Flashcards in Physiology of Cardiac Function Deck (25):
structure of myosin
Each myosin molecule contains 2 heads that contain myosin ATPase.
Each thick filament surrounded by 6 thin filaments.
what is hydrolysis of ATP needed for
Hydrolysis of ATP is necessary to allow actin & myosin to interact-forming a cross-bridge.
Cross –bridge formation & cycling leads to an increase in overlap & contraction.
structure of actin
Composed of Actin-a globular protein, forming 2 helical strands.
Between the 2 strands are rod-shaped proteins called tropomyosin.
Attached to tropomyosin at regular intervals is Troponin regulatory complex.
what is tropoinin complez made up
composed of 3 subunits:
Troponin-T (TN-T)-attaches to tropomyosin;
Troponin-C (TN-C) -binding site for Ca2+ ions that are released from sacroplasmic reticulum which triggers contraction process;
Troponin –I (TN-I)-which inhibits myosin binding to actin.
Assays for cardiac TN-T & TN-I are released into circulation & used as biomarkers for cardiac damage.
what is excitation contraction coupling
A process where an action potential triggers a myocyte to contract.
what is relaxation
When pumps run faster [Ca2+]i drops to resting level (0.1µmol/L) more quickly.
Rapid decrease in sarcoplasmic [Ca2+] allows contractile machinery to relax faster-this prolongs time available for ventricular filling during HR increases.
When SR pumps faster, more Ca2+ stored in SR, less is returned to extracellular space compared to previously.
Stocking stores with additional Ca2+ makes more available for release on next contraction-so contractile force increases as a result.
Affinity for Calcium:
Binding affinity of TN-C for Ca2+ influences lusitropy.
Ca2+ binding to TN-C modulated by PKA phosphorylation of TN-I.
This increases Ca2+ dissociation from TN-C & increases relaxation.
β-adrenoceptor stimulation leads to increased lusitropy.
This related in part to TN-I phosphorylation.
what is regulation onf contraction known as
what part of the NS controls both rate and force of contraction
what NT does the Sympathetic NS release
NA & AD
Regulation of Contraction
Sympathetic Activation release of NA & AD
Ca2+ Channels open & trigger flux of Ca2+ enters & induces Ca2+ release from SR, so-called Calcium Induced Calcium Release; Ca2+ binds to troponin C (Tn-C) cross-bridge cycling.
Relaxation (Lusitropy) relies on 2 transporters to remove Ca2+ from sarcoplasm:
1.Sarcoendoplasmic reticulum calcium ATPase(SERCA) returns Ca2+ to SR.
2. Na+-Ca2+ exchanger in sarcolemma transports Ca2+ out of cell.
where is the SAN positioned
positioned on the wall of the right atrium near the entrance of the superior vena cava
The Cardiac Cycle
A sequence of mechanical events occurs during single heartbeat.
Generation of an AP from SAN triggers cardiac cycle.
This consists of alternating periods of contraction (Systole) & relaxation (Diastole).
Duration normally lasts 0.8s at a Heart rate of 75beats/min:
0.1 seconds--atrial systole
0.3 seconds--ventricular systole
Blood flows along a pressure gradient (from High pressure to Low pressure).
One way valves restrict direction of flow.
what is cardiac output
HR X SV
what CO at rest
what happens to CO during exercise
During exercise, CO can 5 -6 fold. Initially due to an in both HR & SV, but at high CO, it is due to HR.
Volume of blood pumped from one ventricle each minute.
what is SV
Stroke Volume is Volume ejected by each ventricle during each contraction.
formula for SV
what is EDV
Total amount of blood filling ventricles at end of diastole called the End Diastolic Volume
what is ESV
Volume remaining in ventricles at end of a contraction is called End Systolic Volume
what is EF
Fraction of EDV ejected out by each ventricle/beat
what is normal EF in healthy individuals
Normal EF is 55%-75%
what does it mean if EF is less than 50
Reduced EF (<50%) seen in for e.g. in heart failure
what is EF a measure of?