Clinical note: Acute bacterial infections or mastitis can occur in the duct system of the breast, usually secondary to obstruction of ducts by inspissated secretion (dried milk) and stasis of secretion.

Clinical note: Breast cancer most commonly originates in the epithelial cells of the ducts or secretory units of mammary gland tissue.

Compare this section to the micrographs showing mammary tissue during pregnancy (Fig. 22-24) and during lactation (Fig. 22-25). Image lower right.

What hormones stimulate development and secretion in mammary glands?

Examine the electron micrograph of milk and mammary epithelial cells, showing release of lipid droplets (Fig. 22-26).

By what secretory mechanism are lipid droplets released from cells into milk?

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