The Integumentary System Structure and Function

Skin

To major division: Epidermis & the dermis; also known as the integument or cutaneous membrane.

Epidermis

The outer layer of the skin, composed of epithelial tissue. Avascular.

Dermis

Connective tissue layer that is firmly attached to the epidermis by a basement membrane, provides the avascular epidermis with nutrients, and connects the epidermis to the underlying hypodermis.

Hypodermis

Subcutaneous layer. located below the skin and is a major storage site for adipose tissue.

Keratinized stratified squamous epithelium.

The epidermis is what? This is a very thick epithelial layer in comparison with other epithelial layers of the body.

Keratinocytes, melanocytes, Langerhans cells, and Merkel cells.

Types of cell in the epidermis:

Keratinocytes

Comprise 90% of the cells of the epidermis and produce keratin, a tough fibrous protein for protection. Help water proof the skin.

Melanocytes

Comprise 8% of the epidermal cells and produce and secrete the pigment melanin.

Langerhans Cells

Immune system cells that attack pathogens that enter the skin.

Merkel Cells

The least abundant cell type and are found only in the deepest layer of the epidermis. Function as touch receptors and are associated with sensory neurons.

Stratum Basale

A single row of cells attached to the basement membrane, contains stem cells that divide to form new keratinocytes.

Keratinization

Produces tough, dead cells in the superficial layer.

Stratum Spinosum

Contains 8 to 10 rows of cells, mainly keratinocytes.

Stratum Granulosum

This layer contains 3 to 5 rows of flattened keratinocytes that are beginning to die. No dividing cells are present in this layer or in more superficial layers.

Stratum Lucidum

Contains 3 to 5 rows of flat, dead keratinocytes. Present in only thick skin. Appears translucent.

Stratum Corneum

The outermost layer, a very thick layer containing 25 to 30 or more rows of dead, squamous-shaped keratinocytes. This layer is tough and water-repellent.

Thick Skin

Found on the palms of the hands and the soles of the feet. Has all five strata.

Thin Skin

Covers the rest of the body, does not have a visible stratum lucidum and has a thinner stratum corneum.

Papillary & Reticular Region

Regions of the dermis:

Papillary Layer

A thin layer of areolar connective tissue that is deep to the stratum basale of the epidermis and the basement membrane.

Dermal Papillae

Fingerlike projections of the papillary region that extend into the epidermis. Cause genetically determine whorls in the epidermis.

Epidermal Ridges

Genetically determined whorls in the epidermis. Increases surface area, friction, and grip.

Reticular Layer

The deeper and much thicker region of the dermis. Composed mainly of dense, irregular connective tissue whose collagen fibers provide the skin with strength and whose elastic fibers provide elasticity.

Sudoriferous Glands

Sweat glands, secrete a watery substance that is important in excretion and body temperature regulation.

Eccrine & Apocrine Glands

Types of Sudoriferous Glands:

Eccrine Glands

Most common type of sudoriferous glands and are found on most areas of the body.

Apocrine Glands

Found only in the axilla, genital area, and pigmented area around the nipples.

Ceremonious Glands

Found in the ear canal and secrete a waxy substance called cerumen that prevents foreign substances from entering the auditory canal.

Mammary Glands

Found in the breasts and synthesize and secrete milk after appropriate hormonal stimulation.

Ceremonious & Mammary Glands

Modified Sudoriferous Glands:

Sebaceous Glands

Oil glands, found surrounding hair follicles and deposit sebum into the neck of the follicle.

Sebum

An oily substance that lubricates the skin and hair.

Hairs

Found all over the body with the exception of the palms, soles, lips, and other parts of the external genitalia. Consists of dead, keratinized epithelial cells.

Shaft & Root

The Main Sections of Hair:

Shaft

Part of hair that projects from the skin surface

Hair

Part of hair that extends into the dermis of the skin and sometimes the hypodermis.

Hair Follicle

Surrounds the hair root, is formed from epidermal layers that project into the dermis.

Hair Bulb

The expanded base of the hair follicle that contains the papilla of the hair and the matrix.

Papilla

A projection of connective tissue into the hair follicle and contains blood vessels that provide nutrients to the dividing cells of the matrix.

Matrix

Derived from the stratum basale of the epidermis, forms new hair cells that are added to the base of the hair root.

Connective Tissue Sheath

Surrounding the hair follicle and is comprised of dermal tissue.

Arrector Pili

A bundle of smooth muscles cells attached to the connective tissue sheath around the hair follicle. Contraction of this moves the hair from its normal angle to a 90 degree angle with the skin surface.

Cuticle

The layer of hair that we see, is a thin layer of dead, flattened, keratinized cells that overlap each other like shingles on a roof.

Nails

Found on the distal ends of the digits, assist in grabbing and manipulating objects, and protect the digits.

Nail Body

The part of the nail that is visible.

Free Edge

Part of the nail that extends beyond the digit.

Root

Part of the nail that is within the fold of skin at the proximal end of the nail body.

Lunula

The crescent-shaped area of the nail body distal to the nail root.

The cuticle (eponychium)

The thickened epithelial tissue along the proximal border of the nail body.

Hyponychium

Nail bed is deep to the free edge and attaches the nail to the fingertip.

Nail Matrix

The epithelial tissue deep to the nail root that divides to produce new cells that are added to the nail body as it grows.

Dactyloscopy

The practice of using fingerprints to identify someone.

Fingerprints

Develop from the dermal papillae that form epidermal ridges. Unique for every human being.