Integumentary System

Functions:

1) Protection

2) Immune Defense = contains epidermal deendritic cells

3) Excretion = sweat

4) Temperature regulation

5) Water regulation= water resistant

6) Synthesis = vitamin D3

7) Sensory reception 

Structure

largest organ

7-8% of body weight

1.5-4+ mm thick; size of a blanket

skin layers = epidermis, dermis (hypodermis)

accesory structures = hair, nails, glands (sweat & oils)

Epidermis

~epithelial tissue only - keratinized stratified squamous

~avascular

4 distinct cell types found within the epidermis

~keratinocytes

~melanocytes

~ tactile (merkel cells)

~ epidermal dendritic (langerhorns) cells (immune cells)

Epidermis is organized into specific layers called...

Strata

Layers of the epidermis~

Thin skin (4 layers)                 Thick skin

~ stratum basale                 ~ stratum lucidum

~ stratum spinosum

~ stratum ganulosum

~ stratum corneum

Stratum basale

~single bottom layer attached to basement membrane

~consists of cuibodal cells

~major site of cell division

~ cells found = kearatinocytes (most abundant), melanocytes (scattered among the basal cells),

tactile cells (few in number, sensitive to touch)

stratum spinosum

~formed by 3-8 layers of polygonal keratinocytes

~"spiny" cells are joined toggether via desosomes

~also contains dendritic cells (immune cells that fight infection in the epidermis)

Stratum ganulosum

~ 3-5 layers of keratinocytes

~ the process of keratinization (by which the keratinocytes fill with the keratin protein)

~ strong because it contains keratin

Stratum lucidum

~ only visibile in thick skin of soles, palms, and lips

~ clear layer that is think and translucent

~ cells appear pale and featureless but have a distinct border

~ filled with protein eleidin

Stratum corneum

~ most superficial layer of epidermis

~ many layers of dead, keratinized cells

~ continually sloughed off = desquamation

Thick epidermis

~ palm, soles, lips

~ S. lucidum visible

~ thick S. corneum

~ sweat glands, but no hair or sebacious glands

Thin epidermis

~ everywhere else

~ S. lucidum is not visible

~ Thin S. corneum and S granulosum

~ hair plus sweat and sebacious glands

Variations in epidermis

~ Normal skin = the combonation of hemoglobin in the blood of the epidermis and of melannin and carotene pigments

~ Hemangioma = where the blood cells forms a benign tumor that discolors the skin

~ Contours = follow ridge patterns called "friction ridges" (toes, palm). Forms finger prints, palm prints and toe prints

4 Basic Fingerprints

~ arch

~ whirl

~ loop

~ combination

Dermis

~ thicker layer of connective tissue

~ collage and elastin fibers

- forms cleavage

- temperature control

~ contains never endings muscle tissues and accessory structures

2 Layers of Dermis

~ Papillary Layer

~ Reticular Layer

Papillary Layer

~ directly adjacent to the epidermis

~ consists of areolar connective tissue

~ forms dermal papillae

~ dermal papillae interlock with deep projections of the epidermis called epidermal ridges

~ never endings - Meissner's corpuscles

Reticular Layer

~ forms the deepest, major portion of the dermis

~ extends from the thin, overlying papillary layer to the underlying subcutaneious layer

~ consisnt of dense irregular connective tissue

Striae

stretch marks caused by skin stretching due to weight gain or pregnancy

Age, hormones and the destructive effects of UV radiation...

reduce the thickness and flexibility of the dermis

Lines of cleavage in the skin indicates..

the predominate direction of the underlying bundles of collagen fibers

Hypodermis (subcataneous layer)

~ not considered part of integument

~ binds dermis to underlying structures

~ consists of adipose & aerolar tissues

~Functions: pads the body, acts as energy reservoir, stabilizes the skin, provides thermal insulation

Accessory Structures (Epidermis Derivatives)

~ Nails

~ Hair

~ Exocrine glands of the skin

Nails

~ compressed stratum corneum cells with added keratin

~ Free edge - whitish layer

~ nail root - proximal part embedded in the skin

~ nail bed - layer of epidermis the nail rests on

~ nail folds - portions of skin that overlap the nail

~ nail matrix under eponychium (cuticle) - the growth part of the nail

~ lunula - whitish semilunar area

~ hyponychium= quick

Growth rate = 1mm/7-10 days

Hair Parts

Root = portion in skin

Shaft = portion outside

Bulb = enlarged based

Hair Layers

Medulla = inner; loose and air spaces; contains soft keratin

Cortex -middle; layers of flattened cells; contains hard keratin

Cuticle = outer; multiple cell layers; coats the hair

Hair Follicle

an oblique tube that surrounds the hair

Two principal concentric layers

1) connective tissue root sheath which originates from the dermis

2) epithelial root sheath which orginates from the epidermis

Hair color

result of the sythesis of melanin in the matrix adjacent to the papillae

arrector pili

thin, smooth , muscle strips, contract upon stimulation to elevate hairs

Hair Functions

~ protection

~ heat retention

~ facial expression

~ sensory reception

~ visual identification

~ chemical signal dispersal

Exocrine Glands

has 2 glands:

~ Sebaceous

 ~ Sudofierious (sweat)

Sebaceous Gland

~ produces an oily substance that coats hair shafts and epidermal surface called sebum

~ secreted by holocrine glands

~ inactive during childhood but are activated during puberty when production of sex hormones increases

Sweat (Sudoriferous) Glands

~ Two Types: Merocrine and Apocrine

~ Merocrine = procues a thin water secretion called sweat

~ Apocrine = produces a thick cloudy secretion (proteins and lipids) that becomes odorous after exposure to bacteria on the skin surface

Other Integumentary Glands

Ceruminous Glands

~ modified sweat glands

~ located only in the external ear canal

~ produces a waxy produce = cerumen

~ lubricates the external auditory canal and eardrum

Mammary Glands

~ modified sweat gland

~ only activated during preganacy to produce milk

~ present in both men and women

Repair and Regeneration

~ skin has the ability to regenerate after considerable damage because of the stem cells in both its epithelial and connective tissues

~ mitosis replaces damaged or destroyed S. basale cells while the division of msenchymal cells replace dermal cells

~ severed damage to the dermis and accessory structures of the skin cannot be repaired

Aging

~ as you age, skin repaire takes longer

~college fibers in the dermis decrease and elastic fibers lose their elasticity

~skins immune responsiveness diminishes and becomes drier and sometimes scaly

~ less sweating and decrease in melanocytes

~dermal blood vessles lose some permeability

~vitamin D3 production diminishes

Development of the Integumentary System

~ the epidermis is derived from the ectoderm and the dermis is derived from the mesoderm

~ surface ectoderm forms a covering called periderman and an underlying basal layer

~nails from from thickened epitherlial ridges called nail fields

~hair follicles form from hair buds that differentiate into hair bulbs, hair papillae and sebaceous glands

~both sebaceous and sweat originate from the epidermis

~ primary mammary bud develops as an epidermal outgrowth in the underlying dermis