• Organization– Skin

• Epidermis• Dermis

– Accessory Structures• Hair & Hair follicles• Exocrine glands• Arrector pili• Sensory Receptors

• Layers beneath the skin

– Subcutaneous layer

– Deep fascia

________________________

• Functions of the Skin

– Protection

– Water-resistance

– Temperature regulation

– Vitamin D synthesis

– Sensations

– Immunity

– Social signaling

–Stratum Germinativum

• Stem cells

• Melanocytes

• Merkel cells

The Epidermis

– S. Spinosum

• “Pre-keratinocytes”

• Melanocytes

• Langerhans cells

The Epidermis

– S. Granulosum

– S. Lucida

• Keratinocytes in both layers

The Epidermis

– S. Corneum

• Dead keratinocytes

The Epidermis

Skin cell-eating mite

The Dermis

The Dermis

• Reticular layer

– Dense irregular CT

– Provides strength and elasticity

The Dermis• Papillary layer

– Areolar CT– Contains

cap’s and sensory neurons for epidermis

– Arranged as dermal papillae

–

Pigmentation

• Melanin

• Carotene

• Hemoglobin

Epidermal Derivatives

• Hair Follicles and Hair

• Skin Glands

Hair

• Function– Protection– Touch

Sensation• Structure

– Root– Shaft– Bulb

Hair

• Hair Follicle

– Sheath of epithelial cells

– Surrounds root

– Merges with bulb

Hair

• Associated structures

– Dermal papilla

– Sebaceous glands

– Arrector pili

Hair

• Growth Cycle

– 2-5 yrs: growth stage

– 2 yrs: resting stage

Skin Glands

• Sebaceous glands

– secrete sebum

– help to protect hair and skin

Skin Glands

• Merocrine (eccrine) sweat glands

– BT control

– excretion

– protection

Skin Glands

• Apocrine sweat glands

– Secrete pheromones?

Skin Glands

• Mammary glands

• Ceruminous glands

Skin Sensory Receptors

• Free nerve endings

• Pacinian corpuscles

• Meissner’s corpuslces

Lines of Cleavage

•