Final answer:
The three types of exocrine gland secretions are Merocrine, Apocrine, and Holocrine; each with a distinctive process involving either vesicle exocytosis, apical cell portion release, or complete cell rupture to discharge their products.
Step-by-step explanation:
The three main types of secretions by exocrine glands are Merocrine, Apocrine, and Holocrine. In Merocrine secretion, cells release their products via exocytosis without any loss of cell material, for instance, the eccrine sweat glands. Apocrine glands, like those found in the breast, lose a part of their cell body during secretion. Lastly, Holocrine secretion involves the entire glandular cell disintegrating to release its product, as seen in sebaceous glands of the skin.
Each mode of secretion has a distinct process. Merocrine glands package secretions into vesicles that move to the apical surface, which then burst to release their content. In contrast, Apocrine glands have their apical portion pinched off with the secretion. Meanwhile, Holocrine glands accumulate their products until the cells rupture completely, releasing both cellular debris and the secretory product into the duct system.