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Biomedical subjects

F C Voon

Publications and source records attributed to F C Voon.

14 recordsLinked to original sources
PubMed1991

The effects of retinoic acid on heart formation in the early chick embryo.

The vitamin A derivative retinoic acid has previously been shown to have teratogenic effects on heart development in mammalian embryos. The craniomedial migration of the precardiac mesoderm during the early stages of heart formation is thought to depend on a gradient of extracellular fibronectin associated with the underlying endoderm. Here, the effects of retinoic acid on migration of the precardiac mesoderm have been investigated in the early chick embryo. When applied to the whole embryo in culture, the retinoid inhibits the craniomedial migration of the precardiac mesoderm resulting in a heart tube that is stunted cranially, while normal or enlarged caudally. Similarly, a local application of retinoic acid to the heart-forming area disrupts the formation of the cardiogenic crescent and the subsequent development of a single mid-line heart tube. This effect is analogous to removing a segment of endoderm and mesoderm across the heart-forming area and results in various degrees of cardia bifida. At higher concentrations of retinoic acid and earlier developmental stages, two completely separate hearts are produced, while at lower concentrations and later stages there are partial bifurcations. The controls, in which the identical operation is carried out except that dimethyl sulphoxide (DMSO) is used instead of the retinoid, are almost all normal. We propose that one of the teratogenic effects of retinoic acid on the heart is to disrupt the interaction between precardiac cells and the extracellular matrix thus inhibiting their directed migration on the endodermal substratum.

Animals↗
PubMed1990

Unusual variant of right paraduodenal hernia.

An unusual case of internal hernia was encountered. Its clinical features, radiological investigation and anatomical findings at operation were discussed in relation to right paraduodenal hernia. Embryological consideration supported the view that this was, in fact, a variant of right paraduodenal hernia. No identical case has been reported in the literature.

Adult↗
PubMed1990

The integration of knowledge through interactive Computer-Enhanced Learning in medicine.

Rapid advances in Information Technology in recent years have provided powerful computers and software that can be innovatively applied to create powerful pedagogical courseware that go beyond what precursors like the PLATO project could do on the mainframes of yesteryear. This article focusses on the research and development that we have carried out which is applicable to the whole area of education (including medical education). It introduces the elements of hypertext, hypermedia and the pedagogical user interface. It illustrates the principles necessary for the communication of conceptual, functional and structural knowledge. It emphasises the key aspect of mastery of Information Technology necessary for a new dimension in Computer-Enhanced Learning that will be of relevance to the Information Society of the 21st century.

Computer-Assisted Instruction↗
PubMed1990

The effective learning of spatio temporal concepts of human structure.

The recent availability of increasingly powerful and user friendly computers is making a noticeable impact in the field of medical education. Over the past year, the power of the computer is being harnessed here in the field of anatomy to enable medical and dental students to learn the subject more effectively. Machines with excellent graphics, text and animation capabilities have made it possible to allow students to comprehend structural complexity as seen in gross anatomy or, temporal alterations of structure as seen in embryology by the use of computer based, tutorial style or self paced interactive style of learning. Positive student response to sample learning packages has encouraged the undertaking of courseware development for future use at computer workstations.

Anatomy↗
PubMed1990

Hypertext-based enhancement of medical and dental undergraduate learning.

The use of the microcomputer in medical education began about 1977. Since then man computer-assisted learning packages have been developed for preclinical and clinical subjects. The experiences of the authors with the Macintosh microcomputer in the development of courseware and tutorware on some aspects of Anatomy in the Department of Anatomy of the National University of Singapore are shared in the present paper. It describes how textual and instructive material can be prepared along with graphics support using a software called HYPERCARD (Apple Inc.). Elementary levels of animation can also be achieved. In this way it illustrates how a study of Anatomy, for example, can be made using the computer to "dissect" the human body.

Anatomy↗
PubMed1989

Computer-enhanced learning in neuroanatomy.

The recent development of powerful microcomputers and the introduction of object-oriented programming languages has now made available to educationists software that can be easily used to design and develop computer-based learning material. We have developed courseware and tutorware in the field of neuroanatomy which are pedagogically structured and yet provide multiple paths of learning for the individual student. Neuroanatomy is a difficult subject to learn because of the structural intricacy and functional correlations that it entails. The courseware enables students to approach the subject at different levels of difficulty and progress at their own pace towards a comprehensive understanding of structure and function aided by text integrated with graphics, sound and animation. A significant advantage to authors of similar courseware is the option to update the contents easily when necessary in the future.

Computer-Assisted Instruction↗
PubMed1986

A simulation approach to understanding the masticatory process.

An analysis of the reduction of food particle sizes during human mastication is presented in terms of the probability of a particle being broken (selection function) and the distribution of fragment sizes produced when it fails (breakage function). Both selection and breakage functions are defined and a general equation produced. Several feasible behaviours for these two variables that have been suggested in the literature are modelled by computer simulation and the results are compared to published breakdown patterns. The conclusions are that selection and breakage functions probably behave very simply with respect to particle size, and that these behaviours could be deduced from an analysis of food particle size distributions and the rate at which particle sizes are reduced per chew.

Computers↗
PubMed1986

Food breakdown patterns produced by human subjects possessing artificial and natural teeth.

The abilities of thirty-two complete denture wearers and thirty-two dentate subjects to break down raw carrot particles were compared. The particle size distributions produced were broader in those subjects that broke down food rapidly per chew and, conversely, narrower in those that were slower. This did not appear to depend on dental status. An analysis of mastication as composed of two separable processes, one describing the means by which particles come to be broken (selection) and the other, the size distributions of a particle upon fracturing (breakage), indicated that both processes were variable. It is concluded that no qualitative differences in the manner by which the two groups reduce food is apparent. To support this, a small study on dentate subjects suggests the covering of the palatal mucosa with an acrylic plate does not affect masticatory performance.

Adult↗
PubMed1985

Muscular dystrophy in the duck.

Clinical and gross anatomy features of myopathic ducks are reported. Light microscopic examination of the leg muscles showed necrosis, degeneration and inflammation, and some degree of regeneration was also observed. There was infiltration and replacement of muscle fibres with fibrous tissue. Electron microscopy showed the early stages of myofilament dissolution and accumulation of glycogen in the presynaptic terminal of the neuromuscular junction.

Animals↗
PubMed1985

Epiplexus cells in the embryos of the turtle, Trionyx sinensis.

The epiplexus cells in the embryos of the turtle, Trionyx sinensis were examined in scanning and transmission electron microscopy. Although the cells showed diverse morphological forms, the majority of the cells however had a stellate cell body each with 3-5 radiating long processes with secondary processes terminating on the ventricular surface of the choroid epithelial cells. The cell body was relatively smooth. Occasional epiplexus cells displayed blebs on their cell bodies and processes. In the transmission electron microscope, the nucleus contained coarse chromatin clumps. The cytoplasm was endowed with large lysosomal bodies. Based on these observations, it is suggested the epiplexus cells in the turtle embryos are phagocytic even though most of them probably are at the resting stage.

Animals↗
PubMed1983

The ultrastructure of polygonal networks in chick embryonic cells in vitro.

Polygonal networks in cultured chick endoderm cells are ordered arrays of actin microfilaments situated just beneath the dorsal cell surface. Each strut is formed from a bundle of microfilaments and 5-7 bundles intersect at each node. Dense bodies are seen in nodes and some struts. At its periphery the network is attached to the substrate at the termini of long radial struts. Most of the network is resistant to detergent extraction. Sliding microfilaments can explain the observed behaviour of networks in live cells.

Animals↗
PubMed1983

Isolation and culture of amoeboid microglial cells from the corpus callosum and cavum septum pellucidum in postnatal rats.

In phase contrast and scanning electron microscopy, diverse structural forms of cells tenaciously adherent to glass coverslips were observed in the culture of the corpus callosum and cavum septum pellucidum from postnatal rats. In day 1 culture, many of the cultured cells were round, with well spread peripheral cytoplasm which appeared homogeneous. Cell organelles aggregated mainly around the reniform or round nucleus. Some cells showed spinous projections. In day 3-5 culture, the cells became irregular, sending out long branching pseudopodial processes; often they displayed a vacuolated cytoplasm. The cultured cells were highly phagocytic, as shown by their uptake of colloidal carbon particles and latex beads, in light microscopy and scanning electron microscopy, respectively. Cytochemical studies have shown that the cells were peroxidase-negative but were strongly positive for non-specific esterase, similar to the amoeboid microglial cells in the postnatal corpus callosum. On the basis of their structural features, both in phase contrast and scanning electron microscopy, experimental as well as cytochemical properties, it is concluded that the cells in the present culture are in fact amoeboid microglial cells which are active macrophages in the developing corpus callosum.

Animals↗
PubMed1981

Polygonal networks in living chick embryonic cells.

Regular polygonal networks have been found in explants and dissociated cells of early chick embryos. These networks are readily observable in live cells with phase-contrast optics thus allowing time-lapse cinemicroscopy. They consisted of a regular pattern of nodes and radiating struts found predominantly in the lamelliplasm of the free edges of the cells bordering explants. At the outer edge, the network was terminated by radial struts associated with substrate-attached retraction processes whilst toward the centre of the cells it faded out. The network was also associated with stress fibres running across the cell and with microextensions on the dorsal surface. Even within one cell the network varied in size. Time-lapse films showed that microvilli were protruded from the dorsal surface over the nodes. Although the cells containing the networks were poorly motile the network itself was a mobile structure. Many explants from regions differing in prospective fates developed these networks after 2-4 days in culture. They appeared earlier in the smaller less yolky cells of definitive endoblast and epiblast. Experiments with dissociated and reaggregated cells confirmed their occurrence mainly in free edges of cells. The relationship between these networks seen in living chick embryo cells and those seen in other cell types using immunofluorescent techniques is discussed and a mechanism is proposed for their formation.

Animals↗