Journal of Cell Science, Vol 9, 805-821, Copyright © 1971 by Company of Biologists

Submitted on April 27, 1971

The Mechanism of Secretion of the Milk Fat Globule

¹ Agricultural Research Council, Institute of Animal Physiology Babraham, Cambridge, England

The morphology of secretion of the fat globule is identical in goat, guinea-pig and cow. The smallest fat droplets, which are found in the basal cytoplasm of the secretory cell, have no membrane separating the lipid from the cytoplasm and no direct association with rough endoplasmic reticulum. In the apex of the cell, fat droplets have numerous peripheral vesicles, most of which appear to be derived from the Golgi body. The progressive fusion of these vesicles results in the extrusion of the fat droplet surrounded by a unit membrane originating partly from the originally peripheral vesicles and partly from the plasmalemma. This membrane bears on its inner surface a zone of dense material which appears to be derived from the cytoplasm, and this is also seen around fat globules in secreted milk. Thus the term apocrine secretion is considered a valid description of the process.