The epidermis is derived from ectoderm during embryonic development. Cells of ectoderm (forming epidermis) grow downward into the dermis and give rise to hair follicles, fingernail, toenails, sweat glands, and sebaceous glands. Hence, they are named, epidermal or skin appendages.
Hair is formed from 3 segments:
Internal root sheath is soft keratin and is broken down at the isthmus level, where sebaceous secretions enter follicle.
Dividing matrix cells in germinative layer differentiate into keratin producing cells of internal root sheath, which has three layers:
The nail is formed from the following:
Eccrine are the most common glands, distributed all over the body except lips and part of the external genitalia; no loss of cytoplasm (merocrine secretion). Apocrine glands limited to the axilla, areola, nipple, skin around anus and external genitalia. Ceruminous glands of external meatus of the ear and glands of eyelashes were originally thought to be apocrine secretion (membrane budding) but are merocrine.
Eccrine Sweat Glands
Apocrine sweat glands
Sebaceous Gland Function
The process of sebum secretion starts with the proliferation of cells at the basal layer (the secretory portion of the gland).
Apocrine Sweat Gland Function
Eccrine Sweat Gland Functions
Apocrine Sweat Gland Function
When a skin biopsy is performed, the sample is put in a fixative solution of neutral buffered formalin to preserve the tissue structure by forming cross-links between lysine residues. In the laboratory, the sample is rapidly placed in formol saline for at least 24 hours before being processed.
The specimen is then put in a small cassette which plays the role of the support for the paraffin block.
Then, paraffin blocks are made to help cut the tissue into thin sections. Alcohol dehydration eliminates the water. Dimethylbenzene helps to remove alcohol allowing the tissue to be incorporated in paraffin wax. The tissue is removed from the cassette, put in a mold and covered with hot liquid paraffin wax. When the wax cools, it becomes solid and forms the block to be sectioned. Finally, the block is cut into thin slices before being stained.
Hair and Nail Examination
Hair and nails may be studied in microscopy without performing a biopsy. Usually, a hair sample is collected by either clipping or plucking for microscopy. Clipping is done when hair shaft disorders are suspected while plucking is done when examination of the root is needed as in alopecia areata.
There are mainly 2 types of tissue preparation clinicians use.
Skin biopsy with histopathological examination may be indicated in inflammatory and tumoral diseases of the sebaceous or sweat glands, as well as in some hair follicle anomalies.
Nail plate biopsy followed by periodic acid Schiff stain may be useful in onychomycosis with a negative mycological examination. Nail biopsy may also be done in inflammatory or tumoral changes.
Polarized light microscopy is done if anomalies of the hair shaft are suspected. Dermoscopy (trichoscopy) may also be used in this indication.
Anomalies of Hair Follicles
Anomalies of Nails
Anomalies of Sebaceous Glands
Anomalies of Sudoral Glands