A & P: Ch. 6 Integumentary System

Integument

skin

Skin consists of 2 layers

Epidermis - stratified squamous epithelium

Dermis - deeper connective tissue layer

Hypodermis - subcutaneous tissue

Epidermis layer

stratified squamous epithelium

Dermis layer

deeper connective tissue layer

Hypodermis

subcutaneous tissue; not part of skin

Functions of the Skin

Resistance to trauma and infection
- Keratin provides physical protection
Other barrier functions
- Barrier to water, ultraviolet (UV) rays, harmful chemicals
Vitamin D synthesis
- Skin carries out first step
Sensation
- Many nerve endings that react to various stimuli
Thermoregulation
- Alter blood flow to release or retain heat

Epidermis

• Keratinized stratified squamous epithelium

• Avascular (lacks blood vessels)

• Contains sparse nerve endings for touch and pain

Layers of Epidermis

• Stratum Basale

• Stratum Spinosum

• Stratum Granulosum

• Stratum Lucidum

• Stratum Corneum

Stratum Basale

• Single layer of stem cells and keratinocytes resting on
the basement membrane
• Contains scattered melanocytes and tactile cells

Stratum Spinosum

• Several layers of keratinocytes; desmosomes and
tight junctions
• Named for spiny appearance of cells
• Contains some dendritic cells

Stratum Granulosum

• Three to five layers of keratinocytes
• Contain dark-staining keratohyalin granules

Stratum Lucidum

• Thin, pale layer found only in thick skin
• Keratinocytes packed with clear protein eleidin

Stratum Corneum

• Up to 30 layers of dead, scaly, keratinized cells
• Resists abrasion, penetration, water loss

Epidermal Cells

• Keratinocytes

• Stem Cells

• Melanocytes

• Tactile Cells

• Dendritic Cells

Keratinocytes function

Synthesize keratin

Stem Cells function

Undifferentiated cells that give rise to keratinocytes

Melanocytes function

Synthesize pigment melanin that shields DNA from ultraviolet radiation

Melanocytes function

Synthesize pigment melanin that shields DNA from ultraviolet radiation

Tactile Cells function

Touch receptor cells associated with dermal nerve fibers

Dendritic Cells function

Phagocytic immune cells that guard against toxins, microbes

What is skin thickness based on?

epidermis

Thick Skin

• Covers palms, soles, fingers and toes

• Has sweat glands, but no hair follicles or sebaceous (oil) glands

• Thick stratum corneum

Thin Skin

• Covers rest of body; no stratum lucidum

• Has hair follicles, sebaceous glands, and sweat glands

Dermis

• Composed mainly of collagen; also contains elastic and reticular fibers
• Highly vascularized
• Contains sweat glands, sebaceous glands, and nerve endings
• Houses hair follicles and nail roots
• Dermal papillae are upward, finger- like extensions of dermis

Layers of the Dermis

Papillary Layer and Reticular Layer

Papillary Layer

• Thin zone of areolar tissue in dermal papillae

• Allows for mobility of leukocytes and other defense cells

Reticular Layer

• Deeper, thicker layer of dermis

• Composed of dense irregular connective tissue

• Stretch marks occur due to tearing of collagen fibers

Eumelanin

brown and black eumelanin; responsible for tan, brown, and black skin

Pheomelanin

reddish-yellow tones in Asians and native Americans; pinkish tones of white skin

Other factors of skin color

• Accumulation of carotene pigment from yellow and orange vegetables

• UV radiation, which stimulates melanin synthesis

Skin Color Abnormalities

• Cyanosis

• Erythema

• Pallor

• Albinism

• Jaundice

• Hematoma

Cyanosis

blueness due to oxygen deficiency

Erythema

redness due to increased blood flow to skin

Pallor

paleness; decreased blood flow to skin

Albinism

white skin; genetic lack of melanin

Jaundice

yellowing due to bilirubin in blood; caused by compromised liver function

Hematoma

bruising; clotted blood under skin

Appendages of Skin

• Hair, nails, and cutaneous glands

• All derived from the epidermis, but move into the dermis

Hair

• “Pilus”
• Compact hard keratin surrounded by hair follicle
• Structure of a hair:
• Shaft: above skin surface
• Root: below skin surface; ends with bulb
• Bulb contains dermal papilla—provides
nutrition to hair
• Hair matrix—mitotically active cells
• Three layers:
• Medulla—core; cells and air spaces
• Cortex—bulk of the hair; layers of elongated
cells
• Cuticle—outermost region; multiple layers of
thin scaly cells

Shaft

above skin surface

Root

below skin surface; ends with bulb

• Bulb contains dermal papilla - provides nutrition

• Hair matrix - mitotically active cells

Three Layers of Hair

Medulla, Cortex, Cuticle

Medulla Layer

core; cells and air spaces

Cortex layer

bulk of the hair; layers of elongated cells

Cuticle layer

outermost region; multiple layers of thin, scaly cells

Hair Follicles

• Invaginations of epidermis that produce hair.
Epithelial root sheath
• extension of epidermis.
• Directly adjacent to hair cuticle.
Connective tissue root sheath
• Derived from the dermis.
• Extra firm anchor for follicle.

Epithelial root sheath

• extensions of epidermis

• directly adjacent to hair cuticle

Connective tissue root sheath

• derived from dermis

• extra firm anchor for follicle

Hair follicle receptor

nerve wrapping around hair follicle

• sensitive to hair movement

Arrector pili

smooth muscle that raises hair

• Warmth

• Aggression

• Force sebum (oil) out of follicles

Hair color

Results from melanin produced at the matrix, transferred to cells of the cortex

Hair texture

Related to cross-sectional shape of hair

• Straight hair is round

• Wavy hair is oval

• Curly hair is flat

Hair growth cycle

Hair follicles have 3 developmental phases

• Anagen

• Catagen

• Telogen

Anagen

Growth cycle (6 to 8 years)

• 90% of scalp follicles at any given time

• Stem cells multiply; root sheath cells above papilla form hair cells of hair matrix; hair cells make keratin and die as they are pushed upward

Catagen

Degeneration stage (2 to 3 weeks)

• Mitosis in hair matrix ceases (stops), follicles shrink, hair loses anchorage

• Base of hair keratinizes into a hard knot—hair is called a club hair is easily pulled out by brushing

Telogen

Resting stage (1 to 3 months)