White fibers

Figure 6.24B The source of the seed hairs in Fig. 6.24A. These plants grew immediately around the cooling tower. The white fibers are seed hairs.

This is true of skeletal muscle, particularly the white fibers, where the rate of work output—and therefore the need for ATP formation—may exceed the rate at which oxygen can be taken up and utilized. Glycolysis in erythrocytes, even under aerobic conditions, always terminates in lactate, because the subsequent reactions of pymvate are mitochondrial, and erythrocytes lack mitochondria. Other tissues that normally derive much of their energy from glycolysis and produce lactate include brain, gastrointestinal tract, renal medulla, retina, and skin. The liver, kidneys, and heart usually take up... 

Chemical Cellulose White fibers, consisting mostly of alpha-cellulose, obtained from vegetable matter(such as wood or cotton linters) by treatment with sulfite dilute NaOH soln or other reagent. Material obtained by treatment of cotton linters with dilute NaOH is also known as chemical cotton (See also CELLULOSE AND DERIVATIVES) Ref Merriam-Webster s(196l), 360 384... 

In fast white fibers, glycolysis catabolizes glucose. The relative lack of mitochondria in these fibers causes the white appearance. The rapid breakdown of glucose by anaerobic metabolism means that ATP is made rapidly. These muscles are used in rapid, short-duration movement and exhibit a fast twitch when electrically stimulated. The flight muscles of birds are of this type—remember that you find the white meat of a chicken on the breast. 

The same distinctions hold in humans. Sprinters and marathon runners have different proportions of muscle fibers, and therefore different metabolisms. Sprinters have relatively more fast white fibers, and can run very rapidly, but not for long distances. Marathon runners, on the other hand, have more slow red fibers and can carry out aerobic metabolism for very long periods of time, although they can t go as fast. Well-trained, world-class runners may have as much as 90 percent of their leg muscle of one type or the other, depending on their sport. Some sports, such as basketball and soccer, involve both aerobic endurance and anaerobic sprinting these athletes tend to have both types of muscle fiber. Untrained individuals have about 50 percent of each type. The relative contributions of training and heredity to each type of metabolism remain unknown, although both play some part. 

WHITE FIBERS ARE NOT CONVERTED TO RED DURING AEROBIC TRAINING... 

Figure 2. The Influence of exercise intensity (treadmill running) on muscle cytochrome c content in the rat. Red vastus = fast-twitch red fiber section Soleus = slow-twitch red fiber section White vastus = fast-twitch white fiber section. "Reproduced with permission from Ref. 44. Copyright 1982, American Physiological Society. "...

Skeletal muscle (type 11, fast twitch, or white fibers) 50,000 <1 1 99... 

Cellulose content varies. Virgin fibers produced Irom wood pulp contain 99.6% cellulose and are white. Fibers manufactured from reclaimed materials contain 75% and are gray or brown. Cellulose fibers (especially virgin materials) have a complex morphological structure which facilitates reinforcement (Figure 2.80). 

Mechanical pnlps are bleached with as little dissolved organic matter as possible either reductively with dithionite (Y) (hydrosulfite) or oxidatively with alkaline hydrogen peroxide (P). This so-called lignin retaining bleaching cannot produce a completely white fiber since trace amounts of chromophoric structures seem to be either inaccessible or nnreactive to the bleaching agent. 

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