Early Development, Devel. Physiol., Dr. D. Penney
Table 2.02 - How Early Heart Growth Is Controlled:
Intrinsic factors not related to functional demands.
A. Synthesis of contractile machinery - not dependent upon presence of hemodynamic forces.
B. Looping - linear tube to "C" shape:
- Therefore, not dependent on hemodynamic forces (high K+ stops heart beat, but not morphogenesis).
- Critical mass of myofibrils required (e.g. inhibition by cycloheximide).
- {conclusion: morphogenesis is due to intrinsic properties of heart itself!}
Extrinsic factors which can be related to functional demands.
- C. Post-looping:
- Decreased inflow of blood thru atrioventricular canal results in abnormally small LA and ventricle (hypoplasia); modification of aorta by selective occlusion of aortic arches.
- {conclusion: embryogenesis after looping is affected by hemodynamic forces!}
- D. Postnatal:
- Pressures, ie. workload of RV & LV about equal before birth; increased total systemic peripheral resistance post-birth results in faster growth of LV relative to RV.
- Increased workload on either ventricle results in compensatory hypertrophy, either normal or abnormal growth.
- Therefore, dependent on hemodynamic forces.
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