Histology of the Normal Skin
The skin consists of a keratinised squamous epithelium (epidermis) and a fibroelastic connective tissue layer (dermis) separated by a basement membrane zone (dermal-epidermal junction).
The dermis is attached to underlying loose connective tissue (subcutaneous layer or hypodermis) which contains primarily adipose tissue.
The junction between the epidermis and dermis is characterised by downward folds of the epidermis called epidermal ridges or rete which interdigitate with upward projections of the dermis called dermal papillae.
1. Stratum basale
2. Stratum spinosum
3. Stratum granulosum
4. Stratum corneum
2. Langerhans cells
3. Merkel cells
1) Hair follicles
2) Sebaceous glands
3) Sweat glands (eccrine and apocrine glands)
Regional variation of skin:
Scalp - The terminal hair follicles extend into subcutaneous fat.
Face - Numerous piloseaceous units are present. Sebaceous glands are particularly large and prominent on the nose.
Eyelid - The epidermis is thin and there are glands of Moll in the dermis
Trunk - Thicker reticular dermis than elsewhere.
Palms and soles - The stratum corneum is thick and compact. There is no basket weave pattern of keratin and no pilosebaceous units are present in the dermis.
Lower leg - Thick walled venules in the papillary dermis due to effects of gravity and stasis.
Genitalia and areola -
Contain muscle fibres.
The hair follicles are cylindrical downgrowth of surface epithelium.
The pilosebaceous unit consists of follicle, attached smooth muscle (arrector pili muscle) and a sebaceous gland.
Hair follicle is divided into 3 regions:
1. Lower segment (bulb & suprabulb)-
Extends from the base of the hair follicle to the insertion of the arrector pili muscle.
2. Middle segment (isthmus) -
Extends from the insertion of the arrector pili muscle to the entrance of the sebaceous gland duct.
3. Upper segment (infundibulum)-
Entrance of the sebaceous gland duct to the follicular orifice.
The hair bulb encloses dermal papilla.
The hair follicle consists of five concentric layers:
1. Medulla 2.Cortex 3.Cuticle 4.Internal root sheath 5.External root sheath
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