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Unformatted text preview: nd surface epithelium. Proliferating cells are stained with
antibody against a cell cycle protein (brown nuclei). (From F. Radtke and
H. Clevers, 2005. Science 307: 1904.) release oils that lubricate the skin surface. Each of these three cell populations is maintained by their own stem cells (Figure 17.20). The epidermis is
a multilayered epithelium, which is undergoing continual cell renewal. In
humans, the epidermis turns over every two weeks, with cells being
sloughed from the surface. These cells are replaced by epidermal stem cells,
which reside in a single basal layer. The epidermal stem cells give rise to
transit-amplifying cells, which undergo three to six divisions before differentiating and moving outward to the surface of the skin. The stem cells
responsible for producing hair reside in a region of the hair follicle called
the bulge. The bulge stem cells give rise to transit-amplifying matrix cells, This material cannot be copied, reproduced, manufactured, or disseminated in any
form without express written permission from the publisher.
© 2009 Sinauer Associates, Inc. UNCORRECTED PAGE PROOFS
20 CHAPTER 17 Epidermis Hair follicle
Hair shaft Cell loss Sebaceous gland
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