Myocardial capillaries in the fetal and the neonatal rat: A morphometric analysis of the maturing myocardial capillary bed

G. A. Porter, Patrick Bankston

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Abstract

Developing myocardial capillaries from 16-day-gestation fetus to adult undergo several morphological changes including a thinning of the lateral extensions of the capillary endothelial cells, the formation of a basal lamina, and an increase in the number of plasmalemmal vesicles. A decrease in the extracellular space, an increase in the number of capillaries, and a decrease in the capillary diameter were also observed during the developmental period. In view of these ultrastructural changes, a morphometric analysis was made on the developing myocardial wall to demonstrate specific quantitative changes. The volumes which were occupied by capillary endothelial cells, capillary lumina, extracellular space, and myocardial myocytes within a reference volume of myocardium were measured; and we found that 8% of the reference myocardial volume was occupied by capillary endothelial cells, 85% was occupied by myocardial myocytes, 4% was occupied by capillary lumina, and, except for a significant change in extracellular space at 16 days gestation, 3% was occupied by extracellular space. Each volume ratio was found to be nearly constant throughout the studied period. In contrast to this constancy in the volume ratios, other parameters which were measured demonstrated significant changes during the developmental period studied. These overall changes include a 135% increase in capillary density, a 63% increase in luminal surface area of capillary endothelial cells, a 24% decrease in capillary diameter, a 12% decrease in diffusion distance, and a 35% decrease in the diameter of the erythrocyte population. The decrease in capillary diameter occurs concomitantly with and may be correlated to the decrease in erythrocyte diameter. Also, the increasing number of capillaries offset the effect of the decrease in capillary diameter, resulting in constant volume ratios. This constancy in the volumes of the measured myocardial compartments during development, despite the considerable changes in morphology and in the other measured parameters which are occurring in the myocardial wall, can be interpreted to mean that some functional constraints are operating to maintain capillary-to-myocardium volume ratios within very narrow limits.

Original languageEnglish
Pages (from-to)108-115
Number of pages8
JournalAmerican Journal of Anatomy
Volume179
Issue number2
StatePublished - 1987

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Extracellular Space
Endothelial Cells
Erythrocyte Indices
Muscle Cells
Myocardium
Pregnancy
Basement Membrane
Fetus
Population

ASJC Scopus subject areas

  • Anatomy

Cite this

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title = "Myocardial capillaries in the fetal and the neonatal rat: A morphometric analysis of the maturing myocardial capillary bed",
abstract = "Developing myocardial capillaries from 16-day-gestation fetus to adult undergo several morphological changes including a thinning of the lateral extensions of the capillary endothelial cells, the formation of a basal lamina, and an increase in the number of plasmalemmal vesicles. A decrease in the extracellular space, an increase in the number of capillaries, and a decrease in the capillary diameter were also observed during the developmental period. In view of these ultrastructural changes, a morphometric analysis was made on the developing myocardial wall to demonstrate specific quantitative changes. The volumes which were occupied by capillary endothelial cells, capillary lumina, extracellular space, and myocardial myocytes within a reference volume of myocardium were measured; and we found that 8{\%} of the reference myocardial volume was occupied by capillary endothelial cells, 85{\%} was occupied by myocardial myocytes, 4{\%} was occupied by capillary lumina, and, except for a significant change in extracellular space at 16 days gestation, 3{\%} was occupied by extracellular space. Each volume ratio was found to be nearly constant throughout the studied period. In contrast to this constancy in the volume ratios, other parameters which were measured demonstrated significant changes during the developmental period studied. These overall changes include a 135{\%} increase in capillary density, a 63{\%} increase in luminal surface area of capillary endothelial cells, a 24{\%} decrease in capillary diameter, a 12{\%} decrease in diffusion distance, and a 35{\%} decrease in the diameter of the erythrocyte population. The decrease in capillary diameter occurs concomitantly with and may be correlated to the decrease in erythrocyte diameter. Also, the increasing number of capillaries offset the effect of the decrease in capillary diameter, resulting in constant volume ratios. This constancy in the volumes of the measured myocardial compartments during development, despite the considerable changes in morphology and in the other measured parameters which are occurring in the myocardial wall, can be interpreted to mean that some functional constraints are operating to maintain capillary-to-myocardium volume ratios within very narrow limits.",
author = "Porter, {G. A.} and Patrick Bankston",
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T1 - Myocardial capillaries in the fetal and the neonatal rat

T2 - A morphometric analysis of the maturing myocardial capillary bed

AU - Porter, G. A.

AU - Bankston, Patrick

PY - 1987

Y1 - 1987

N2 - Developing myocardial capillaries from 16-day-gestation fetus to adult undergo several morphological changes including a thinning of the lateral extensions of the capillary endothelial cells, the formation of a basal lamina, and an increase in the number of plasmalemmal vesicles. A decrease in the extracellular space, an increase in the number of capillaries, and a decrease in the capillary diameter were also observed during the developmental period. In view of these ultrastructural changes, a morphometric analysis was made on the developing myocardial wall to demonstrate specific quantitative changes. The volumes which were occupied by capillary endothelial cells, capillary lumina, extracellular space, and myocardial myocytes within a reference volume of myocardium were measured; and we found that 8% of the reference myocardial volume was occupied by capillary endothelial cells, 85% was occupied by myocardial myocytes, 4% was occupied by capillary lumina, and, except for a significant change in extracellular space at 16 days gestation, 3% was occupied by extracellular space. Each volume ratio was found to be nearly constant throughout the studied period. In contrast to this constancy in the volume ratios, other parameters which were measured demonstrated significant changes during the developmental period studied. These overall changes include a 135% increase in capillary density, a 63% increase in luminal surface area of capillary endothelial cells, a 24% decrease in capillary diameter, a 12% decrease in diffusion distance, and a 35% decrease in the diameter of the erythrocyte population. The decrease in capillary diameter occurs concomitantly with and may be correlated to the decrease in erythrocyte diameter. Also, the increasing number of capillaries offset the effect of the decrease in capillary diameter, resulting in constant volume ratios. This constancy in the volumes of the measured myocardial compartments during development, despite the considerable changes in morphology and in the other measured parameters which are occurring in the myocardial wall, can be interpreted to mean that some functional constraints are operating to maintain capillary-to-myocardium volume ratios within very narrow limits.

AB - Developing myocardial capillaries from 16-day-gestation fetus to adult undergo several morphological changes including a thinning of the lateral extensions of the capillary endothelial cells, the formation of a basal lamina, and an increase in the number of plasmalemmal vesicles. A decrease in the extracellular space, an increase in the number of capillaries, and a decrease in the capillary diameter were also observed during the developmental period. In view of these ultrastructural changes, a morphometric analysis was made on the developing myocardial wall to demonstrate specific quantitative changes. The volumes which were occupied by capillary endothelial cells, capillary lumina, extracellular space, and myocardial myocytes within a reference volume of myocardium were measured; and we found that 8% of the reference myocardial volume was occupied by capillary endothelial cells, 85% was occupied by myocardial myocytes, 4% was occupied by capillary lumina, and, except for a significant change in extracellular space at 16 days gestation, 3% was occupied by extracellular space. Each volume ratio was found to be nearly constant throughout the studied period. In contrast to this constancy in the volume ratios, other parameters which were measured demonstrated significant changes during the developmental period studied. These overall changes include a 135% increase in capillary density, a 63% increase in luminal surface area of capillary endothelial cells, a 24% decrease in capillary diameter, a 12% decrease in diffusion distance, and a 35% decrease in the diameter of the erythrocyte population. The decrease in capillary diameter occurs concomitantly with and may be correlated to the decrease in erythrocyte diameter. Also, the increasing number of capillaries offset the effect of the decrease in capillary diameter, resulting in constant volume ratios. This constancy in the volumes of the measured myocardial compartments during development, despite the considerable changes in morphology and in the other measured parameters which are occurring in the myocardial wall, can be interpreted to mean that some functional constraints are operating to maintain capillary-to-myocardium volume ratios within very narrow limits.

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