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. Author manuscript; available in PMC: 2012 Dec 5.
Published in final edited form as: Mol Cell Endocrinol. 2011 Jun 1;347(1-2):80–89. doi: 10.1016/j.mce.2011.05.017

Figure 4. Hair follicle cycling.

Figure 4

The initial developmental phase of hair follicle development terminates with catagen and the first telogen, after which repetitive cycles of anagen (the growth phase), catagen (the regression phase), and telogen (the resting phase) occur throughout the life span of the animal. In general the hair follicle spends most of its time in anagen. But cycle duration varies according to location, gender, age, species. The bulge is the source of stem cells for the regenerating hair follicle, responding to signals from the dermal or follicular papilla (FP). Although VDR is not required for the developmental phase of the hair follicle, it is essential for subsequent hair follicle cycling. ORS: outer root sheath, IRS: inner root sheath, HS: hair shaft, mel: melanin for the hair shaft, HM: hair matrix, BM: basement membrane, SG: sebaceous gland, APM: arrector pili muscle. Figure adapted from figure 1 in KS Stenn and R Paus, Physiol Rev:81:449–494, 2001.