Skin-nontumor / Clinical dermatology
General
Normal adnexae

Author: Mowafak Hamodat MB.CH.B, MSc., FRCPC (see Authors page)

Revised: 19 May 2016, last major update August 2010

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PubMed Search: Normal adnexae

Definition / General
  • Skin adnexa include hair follicles, sebaceous glands, eccrine sweat glands and apocrine glands

  • Follicular unit:
    • Functional complex of terminal and vellus hair follicle, sebaceous gland, erector pili muscle and (depending on site) apocrine gland
    • Often contains Demodex folliculorum mites, clumps of Staphylococcus epidermidis or Pityrosporum yeasts
    • Each follicle has an epithelial and mesenchymal component
    • Embryologically, the epithelial buds (hair germs) derive from the fetal epidermis and project downward, interacting with mesenchymal cells which form the dermal sheath and dermal papillae

  • Hair follicle:
    • Contains protected repositories of epithelial stem cells
    • Forms hair via cyclic process of (a) anagen or growing phase, (b) catagen or involuting phase and (c) telogen or resting phase
    • Matrix (regenerative) cells line the dermal papillae, are mitotically active, give rise to hair shaft and inner root sheath

  • Outer root sheath:
    • Layer of large cells that surround inner root sheath
    • Undergo abrupt keratinization without a granular layer, at level of isthmus (mid hair follicle, extends to sebaceous duct), called trichilemmal keratinization
    • Usual type of keratinization occurs by cells of infundibulum (upper hair follicle)

  • Acrotrichium:
    • Intraepidermal portion of hair follicle

  • Sebaceous glands:
    • Lobulated structures which develop as a lateral protrusion from the outer root sheath of hair follicles
    • Have outer germinative cells that differentiate, move inward and accumulate intracytoplasmic lipid droplets, causing multivacuolation and multiple indentations of nuclei
    • Excretory ducts of these glands empty into infundibulum of hair follicle

  • Sweat glands:
    • Sweat glands are either eccrine (regulate body temperature), apocrine or mixed

  • Eccrine sweat glands:
    • Tubular with secretory and excretory portions
    • Secretory coil is in deep dermis or subcutis, has secretory and myoepithelial cells
    • Excretory portion has dermal (straight) and intraepidermal (spiral, also called acrosyringium) portions

  • Apocrine glands:
    • Concentrated in axilla, groin and perineum; also in face, external auditory meatus, eyelid and areola.
    • Have secretory and excretory components
    • The secretory portion has an outer discontinous layer of myoepithelial cells and an inner layer of cuboidal to columnar eosinophilic cells
    • Decapitation secretion is conspicuous
    • Secretory cells have abundant eosinophilic cytoplasm with lipid, iron or lipofuscin
    • Positive for GCDFP-15 and CAM 5.2
Diagrams / Tables

Images hosted on other servers:

Hair follicles



Sweat glands

Micro Images

Images hosted on other servers:

Hair follicles



Sweat glands

Positive Stains