Mechanical loading metabolism

Almost every phase of biomedical engineering involves the measurement, replacement, or modification of tissues and organs. For this reason it is essential that workers in biology, medicine, and biomedical engineering understand the relationship among biochemical pathways, mechanical loading, tissue structure, and normal function. The purpose of this text is to integrate this material in order to provide a conceptual framework needed to understand how external forces affect tissue metabolism. 

Skeletal muscle is composed of muscle cells, thin and thick filaments, and endomysium, a connective tissue containing fibroblasts that holds the fibers together. Mechanical loading regulates normal muscle metabolism in the absence of normal tensile loading muscle atrophy results. Interactions between thick (myosin) and thin (actin) filaments result in lines or bands containing one or more of the muscle fiber components. The H band represents overlap of only the thick filaments whereas the I band represents the area of overlap of thin and thick filaments. The z lines are the points at which the sarcomere repeats itself. 

Steinmeyer, J., and Knue, S. (1997), The proteoglycan metabolism of mature bovine articular cartilage explants superimposed to continuously applied cyclic mechanical loading, Biocfrcm. Biophys. Res. Common. 2 1) 216-221. 

Knothe-Tate, M.L., Knothe, U., and Niederer, R Experimental elucidation of mechanical load-induced fluid flow and its potential role in bone metabolism and functional adaptation. Am.. Med. Sci., 316,189,1998. 

An issue sometimes raised in relation to bone maintenance in the elderly concerns the endogenous acid generated by the metabolism of dietary protein, which when regularly excreted in the urine can cause calciuresis via various mechanisms (Dawson-Hughes, 2003a,b). Opinions have varied in terms of the extent to which protein-induced increases in Ca excretion may impact bone mass via bone dissolution and/or resorption (Barzel and Massey, 1998 Heaney, 1998, 2002). Protein intake in conjunction with Ca supplementation has now been positively associated with bone accrual, and only more recently has the notion of Ca economy been considered as a compensatory mechanism in response to an acute increase in the dietary protein load (Bonjour, 2005 Kerstetter et ah, 2005). 

Anemia may result from other complications even when iron supply is sufficient. A decrease in hemoglobin synthesis, a fault in transport mechanisms or destruction of erythrocytes have all been noted. Sideroblastic or iron-loading anemias are characterized by a fault in iron metabolism (see Section 62.2.3.2). There are also several other syndromes of iron deficiency known clinically, including pica and Goodpasture s syndrome (an immune-related lung and kidney disease). The different categories of anemia have been discussed in detail by Prasad.48... 

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