Unit 4.2 - Skin Type, Function, and Healing

Stratum Corneum

50 or more layers of dead keratinocytes.

Cells are constantly shed and replaced by cells from deeper layers.

Stratum Lucidum

4-6 layers of flattened clear, dead keratinocytes.

Present mostly in the thick areas of the skin like fingertips, palms, and soles.

Stratum Granulosum

3-5 layers of flattened keratinocytes.

Nuclei and organelles of these cells begin to degenerate.

Stratum Spinosum

Consists of numerous keratinocytes.

Macophages and melanocytes also present.

Stratum Basale

Deepest layer of the epidermis.

Single row of cuboidal and columnar keratinocytes.

Also contains melanocytes and tactile epithelial cells.

Thick vs Thin Skin

Thick Skin: hairless, no sebaceous glands, more sudoriferous (sweat) glands, more sensory receptors.

Thick Skin: hairy, sebaceous glands present, fewer sudoriferous (sweat) glands, fewer sensory receptors.

Epidermal Wound Healing

1. Basal cells surrounding the wound break contact with basal membrane.

2. Basal cells around the wound enlarge and migrate toward each other until they meet

3. Growth, proliferation, and differentiation of the basal cells is stimulated by the epidermal growth factor.

Deep Wound Healing

4 phases: inflammatory, migratory, proliferative, and maturation phase.

Inflammatory Phase

Blood clot adheres loosely to the wound edges.
Requires appropriate response for the elimination and removal of microbes, foreign substances, and dead tissue.

Migratory Phase

1. Clot becomes a scab.

2. 2-3 days after the injury, fibroblasts begin to migrate to the site of injury.

3. Angiogenesis (regrow of blood vessels) begins.

Proliferative Phase

Extensive growth of epithelial cells beneath the scab.

Maturation Phase

Degradation of the scab.

Epidermis thickness restored.