A&P Chapter 6

Thick skin

Palms and soles; 5 layers; sweat glands only; no hair follicles or sebaceous glands.

Thin skin

Most of body; 4 layers; has hair follicles, sweat and sebaceous glands.

Cleavage lines are formed by

Collagen and elastic fibers.

Skin layer with blood vessels

Dermis (papillary and reticular layers).

9 Functions of the skin

Protection, water balance, vitamin D synthesis, secretion, absorption, immune function, temperature regulation, sensation.

Sebaceous glands

Holocrine glands producing sebum; lubricate skin and hair; bactericidal; activated at puberty.

Keratinocytes

Most common epidermal cell; produce keratin; alive in basale, dead in corneum.

Melanocytes

Located in stratum basale; produce melanin to protect DNA from UV light.

Types of melanin

Eumelanin (brown/black), pheomelanin (tan/red).

Albinism

Inability of melanocytes to produce melanin.

Molecule damaged by UV light

DNA.

Transpiration

Slow loss of fluids through epidermis; not sweat.

Stratum basale

Deepest layer; dividing cells; keratinocytes, melanocytes, tactile cells.

Stratum spinosum

New cells pushed upward; dendritic cells for immune defense.

Stratum granulosum

Keratinization begins; cells die; nucleus disintegrates.

Stratum lucidum

Only in thick skin; translucent; contains eleidin.

Stratum corneum

Top layer; 20–30 layers of dead keratinized cells.

Function of melanin

Darkens skin and protects DNA from UV radiation.

Correct order of wound healing

Bleeding → clot & leukocytes → granulation tissue → epithelial regeneration & fibrosis.

How sweat cools the body

Evaporation removes heat from the skin.