A Comprehensive Guide for the Accurate Classification of Murine Hair Follicles in Distinct Hair Cycle Stages Flashcards
Hair Follicle Cycles
Rapid growth (anagen), apoptosis-driven regression (catagen), relative quiescence (telogen), and speculative shedding (exogen)
Epidermis
The outer, nonvascular, nonsensitive layer of the skin
Dermis
The thick layer of living tissue below the epidermis that forms the true skin, containing blood capillaries, nerve endings, sweat glands, hair follicles, and other structures.
Subcutis
The deeper layer of the dermis, containing mostly fat and connective tissue.
Panniculus carnosus
Part of the subcutaneous tissues. It is a layer of striated muscle deep to the panniculus adiposus
Arrector Pili muscle (APM)
Small muscles attached to hair follicles in mammals. Contraction of these muscles causes the hairs to stand on end - known colloquially as goose bumps.
Basement membrane (BM)
A thin, delicate membrane of protein fibers and glycosaminoglycans separating an epithelium from underlying tissue.
Dermal papilla (DP)
Located at the bottom of the epithelial compartments and it functions as a signaling center.
Mesodermal part of the Hair Follicle, which consists of closely packed mesenchymal cells; framed by the bulb matrix during anagen
Hair shaft (HS)
The hair per se, composed of trichocytes (= terminally differentiated HF keratinocytes), divided into hair cuticle, cortex and medulla
Inner root sheath (IRS)
An important structure of the lower part of the hair follicle that surrounds and protects the growing hair.
Multilayered structure composed of terminally differentiated HF keratinocytes surrounded by the ORS; consists
of Henle’s layer, Huxley’s layer and cuticle; surrounds the hair shaft up to the hair canal
Melanin (mel)
A dark brown to black pigment occurring in the hair, skin, and iris of the eye in people and animals. It is responsible for tanning of skin exposed to sunlight.
Outer root sheath (ORS)
The outer root sheath of the hair follicle encloses the inner root sheath and hair shaft. It is continuous with the basal layer of the interfollicular epidermis.
Sebaceous gland (SG)
A small gland in the skin which secretes a lubricating oily matter (sebum) into the hair follicles to lubricate the skin and hair.
Glandular structure close to the insertion of the m. arrector pili with holocrine function; composed of lipid-filled sebocytes with a foamy appearance
Bulge
Contains the stem cells themselves in the stem cell niche. It maintains the ability to produce new hair progenitors
Bulb
Prominent, onion-shaped thickening on the proximal end of the Hair Follicle; consists of relatively undifferentiated matrix cells, Hair Follicle melanocytes and of cells from the proximal Outer Root Sheath
Club Hair
Resting hair shaft with a hollow brush of keratinized keratinocytes on the proximal end, tightly attached to the cortical cells of the hair cortex
Connective Tissue Sheath
Part of the dermal connective tissue, tightly attached to the outer side of HF, composed of fibroblasts (and macrophages) and connective tissue
Epithelial Strand
Column of epithelial cells between the germ capsule and the compact DP; laterally demarcated by the thickened glassy membrane
Secondary germ capsule (secondary hair germ)
Bag-like structure of glycogen-free cells (germ cells) of distal ORS, surrounding the club hair
Hair shaft medulla
Central part of the hair shaft, composed of large, loosely connected keratinized cells with large intercellular air spaces
Hair shaft cortex
The mass of the hair shaft, composed of keratinized cells, longitudinally packed with keratin filaments (and melanin granules in pigmented hair shafts)
Hair canal
Passage way between epidermal surface and the most distal part of the IRS, demarcated by surrounding ORS.
Hyaline membrane
syn: vitreous membrane, glassy membrane
Outermost noncellular part of the HF; composed of basal lamina and two layers of orthogonally arranged collagen fibers; separates ORS from CTS
Infundibulum
Most distal part of the HF in the dermis extending from sebaceous duct to the epidermal surface (including hair canal and distal ORS)
Isthmus
Middle portion of the HF extending from the sebaceous duct to the insertion of the m. arrector pili (bulge region)
Papillary stock syn: papillary stalk
Fibroblasts that link the proximal pole of the DP and the perifollicular CTS
Basic classification criteria for HF stage
Can by identified via light microscopy
Auxiliary classification for HF stage
Additional staining required
Telogen basic classification
- Entire hairfollicle resides in the dermis
- no inner root sheath
- Compact ball-shaped Dermal papilla attached to the germ cell cap
Teogen auxilliary classification
- AP+ Dermal papilla in the dermis
2. IL 1-RI+ keratinocytes in the germ capsule, germ cell cap and Outer root sheath
