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Chapter 4

BISC 3221 Chapter Notes - Chapter 4: Tretinoin, Calcitriol, Merocrine

Biological Sciences
Course Code
BISC 3221
Craig Frank

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Chapter 4: Integumentary System
Integument: skin + hair/nails/sweat glands/oil glands/mammary glands
4.1 Integumentary Structure and Function
Covers entire body surface, including anterior surfaces of eyes, tympanic membranes
At nostrils, lips, anus, urethra, vagina, integument turns in and meets mucous membranes
All four tissue types are found in integument; epithelium covers surface, connective tissue
underneath with blood vessels, smooth muscle to control hairs and vessel diameter, neural tissue
Skin: 2 components; superficial epithelium AKA epidermis; connective tissue of dermis; loose
connective tissue is deep to dermis, AKA subcutaneous layer AKA hypodermis AKA superficial
fascia (not part of integument, separates integument from deep fascia around other organs)
Accessory structures: hair, nails, glands; located in dermis, protrude to surface
4.2 The Epidermis
Stratified squamous epithelium, four cells types: keratinocytes, melanocytes, Merkel cells,
Langerhans cells
Keratinocytes: most abundant epithelial cells, form several layers, found in 5 layers in thick skin
(palms of hand, soles of feet), 4 layers everywhere else
Melanocytes: pigment producing cells in epidermis
Merkel cells have role in detecting sensation
Langerhans cells: wandering phagocytic cells, important in immune response
Layers of the Epidermis
5 layers above basal lamina: Basal lamina stratum basale stratum spinosum stratum
granulosum stratum lucidum stratum corneum (at surface)
Stratum Basale
o AKA stratum germinatvum
o Single layer of cells, attached to basal lamina
o Basal cells: dominant cell type, large stem cells, divisions replace superficial
keratinocytes shed at the surface
o Melanocytes: pigment cells in stratum basale, inject melanin into keratinocytes in this
layer and more superficial layers (melanocytes : stem cells = 1:4 1:20)
o Differences in skin color result from levels of melanocyte activity, NOT different
numbers of melanocytes (albinism is melanocytes that cannot produce melanin)
o Merkel cells: surfaces that lack hair, when compressed release chemicals that stimulate
sensory nerve endings
Stratum Spinosum
o Several cells thick, keratinocytes contain tonofibrils (bundle of protein filaments, extend
spider to side for cell, begin and end at macula adherens AKA desmosome)
o Tonofibrils connect keratinocyte to other adjacent cells
o Some cells entering layer from stratum basale divide and increase spinosum thickness
o Contains melanocytes
o Langerhans cells: 3-8% dermis, most common in superficial stratum spinosum, play role
in immune response against pathogens that penetrated epidermis/epidermal cancer cells
Stratum Granulosum

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o Most superficial layer of epidermis in which ALL cells have a nucleus
o Cells are mature enough to manufacture large quantities of keratohyalin and keratin
Keratohyalin: accumulates in granules, form intracellular matrix to surround
keratin filaments
o Cells contain granules that release contents by exocytosis, forms sheet of lipid rich
substance that coats cells of stratum granulosum (water resistant)
o Rate of keratohyalin/keratin production depends on environmental factors (i.e. calluses)
Stratum Lucidum
o In thick skin, this clear layer covers stratum granulosum
o Cells lack organelles and nuclei, flattened, densely packed, filled with keratin filaments
parallel to surface of skin
Stratum Corneum
o Most superficial layer, flattened, dead cells with thick plasmalemma
o Dehydrated, no organelles, no nucleus, lots of keratin
o Still interconnected, shed in large groups/sheets
o Keratinized: epithelium with large amounts of keratin; maintained by secretions of
integumentary glands, keratinization occurs on all exposed skin EXCEPT surfaces of
o Water resistant, not waterproof (insensible perspiration, lose water to environment)
o Takes 15-30 days for cell from stratum basale to reach stratum corneum (stay there 2
Thick and Thin Skin
Thin skin: four layers, covers most of body, stratum corneum a few cell layers deep
Thick skin: palms, soles, 30 or more layers of keratinized cells
Epidermal Ridges
Epidermal ridges: from stratum basale, increases area of contact
Dermal papillae: projections from dermis toward epidermis, extend between ridges
Ridges on palms and soles increase SA and friction, for grip (genetically determined shapes)
Skin Color
Due to dermal blood supply, thickness of stratum corneum, quantities of carotene and melanin
When blood vessels dilate (oxygenated blood) reddish tint is more pronounced
Dermal Blood Supply
o Temporary reduction in circulatory supply = skin pales
o Sustained reduction, blood loses oxygen, hemoglobin turns darker red, skin takes on blue
color (cyanosis) more common in thin skin areas
Epidermal Pigment Content
o Carotene: orange-yellow content, converted to Vit A, required for epithelial maintenance
and synthesis of pigments by eye photoreceptors
o Carotene accumulates in keratinocytes
o Melanin: produced/stored in melanocytes, forms in vesicles called melanosomes
o Melanosomes color keratinocytes temporarily until destroyed by lysosomes
o Cells in superficial layers lighten as number of intact melanosomes decreases
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