Mechanisms of contraction of the heart Flashcards
What do gap junctions between intercalated discs do?
Provide physical connections that enable electrical signals to be passed from cell to cell
What is the contraction mechanism in the heart?
Sliding filament model
What are actin and myosin arranged into?
Myofibrils
Describe the actin I band molecule?
Globular actin molecules joined to form a helix - has a binding site for myosin head and coupled to troponin and tropomyosin at every 7th molecule
What is Troponin?
3 polypeptides T - tropomyosin, I - actin , C- calcium
How many Calcium ions need to bind to troponin for a conformational change to move tropomyosin?
4
Describe Myosin? A band
myosin II
2 identical heavy and light chains
Amino terminal - motor head
Carboxyl end - elongated tail forms alpha helix with 2nd heavy chain to make a dimer
What do dimers undergo?
Polymerisation
How is contraction achieved?
Through excitation -released calcium from SR - bind to Troponin C so myosin heads bind to actin binding site
How is muscle contraction driven?
ATP to ADP
How does cardiac muscle produce ATP?
aerobic oxidation of fatty acids, glucose lactic acid, AA and Ketones
How does cardiac muscle gain oxygen for ATP?
oxygen diffuses from blood pumped through coronary blood circulatory system at rest majority of atp from metabolism of fatty acids and glucose
What happens to heart during exercise?
use lactic acid to increase metabolism
How else does heart muscle produce ATP in regards to enzyme reaction?
Intracellular enxyme of Creatin Kinase CK - catalyses transfer of phosphate from creatin phosphate to ADP
How many mechanisms results in disturbances in cardiac rhythm? (dysrhythmia)
4 - delayed after depolarisation, re entry, abnormal pacemaker activity and heart block
What happens in delayed after depolarisation?
repetitive myocyte activity not driven by potentials arising from other cells - after normal AP and occurs due to intracellular calcium conc increasing normal range
What happens upon re-entry?
cardiac AP dies out in ventricles -unusual anatomical variations form a network of cells that form a conductive ring - also to slow conducting pathways of myocardial damage
What happens with abnormal pacemaker activity?
pacemaker elsewhere in the heart - ectopic pacemakers by excess sympthetic stimulation (caffeins hypoxia)
depolarisation results from ischemia from decreases sodium pump activity low RMP
What happens in heart block?
AV node electrically isolated
partial in every 2 to 3 atrial contractions the ventricle will contract independently
Sporadic total AV node block causes random unconsiousness
How is bradycardia treated?
Pacemaker systems
How is Tachycardia treated?
oblation procedures with range of drugs - block voltage sensitive sodium channels
B-adrenoreceptor antagonists
elongate refractory period
calcium channel blockers
