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Form and function in mammary epithelium: the interpretation of ultrastructure.

Abstract Introduction An inherent limitation of electron microscopy is that one must kill a cell to examine it at high resolution with an electron beam. At the very best, an electron micrograph illustrates a single, fixed moment in the life of the cell; it never can show a process happening. Nonetheless, it is possible to look at an electron micrograph of a thin-sectioned, lactating mammary epithelial cell and identify with confidence the general functions of the major structures visible there. This correlation of form and function is the product of the parallel evolution, over the last 30 yr, of techniques in biological electron microscopy and in biochemistry that have made it both possible and mandatory that each method continuously cross-check and amplify the other. This paper will illustrate briefly the kind of information that ultrastructure research, in symbiosis with biochemistry, has contributed to mammary gland biology; it then will outline some questions of function raised by recent ultrastructural investigations.