Cluster-tissue

Figure 15-5. a) Schematic structure of solid Na20-Si02, crystal and glass. Si4+ Al3+ O 02 Na+. b) Cluster tissue model of glass. areas of increased stresses. 

Insulin resistance occurs when the normal response to a given amount of insulin is reduced. Resistance of liver to the effects of insulin results in inadequate suppression of hepatic glucose production insulin resistance of skeletal muscle reduces the amount of glucose taken out of the circulation into skeletal muscle for storage and insulin resistance of adipose tissue results in impaired suppression of lipolysis and increased levels of free fatty acids. Therefore, insulin resistance is associated with a cluster of metabolic abnormalities including elevated blood glucose levels, abnormal blood lipid profile (dyslipidemia), hypertension, and increased expression of inflammatory markers (inflammation). Insulin resistance and this cluster of metabolic abnormalities is strongly associated with obesity, predominantly abdominal (visceral) obesity, and physical inactivity and increased risk for type 2 diabetes, cardiovascular and renal disease, as well as some forms of cancer. In addition to obesity, other situations in which insulin resistance occurs includes... 

Fak (focal adhesion kinase) is expressed in most tissues and is evolutionary conserved across species. It is activated by integrin clustering and by stimulation of several G protein-coupled recqrtors and RTKs. Fak is associated with focal adhesions and regulates cell spreading and migration. The kinase is essential for embryonic development since the homozygote Fak knockout is embryonic lethal. Pyk2 (proline-rich tyrosine kinase 2), the second member of the Fak kinase family has a more restricted expression pattern (primarily neuronal and hematopoietic cells) and does not localize to focal adhesions. 

This complex consists of at least 25 separate polypeptides, seven of which are encoded by mtDNA. Its catalytic action is to transfer electrons from NADH to ubiquinone, thus replenishing NAD concentrations. Complex I deficiency has been described in myopathic syndromes, characterized by exercise intolerance and lactic acidemia. In at least some patients it has been demonstrated that the defect is tissue specific and a defect in nuclear DNA is assumed. Muscle biopsy findings in these patients are typical of those in many respiratory chain abnormalities. Instead of the even distribution of mitochondria seen in normal muscle fibers, mitochondria are seen in dense clusters, especially at the fiber periphery, giving rise to the ragged-red fiber (Figure 10). This appearance is a hallmark of many mitochondrial myopathies. 

Some of this differential expression is achieved by having different regions of chromatin available for transcription in cells from various tissues. For example, the DNA containing the P-globin gene cluster is in active chromatin in the reticulocyte but in inactive chromatin in muscle cells. All the factors involved in the determination of active chromatin have not been elucidated. The presence of nucleosomes and of complexes of histones and DNA (see Chapter 36) certainly provides a barrier against the ready association of transcription fac-... 

The malignant lymphomas are hematologic cancers that consist of a cluster of diseases of the lymphoid tissue. The primary malignant cells for lymphomas are lymphocytes of B-cell, T-cell, and NK-cell origin. These cells originate from a small population of... 

Other kinds of bloassays have been used to detect the presence of specific allelochemical effects (8), effects on N2 fIxatlon (9), the presence of volatile compounds (10) and of Inhibitory substances produced by marine microalgae (11). Putnam and Duke (12) have summarized the extraction techniques and bioassay methods used In allelopathy research. Recent developments In high performance liquid chromatography (HPLC) separation of allelochemlcals from plant extracts dictates the need for bloassays with sensitivity to low concentrations of compounds contained In small volumes of eluent. Einhellig at al. (13) described a bloassay using Lemna minor L. growing In tissue culture cluster dish wells that maximizes sensitivity and minimizes sample requirements. 

TABLE V. Comparison of Allelochemlcals on the Final Frond Number of L. minor Growing for 7 Days In 24-well Tissue Culture Cluster Dishes... 

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