Essay About Epidermal Replacement Of Cells And Layers Of The Epidermis

Integumentary System
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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)
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
Meissners 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