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PubMedDate not supplied

The cerebrospinal fluid: current concepts of its formation.

Until recently it has been generally accepted that the choroid plexuses are the major source of the cerebrospinal fluid (CSF). However, data now indicate that significant contributions to the CSF are made at extrachoroidal sites. CSF production studies and 24Na transport studies in normal and plexectomized rhesus monkeys supportive of substantial extrachoroidal CSF formation will be presented. Although the exact mechanisms of CSF formation remain to be defined, ultrafiltration is probably involved to a considerable extent. Data indicative of a lymphatic-like role for the CSF will be considered.

Animals↗
PubMed1990

Recent concepts in bile formation and cholestasis.

Progress has recently been made in the understanding of normal bile secretion mechanisms. The membrane carriers for bile acids have been identified and new insights into intracellular transport mechanisms have been obtained. In particular, characterization of a vesicular pathway involving the Golgi apparatus is well under way. Hypercholeretic bile acids, such as ursodeoxycholic acid, have been discovered. Their choleretic effect is far greater than that of physiological bile acids and they stimulate bicarbonate secretion. Testable hypotheses to explain their hypercholeretic effect have been proposed, in particular the chole-hepatic shunt hypothesis. Several mechanisms capable of inducing cholestasis have been identified: a) inhibition of Na+, K(+)-ATPase; b) increased permeability of the paracellular pathway leading to leakage of bile constituents back into plasma; c) microtubule or microfilament dysfunction; d) increased cytosolic free calcium concentration due to permeabilization of the endoplasmic reticulum calcium stores. It is not yet possible, in a given case, to establish which of these mechanisms is predominant. Several may operate. A better knowledge of the mechanisms involved may lead to improved treatment.

Actin Cytoskeleton↗
PubMed1990

A new concept of fibrin formation based upon the linear growth of interlacing and branching polymers and molecular alignment into interlocked single-stranded segments.

In a previous electron microscopic study of early fibrin polymers processed by freeze drying and rotatory shadowing, a large proportion of loosely constructed, frequently branching linear molecular chains was observed; their structural organization was inconsistent with a half-staggered double-stranded model for fibrin polymerization. These conflicting results prompted us to investigate the structure of early fibrin polymers prepared according to a large variety of methods currently used for electron microscopy of macromolecules. By use of a systematic random sampling procedure, fibrin polymers were photographically recorded. They were classified according to their morphological form, and the frequency of occurrence of each configuration was determined. Half-staggered double-stranded forms accounted for less than 1% of all types encountered. Interpretation of the structural organization manifested in the diverse polymer forms observed necessitated the construction of a new interlocked single-strand model for fibrin polymerization. The fibrin polymerization process combines simultaneous propagation of linear growth, branching, and lateral interlocking (leading to lateral association), resulting in the rapid formation of a fibrin network. The structural pattern developing during growth of fibrin polymers appears to be determined principally by the enzymatic mechanism and not solely by the intrinsic molecular structure of fibrinogen. The validity of the interlocked single-strand model was tested by selective fibrinopeptide-B-releasing experiments. Under such activation conditions, the polymer forms predicted according to this and the half-staggered double-strand models should differ; the structures observed were indeed consistent with the interlocked single-strand hypothesis. The compatibility of existing data with this model is discussed.

Fibrin↗
PubMed1985

HLA-DR antigens in epithelioid cell granulomas of sarcoidosis, using semithin frozen sections. A concept about granuloma formation.

Mediastinal lymph nodes of 11 patients with Sarcoidosis were studied. The immunoperoxidase technique using monoclonal antibody to HLA-DR antigen revealed on conventional frozen sections epithelioid cell granulomas with intense staining. Localization of this HLA-DR + material on or in cells in these granulomas was possible with 1 mu semithin frozen sections. Epithelioid cells as well as multi nuclear giant cells were seen in these sections with membrane bound HLA-DR antigens. Some problems about HLA-DR antigens in relation with antigen handling, the presence on epithelioid, (and) giant cells and granuloma formation will be discussed.

Frozen Sections↗
PubMed1984

[Our concept of the formation and closure of a tracheostoma].

Better functional and cosmetic results are achieved after the closure of an epithelialized tracheostomy if a method suited to the closure technique is selected when the stoma is first created. We choose a horizontal skin incision which also allows an incision running along the tension lines of the neck to be used when closing the tracheostomy. The flap from the anterior tracheal wall reported by Björk is of functional value and for closure of the stoma also. When the skin has been previously damaged, we suggest covering the defect in patients with tracheal fistulae by a bridge flap from the neck skin, avoiding the use of distant flaps which are cosmetically less favourable.

Female↗
PubMedDate not supplied

Current concepts of the formation and composition of amyloid.

Immunochemical and chemical studies of purified amyloid fibril protein from a wide variety of human tissues reveals that amyloid fibrils may derive from immunoglobulin proteins most frequently in the "primary" disease and can be classified as of kappa- or lambda-type. In addition a protein of unknown origin is the source of amyloid fibrils in another group of cases usually of "secondary" type. The creation of fibrils with all the characteristics of amyloid fibrils has been accomplished by proteolysis of some Bence Jones proteins. This indicates that amyloid fibrils may be formed by proteolytic digestion of circulating light polypeptide chains of immunoglobulin proteins.

Amyloid↗