Molecular Mechanics Of Cardiac Contraction Flashcards
What are the main components of the myocardium?
Contractile tissue
Connective tissue
Fibrous frame
Specialised conduction system
What does the pumping action of the heart depend on?
Depends on interactions between the contractile proteins in its muscular walls.
What do the interactions between contractile proteins do?
The interactions transform the chemical energy derived from ATP into the mechanical work that moves blood under pressure from the great veins into the pulmonary artery, and from the pulmonary veins into the aorta.
What are contractile proteins activated by?
The contractile proteins are activated by a signalling process called excitation-contraction coupling.
When does excitation-contraction coupling begin?
Excitation-contraction coupling begins when the action potential depolarizes the cell and ends when ionized calcium (Ca2+) that appears within the cytosol binds to the Ca2+ receptor of the contractile apparatus.
Movement of Ca2+ into the cytosol is a passive (downhill) process mediated by Ca2+ channels.
When does the heart relax?
The heart relaxes when ion exchangers and pumps transport Ca2+ uphill, out of the cytosol.
Explain the working myocardial cell
Filled with cross-striated myofibrils.
Plasma membrane regulates excitation-contraction coupling and relaxation.
Plasma membrane separates the cytosol from extra-cellular space and sarcoplasmic reticulum.
Mitochondria: ATP, aerobic metabolism and oxidative phosphorylation.
What is myocardial metabolism?
Relies on free fatty acids during aerobic metabolism (efficient energy production)
During hypoxia, there is no FFA metabolism, thus anaerobic metabolism ensues. This relied on metabolising glucose (anaerobically) producing energy sufficient to maintain the survival of the affected muscle without contraction.
How are contractile proteins arranged?
Contractile proteins are arranged in a regular array of thick and thin filaments (The so called Myofibrils).
A-band: the region of the sarcomere occupied by the thick filaments.
I-band: is occupied only by thin filaments that extend toward the centre of the sarcomere from the Z-lines. It also contains tropomyosin and the troponins.
Z lines bisect each I-band.
What is the sarcomere?
The sarcomere: the functional unit of the contractile apparatus,
The sarcomere is defined as the region between a pair of Z-lines,
The sarcomere contains two half I-bands and one A-band.
What is the sarcoplasmic reticulum?
The sarcoplasmic reticulum is a membrane network that surrounds the contractile proteins
The sarcoplasmic reticulum consists of the sarcotubular network at the centre of the sarcomere and the subsarcolemmal cisternae (which abut the T-tubules and the sarcolemma).
What is the transverse tubular system?
The transverse tubular system (T-tubule) is lined by a membrane that is continuous with the sarcolemma, so that the lumen of the T-tubules carries the extracellular space toward the center of the myocardial cell.
Mitochondria
Explain a contraction
Sliding of actin over myosin by ATP hydrolysis through the action of ATPase in the head of the myosin molecule.
These heads form the crossbridges that interact with actin, after linkage between calcium and TnC, and deactivation of tropomyosin and TnI.
What is Myosin?
2 heavy chains, also responsible for the dual heads.
4 light chains.
The heads are perpendicular on the thick filament at rest, and bend towards the centre of the sarcomere during contraction (row.)
Alpha-myosin and Beta-myosin.
What is Actin?
Globular protein.
Double-stranded macromolecular helix (G).
Both form the F actin.
