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K Tiedemann

Publications and source records attributed to K Tiedemann.

70 records · Page 4Linked to original sources
PubMed1979

Architecture of the mesonephric nephron in pig and rabbit.

As a precondition for determining nephron profiles in sections, mature mesonephric nephrons from pig and rabbit embryos were isolated by a maceration technique in order to demonstrate nephron architecture, length, and diameter. In the pig the proximal tubule is largely constant. In the distal tubule the pre-attachment zone shows the greatest variation. The zone of attachment ot the corpuscle and the ventrolaterally directed post-attachment coil has a predictable course as does the collecting tubule. In contrast to earlier reports, the nephron shows no drastic differences in tubule diameter and is up to 33 mm long. The proportional length of the three major nephron segments is surprisingly constant. The rabbit nephron, although much shorter (4 mm) and simpler, with an alomst S-shaped pattern, is less easily understood in sections. Marked irregularities in its course are caused by the different behaviour of the terminal proximal segments. The distal tubule shows an ampullary dilatation in the attachment zone but can be very narrow in the pre-attachment part.

Animals↗
PubMed1977

On the yolk sac of the cat. II. Erythropoietic phases, ultrastructure of aging primitive erythroblasts, and blood vessels.

The phase of primitive erythropoiesis in the feline yolk sac lasts from the 14th to the 20th day after malting. The globular nucleated primitive erythroblasts are formed extravascularly to some extent, but they can be clearly distinguished from the endoderm. They do not undergo a denucleation and are still present in the circulating blood on the 45th day. Aging primitive erythroblasts are characterized by a loss of polysomes, by the appearance of long intracytoplasmic electron-lucent channels, and by a nuclear pyknosis which can turn into a karyolysis. Definitive erythropoiesis begins around the 17th day but, even by the 19th day, it is not particularly prominent. It ends around the 45th day. It is almost exclusively intravascular. The distinction of immature primitive erythroblasts from erythroblasts of the definitive series is difficult, because it is based upon only slight differences in the heterochromatinization, in the nuclear-cytoplasmic ratio, and in the organelle content of the cells. In the definitive series, the nuclear divisions follows the law of the rhythmical halving of the nuclear volume. The cells exhibit more clearly identifiable maturation stages here, and the 'checkerboard nucleus' is more distinct. The vascular endothelium is largely attenuated and moderately fenestrated; it lacks a distinct basement membrane. Organelle-rich adventitial cells are found in close apposition.

Aging↗
PubMed1976

On the yolk sac of the cat. Endoderm and mesothelium.

The ultrastructure of feline yolk sacs from 11 stages between the 14th and the 66th day is described with reference to the endoderm and the mesothelium; supplementary histochemical and cytochemical studies are included. Despite the absence of yolk, the endodermal epithelium shows a high degree of differentiation and activity, especially in the period between the 25th and the 38th day. Large stacks of RER, abundant SER, mitochondria enveloped by RER cisternae, and a peculiar type of lysosome are the most prominent organelles. Acid phosphatase, succinic dehydrogenase and NAD- and NADP-diaphorases are found with high activity, whereas the 17beta-hydroxysteroid dehydrogenase assay stains the endothelium only moderately. Indications of reabsorption are less marked. In view of the apparent immaturity of the liver parenchymal cells at this stage, the yolk sac endoderm of cat is suggested to act as an important extraembryonic site of biosynthesis. As preliminary results of a chemical analysis show that the yolk sac fluid has nearly no nutritional value, the substances synthesized are believed to be transported directly to the fetus. The mesothelium shows relatively few alterations over the period studied, is less rich in organelles and is obviously far less active than the endoderm.

Animals↗
PubMed1975

Histochemical localization of Mg2+-Na+-K+-adenosine triphosphatase in different stages of the sheep mesonephros.

Mesonephroi of sheep embryos ranging from 12 to 100 mm C.R. length were examined for the occurrence and localization of transport-ATPase. Native cryostat sections were incubated according to the technique of Guth and Albers for demonstrating the nitrophenylphosphatase activity of Mg2+-Na+-K+-adenosine triphosphatase. The basal cytoplasm of the collecting tubule of the narrow segment of the distal tubule exhibit strong activity, the wide segment of the distal tubule is moderately active. Glomeruli, proximal tubule, and Wolffian duct remain unstained. The basal labyrinths of the reactive nephron segments are believed to be the sites of a Na+-K+ exchange pump. In mature and regressing mesonephroi, the findings fully agree with biochemical data; in maturating mesonephroi, whose basal labyrinth is not yet fully established, the biochemical assay proves to be more sensitive. The specifity of the reaction was ascertained by diverse inhibitors and activating ions. The localization of Mg2+-ATPase is different to the above mentioned reaction pattern, as it shows moderate activity in the proximal tubule, too (mature mesonephros). Mesonephroi of very young embryos exhibit strongest Mg2+-ATPase activity in the proximal tubule; here the distal and collecting tubule stain only moderately.

Adenosine Triphosphatases↗
PubMedDate not supplied

Squamous cell carcinoma of the tongue in a child with Fanconi anemia: a case report and review of the literature.

This report documents a case of squamous cell carcinoma (SCC) of the tongue in a child with Fanconi anemia (FA). FA is an autosomal recessive syndrome defined by chromosomal breakage in response to diepoxybutane or mitomycin C in which many patients present with pancytopenia, hypoplastic bone marrow, hyperpigmentation of the skin, skeletal malformations, small stature, hypogonadism, and chromosomal aberrations. Such patients are prone to the development of hematological malignancies and squamous cell carcinoma, especially of the head and neck. Although FA appears to be genetically heterogeneous, all cases display abnormalities of DNA repair. A gene defective in one of the four subsets of FA patients has been defined. Defects in this gene are thought to play a role in the development of neoplasia in FA patients. However, many other factors may also contribute to the development of malignancies, including immune deficiencies, therapeutic strategies, and bone marrow transplantation. This report reviews the association of FA and SCC and highlights the many factors involved in the development of neoplasia within a single patient, including FA, cyclophosphamide, immunosuppression, X-irradiation, and chronic oral graft-versus-host disease. In addition, the human papillomavirus status, although negative, is documented for the first time in such a case.

Adolescent↗
PubMedDate not supplied

Renal ontogeny: epithelial transport in the mammalian mesonephric proximal tubule.

The role of the mammalian mesonephric kidney is not completely understood. It has been established that outpouchings of the mesonephric excretory ducts give origin to parts of the urogenital system of the adult. It is also known that mammalian mesonephric urine is formed as an ultrafiltrate. The mesonephric renal tubules have Na+/K+ adenosine triphosphatase (Na+/K+ pump), secrete phenol red, and reabsorb protein. Prior to this work, the possibility of epithelial transport of ions and metabolic substrates across mammalian mesonephric tubules had not been directly evaluated. Proximal mesonephric tubules obtained from 17 to 18-days-old rabbit embryos were isolated and perfused in vitro. Continuous intracellular electrical recordings were obtained with Ling-Gerard-type microelectrodes and a high input impedance electrometer. In tubules perfused and bathed in standard mammalian Ringer's solutions, the average transmembrane electrical cell potential difference (PD) was -43 +/- 0.5 mV (76 cells). The cellular PD decreased by 30 percent when the temperature of the bath was cooled from 37 degrees C to 30 degrees C. The cells also depolarized by 25 percent in the first five minutes of exposure to 0.1 mM ouabain. In addition, the cell PD decreased by 40 and 60 percent when the extracellular potassium concentration was raised from five to 25 and 50 mM, respectively. The uptake of glucose and alanine was similarly electrogenic (delta:1 mV/mM). The cell PD, the K+ conductance, and the electrogenicity induced by luminal exposure to 5 mM glucose or alanine are significantly lower in the mesonephric as compared to the metanephric proximal tubules of the rabbit. These observations suggest that sodium-coupled transepithelial transport mechanisms, driven by the Na+/K+ pump, are already present in the mammalian mesonephric proximal tubule. Increases in the number of Na+/K+ pumps, conductive K+ channels, and sodium-substrate cotransporters seem to be at the core of proximal tubular ontogeny.

Animals↗