Is the eccrine gland an integral, functionally important component of the human scalp pilosebaceous unit?

Abstract

The pilosebaceous unit (PSU) and the eccrine sweat gland (ESG) are classically described as completely independent skin appendages. However, careful inspection of scalp follicular units reveals that the secretory segment of the ESG spatially approximates the hair follicle in a position below the sebaceous gland and the insertion of the arrector pili muscle. Therefore, we propose here that, contrary to conventional wisdom, the PSU and the ESG should not be viewed in isolation, and may form instead, along with the arrector pili muscle and the apocrine gland (where present),one functional unit. For this, we suggest the more inclusive term of 'Hair Cluster' (HC). If confirmed, e.g. by 3D imaging techniques, the novel concept of a functional HC, whose individual components may communicate via secreted molecules and may share selected progenitor cell populations for HC repair/ regeneration, has major physiological and pathological implications, which are briefly discussed.

Eccrine sweat glands associate with the human hair follicle within a defined compartment of dermal white adipose tissue

“…However, when following the whole trajectory of the ESG from the skin surface to the hypodermis, we recently observed that the secretory coiled portion of most ESGs progressively moves closer to the HF and becomes spatially closely associated with it . In the current study we have therefore systematically followed up the hypothesis that these ESGs actually form an integral component of the PSU, using a three‐dimensional (3D) reconstruction methodology on human scalp skin sections, and observation of follicular unit (FU) transplant grafts and intravital dye staining of whole‐mount human‐scalp skin strips ex vivo .…”

Frontal Fibrosing Alopecia and Increased Scalp Sweating: Is Neurogenic Inflammation the Common Link

“…Each eccrine sweat gland consists of a secretory coil deep in the dermis and a duct that conveys the secreted sweat to the skin surface. Traditionally, the sweat gland is viewed as anatomically separate from the pilosebaceous unit; however, a recent morphological study suggests a much closer physical association with the HF, with the secretory coil consistently situated below the insertion of the arrector pili muscle close to the outer root sheath [8]. The primary function of the eccrine unit is thermoregulation, which is accomplished through the cooling effects of evaporation of sweat from the skin's surface.…”

Do human dermal adipocytes switch from lipogenesis in anagen to lipophagy and lipolysis during catagen in the human hair cycle?

“…Although autophagy has been linked to lipodystrophy in adipocytes differentiated from murine embryonic fibroblasts and in human skin fibroblasts, previous research has failed to consider lipophagy as a possible mechanism within mature DAs. In this context, it may be productive to examine DAs surrounding human hair follicles (HFs), including the stem cell–rich bulge area . While DAs undergo size oscillations during synchronized murine HF cycling, being larger in anagen, it remains unknown whether human DAs undergo changes in cell size during the anagen‐catagen transition.…”