Integumentary System

Ch 5: Integumentary System

Integument

Developmental Aspects: Adolescent to Adult

Skin and hair become oilier and acne may appear

Skin shows the effects of cumulative environmental assaults around age 30

Scaling and dermatitis become more common

Developmental Aspects: Old Age

Epidermal replacement of cells slows and skin becomes thinner

Skin becomes dry and itchy

Subcutaneous fat layer diminishes, leading to intolerance of cold

Decreased elasticity and loss of subcutaneous tissue leads to wrinkles

Decreased numbers of melanocytes and Langerhans' cells increase the risk of skin cancer

Epidermis

Composed of keratinized stratified squamous epithelium consisting of:

four distinct cell types

and four or five layers

Cell types include:

keratinocytes,

melanocytes,

Merkel cells,

Langerhans' cells

Outer portion of the skin is exposed to the external environment and functions in protection

Cells of the Epidermis

Keratinocytes - produce the fibrous protein keratin

Melanocytes - produce the brown pigment melanin

Langerhans' cells - epidermal macrophages that help activate the immune system

Merkel cells - function as touch receptors in association with sensory nerve endings

Skin (Integument)

Layers of the Epidermis

Epidermal Layers: Stratum Basale (Basal Layer)

Deepest epidermal layer

Firmly attached to the dermis

Consists of a single row of the youngest keratinocytes

Cells undergo rapid division, hence its alternate name, stratum germinativum

Epidermal Layers: Stratum Spinosum (Prickly Layer)

Cells contain a weblike system of intermediate filaments attached to desmosomes

Melanin granules &

Langerhans' cells are abundant in this layer

Epidermal Layers: Stratum Granulosum (Granular Layer)

Thin

Three to five cell layers

Keratinocytes change appearance drastically

Granules accumulate

Epidermal Layers: Stratum Lucidum (Clear Layer)

Thin, transparent band

Superficial to the stratum granulosum

A few rows of flat, dead keratinocytes

Present only in thick skin

Soles of feet

Palms of hands

Elbows

Epidermal Layers: Stratum Corneum (Horny Layer)

Outermost layer of keratinized cells

Accounts for three quarters of the epidermal thickness

Functions include:

Waterproofing

Protection from abrasion and penetration

Renders body relatively insensitive to biological, chemical, and physical assaults

Dermis

Second major skin region

Contains strong, flexible connective tissue

Cell types include

fibroblasts

macrophages

occasionally mast cells and white blood cells

Composed of two layers -

Papillary

Reticular

Layers of the Dermis: Papillary Layer

Areolar connective tissue

collagen and elastic fibers

Surface contains nipplelike projections called dermal papillae '(papilla' = 'nipple')

Dermal papillae contain

capillary loops

Meissner's corpuscles

free nerve endings

Layers of the Dermis: Reticular Layer

80% of the thickness of the skin

Collagen fibers

add strength and resiliency to the skin

Elastin fibers

provide stretch-recoil properties

Hypodermis

Subcutaneous layer deep to the skin

Adipose connective tissue

Areolar connective tissue

Blood vessels

Skin Color

Three pigments contribute to skin color

Melanin - yellow to reddish-brown to black pigment

responsible for dark skin colors

Freckles and pigmented moles - result from local accumulations of melanin

Carotene - yellow to orange pigment

most obvious in the palms and soles of the feet

Hemoglobin - reddish