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Chapter 5

BIOL 2404 Chapter Notes - Chapter 5: Stratum Lucidum, Stratified Squamous Epithelium, Loose Connective Tissue

Course Code
BIOL 2404

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Chapter 5: Integumentary System
Functions of the Integumentary System
Consists of the skin, hair, glands, and nails
1. Protection
Against abrasion and UV light
Prevents entry of microorganisms
Prevents dehydration
2. Sensation
Sensory receptors that can detect heat, cold, touch, pressure,
and pain
3. Temperature regulation by controlling
Blood flow through the skin
Sweat gland activity
4. Vitamin D production
5. Excretion of small amounts of waste products
SA 1.2-2.2 m2 and weighs 4-5 kg (9-11 lbs)
Consists of three major regions
1. Epidermis: outermost region (superficial)
Resists abrasion
Reduces water loss
2. Dermis: middle region (bulk of skin)
Responsible for most of the structural strength of the skin
Leather is produced from the dermis of animals
3. Subcutaneous tissue (hypodermis): deepest region
Not really part of the skin
Connects the skin to underlying muscle or bone
Composed of keratinized stratified squamous epithelium, consisting of four
distinct cell types and four or five layers
Cell types include keratinocytes, melanocytes, Merkel cells, and Langerhans’
Outer portion of the skin is exposed to the external environment and
functions in protection
Cells of the Epidermis
1. Most abundant cell type
2. Produce the fibrous protein keratin
3. Gives skin its protective properties
1. Produce the brown pigment melanin
2. Found in the deepest layers of the epidermis
Langerhans’ cells
1. Epidermal macrophages
2. Help activate the immune system
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Merkel cells
1. Touch receptors in association with sensory nerve endings
Layers of the Epidermis
Stratum Basale (Basal Layer)
1. Deepest epidermal layer firmly attached to the dermis
Structural strength is provided by desmosomes and
2. Consists of a single row of the youngest keratinocytes
3. Cells undergo mitotic divisions ~every 19 days
4. 10-25% are melanocytes
Stratum Spinosum
1. Melanin granules and Langerhans’ cells are abundant in this layer
Melanin is taken up by the keratinocytes and accumulates on
the sunny side to protect the nucleus from UV damage
Stratum Granulosum
1. Drastic changes in keratinocyte appearance occurs
2. Keratohyaline and lamellated bodies (waterproofing) accumulate in
the cells of this layer
3. Above this layer the epithelial cells die because they are too far from
the dermis
Stratum Lucidum
1. Thin, transparent band superficial to the Stratum Granulosum
2. Consists of a few rows of flat, dead keratinocytes
3. Present only in thick skin
Stratum Corneum
1. Outermost layer of keratinized cells
2. Accounts for three quarters of the epidermal thickness
3. 20-30 cell layers thick, all dead.
4. Millions rub off everyday. Totally new every 25-45 days.
5. Functions include:
Protection from abrasion and penetration
Rendering the body relatively insensitive to biological,
chemical, and physical assaults
Thick and Thin Skin
Thick skin has all five epithelial strata
Thin skin contains fewer cell layers per stratum
1. Stratum lucidum is usually absent
2. Hair is found only in thin skin
Skin Color
Melanocytes produce melanin inside melanosomes and then transfer the
melanin to keratinocytes
1. The size and distribution of melanosomes determine skin color
2. Melanin production is determined genetically but can be influenced
by UV light (tanning) and hormones
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