Ch 5

• Skin
• -largest organ (7% to 8% of body weight)

-Two layers

*Epidermis:superficial layer of stratified squamous epithelium

• *Dermis:Deeper layer of areolar and dense irregular connective tissues
• (hypodermis- lies under dermis, mostly adipose connective tissue)
• 

• Protection
• Prevention of H2O loss
• Temperature regulation
• Metabolic regulation
• Immune defense
• Sensory reception
• Excretion/Secretion

*Most superficial layer 

*Avascular

• *Keratinized Stratified squamous epithelium
• - Keratin is a water-insoluble protein
• -4 to 5 layers(strata) of distinct cell types
• 

-Stratum Basale

-Stratum Spinosum

-Stratum Granulosum

-Stratum Lucidum(found only in thick skin)

• -Stratum Corneum
• 

One layer that undergoes mitosis

• One layer of cells adjacent to the dermis
• 

Keratinocytes: most abundant; produce keratin to waterproof the skin

• Melanocytes: produce pigment(black, brown, yellow)
• absorbs UV light to prevent DNA damage

Tactile: sense touch

Several layers thick

Daughter cells from the Stratum Basale

• Epidermal Dendritic Cells
• -phagocytes that engulf invading pathogens
• 

3 to 5 layers of Keratinocytes

cytoplasm fills with keratin filaments

organelles begin to degrade

• fully keratinized cells are dead but strong and water-insoluble
• 

*Thin, translucent region, 2 to 3 layers thick

*Present only in thick skin such as sole of feet and palms of hands

• *Cells lack organelles, filled with eleidin
• (transparent, intermediate product of keratin maturation)
• 

*Most superficial layer of epidermis

*Thickness varies from a few to 30 layers thick depending on location 

• *Comprised solely of dead keratinocytes
• (sloughed off by abrasion=dust)
• 

*Hemoglobin{hee-muh-gloh-bin}: blood pigment: causes light complexions to look pink or blue

*Melanin{mel-uh-nin}: increases in people exposed to more UV light

*Carotene{kar-uh-teen}: yellow-orange pigment from food that builds up in the skin

*Lies deep to the epidermis

*contains blood vessels

*important in controlling blood supply

*Papillary- superficial

• *Reticular-deeper
• 

*Directly below stratum basale cells of epidermis

*Dermal papillae and Epidermal ridges interlock-increase surface between epidermis and dermis

• *Dermal Papillae supply nutrients to epidermal cells
• 

*forms majority of dermis

• *dense irregular connective tissue, bundles collagen fibers, blood vessels, glands
• 

*tactile(touch) receptors

*control blood flow

*control glandular secretion

*Lowering body temperature

*Widening blood vessels body heat

*areolar and adipose connective tissues

*protects underlying structures

• *stores energy
• 

• *thermal insulation
• 

*Nails

*Hairs

• *Glands
• 

Goose bumps

*Hair Papilla: connective tissue, nerves and blood vessels below follicle that support the keratinocytes

*Hair Bulb: inctrease in hair matrix causes hair growth

• *Arrector Pili: involuntary smooth muscle attached to hair
• shaft; responds to EMOTIONAL states(fear or rage) goose bumbs 
• 

*Protection

*Heat retention

*Facial Expressions

*Sensory Reception

*Visual Identification

*Chemical Signal Dispersal

• *Sweat Glands: produce watery solution
• (merocrine and apocrine)

*Sebaceous Glands: produce oily secretions

Ceruminous Glands: ear wax

Mammary Glands: produce milk

*Secretion is 99% H2O, clear, controlled by nervous system

*Forehead, palms and soles

Thermoregulation(temp)/Secretion/ Protection

coiled glands- nipples,armpits,groin, anus

*Secrete oily sebum into hair follicles

*lubricates hair and skin

• *activates in puberty
•