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Biomedical subjects

P W Tank

Publications and source records attributed to P W Tank.

17 recordsLinked to original sources
PubMed1996

Assessing clinical skills of medical students.

The clinical skills of sophomore medical students at the University of Arkansas are being assessed through the use of the Objective Structured Clinical Examination (OSCE). This exam was developed in order to better standardize the evaluation of practical clinical skills. The exam uses standardized patients, who are lay people trained to accurately and consistently portray a patient encounter. Faculty members at UAMS authored clinical cases for 20 patient encounters that test history taking, physical examination and communication skills. Each student interacts with the patient while being assessed in a standardized way, and then is given educational feedback by a faculty member. Students who do not pass the exam, undergo a remediation program prior to entering the junior year.

Arkansas↗
PubMed1989

Cellular contribution to symmetrical forelimbs from triploid-marked "polarizing region" in the embryo of axolotl, Ambystoma mexicanum.

Grafts of posterior tissue placed anterior to the limb bud in the salamander embryo exert a polarizing influence. To explain this result, the idea that the anteroposterior axis of the developing forelimb is polarized by a diffusible morphogen has been proposed. An alternative hypothesis, and the working hypothesis of the present study, is that the polarization of the developing salamander forelimb is accomplished by short-range cellular interactions resulting in intercalation rather than by the more global influence of a diffusible morphogen. One prediction of this intercalation hypothesis is that cells will be contributed to the limb from the "polarizing tissue." To test this idea, grafts of triploid marked polarizing tissue were implanted anterior to the limb bud in 82 diploid axolotl embryos at stages 32-34 of development. A total of 27 (33%) of the limbs that resulted were symmetrical and ranged in complexity from one to seven digits. Histological analysis of a subgroup of the original symmetrical limbs revealed that mesodermally derived tissues in the anterior side of these limbs (the side which formed as a duplication in response to the influence of the graft) contained high percentages of trinucleolate cells (muscle, 12.1%; connective tissue tissue, 12.5%; and cartilage, 13.4%) when compared to similar tissues in the posterior side of the same symmetrical limbs (muscle, 1.8%; connective tissue , 0.7%; and cartilage, 0.6%). When symmetrical limbs were amputated, 73% regenerated symmetrical limbs. When these regenerated limbs were again amputated, 63% formed symmetrical secondary regenerates. Histological analysis of the first generation of regenerated limbs revealed that the pattern of distribution of trinucleolate cells in each regenerate was similar to the pattern seen in the original symmetrical limb. These results indicate that there is considerable cellular contribution to the anterior side of the symmetrical forelimb from the mesoderm of grafted "polarizing tissue." This result supports the idea that short-range cellular interaction are sufficient for formation of symmetrical forelimbs in salamander embryos.

Ambystoma↗
PubMed1985

Cellular behavior in the anteroposterior axis of the regenerating forelimb of the axolotl, Ambystoma mexicanum.

Cellular behavior along the anteroposterior axis of the regenerating axolotl forelimb was studied by use of triploid (3N) tissue grafted into diploid (2N) hosts and three-dimensional computer reconstructions. Asymmetrical upper forelimbs were surgically constructed with one half (anterior or posterior) 3N and the other half 2N. Limbs were amputated immediately after grafting or were permitted to heal for 5 or 30 days prior to amputation. When regenerates had attained the stage of digital outgrowth, the limbs were harvested and sectioned in the transverse axis for histological analysis. When all limbs bearing anterior grafts were considered as a group, 77% of the 3N mesodermal cells were observed in the anterior side of the regenerates and 23% were located in the posterior side of the regenerates. When all limbs bearing posterior grafts were considered as a group, 76% of the 3N mesodermal cells were found in the posterior side of the regenerate and 24% had crossed into the anterior side. Healing times of 0, 5, or 30 days prior to amputation had no effect on the experimental outcome. Three-dimensional computer reconstructions revealed that most 3N cells of mesodermal origin underwent short-distance migration from anterior to posterior or from posterior to anterior and intermixed with diploid mesodermal cells near the midpoint of the regenerated anteroposterior axis. Some 3N cells were observed at greater distances from the graft-host interface. By contrast, labeled epidermal cells from both anterior and posterior grafts exhibited long-distance migration across all surfaces of regenerated limbs. Details of a computer-assisted reconstructive method for studying the three-dimensional distribution of labeled cells in tissues are presented.

Ambystoma mexicanum↗
PubMed1983

Pattern regulation in the anterior half of the embryonically produced symmetrical forelimb of the axolotl, Ambystoma mexicanum.

Symmetrical forelimbs were created in the axoltl by performing surgery on embryos at stages 32-34. The technique of J.M.W. Slack (J. Embryol. Exp. Morphol., 39:151-168, 1977) was utilized. Several experiments were then performed to test the ability of these symmetrical forelimbs to participate in pattern formation. When symmetrical limbs were amputated without previous surgery, 58% failed to regenerate. When symmetrical limbs were wounded in the plane of symmetry and permitted to heal for 30 days prior to amputation, 75% failed to regenerate. When the anterior half of the symmetrical limb was exchanged with the posterior half of the contralateral forelimb followed by amputation 30 days later, both limbs failed to regenerate. When the anterior half of the symmetrical limb was exchanged with the anterior half of an asymmetrical limb followed by amputation 30 days later, the previously symmetrical limbs regenerated asymmetrical hands, and previously asymmetrical limbs failed to regenerate. These results indicate that wounding increases the occurrence of regenerative failure in embryonically produced symmetrical forelimbs. The anterior half of the embryonically produced symmetrical forelimb behaves unpredictably and in a manner not easily described with any of the current models of pattern regulation. The posterior half of the embryonically produced symmetrical forelimb behaves predictably during pattern formation.

Ambystoma mexicanum↗
PubMed1982

Pattern regulation during regeneration of embryonically produced symmetrical forelimbs in the axolotl, ambystoma mexicanum.

Embryonic axolotls (Stages 32-34) underwent surgery during which a graft of flank tissue was transferred from a donor animal to the anterior margin of the forelimb field in a host animal. Double-posterior forelimbs containing from one to eight digits developed. These limbs were amputated at a level proximal to the elbow to assess their regenerative ability. The majority (62%) of these limbs failed to regenerate externally visible structures. Symmetrical limbs bearing five digits or more than five digits regenerated with greatest frequency (54%). Symmetrical forelimbs bearing four digits or fewer that four digits regenerated less frequently (31%). All regenerates displayed double-posterior symmetry and usually contained fewer digits than were present in the original limb. The significance of these findings is discussed in the context of the current model for pattern regulation in epimorphic fields.

Ambystoma↗
PubMed1981

The ability of localized implants of whole or minced dermis to disrupt pattern formation in the regenerating forelimb of the axolotl.

The ability of localized grafts of dermis to alter pattern formation in the regenerating limb of the axolotl was studied. Longitudinal pieces of skin (1/4 of circumference of the limb) were removed from either the anterior or the posterior surface of the upper forelimb. Epidermis was removed by immersion in versene followed by mechanical stripping. The resulting dermis was cross transplanted directly beneath the skin on the opposite side of the limb from which it originated. After 5 days of healing each limb was amputated through the graft at the midpoint of the humerus. High percentages of multiple regenerates resulted. Similar results were obtained when dermis was minced into 1 mm3 fragments prior to cross-transplantation. Freezing or x-raying (2000 rads) the grafts prior to cross-transplantation abolished the effect. Dermis obtained form head skin rarely caused multiple regeneration when implanted into the upper forelimb followed by amputation 5 days later. These results demonstrate that addition of dermis to an intact limb stump profoundly alters pattern formation during regeneration. The effect is dependent upon viable cells that are capable of cell division.

Ambystoma↗
PubMed1979

Interactions between irradiated and unirradiated tissues during supernumerary limb formation in the newt.

The interactions between irradiated and unirradiated blastemas and stumps in the newt forelimb were studied. Irradiated right blastemas at the stage of early digits were grafted to unirradiated left stumps and unirradiated left blastemas were grafted to irradiated right stumps. Grafts were oriented with their anterior-posterior axes opposed to that of the stumps. Supernumerary limbs ranging in completeness from one to four digits were found to arise predominantly on the anterior or posterior sides of the host limb. The graft developed well when the blastema was unirradiated and had reversed handedness with respect to the stump. Irradiated grafts developed poorly. On occasions, limbs with two supernumerary structures were found. The results are discussed in terms of the origin of the cells which comprise the supernumerary limbs and their bearing on a recently presented model concerned with pattern specification and regulation in epimorphic fields.

Animals↗
PubMed1978

The failure of double-half forelimbs to undergo distal transformation following amputation in the axolotl, Ambystoma mexicanum.

Although capable of initiating early regenerative responses, axolotl forelimb stumps which are composed of double-half limb tissues fail to undergo the events that normally lead to the replacement of missing parts. In the present study, the posterior halves of right forelimbs were exchanged with the anterior halves of left forelimbs, or the dorsal halves of right forelimbs were exchanged with the ventral halves of left forelimbs. Forelimbs were amputated through the graft region 30 days after grafting. Limb stumps bearing double-dorsal, double-ventral or double-posterior tissues either produced hypomorphic regenerates or failed to form any externally visible outgrowth. When the limb stump bore double-anterior tissues, no externally visible structures were formed. Normal and multiple regenerates were never formed by double-half limbs. These results are discussed in terms of the polar coordinate model and suggest that the regeneration blastema requires a complete circumference of positional values in order to complete distal transformation.

Ambystoma↗
PubMed1977

A scanning electron microscopic comparison of the development of embryonic and regenerating limbs in the axolotl.

A comparison between the surface features of embryonic limb development and limb regeneration was made in the axolotl. Scanning electron microscopy revealed an overall similarity between embryonic and regenerating limbs. A notable feature was the lack of a morphologically discrete apical epidermal specialization on the surface of any of the limbs. Histological preparations revealed no thickening of the apical epidermis in embryonic limbs. There is a definite thickening of the apical epidermis in regenerating limbs during the stages of dedifferentiation and the early blastemal phases, but the thickening projects into the underlying tissues rather than altering the smooth surface contours of the blastema. Minor differences in epidermal specializations (ciliated cells scattered over the entire body and very irregularly shaped cells with knob-like projections at the tips of digits in embryos) may be attributable to differences in overall activity of the animals at various stages in their life history.

Ambystoma↗
PubMed1976

A staging system for forelimb regeneration in the axolotl, Ambystoma mexicanum.

A staging system has been devised for normal regeneration from the upper arm in the mature axolotl. It consists of seven externally definable stages: (1) Wound healing (WH): (2) Dedifferentiation (DD); (3) Early bud (EB); (4) Medium bud (MB); (5) Late bud (LB); (6) Palette (Pal), and (7) Digital outgrowth (DO). Serial histological sections of 38 regenerating limbs were used to correlate gross stages with microscopic events in the regenerative process.

Ambystoma↗