RESUMEN

The organic component of the avian eggshell can be divided into 3 portions, the shell membranes, the matrix and the cuticle. These have been well characterised in the chicken but little has been published with regard to the ostrich (Struthio camelus). A number of recent studies have indicated that the cause of intra-shell embryonic deaths in the ostrich is similar to intra-shell embryonic deaths that occur in the chicken. These deaths in the chicken are associated with the loss of or damage to the waxy cuticle and other organic components of the eggshell, which is reported to be absent in the ostrich eggshell. In this study, preliminary morphological and histochemical analyses, at the level of the light and electron microscope, have characterised the various organic components of the ostrich eggshell. The results of the histochemical and electron microscopical analyses suggest that there may only be 1 shell membrane in this species, which could play a major role in the limitation of bacterial penetration to the embryonic chamber The shell membrane has a distinct elemental profile as determined by EDS analysis. The matrix is shown to decrease in mesh size from the mammillary layer to the vertical crystal layer. The closer packing of the mesh may indicate the presence of a morphologically discernible termination signal to calcification or the remnants of an evolutionary calcified cuticle. The matrix of the pores may also form a defensive barrier against bacterial invasion, which could be damaged as a result of dipping the eggs before incubation.

Asunto(s)

RESUMEN

Clinical anatomy is usually defined as anatomy applied to patient care. The question is asked whether students of a new horizontally and vertically integrated medical curriculum recognize the subject as the basis for clinical examination. A clinical anatomy practicum was developed in the special activity, "Introduction to Clinical Medicine," held in the second year of the Pretoria medical curriculum. The practicum was conducted on a station basis to anatomically prepare the student for the inspection, palpation, percussion, and auscultation of the cardiovascular, respiratory, abdominal, and urogenital systems. A total of 23 stations consisting of eight cardiovascular, seven respiratory, and eight abdominal/urogenital stations were designed. Standardized patients, cadavers, skeletons, prosected specimens, x-rays, computed tomography (CT) scans, magnetic resonance imaging (MRI), multimedia programs, and clinical case studies were used as resources. A Likert-type questionnaire was used for student evaluation of the practicum. Most students realized the importance of surface anatomy for a family physician. More than two-thirds thought the practicum improved their understanding of the anatomical basis for clinical examination. The minority of students were stimulated to do further reading on clinical examination. The students' response to their ability to integrate the clinical examination with the radiological anatomy was average. Most students were continuously aware of the appropriateness of the practicum for their future career. We conclude that medical students recognize the importance of anatomy as the basis for clinical examination when exposed to an appropriate integrated presentation format.

Asunto(s)

RESUMEN

Problem oriented medical curricula claim to be based on the fact that the clinical sciences facilitate and encourage the understanding of basic sciences. The question was asked whether the correlation of gross anatomy in the Abdomen Block in the new Pretoria medical curriculum, with clinically relevant content (i.e. relevant physical examination, imaging anatomy, clinical procedures, clinical presentations and clinical case studies) facilitates the understanding of human anatomy and enhances the development of the clinical thinking fundamental to clinical practice. The clinical anatomy component of the Abdomen Block (11 weeks duration) in the third year was developed by using standardized patients, cadaver material, skeletons, X-rays, CT scans, MRIs and multimedia programs. Student perceptions were assessed by a Likert scale questionnaire. Most students thought that integrating the physical examination enhanced their understanding of the relevant anatomy (mean: 3.55). A substantial number of students thought the clinical anatomy in the block laid a good foundation for imaging anatomy of the abdomen (mean: 3.41). The majority of students thought the clinical anatomy laid a good basis for the understanding of surgical procedures relevant to the abdomen (mean: 3.63). Students were mostly confident that clinical anatomy enhanced their understanding of clinical presentations (mean: 3.68). Although slightly fewer, the majority reckoned that the clinical case studies gave them a better understanding of the relevant anatomy (mean: 3.30). It seems evident that the integration of clinically relevant content facilitates and encourages the understanding of anatomy and thus aids in the development of clinical thinking.

Asunto(s)

RESUMEN

Change in medical curricula is a worldwide trend. Concomitant with this is a change in the role of the microscope and its contribution to a student's career. In this questionnaire-based study the perceptions of medical, dental and veterinary students to microscopy and alternative forms of histology tuition, as well as the role of microscopy in their future careers, was assessed. Veterinary students indicate a strong preference for the microscope and microscopy training due to the importance of the microscope in their chosen career, whilst medical and dental students are somewhat ambivalent. However, the students would not choose to eliminate the microscope entirely from their studies.

Asunto(s)

RESUMEN

The ultrastructure of the eggshell of the domestic hen has been well researched and structural studies of other avian species, such as the ostrich, often base their interpretation of egg shell structure on that of the chicken. In the ostrich, lowered hatchability and hatching trauma may be due to shell ultrastructural abnormalities. In the present study the ultrastructure of the calcified portion, and the outer shell membrane (OSM), of domesticated ostrich eggshells was investigated using standard electron microscopic techniques. Transmission and scanning electron microscopy studies demonstrated intimate contact between cup-shaped structures present on the OSM and the mammillary layer of the calcified portion of the shell. The initial calcium carbonate growth of the calcified shell was of a dendritic nature with nucleation sites on the surface of the cup's contents. The dendritic growth gave way to a more randomly-orientated, smaller crystallite growth structure, which changed in form as it neared the vertical crystal layer (VCL). The VCL is described as being both amorphous and 'crumbly' depending on the plane of fracture. These observations suggest that firstly, initial calcification is contained within the cups and is then directed outwards to form the shell and that secondly, the VCL may contain an evolutionary, calcified cuticular layer. These observations serve as a baseline for studies investigating the effect of shell structure and strength on hatchling trauma and the influence of maternal diet.

Asunto(s)

RESUMEN

The histochemistry technique for localizing adenylate cyclase has been developed over the past two decades. Early efforts were directed at overcoming the criticism of the lead capture technique, the inhibition of the enzyme by fixation, and problems associated with the substrate. The introduction of alternative metal ions, strontium and cerium, offered solutions to the criticism of the lead capture technique. The inhibition of the enzyme by the various fixation methods used has been rarely overcome satisfactorily and the use of non-fixed material during incubation is one of the alternatives that has been suggested. The introduction of adenylate (beta-gamma-methylene) diphosphate as an alternative substrate offers a solution to the problems associated with commercially available adenylyl imidodiphosphate. Although no standard medium or method has been accepted by all researchers, the histochemical technique still has a place in the arsenal of the modern cell biologist. The technique localizes the active enzyme, as opposed to the protein, active and nonactive, by immunocytochemistry and the precursors of the protein by in situ hybridization methods.

Asunto(s)

RESUMEN

The enzyme adenylyl cyclase (AC) plays a pivotal role in smooth muscle relaxation. Biochemical evidence suggests that AC is predominantly located in the outer layers of the myometrium; however, neither immunocytochemical nor histochemical studies have been undertaken to demonstrate the specific cellular distribution of the enzyme in this tissue. As part of an ongoing study of the human myometrium, a polyclonal antibody against types V and VI AC was used to detect the presence of these isoforms in sections of formalin-fixed, wax-embedded myometrial tissue. A positive reaction was seen in the cytoplasm of the smooth muscle cells with the midmyometrial area having the greatest number of positive cells, when compared to the subserosal and subendometrial areas. It is hypothesized that AC isoform type VI is the predominant isoform present in the myometrium and that the percentage distribution of positive cells reflects the area of highest myometrial activity during parturition.

Asunto(s)

RESUMEN

The aim of this study was to determine whether the ultrastructure of the non-neoplastic myometrial portion (host myometrium) of fibromyomatous uteri is normal or abnormal when compared to that of fibromyomata and normal myometria. Myometrial samples from 23 normal and 54 fibromyomatous uteri were examined at the ultrastructural level using standard electron microscopy techniques. Ultrastructural abnormalities of certain cellular organelles were noted in myocytes of fibromyomata but not in those of normal or host myometria. The sarcolemmal dense bands of host myometrial myocytes were of significantly greater length than those of normal myometria, but not significantly different to those of fibromyomata. Consequently, the numbers of caveolae in host myometria and fibromyomata are conceivably decreased in comparison to normal myometria. Host myometria can be, therefore, considered to be structurally abnormal. The specific structural abnormality noted may affect calcium metabolism in these tissues by causing a decrease in the cellular calcium extrusion mechanism and thus raising intracellular calcium concentrations. Such an abnormality may provide an answer, in terms of contraction abnormalities, for the unexplained infertility that occurs in a small percentage of symptomatic myomatous patients.

Asunto(s)

RESUMEN

Myometrial tissues from a total of 30 normal and 30 fibromyomatous uteri were compared in order to assess whether the oestrogen receptor distribution is similar for both types. All patients concerned were premenopausal with no history of exogenous hormone usage. Material taken from the subserosal, midmyometrial and subendometrial regions of both the fundus and the lower segment was stained by immunocytochemistry for the oestrogen receptor. No significant difference in the oestrogen receptor content was noted between the fundus and the lower segment in either the normal or the fibromyomatous myometria. Similarly, the phase of the menstrual cycle did not affect the total receptor content of either group of tissue. The oestrogen receptor content in the non-neoplastic portion of the fibromyomatous myometria was highest in the subendometrial and lowest in the subserosal region. The differences in receptor content between normal and fibromyomatous myometria were minimal in the subendometrial region but marked in the subserosal region. The myometrium of fibromyomatous uteri thus expresses significantly increased levels of oestrogen receptor, and the pathogenesis of fibromyomata may be related to an inherent abnormality in the myometrium.

Asunto(s)

Asunto(s)

RESUMEN

Tissue from 20 surgically resected uteri was examined in order to test the hypothesis that the oestrogen receptor content of the myometrium may not be uniform throughout the uterus. All patients were premenopausal, had no history of any exogenous steroid hormone use and were in the proliferative phase of the menstrual cycle. Material was taken from the subserosal, midmyometrical and subendometrial regions of both the fundal and lower uterine segments. Care was taken to remove all endometrium. Suitable samples were analysed by radioimmunoassay (RIA) for oestrogen receptors. An adjacent block from each area was fixed in formalin and stained immunocytochemically for oestrogen receptors. The results of the RIA show a significantly higher receptor content in the subendometrial region than in either the midmyometrial or the subserosal region. No significant difference was demonstrated between the numbers of receptors in the fundus and in the lower uterine segments. The differences were also well demonstrated by immunocytochemistry, according to which 83% of all cells counted in the subendometrial region were positive, while only 61% of cells in the middle and 47% of those in the subserosal region were positive.

Asunto(s)

Asunto(s)

Asunto(s)

Asunto(s)

Asunto(s)

Asunto(s)

Asunto(s)

RESUMEN

A new surface adsorbent technique has been compared with the widely used resin sponge T3 uptake method. The new technique has the desired attributes, correlates very highly with the resin sponge method (r = 0.93) and has been accepted as a simple, rapid and reliable method under normal temperature conditions. However, under extreme conditions (0-20 degrees C and 30-60 degrees C) the test is unreliable.

Asunto(s)

Asunto(s)

RESUMEN

The ventriculus or midgut of adult fleas of the genus Ctenophthalmus (Hystricopsyllidae) is surrounded by a complex investment consisting of a "beaded layer," circumferential and longitudinal muscles, minute fibrils of the sort commonly called collagenous, and a granular layer at the boundary of the hemocoel. The beaded layer is remarkable in consisting of two types of short cylinders of greatly different diameters, each type arranged in a mixed hexagonal array.

Asunto(s)