The Release of Fat into Milk from the Alveolar Cell Involves Constriction of the Plasma Membrane Around the Fat Droplet; Fats Are Dispersed in Milk in Droplet Form

The synthesis and release of milk by alveolar epithelial cells is a remarkable physiological process (Figure 39-7). Alveolar cells synthesize fats, proteins, and carbohydrates and extrude the products into the lumen of the alveolus. Fat droplets first accumulate in the basal cytoplasm of the cell and then move to the apex, where the droplet protrudes into the alveolar lumen. The cell membrane constricts about the base of the fat droplet, so fat is dispersed in milk in small droplets, surrounded by cell membranes; the droplet often contains portions of cell cytoplasm.