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Biomedical subjects

J Lück

Publications and source records attributed to J Lück.

18 recordsLinked to original sources
PubMed2004

Deterministic cellular descendance and its relationship to the branching of plant organ axes.

A double-wall map L-system, designated as S(5-5), was developed to simulate the cellular pattern found at the summit of shoot apices of Psilotum nudum. Commencing from a 3-sided autoreproductive founder cell, fives steps of simulation established a basic set of ten different cell types. Continuing the simulation beyond the fifth step revealed that, in addition to the regular production of new 3-sided cells, a group of autoreproductive 5-sided cells came into being. A close correspondence exists between the cells of the two-dimensional simulation and the two-dimensional cellular patterns found on the epidermis of the apices of Psilotum species. The 3-sided cells produced during the simulation correspond to the potentially organogenetic 3-sided cells that can be seen upon the apical surfaces. Successive generations of these 3-sided apical cells (which are actually 4-sided tetrahedral cells when viewed in three dimensions) and their immediate descendants are thought to be selected to organise the successive pairs of apices that bring about the repeated bifurcation of the Psilotum shoots. The 5-sided cells contribute to the cellular "pavements" which separate these pairs of organogenetic centres, each with their 3-sided apical cells. The cellular patterns simulated by the S(5-5) system may also correspond to the cellular patterns found on the surfaces of some other pteridophyte apices, including that of the rhizophores of Selaginella species. Tritiated-thymidine labelling of rhizophore apices revealed a group of nonproliferating cells that was associated with rhizophore bifurcation and which may correspond to a group of pavement cells. Nonproliferating cells, by regulating the siting of new organogenetic centres, may have evolved as an accompaniment to branching events such as the bifurcation of root and organ axes.

Algorithms↗
PubMed2001

Autoreproductive cells and plant meristem construction: the case of the tomato cap meristem.

Root apical meristems are composed of two zones in which either formative or proliferative cell divisions occur. Within the formative zone, autoreproductive initial cells (a-cells) occupy distinctive locations. By means of graph-L-systems, the behavior of one such type of a-cells has been investigated, with particular reference to root caps within the developing primordia of lateral roots of Lycopersicon esculentum cultivated in vitro. Here, the a-cells constitute the "protoderm initials", cells which are found also in the root cap of many angiosperm species. A set of cuboidal (i.e., six-sided) a-cells develops early in the ontogeny of a lateral-root primordium. Then, according to both anatomical observations and theoretical simulations obtained by the application of graph-L-systems, sequential production of descendents from each a-cell leads to the formation of a new autoreproductive cell (a), a cap columella initial (c), and two mother cells (e and f) whose respective descendents differentiate as root epidermis and cap flank cells. In this graph-L-system, there is specification of the location of sister cells with respect to the three orthogonal directions of a cuboidal. In the early stage of root cap formation, only a few rounds of these formative cell divisions by each a-cell and its four types of descendents are required to provide the basic set of cells necessary for full cap development. After the lateral root emerges from the parent root, there may be a temporary cessation of the formative divisions of the a-cells which give rise to columella initials. Columella production is then supported entirely by its own independent set of autoreproductive c-initials. At the same time, division of the autoreproductive protoderm initial cell is directed towards maintaining the cap flank and the epidermal cell files. The regulation of the types of formative division by the a-cell may be represented by means of a division counter which may be specific for a given species.

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PubMed1994

Cell genealogies in a plant meristem deduced with the aid of a 'bootstrap' L-system.

The primary root meristem of maize (Zea mays L.) contains longitudinal files of cells arranged in groups of familial descent (sisters, cousins, etc.). These groups, or packets, show ordered sequences of cell division which are transverse with respect to the apico-basal axis of the root. The sequences have been analysed in three zones of the meristem during the course of the first four cell generations following germination. In this period, the number of cells in the packets increases from one to 16. Theoretically, there are 48 possible division pathways that lead to the eight-cell stage, and nearly 2 x 10(6) that lead to the 16-cell stage. However, analysis shows that only a few of all the possible pathways are used in any particular zone of the root. This restriction of pathways results from inherited sequences of asymmetric cell divisions which lead to sister cells of unequal length. All possible division pathways can be generated by deterministic 'bootstrap' L-systems which assign different lifespans to sister cells of successive generations and hence specify their subsequent sequence of divisions. These systems simulate propagating patterns of cell divisions which agree with those actually found within the growing packets that comprise the root meristem. The patterns of division are specific to cells originating in various regions of the meristem of the germinating root. The importance of such systems is that they simulate patterns of cellular proliferation where there is ancestral dependency. They can therefore be applied in other growing and proliferating systems where this is suspected.

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PubMed1982

[Mitral valve prolapse and platelet activity in young patients with cerebral ischaemia (author's transl)].

In 47 patients under 45 years of age (average age 35.4 years) with more or less localised cerebral ischaemia without evidence of arteriosclerosis echocardiography showed mitral valve prolapse in 13 cases. This was slightly more frequent than in an age and sex-matched control group. The difference was not statistically significant. In three quarters of the patients (n = 35) a significantly raised beta-thromboglobulin level was found indicating increased platelet activity. No definite conclusions can be drawn as to the cause of cerebral ischaemia which is probably due to embolism. However, treatment with platelet aggregation inhibitors should be considered.

Adult↗
PubMed1977

[Hemodynamics after mitral valve replacement with Starr-Edwards, Björk-Shiley and Lillehei-Kaster protheses (author's transl)].

After mitral valve replacement hemodynamic abnormalities persist. These abnormalities were studied 1 year postoperatively. In 50 randomized patients; 15 with Starr-Edwards (SEM), 15 with Lillehei-Kaster (LKM) and 20 with Björk-Shiley (BSM) prostheses at rest and during exercise. Simultaneously were determined: pulmonary arterial pressure, left atrial pressure, left ventricular enddiastolic pressure, mean diastolic pressure gradient across the prostheses, cardiac index, stroke volume index, valve orifice area, and ejection fraction. The results show an important stenosis by the prostheses leading to high pressure increase in pulmonary artery and left atrium during excercise. This stenosis depends on valve size and type. Björk-Shiley tilting disc valves show the best hemodynamic results. This may be due to the most favourable ratio between internal and external diameter. Starr-Edwards prostheses with identical sizes show the most identical results if compared to each other. Therfore we suggest that Starr-Edwards prostheses open completely in every case. However, there is an important pressure gradient caused by the small internal diameter. Lillehei-Kaster pivoting disc valves reach surprisingly small functional valve areas. This may be caused by an incomplete opening of the disc.

Adult↗
PubMed1977

[Evaluation of social status and hemodynamic results four to six years after prosthetic valve replacement (author's transl)].

In 72 patients the professional and social status before and after prosthetic valve replacement was examined. In 60 of these patients the hemodynamic data (cardiac index, stroke volume index, pulmonary arterial pressure at rest and during exercise) were measured. The patients were classified according to their professional training, their last occupation, and their social status before operation. Postoperative changes in professional life and the daily work load were correlated to the hemodynamic results. The study shows that the social status plays a more important role in regaining the professional position postoperatively than the hemodynamic parameter.

Adolescent↗