Constant Supply Of Nutrients Research Articles

Züchtung menschlichen Knorpelgewebes mit Hilfe einer Perfusionskammer

In the field of otolaryngology cartilage grafting is commonly performed to reconstruct skeletal defects. Knowledge of chondrocyte growth and differentiation can now be used to engineer cartilage tissue for grafting. The first condition is that chondrocytes maintain their differentiated phenotype besides being able to produce a new cartilage matrix. The target of this study was to develop a three-dimensional culture system for in-vitro formation of vital cartilage transplants. Chondrocytes were isolated by digesting the cartilage matrix with collagenase and hyaluronidase. After embedding in "low-melting" agarose, the chondrocytes were placed into a perfusion culture chamber to provide a constant supply of nutrients to the cultures. The peristaltic pump was operated with on/off intervals of 30 min. Ham's F12 supplemented with 2% FCS and 50 micrograms/ml ascorbic acid was employed as culture medium. Monoclonal antibodies specific to collagens type I and type II were used to characterise cells and matrix synthesis. Synthesis of proteoglycans and collagens was achieved using toluidine blue and azan staining. Under the described culture conditions, the chondrocytes maintained a differentiated phenotype (expression of collagen type II) with synthesis of collagens and proteoglycans. An accumulation of matrix products was achieved pericellularly. After 2-8 weeks the obtained tissue exhibited an excellent histological appearance showing the typical features of cartilage tissue. The results show that the perfusion chamber allows a quick in-vitro fabrication of a piece of pure cartilage tissue for transplantation.

Engineering of cartilage tissue using bioresorbable polymer carriers in perfusion culture

Bioresorbable polymer fleeces with a high internal surface area were used as temporary matrices to establish three-dimensional cultures of isolated human articular chondrocytes. The polymer surface was coated with poly- l-lysine to support cell attachment. The resulting cell-polymer tissues were cultured in perfusion culture chambers to achieve a constant supply of nutrients by diffusion. Retention and accumulation of extracellular matrix components synthesized by the chondrocytes were improved by encapsulation of the cell-polymer integrate in agarose gel. The cell-polymer tissues formed abundant collagen fibrils in vitro with a typical cross-triation clearly visible in electron microscopy analysis. Chondrocytes and intercellular matrix stained positively with monoclonal antibodies specific for differentiated chondrocytes and type II collagen. Synthesis of proteoglycans and collagen was also evident by further analysis with alcian blue and azan staining of cell-polymer tissue sections. The presented experimental tissue culture technique offers a novel concept for the in vitro formation of vital cartilage implants for reconstructive surgery or treatment of destructive joint diseases and possibly for the in vitro engineering of human tissues in general, with applications in drug testing and replacement of animal experiments.

The strategies of energy conservation in helminths.

From the above discussion it is quite obvious that the bioenergetics in helminths are different in many ways from those found in higher organisms. All adult helminths appear to be able to consume oxygen when it is available but none of them can use it to drive the pathways of complete substrate degradation, like typical aerobic organisms, as a major strategy for energy generation. These properties hold also true for those worms residing in a highly aerobic environment, such as the blood stream or the muscle and lung tissues. Although in a number of recent studies oxygen was found to play apparently a greater role in the bioenergetics of adult helminths than originally thought, energy-generating mechanisms in adult worms seem to place greater emphasis on fermentations and anaerobic electron transport processes. These exhibit relatively low energy conservation efficiencies and result in the formation of a variety of organic end products, most of which must be excreted. The obvious correlation between the type of bioenergetic strategy operative in a particular helminth species and its environmental conditions is not well understood. The increased capacity to generate chemical energy and key metabolites of helminths possessing multiple fermentations and anaerobic respirations may give the organism greater versatility and metabolic flexibility to respond to the environmental changes observed in its corresponding habitat. Other helminths, such as schistosomes and filariids, which have continuous access to a fairly constant nutrient supply, were found to depend primarily on the more inefficiently functioning and primitive strategy of glycolysis for energy production. The reason for the occurrence in helminths of limited oxidative capacities is not completely clear. It may be assumed that the variety of alternative anaerobic pathways have evolved in response to the lack of a circulatory system and/or to the specific, often peculiar, environmental conditions prevailing in most parasitic habitats. An alternative idea put forward by Barrett [8] is that helminth metabolism represents a form of biochemical economy. Most endoparasites have an abundant supply of food and swim as if in a land of Cockain, obviously without any need to extract a maximum amount of chemical energy from the nutrients they take up. On the other hand, the fact that free-living and other larval or juvenile stages of helminths often have a typical aerobic bioenergetic pattern is a clear indication that the DNA of these organisms carries the genetic message for all the enzymes involved in complete substrate degradation.(ABSTRACT TRUNCATED AT 400 WORDS)

The Equilibrium and Stability of Simple Marine Biological Systems. III. Fluctuations and Survival

In even simple planktonic systems, consisting of a constant nutrient supply to primary nutrient users being cropped by herbivores, the possible equilibrium of the system is unstable. The number densities and nutrient concentration in such a system will oscillate widely. An important ecological question is whether or not the system will survive-if one of the number densities becomes very small, under what conditions will it ultimately recover or become extinct? If the population necessarily recovers, the system as a whole can be said to be ecologically stable, even if the equilibrium point is unstable. Two simple systems are studied from this point of view. The first is a linear chain, in which a single nutrient influences the growth of one phytoplankton species, which is cropped by one species of herbivore. If by some chance or another the number density of phytoplankton becomes small, it is shown unconditionally that the number density will, within a finite time, recover. If the herbivore number density becomes very small, condition (17) or (19) is derived for recovery and survival of the system. An interpretation of this condition suggests strongly that in nature it is always satisfied, so that the three-level linear chain is indeed ecologically stable. A second example is considered in which an additional species of phytoplankton is present (such as blue green algae) but is not cropped by the herbivore. It is found unconditionally that the system will recover from events in which the number densities, of either the herbivores or the primary nutrient users being cropped, are very small. Whether the same is true when the numbers of blue green algae become very small is not proved, but there are grounds for conjecturing that it is. In a sense, the presence of blue green algae buffers the rest of the system, decreasing more rapidly under conditions of nutrient depletion and increasing rapidly when nutrients are enriched.

Einfluß von konstantem und abnehmendem Nährstoffangebot auf Aufnahme und Verteilung von K, Ca und Mg bei Sonnenblumen

Influence on the uptake of K, Ca and Mg in sunflowers with a constant and a diminishing supply of nutrients..In a model‐test with sunflowers it was investigated how the K‐, Ca‐ and Mg‐content in the plants is reacting when (a) a nutrient solution maintained constantly at the same level is given as in a „good soil”︁ with a constant supply of nutrients, compared to (b) a solution with diminishing as in a highly fertilized soil but which hardly supplies nutrients itself. It was shown that, if the offer of the nutrient was constant, the cation content in the leaves could be maintained at the same level (the relation of cations is also maintained at the same time).Contrary to this with a diminishing nutrient solution due to removal of nutrients out of the solution without replenishing nutrients and the differentiated nutrient translocation the result was a lesser and lesser content of the nutrients inside the plant and more evident changes in the relation of cations, even before the insufficient supply was noted in a decreasing crop. Only in the leaves the relation of cations was nearly constant (K:Ca:Mg = 6:3:1).From these results it can be concluded that, through a high single supply of nutrients the effect of a constant flow of nutrients from the soil to the plant concerning the mineral contents of the plant cannot be compensated.

The Local Control of Blood Flow: An Illustration of Homeostasis

is a principle found in any general chemistry textbook which states: If a stress, such as a change in concentration, pressure or temperature, is applied to a system in equilibrium, equilibrium is shifted in a way that tends to undo effect of stress. (Nebergall et al., 1963). This is known as Le Chatelier's principle and, as is obvious, applies to chemical reactions in equilibrium states. Now if one stops to think about it, isn't this almost what Claude Bernard (1878) was saying when he wrote: is fixity of 'milieu interieur' which is condition of free and independent life. All vital mechanisms, however varied they may be, have only one object, that of preserving constant conditions of life in internal And when he said, Admitting that vital phenomena rest upon physico-chemical activities, which is truth, essence of problem is not thereby cleared up; for it is no chance encounter of physico-chemical phenomena which constructs each being according to a pre-existing plan, and produces admirable subordination and harmonious concert of organic activity. There is an arrangement in living being, a kind of regulated activity, which must never be neglected, because it is in truth most striking characteristic of living beings .... Vital phenomena possess indeed their rigorously determined physicochemical conditions, but, at same time, they subordinate themselves and succeed one another in a pattern and according to a law which pre-exists; they repeat themselves with order, regularity, constancy, and they harmonized in such manner as to bring about organization and growth of individual, animal or plant (Bernard, 1878). We find that this thought of constancy within organism so aptly termed the fixity of 'milieu interieur' was not an isolated thought of one scientist with much vision, for we find following statement made by Pfluger in 1877, a year before Bernard wrote above, cause of every need of a living being is also cause of satisfaction of need. Again in 1885 one finds a restatement of same thought by Leon Fredericq: living being is an agency of such sort that each disturbing influence induces by itself calling forth of compensatory activity to neutralize or repair disturbances. The higher in scale of living beings, more numerous, more perfect and more complicated do these regulatory agencies become. They tend to free organism completely from unfavorable influences and changes occurring in This was followed in 1900 by Charles Richet's observation: living being is stable. It must be so in order not to be destroyed, dissolved or disintegrated by colossal forces, often adverse, which surround it. By an apparent contradiction it maintains its stability only if it is excitable and capable of modifying itself according to external stimuli and adjusting its response to stimulation. In a sense it is stable because it is modifiable slight instability is necessary condition for true stability of organism. What really have these great men been trying to say? What very fundamental law of living and surviving have they in their times observed and written down as a guide to all in delving into phenomena of life? In 1929, Walter B. Cannon supplied us with answer to this with his invention of term homeostasis. He states: coordinated physiological processes which maintain most of steady states in organism are so complex and so peculiar to living beingsinvolving, as they may, brain and nerves, heart, lungs, kidneys, and spleen, all working co-operatively that I have suggested a special designation for these states, homeostasis. The word does not imply something set and immobile, a stagnation. It means a condition a condition which may vary, but which is relatively constant. Cannon here is referring to whole organism with its constancy, its state of dynamic equilibrium between internal and external environment. But in view of this it is reasonable to believe that if whole organism has this attribute of homeostasis that organs and organ systems, which make up whole organism, have within them also this property of maintaining their own environment in equilibrium with that external to them, that of whole. Based on this assumption, much work has been done over years to uncover such mechanisms as might be operating to keep at all times and under all conditions of stress a constant supply of nutrients moving from external to internal environment, and to allow for movement from internal to external environment of end products and waste materials. Krogh (1924) states it thus: . we want to find out meaning, part played by reactions in delicate regulations by which organism and organs are adapted to ever changing environmental conditions.