ch 4 integument dissection

Dermis

Location:

• Skin (between epidermis and hypodermis)

Description:

• Two layers: papillary (superficial), composed of areolar connective tissue; and reticular (deep), composed of dense irregular connective tissue

• Contains appendages of skin: hair follicles and glands (sweat and sebaceous)

• Contains sensory nerve endings and dense network of blood and lymphatic vessels

• Includes part of hair follicle (which develops as invagination from epidermis)

Function:

• Supports epidermis

• Dense concentration of collagen and elastin gives skin strength

• Receives general sensory stimuli (pain, touch, and temperature) via nerve endings and specialized receptors

• Regulates body temperature

Comment:

• Muscles of facial expression insert on dermis

Epidermis

Location:

• Skin (superficial to dermis)

Description:

• Keratinized stratified squamous epithelium of variable thickness

• Avascular

• Major cell type is keratinocyte

• Thick skin has five layers (superficial to deep): stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, and stratum basale

• Thin skin has four layers (stratum lucidum is missing)

• Cells of stratum lucidum and stratum corneum lack nuclei

Function:

• Physical barrier

• Protection of underlying structures

Comment:

• Also contains stem cells, melanocytes, Merkel cells, and dendritic cells

• Depends on underlying dermis for nutrients (i.e., vascular supply)

Hair

Location:

• Thin skin

Description:

• Accessory organ of skin

• Fine, keratinized filament

• Grows from oblique tube in skin called hair follicle

• Each hair has three zones: bulb, root, and shaft

• Projects from epidermal surface (length varies by body region)

• Usually pigmented (hair color due to melanin pigment granules in hair cortex)

Function:

• Protection (e.g., from sunburn)

• Heat retention (esp. on scalp)

• Cutaneous sensation

• Dispersion of chemical signals

• Facial recognition/visual identification

Comment:

• Hair not found in thick skin of palms (hands) or soles (feet)

• Genetic and hormonal factors determine body hair distribution

• Single hair also known as pilus (plural, pili)

Hypodermis

Location:

• Deep to skin

Description:

• Layer of loose areolar connective and adipose tissue

• Contains cutaneous nerves and blood vessels, and glands (sweat and sebaceous)

• Contains lamellated (Pacinian) corpuscle (pressure receptor)

• Contains portions of hair follicles associated with thin skin

Function:

• Fat storage

• Thermal regulation

• Permits movement of skin

Also known as:

• Subcutaneous tissue or superficial fascia

Dermis

Location:

• Skin (between epidermis and hypodermis)

Description:

• Two layers: papillary (superficial), composed of areolar connective tissue; and reticular (deep), composed of dense irregular connective tissue

• Contains appendages of skin: hair follicles and glands (sweat and sebaceous)

• Contains sensory nerve endings and dense network of blood and lymphatic vessels

• Includes part of hair follicle (which develops as invagination from epidermis)

Function:

• Supports epidermis

• Dense concentration of collagen and elastin gives skin strength

• Receives general sensory stimuli (pain, touch, and temperature) via nerve endings and specialized receptors

• Regulates body temperature

Epidermis

Location:

• Skin (superficial to dermis)

Description:

• Keratinized stratified squamous epithelium of variable thickness

• Avascular

• Major cell type is keratinocyte

• Thick skin has five layers (superficial to deep): stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, and stratum basale

• Thin skin has four layers (stratum lucidum is missing)

• Cells of stratum lucidum and stratum corneum lack nuclei

Function:

• Physical barrier

• Protection of underlying structures

Comment:

• Also contains stem cells, melanocytes, Merkel cells, and dendritic cells

• Depends on underlying dermis for nutrients (i.e., vascular supply)

Eponychium

Location:

• Fingers and toes

• Dorsal aspect of distal phalanx

• Overlies nail root

Description:

• Stratum corneum of proximal nail fold

Also known as:

• Cuticle

Nail bed

Location:

• Fingers and toes

• Dorsal aspect of distal phalanx

Description:

• Epidermal layers deep to nail plate

Nail body

Location:

• Fingers and toes

• Nail plate

Description:

• Part of nail plate

• Layers of compacted, highly keratinized epithelial cells

• Corresponds to stratum corneum of epidermis

Function:

• Protection for tip of finger and toe

• Aids in grasping function of finger

Comment:

• Nails are scale-like modifications of epidermis

Nail root

Location:

• Fingers and toes

• Nail plate

• Deep to eponychium

Description:

• Proximal part of nail plate

• Contains cells of nail matrix

Function:

• Growth of nail

Comment:

• Nails are scale-like modifications of epidermis