ABSTRACT
The epidermal lamellar body (LB) is an ovoid, 1/3 1/4 mm membrane bilayerencircled, secretory organelle that is unique to mammalian epidermis (Fig. 1), and some other keratinizing epithelia, including those of the hard palate, the esophagus, and the vagina (reviewed in Refs. 1,2). Their absence in certain other, specialized keratinizing epithelia (e.g., hair and nail), which minimally impede transcutaneous water loss (TEWL), underscores the central role of this organelle in permeability barrier homeostasis. Likewise, few or no LB are present in the severe disorder of cornification, Harlequin ichthyosis (3-6), with drastic consequences for permeability barrier homeostasis (7). Even when barrier requirements are minimal, as in marine cetaceans, pinnipeds, and oral/genital epithelia, abundant LBs continue to be present, though they display subtle differences in structure and composition that reflect requirements unique to a near-isotonic or fully hydrated environment [(7,8); see also Chap. 13]. Thus, based upon its species and tissue distribution alone, LB can be assumed to play a central role in permeability barrier homeostasis.
