Fig. 2.

Theoretically possible schemes of milk fat globule secretion. In Fig. 2a, the classical model of secretion of milk components with the formation of an intracytoplasmic vacuole containing both casein micelles and lipid droplets. The content of this vacuole is then secreted outside the cell via exocytosis. Fig 2b presents the modern, currently accepted model of secretion of milk components. In this model intracellular lipid droplets contact directly with the apical plasma membrane and are secreted outside the cell surrounded by a triple layer of phospholipids. Considering the flux of phospholipid, only the scheme presented in Fig. 2b seems plausible. Abbreviations: APM-apical plasma membrane; CLD-cytoplasmic lipid droplet; MFG-milk fat globule; MC-milk components