Biomedical subjects

A L Karimu

Publications and source records attributed to A L Karimu.

5 recordsLinked to original sources

PubMed1995

Human term placental capillary endothelial cell specialization: a morphometric study.

In the human placental capillary endothelium, two cell types have previously been described with different organelle distribution patterns. This observation was based on examination of cross-sectional profiles. It is known, however, that organelle distribution may vary in different parts of a cell. The present study was undertaken to estimate morphometrically the pattern of organelle distribution in normal term placental capillary endothelium. Ten normal term placentae were processed routinely for electron microscopy. The volume fractions of the different organelles were determined in both the perinuclear and peripheral parts of the cells. In addition, comparisons were made between endothelial cells at the site of vasculosyncytial membranes (VSM) and those forming the remainder of the capillary wall (non-VSM). Multifactor ANOVA showed there was a significant difference between the perinuclear and the peripheral parts in the volume fractions of mitochondria, rough endoplasmic reticulum, intermediate filaments, all these being more in the perinuclear region, whilst vesicles and cytosol were more prevalent in the peripheral parts. In contrast, there was no significant difference between the regions of VSM and the non-VSM except for the volume fractions of microfilaments which were higher in the non-VSM region.

Capillaries↗

PubMed1995

The distribution of microvilli over the villous surface of the normal human term placenta is homogenous.

The study was carried out to estimate stereologically whether regional differences exist in the distribution of microvilli between vasculo-syncytial (VSM) and non-vasculo-syncytial (non-VSM) areas of the villous surface in normal term placenta. In ten placentae a normal lobe was perfusion-fixed at a pressure of 60 mm Hg, and the intervillous space was perfused at 10 mm Hg. The tissue was routinely processed for ultrastructural examination. Stereological estimates relating to the length and diameter of microvilli, and to the villous surface amplification factor in adjacent but contrasting (VSM and non-VSM) regions, were obtained. A paired "t' test showed no significant difference in the villous surface amplification factor between the two regions (5.18 +/- 0.54 and 5.22 +/- 0.54 respectively, mean +/- s.e.m. P > 0.05). In addition, there were no significant differences between the length and diameter of microvilli in both regions (P > 0.05 in both). The results confirm that the normal term placenta has a continuous and even covering of microvilli over the syncytium.

Female↗

PubMed1994

The effects of maternal vascular pressure on the dimensions of the placental capillaries.

OBJECTIVE: The study sought stereological evidence for the sluice flow phenomenon in the human term placenta. DESIGN: Two series of experiments were conducted on caesarean delivered placentae. In both, two fetal arteries were cannulated and perfused. In the first series, five placentae were perfusion-fixed under arterial pressures of 40 mmHg and 60 mmHg, and an external pressure of 10 mmHg in the intervillous space. In the second series, five placentae were perfusion-fixed at arterial pressures of 70 mmHg and 90 mmHg with an external pressure of 30 mmHg. Stereological estimates relating to the size of the capillaries and the thickness of the villous membrane were then made. RESULTS: In each series, as the arterial pressure rose, there was an increase in the volume fraction and surface area of the fetal capillaries, and a concomitant decrease in the mean thickness of the villous membrane. These changes were negated as the external pressure rose, indicating the importance of the pressure differential between the capillary lumen and the intervillous space in determining the dimensions of the fetal capillaries. CONCLUSIONS: The study demonstrated that placental capillaries are elastic and hence deformable. If a sufficiently high pressure is generated in the intervillous space, they may therefore be compressed. This may explain the increase in umbilical vascular resistance demonstrated by doppler studies in pregnant women scanned in the supine position. In this situation the venous drainage from the intervillous space is believed to be impeded by the gravid uterus compressing the inferior vena cava.

Arteries↗

PubMed1994

Significance of changes in fetal perfusion pressure to factors controlling angiogenesis in the human term placenta.

The objective of the study was to determine the effects of mechanical factors on endothelial proliferation in the human placental villous vasculature. Individual fetal lobules were perfused with tissue culture medium at two different standard pressures (40 and 100 mm Hg). The perfused area was then removed and diced into small blocks which were quench frozen in liquid nitrogen. Cryostat sections were obtained and fixed in acetone at 4 degrees C. Proliferating cell nuclear antigen was then identified using Ki67 antibody as a marker. Proliferating nuclei were scored, using a light microscope, and a comparison made between the two pressures used. More proliferating endothelial nuclei were found at 100 mm Hg than at 40 mm Hg (P < 0.05). It is therefore concluded that mechanical factors may play a role in villous angiogenesis and the formation of terminal villi.

Blood Vessels↗

PubMed1993

Star volume estimates of the intervillous clefts in the human placenta: how changes in umbilical arterial pressure might influence the maternal placental circulation.

The study estimated the mean volume of the clefts between adjacent villi in the normal term human placenta, and the effect on this of increasing the fetal perfusion pressure, using a new stereological tool called the 'star volume estimator'. This enables the measurement of irregular and complex structures, including both particles and cavities, in a mathematically defined and unbiased manner. To achieve this, a total of ten term placentae delivered by caesarean section were obtained. Four fetal arteries supplying opposite quadrants of the placental disc were perfusion-fixed under standard pressures of 40, 60, 80 and 100 mmHg respectively. Stereological estimates relating to the star volume of the clefts between the villi, and to the volume density of the intervillous space were obtained. There was a significant rise in the star volume of the intervillous clefts from 26.8 x 10(4) m3 at 40 mm Hg to 75.1 x 10(4) m3 at 100 mmHg (F = 75, df = 1.38, P < 0.05). The volume density of the intervillous space remained unchanged, thus obviating the possibility of fluid leakage into the intervillous space accounting for this change. It is concluded that the fetal vasculature provides hydraulic support to the villous tree, and that changes in the umbilical perfusion pressure can therefore alter the disposition of the villi within the intervillous space. As fetal blood pressure rises, for example during acute hypoxic episodes, the villi will move apart. The enlargement of the clefts between adjacent villi will have a secondary effect upon the maternal circulation, promoting more even perfusion of the intervillous space at higher overall flow rates.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Pressure↗