Overview of the epidermis and the dermis,hematoxylin-eosin, 20x objective .

Epidermis

Constituent Cells:

• Keratinocytes EM
• Langerhan's EM
• Melanocytes EM

Secondary Structures:

• Corneum , (EM) anatomical variation in thickness, normal basket weave pattern (orthokeratosis), compact orthokeratosis, hyperkeratosis , parakeratosis ,
• Granulosum EM , absent, accentuated (hypergranulosis)
• Malpighii (prickle cell layer),(EM of the desmosome of the stratum malpighii)
• Dermoepidermal JunctionEM

Tertiary, Appendageal, and Functionally-defined Structures with their main expression in the skin:

• Rete Ridges
• Skin Associated Lymphoid Tissue
• Epidermal melanocyte units
• The Neuroectodermal Interface

Hair follicles

• Erector Pilae (smooth muscle)
• The Bulge Region
• Dermal Papilla
• The Cuticle
• Sebaceous Glands
• Apocrine Glands
• Eccrine Glands
• Nails
• Mucous membranes
• Genitalia and breasts
  

Dermis

Constituent Cells

• FibroblastsEM
• Collagen and Elastic FibersEM
• Mast Cells: ubiquitous secretory cells of the immune system. Scanning EM , EM , diagram of secretory products
• Dermal Dendrocytes
  

Secondary Structures:

• Papillary layer
• Reticular layer
• Dermal Neurovasculature
• Superficial Vascular Plexus

Subcutis

Constituent Cells:

• Preadipocytes
• Adipocytes ( EM , LM )
• Endothelial Cells, Confocal Microscopy of Cultured Endothelial Cells.

Secondary Structures:

• Fat lobules, LM.
• Neurovascular

Fascia

Appendages

Hair Follicles

Embryologically, the hair follicle appears to form from a downward growing bud of epithelium in about the third month of gestation, depicting its epidermal origin. Lanugo and vellus hair is prresent at birth, and in due course falls out; normal hair, especially on the scalp and eyebrows, commences to grow thereafter within several months. Most hair follicles appear to reach maturity whena person reaches the age of 10. Thereafter, hair follicles continueto grow (anagen), then have a period of normal growth (late anagen), shrink up (catagen), cast out the small "club hair" and have a rest (telogen phase) for 7 to 10 months, then "reawake"and start another growth. In humans, this cycle may take several years, and about 80% of all hair follicles are active at any given time.

There is no molting season, and a normal adult loses about 60-70 hairs a day from scattered sites. Maontagna has shown that hair growth perciptibly slows in the presence of moderate starvation in mice.(ref 1) Undoubtedly, comparable stresses in humans can affect the hair growth pattern. Since the "fight or flight" alarm reaction in an animal causes some muscles to contract, making the hair rise, the ears go flat and the mouth corners pull back, with the eyes opening wide, it is not hard to envisage a taut muscle in a round-headed human who has had a hard day at the office, blanching out the top of his scalp. Plucking hair out will not make hair grow faster or slower; and neither will shaving, althoughhair may appear coarser from the blunt-cut ends.

Androgens, whether testicular, adrrenal or ovarian, stimulate hair growth on the ears, nose, moustache, beard, axillary and pubic areas. Body hair seems to be androgen-dependent, too, though hair on extremities seems to be more a matter of heredity. Scalp hair, as well as eyelash and eyebrow hair, seems to be independent of a healthy pituitary, but dependent on either testosterone or estrogen. Male-pattern baldness can be produced in hereditarily predisposed eunuchs by testosterone injections.

This document is a resource from the
Internet Dermatology Society
Send your comments to:
Rhett Drugge, M.D.
Last update:April,24,1996