Physiology of Cardiac Function Flashcards
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.
Calcium release:
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
Inotropy
what part of the NS controls both rate and force of contraction
ANS
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.
Ca2+ Pumps:
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:
- 1 seconds–atrial systole
- 3 seconds–ventricular systole
- 4 seconds—diastole
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
5l/min
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.
