Is titin paired with thin or thick filaments? Where else is it connected?
Myosin
From M line to Z line (half of sarcomere)
Function of nebulin
Aligns thin filament
Is nebulin paired with thin or thick filament? What else is it connected to?
Actin
Z line to thin filament ends
What are the components of the thin filament
Actin filaments- helical, 13 mcs per turn
Tropomyosin- lies near actin groove
Troponin complex (Tn)
- TnT: tropomyosin binding
- TnC: Ca2+ binding
- TnI: inhibitory
Cross-bridge cycling: what stage is ATP added, ATP hydrolyzed, Pi released, ADP released
ATP added- release myosin head from actin
ATP hydrolyzed- cock myosin head
Pi released- power stroke
ADP released- myosin attached to actin
How much Ca is needed for 50% force generation
1 microM
Where does Ca bind on the thin filament
Troponin C (known as the calcium sensor)
How many binding sites does troponin C have? And name their role
- Site I- dysfunctional in cardiac muscle
Site II- initiates contraction
Site III and IV- high affinity so always occupied
Role of tropomyosin
Block myosin from binding to actin
Name troponin complex parts and their roles
TnT- binds tropomyosin
TnC- binds calcium
TnI- binds actin
How many calcium molecules bind to troponin complex in cardiac vs skeletal
Cardiac- 1
Skeletal- 2
What are the components of myosin
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))
What are the three isoforms of the thick filament heavy chains
Alpha-alpha (fastest) -mouse
Alpha-beta
Beta-beta (slowest) -elephant
humans have more beta
Thyroxine promotes alpha expression
