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Search Results: 1 - 10 of 2070 matches for " Sven Kurbel "
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Arterial hypertension due to fructose ingestion: model based on intermittent osmotic fluid trapping in the small bowel
Sven Kurbel
Theoretical Biology and Medical Modelling , 2010, DOI: 10.1186/1742-4682-7-27
Abstract: In normal digestion of hyperosmolar fluids, also in cases of postprandial hypotension and in patients having the "dumping" syndrome after gastric surgery, any hyperosmolar intestinal content is diluted by water taken from circulation and being trapped in the bowel until reabsorption. High fructose corn sirup (HFCS) soft drinks are among common hyperosmolar drinks. Fructose is slowly absorbed through passive carrier-mediated facilitated diffusion, along the entire small bowel, thus preventing absorption of the trapped water for several hours.Here presented interpretation is that ingestion of hyperosmolar HFCS drinks due to a transient fluid shift into the small bowel increases renin secretion and sympathetic activity, leading to rise in ADH and aldosterone secretions. Their actions spare water and sodium in the large bowel and kidneys. Alteration of colon absorption due to hormone exposure depends on cell renewal and takes days to develop, so the momentary capacity of sodium absorption in the colon depends on the average aldosterone and ADH exposure during few previous days. This inertia in modulation of the colon function can make an individual that often takes HFCS drinks prone to sodium retention, until a new balance is reached with an expanded ECF pool and arterial hypertension. In individuals with impaired fructose absorption, even a higher risk of arterial hypertension can be expected.Despite wide range of daily salt and water ingestion, sodium and fluid homeostasis is maintained through orchestrated action of aldosterone, ADH, ANP and other humoral mediators. Actions of angiotensin II and aldosterone include vasoconstriction; increased glomerular filtration with sodium reabsorption and potassium secretion in the distal tubule; increased thirst and ADH secretion [1]. Beside that, a proabsorptive trophic effect of aldosterone on the pericryptal sheath in colonic mucosa was reported [1-3] and aldosterone exposure leads to increased pericryptal sodium concentratio
Donnan effect on chloride ion distribution as a determinant of body fluid composition that allows action potentials to spread via fast sodium channels
Sven Kurbel
Theoretical Biology and Medical Modelling , 2011, DOI: 10.1186/1742-4682-8-16
Abstract: In many excitable cells, the spreading of action potentials is mediated through fast, voltage-gated sodium channels. Tissue cells share similar concentrations of cytoplasmic proteins and almost the same exposure to the interstitial fluid (IF) chloride concentration. The consequence is that similar intra- and extra-cellular chloride concentrations make these cells share the same Nernst value for Cl-.Further extrapolation indicates that cells with the same chloride Nernst value and high chloride permeability should have similar resting membrane potentials, more negative than -80 mV. Fast sodium channels require potassium levels >20 times higher inside the cell than around it, while the concentration of Cl- ions needs to be >20 times higher outside the cell.When osmotic forces, electroneutrality and other ions are all taken into account, the overall osmolarity needs to be near 280 to 300 mosm/L to reach the required resting potential in excitable cells. High plasma protein concentrations keep the IF chloride concentration stable, which is important in keeping the resting membrane potential similar in all chloride-permeable cells. Probable consequences of this concept for neuron excitability, erythrocyte membrane permeability and several features of circulation design are briefly discussed.This theoretical paper seeks to interpret similarities in pH, electrolyte and protein compositions of body fluids among diverse animals as requirements imposed by their excitable tissues, particularly neurons and muscle cells.The logic that follows is based on a previously published argument that similar body fluid osmolarity in various animals is dictated by the opposed Donnan effects of cell proteins and of sodium ions sequestered in the extracellular fluid (ECF) [1]. The conclusion of the cited paper is that the ubiquitous ECF Na+ concentration is determined by the average osmotic burden on animal tissue cells.The presence of proteins in any solution exerts two effects on the traff
A phase plane graph based model of the ovulatory cycle lacking the "positive feedback" phenomenon
Kurbel Sven
Theoretical Biology and Medical Modelling , 2012, DOI: 10.1186/1742-4682-9-35
Abstract: When hormones during the ovulatory cycle are shown in phase plane graphs, reported FSH and estrogen values form a specific pattern that resembles the leaning “&" symbol, while LH and progesterone (Pg) values form a "boomerang" shape. Graphs in this paper were made using data reported by Stricker et al. [Clin Chem Lab Med 2006;44:883–887]. These patterns were used to construct a simplistic model of the ovulatory cycle without the conventional "positive feedback" phenomenon. The model is based on few well-established relations: hypothalamic GnRH secretion is increased under estrogen exposure during two weeks that start before the ovulatory surge and lasts till lutheolysis. the pituitary GnRH receptors are so prone to downregulation through ligand binding that this must be important for their function. in several estrogen target tissue progesterone receptor (PgR) expression depends on previous estrogen binding to functional estrogen receptors (ER), while Pg binding to the expressed PgRs reduces both ER and PgR expression. Some key features of the presented model are here listed: High GnRH secretion induced by the recovered estrogen exposure starts in the late follicular phase and lasts till lutheolysis. The LH and FSH surges start due to combination of accumulated pituitary GnRH receptors and increased GnRH secretion. The surges quickly end due to partial downregulation of the pituitary GnRH receptors (64% reduction of the follicular phase pituitary GnRH receptors is needed to explain the reported LH drop after the surge). A strong increase in the lutheal Pg blood level, despite modest decline in LH levels, is explained as delayed expression of pituitary PgRs. Postponed pituitary PgRs expression enforces a negative feedback loop between Pg levels and LH secretions not before the mid lutheal phase. Lutheolysis is explained as a consequence of Pg binding to hypothalamic and pituitary PgRs that reduces local ER expression. When hypothalamic sensitivity to estrogen is diminished due to lack of local ERs, hypothalamus switches back to the low GnRH secretion rate, leading to low secretion of gonadotropins and to lutheolysis. During low GnRH secretion rates, previously downregulated pituitary GnRH receptors recover to normal levels and thus allow the next cycle. Possible implications of the presented model on several topics related to reproductive physiology are shortly discussed with some evolutionary aspects including the emergence of menopause.
Tamoxifen control arms in trials of aromatase inhibitors: possible influence on safety data
Sven Kurbel
Medicinski Glasnik , 2008,
Abstract:
Why do we need the reduced dose adjuvant tamoxifen trials for hormone receptor positive breast cancer patients?
S. Kurbel
Medicinski Glasnik , 2006,
Abstract:
On the classification of quasihomogeneous singularities
Claus Hertling,Ralf Kurbel
Mathematics , 2010,
Abstract: The motivation for this paper are computer calculations of complete lists of weight systems of quasihomogeneous polynomials with isolated singularity at 0 up to rather large Milnor numbers. We review combinatorial characterizations of such weight systems for any number of variables. This leads to certain types and graphs of such weight systems. Using them, we prove an upper bound for the common denominator (and the order of the monodromy) by the Milnor number, and we show surprising consequences if the Milnor number is a prime number.
Lattice Enthalpy Drives Hubbard U to Zero  [PDF]
Sven Larsson
Journal of Modern Physics (JMP) , 2013, DOI: 10.4236/jmp.2013.46A007
Abstract:

In the equation U = IA for the Mott energy, the electron-hole interaction of the successor state is missing. Adding the attractive term, the energy for disproportionation (Hubbard U), may adopt any sign. The missing term is related to the Born effect, the Madelung correction and the Lattice Enthalpy.

Cyclic Vitalism: The Dialectics of Life and Death in German Poetry around 1900*  [PDF]
Sven Halse
Advances in Literary Study (ALS) , 2014, DOI: 10.4236/als.2014.21004
Abstract:

Over the past decade, Scandinavian and German scholars have been active in the redefinition of the terms “Vitalism” and “Vitalist” as descriptive categories for analytical purposes in the fields of literary and cultural history. In this context,“Vitalism”has primarily been used to describe an enthusiastic worshipping of life, one that holds youth, health, strength and beauty as its primary attributes, which was prevalent in all aspects of cultural life around 1900. But even the post war founders of the Vitalist re-conceptualisation of this era, Wolfdietrich Rasch and Gunter Martens, warned of taking such a unilateral view ofwhat constituted a Vitalist concept of life. It could lead to a misunderstanding of Vitalist way of thinking, Rasch said, if the focus wasonly set upon the enthusiastic surplus, the worshipping of youth and health. To Vitalists, life is more than that. It is a totality that also encompasses notions of destruction, decay and death. “All life symbols in literature around 1900 are at the same time symbols of death” (Rasch, 1967:24).Through the analyses of three poems, this article aims to show concrete examples of how cyclic Vitalist thinking is embedded in poetry of the era. The analyses include a further sub-categorisation to capture the different types of Life Force dealt with in the texts. By way of an introduction, Vitalism is discussed within the context of the scientific and social developments of the 19th Century.

Minimising Excessive Energy Consumption in Schools While Maintaining Optimal Air Quality  [PDF]
Sven Hallin
Open Journal of Optimization (OJOp) , 2017, DOI: 10.4236/ojop.2017.64010
Abstract: This paper presents an assessment of how to minimise excessive energy consumption in a case study school classroom while maintaining optimal indoor air quality. Using mixed method research with qualitative interview data supporting quantitative key data measurements, essential primary data was extracted from temperature and carbon dioxide monitoring equipment in the classroom. This was then used, along with other ancillary data, to develop an IES computer model of the classroom as a “base case” reflecting existing energy consumption, temperatures and CO2 levels. Eight different interventions were then developed and modelled which reflected improved energy supply and a variety of ventilation strategies. The results show that adequate control and design of energy supply systems is critical to minimising excessive energy consumption, and that adequate internal air quality is achievable through a variety of low cost strategies.
The war and its influence on the malignant tumors’ incidence
B. Dmitrovi?,S. Kurbel,D. Margareti?,V. Bla?i?evi?
Medicinski Glasnik , 2006,
Abstract: We have observed the incidence of malignant tumours among 254 patients of Osijek University Hospital in the pre-war period (1990-92) and 255 patients after the war (June 1992-93. After the war there has been a significant decrease of well differentiated malignant tumors incidence: 84 cases (33,07%) before the war, 30 cases (11,76%) after the war, however, there has been a significantly increased incidence of anaplastic tumours: 9 cases (3,54%) before the war, 21 cases (8,24%) after the war. There has been statistically significant increase of stomach, ovaries and testis malignant neoplasm incidence in the observed period ( 2=76,559, p<0,0001).
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