Functional arrangement of connective tissue in striated muscle with emphasis on cardiac muscle.

The presence and arrangement of connective tissue associated with cardiac and skeletal muscle and composed principally of collagen is clearly demonstrable by scanning and high voltage electron microscopy. The basic organization consists of a perimysium composed of bundles of collagen fibers that connect the epimysium to the endomysium. The endomysium has at least 4 components: (1) a dense weave network that surrounds myocytes, (2) myocyte-myocyte collagen struts that connect adjacent myocytes, (3) myocyte-capillary struts that connect capillaries and myocytes, and (4) a complex of single collagen fibers, glycoproteins, and glycosaminoglycans. The amount of collagen in each component varies with the function of the muscle. Different types of skeletal muscles contain different amounts of collagen depending upon the function and composition of the particular muscle. In cardiac muscle the amount of collagen varies with different species. Different regions of the heart show differences in the amount of collagen due to different functional requirements of those regions. Thus, the amount of collagen in atria is different than in the ventricles due to differences in pressure and volume of these components of the heart.