Repetitive tissues

This estimation (and the distribution of repetitive-sequence DNA) is based on a variety of DNA-RNA hybridization techniques and, more recently, on direct DNA sequencing. Similar techniques are used to estimate the number of active genes in a population of unique-sequence DNA. In brewers yeast Saccha-romyces cerevisiae, a lower eukaryote), about two thirds of its 6200 genes are expressed. In typical tissues in a higher eukaryote (eg, mammalian liver and kidney), between 10,000 and 15,000 genes are expressed. Different combinations of genes are expressed in each tissue,... 

O Paroxysmal supraventricular tachycardia is caused by reentry that includes the AV node as a part of the reentrant circuit. Typically, electrical impulses travel forward (antegrade) down the AV node and then travel back up the AV node (retrograde) in a repetitive circuit. In some patients, the retrograde conduction pathway of the reentrant circuit may exist in extra-AV nodal tissue adjacent to the AV node. One of these pathways usually conducts impulses rapidly, while the other usually conducts impulses slowly. Most commonly, during PSVT the impulse conducts antegrade through the slow... 

The musculoskeletal system consists of the muscles, bones, joints, tendons, and ligaments. Disorders related to the musculoskeletal system often are classified by etiology. Acute soft-tissue injuries include strains and sprains of muscles and ligaments. Repeated movements in sports, exercise, work, or activities of daily living may lead to repetitive strain injury, where cumulative damage occurs to the muscles, ligaments, or tendons.1-3 While tendonitis and bursitis can arise from acute injury, more commonly these conditions occur as a result of chronic stress.3,4 Other forms of chronic musculoskeletal pain, such as pain from rheumatoid arthritis (see Chap. 54) or osteoarthritis (see Chap. 55), are discussed elsewhere in this text. 

Repetitive overuse of a tendon can cause cellular changes in the tissues. Specifically, collagenous tendon tissue is replaced with tissue that lacks the longitudinal structure of a normal tendon.16 As a result, the tendon progressively loses elasticity and its ability to handle stress or weight. This makes the tendon vulnerable to rupture or inflammation (tendonitis and tenosynovitis). 

Open surgical arthroscopic synovectomy reduces replacement-therapy-resistant disease and repetitive hemarthresis of a single joint. This procedure removes inflamed tissue and joint blood vessels. 

Expression of matrix metalloproteinases (MMPs) and their inhibitors is an important function of the RPE, particularly with respect to the maintenance of appropriate permeability of the Bruch s membrane (Ahir et al., 2002). This function can be tested in vitro (Marin-Castano et al., 2006). For example, it has been shown that the expression of MMP-2, TIPM-2s (tissue inhibitor of MMP-2), and type IV collagen by cultured ARPE-19 cells is affected by repetitive exposures to nonlethal oxidant injury with hydroquinone (Marin-Castano et al., 2006). Oxidative stress decreases MMP-2 activity and increases collagen type IV accumulation. 

Figure 3.13 Principal component analysis of repetitive GC/MS profiles of M. truncatula root (R), stem (S) and leaves (L). The first and second principal component of each GC/MS analysis were calculated and plotted. The relative distance between points is a measure of similarity or difference. The clustering shows good reproducibility within the independent tissues but clear differentiation of tissues. The results also show that roots and stems are more similar to each other than to leaves.

The repetitive administration of 10 mg/kg mirex to rats resulted in an accumulation of mirex in several tissues (plasma, liver, kidney, fat), with more accumulating in the fat tissue (Plaa et al. 

Most repetitive sequences are not in coding regions. Because expansion of these sequences in spacer DMA rarely affects any function, they become highly polymorphic in the population and can be used to develop a genetic fir erprint. Such fingerprints are important in paternity testing and forensic medicine. Very small samples containing dried tissue can be analyzed by this technique. 

Most clinical examinations apply robust spin-echo or fast spin-echo sequences. These types of sequences provide tissue contrast changes by variation of the chosen repetition time TR (time interval between succeeding RF excitations) and echo time TE (time delay between RF excitation and signal acquisition). 

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