Integumentary System: Skin Structure, Function, and Pigmentation

Integumentary system

Consists of the skin and its accessory structures

Accessory structures of the skin

Hair, nails, glands, and sensory receptors

Skin as an organ

Skin is an organ because it is made of multiple tissue types performing specific functions

Largest organ of the body

The skin is the largest organ by weight

Barrier function of skin

Separates the internal environment from the external environment

Skin layers

Skin consists of two main layers: epidermis and dermis

Epidermis definition

Thin, outer layer of skin made of stratified squamous epithelium

Dermis definition

Thicker, inner layer of skin made of connective tissue, blood vessels, smooth muscle, and nervous tissue

Basement membrane

Thin layer that separates and anchors the epidermis to the dermis

Subcutaneous layer (hypodermis)

Layer beneath the dermis made of areolar and adipose tissue

Hypodermis classification

Not considered part of the skin

Function of hypodermis

Binds skin to underlying tissues

Adipose tissue function

Insulates the body and conserves body heat

Blood vessels in hypodermis

Contain major blood vessels that supply the skin

Characteristics of the epidermis

Made of stratified squamous epithelium and lacks blood vessels

Blood supply of epidermis

Epidermis receives nutrients from dermal blood vessels

Number of epidermal layers

4 layers in thin skin and 5 layers in thick skin

Thick skin locations

Palms of hands and soles of feet

Stratum basale

Deepest epidermal layer; contains dividing cells

Stratum germinativum

Another name for the stratum basale

Function of stratum basale

Produces new epidermal cells

Keratinocytes

Epidermal cells that accumulate keratin

Keratin

Fibrous protein that hardens and protects skin cells

Keratinization

Process in which keratinocytes migrate upward, harden, dehydrate, and die

Purpose of keratinization

Creates a tough, protective outer layer of skin

Stratum spinosum

Layer above the stratum basale that provides strength and flexibility

Stratum granulosum

Layer where cells begin to flatten and keratinization intensifies

Stratum corneum

Outermost epidermal layer made of dead, flattened, keratinized cells

Cell shedding

Epidermal cells are continuously shed from the stratum corneum

Stratum lucidum

Thin, clear layer found only in thick skin

Location of stratum lucidum

Between the stratum granulosum and stratum corneum

Primary function of epidermis

Protects against water loss, mechanical injury, chemicals, and microorganisms

Melanocytes

Specialized cells that produce the pigment melanin

Location of melanocytes

Found in the deepest layer of the epidermis and in the dermis

Melanin

Pigment that protects skin cell DNA from ultraviolet radiation

Function of melanin

Absorbs UV radiation and prevents DNA damage

Cytocrine secretion

Process by which melanin is transferred from melanocytes to nearby skin cells

Skin color determination

Skin color depends on the amount of melanin produced

Hair color determination

Hair color depends on the type and amount of melanin

Eumelanin

Brownish-black pigment

Pheomelanin

Reddish-yellow pigment found in areas such as lips

Number of melanocytes

All humans have approximately the same number of melanocytes

Cause of skin color variation

Differences in melanin production and distribution

Factors affecting skin color

Genetic, environmental, and physiological factors

Sunlight effect on skin

Increases melanin production, causing skin darkening

UV light exposure

Stimulates melanocytes to produce more melanin

X-ray exposure

Can also increase melanin production

Effect of dermal circulation on skin color

Blood flow and oxygen levels influence skin appearance

Well-oxygenated blood

Gives skin a pinkish color

Poorly oxygenated blood

Causes bluish skin color

Cyanosis

Bluish discoloration of skin due to low oxygen levels

Carotene accumulation

Causes yellowish skin color from excessive intake of orange foods

Jaundice

Yellowish skin color caused by liver disease