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Biomedical subjects

W Humbert

Publications and source records attributed to W Humbert.

23 records · Page 2Linked to original sources
PubMed1979

The midgut of Tomocerus minor Lubbock (insecta, collembola): ultrastructure, cytochemistry, ageing and renewal during a moulting cycle.

The midgut cells of Tomocerus minor (Insecta, Collembola) were examined with the electron microscope and cytochemically. The midgut epithelium consists of a series of cells characterised by numerous mineral concretions scattered throughout the cytoplasm. Mitochondria are abundant; microvilli are well developed at the apical surface of the cell. A zonula continua (continuous junction) characterises the apical contact region of these cells. Polysaccharides, glycoproteins and carbohydrate components have been demonstrated on the surface of microvilli. Peritrophic membranes surround the food bolus and preserve midgut cells from mechanical abrasion. Lysosomes are present during the alimentary period and show strong acid phosphatase activity. During an intermoulting cycle, two stages can be observed: (1) the postexuvial feeding period during which cytoplasmic extrusions appear at the apical part of the cell: lysosomes increase in number and autophagic vacuoles appear. (2) The preexuvial fasting period; a new epithelium grows beneath the old one and pushes it into the lumen. Degeneration processes can be observed in the old epithelium. This excretory reactivity of the midgut epithelium has been compared to the cycle of the cuticle.

Acid Phosphatase↗
PubMed1979

[The reaction of the insect excretory tissue to a heavy metal: uranyl nitrate (author's transl)].

The present paper describes the modifications induced in Malpighian tubules of Locusta migratoria by uranyl nitrate. These modifications are observed only if doses injected are approximately a hundred times higher than those which affect the renal epithelium of Vertebrates. The elimination of the uranyl salts seem to occur by apical excretion of dense metallo-proteic granules. When strong doses are used, metallic particles are seen on the basal membrane and in the extracellular spaces. Such intracytoplasmic particles are rarely observed.

Animals↗
PubMed1978

Intracellular and intramitochondrial binding of lanthanum in dark degenerating midgut cells of a collembolan (insect).

Lanthanum is known to be a marker of extracellular spaces. Intracellular organelles are always devoid of stain. But dark and damaged cells may be entered by the marker, as studied at the cellular level, using the electron probe X-ray microanalyser. The technique may be used to detect increased permeability at a stage when no fine structural abnormality is discernible.

Animals↗
PubMed1978

Cytochemistry and x-ray microprobe analysis of the midgut of Tomocerus minor lubbock (insecta, collembola) with special reference to the physiological significance of the mineral concretions.

Histochemical and cytochemical analyses have been made on the mineral concretions within the midgut cells of Tomocerus minor. The classical histochemical methods are not specific and precise enough and have been supplemented with cytochemical techniques on ultrathin sections. The most interesting of these was the K-pyroantimonate technique combined with glutaraldehyde-osmium fixation. This technique shows the distribution of cations such as Ca++, K+, Mg++ and Na+ on the concentric layers of the concretions. Chloride ions can be detected by means of the silver lactate technique. The action of calcium chelators such as E.D.T.A. shows an important distribution of calcium ions in the concretions. The spectra obtained by electron probe microanalysis from areas of fresh, dried and carbon coated midguts as well as from carbon coated semithin or ultrathin sections reveal the presence of Ca, K, Mg, S, Cl and P principally. Other elements such as aluminium, silicon and manganese have also been detected. Iron is not always present. The chemical and X-ray analytical investigations indicate that the midgut concretions are mainly built up of calcium, potassium, magnesium and sodium phosphates, perhaps associated with chlorides and carbonates. An organic matrix formed by polysaccharides seems to join the different mineral layers. These concretions may be formed within the vesicles of rough endoplasmic reticulum. The midgut cells are highly differentiated and very active in transport. Extensive basal infoldings and apical microvilli as well as lateral membranes are a site of small cationic deposits. The possible pathway of ion transport in the cell and the physiological significance of the concretions are discussed. The principal function of these concretions seems to be the maintenance of the mineral balance and to trap foreign and excess ions.

Aluminum↗