Functions of the skin:

- maintains homeostasis

- protective covering

- prevents water loss

- regulates body temperature

What do skin cells do?

Help produce Vitamin D needed for normal bone and tooth development

Layers of the skin:

1. Epidermis

2. Dermis

3. Subcutaneous layer (hypodermis)

Describe the epidermis.

- Lacks blood vessels (avascular)

- Thickest on palms and soles (0.8-1.4mm)

- Rests on basement membrane

- Replaced every 35 days

1st layer of epidermis

Stratum corneum

2nd layer of epidermis

Stratum lucidum (only in thick skin – palms, soles)

3rd layer of epidermis

Stratum granulosum

4th layer of epidermis

Stratum spinosum

5th layer of epidermis

Stratum basale

Epidermis: Genetic factors

• Varying amounts of melanin
• Varying size of melanin granules
• Albinos lack melanin

Epidermis: Physiological factors

• Dilation of dermal blood vessels
• Constriction of dermal blood vessels
• Accumulation of carotene
• Jaundice

Epidermis: Environmental factors

• Sunlight
• UV light from sunlamps
• X-rays

Describe the dermis.

- On average 1.0-2.0mm thick

- Made up of irregular dense connective tissue

- Contains muscle cells (arrector pili)

Layer to the dermis: Papillary layer

• Thin
• Superficial
• Includes dermal papillae

Layer to the dermis: Reticular layer

80% of dermis

Describe the Subcutaneous/Hypodermis Layer.

- Composed of loose connective tissue and adipose (fat) tissue

- Insulates

- Major blood vessels present

Describe hair follicles

• Dead epidermal cells
• Extends into dermis
• Contains melanin
• Arrector pili muscles are attached to every hair

3 parts to hair follicles:

1. Hair shaft (above the skin)

2. Hair root (below the skin)

3. Hair papilla (base of root)

Nail part: Nail plate

hard outer covering

Nail part: Nail bed

under the plate; vascular

Nail part: Lunula

half moon structure at the base mitotic division/growth

Sebaceous Glands

• Usually associated with hair follicles
• Classified at holocrine glands
• Secrete sebum (oil) for moisturizing
• Absent on palms and soles

Sweat Glands/Sudoiferous Glands

- Widespread in the skin

- Originates deep in the dermis or hypodermis

Eccrine glands

- most numerous

- respond to elevated body temps

- found on head, neck, and back

Apocrine glands

- respond to emotional stress

- become active at puberty

- found in axillary region and groin

- associated with hair follicles

- develop a scent (skin bacteria)

Sweat gland: Ceruminous glands

• External ear canal
• Secrete ear wax

Sweat gland: Mammary glands

Secrete milk

Regulation of Body Temperature

vitally important because even slight shifts can disrupt metabolic reactions.

Hyperthermia

abnormally high body temperature

Hypothermia

abnormally low body temperature

Healing of Wounds and Burns

• Inflammation is a normal response to injury or stress.
• Blood vessels in affected tissues dilate and become more permeable, allowing fluids to leak into the damaged tissues.

Inflamed skin may become:

- Reddened

- Swollen

- Warm

- Painful

First degree burn

superficial, partial-thickness

Second degree burn

deep, partial-thickness

Third degree burn

full-thickness

• Autograft
• Homograft
• Various skin substitutes