Integumentary System (Skin)
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1. Protection
– Chemical
• Low pH secretions (acid) retard bacterial activity
– Physical/mechanical barriers
• block most water and water- soluble substances
• Limited penetration of skin by any substance
2. Body temperature regulation
3. Cutaneous sensations--temperature, touch, and pain
4. Metabolic functions
– Synthesis of vitamin D precursor
– Prevents dehydration
5. Excretion—nitrogenous wastes and salt in sweat
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Consists of three major regions
1. Epidermis—outermost region
2. Dermis—middle region
3. Hypodermis (superficial fascia)—deepest region
•
•
not technically part of skin
Mostly adipose tissue
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Epidermis
• Keratinized stratified squamous epithelium with 4
different types of cells and 4-5 layers
– Keratinocytes—produce keratin (protein); main cell type
– Melanocytes
• Produce melanin pigment—gives skin its coloring–
yellow---black
– Langerhans cells—macrophages that help activate immune
system
– Merkel cells—tactile receptors
– Nutrients reach epidermis by diffusing through tissue fluid
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Stratum corneum
Most superficial layer; 20–30 layers of dead
cells represented only by flat membranous
sacs filled with keratin. Glycolipids in
extracellular space.
Stratum granulosum
Three to five layers of flattened cells,
organelles deteriorating; cytoplasm full of
granules which release lipids and
keratohyaline granules which surround keratin.
Keratinocytes
Stratum spinosum
Several layers of keratinocytes. Cells contain thick
bundles of intermediate filaments made of pre-keratin.
Stratum basale
Deepest epidermal layer; one row of actively
mitotic stem cells; some newly formed cells
become part of the more superficial layers. See
occasional melanocytes and epidermal
dendritic cells.
Melanin granule
Melanocyte
BIOL 105 Lab 5A--Skin
Dermis
Sensory
nerve ending Epidermal
Tactile
dendritic
(Merkel) cell (immune) cell
Figure 5.2b
Layers of Epidermis: superficial  deep
Stratum Corneum (Horny Layer)
• Outermost layer consisting of rows of dead, flat,
keratinized membranous sacs (no nuclei seen in cells)
– Dandruff from scalp or “dander” loose flakes that fall off
dry skin
• Makes up 3/4 of epidermal thickness
• Functions
o Protection from abrasion and penetration
o Waterproofs
o Forms a barrier against biological, chemical, and
physical assaults—makes skin impermeable to most
substances
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• Stratum lucidum found in thick skin e.g. soles of feet,
palms, fingertips; not seen in thinner skin.
• Contains few rows of flat, dead, keratinocytes
Macrophage
(Langerhans
Cell)
Melanin
granules
Melanocyte
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Stratum Granulosum or Granular Layer
Skin layers superficial to this are made up of dying or dead cells;
are too far from blood capillaries to get adequate nutrition and
oxygen
• Thin; 3-5 layers of flattened cells
• Contains cells more resistant to destruction
Stratum Spinosum
• thickest layer of living cells.
• cells start to flatten out
• produce protein keratin and glycolipids that toughen
and water-proof skin.
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Stratum Basale (Basal Layer)
• Deepest epidermal layer
• Firmly attached to dermis
• Single row of stem cells
• cells undergo rapid division
–Takes ~25–45 days for cell to migrate from this layer
to surface
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Dermis-thickest layer
• Equivalent to animal hides used to make leather
• Contains strong, flexible connective tissue
• Only this layer is vascularized
• Cells include fibroblasts, macrophages, and few mast
cells and white blood cells
• Has nerve fibers, blood vessels and lymphatic vessels
• Made up of 2 layers:
– Papillary - outermost
– Reticular
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• Papillary layer of Dermis
– Areolar connective tissue with collagen and elastic
fibers and blood vessels
– Looseness of connective tissue allows defensive
cells to patrol the area for invaders
– Makes dermal papillae which contain:
• Capillary loops, Meissner’s corpuscles, Free
nerve endings
• Epidermal ridges on top dermal papillae make our
fingerprints and allow us to grip items better
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• Reticular layer
– ~80% of the thickness of dermis
– Collagen fibers provide strength and resiliency
• bind with water to keep skin hydrated
– Elastic fibers provide stretch-recoil properties
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Skin Color
• Three pigments contribute to skin color:
1. Melanin
• Yellow to reddish-brown to black, responsible for dark
skin colors
– darker skinned people produce melanocytes with
more pigment and their keratinocytes retain color
longer than lighter skinned people
– Freckles and pigmented moles result from local
accumulations of melanin
2. Carotene
• Yellow to orange, most obvious in the palms and soles
3. Hemoglobin--not a skin pigment but gives the pinkish hue
of skin because blood vessels are close to the skin surface
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Skin Appendages: Sweat Glands
• Two main types of sweat (sudoriferous)
glands
1. Eccrine or merocrine sweat glands—abundant on
palms, soles, and forehead
•
•
Sweat ducts connect to pores
Function in temperature regulation
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2. Apocrine sweat glands—confined to axillary and
anogenital areas (animals use smells from these to
identify the opposite sex)
• Secretion is sweat + fatty substances and proteins;
odorless secretion but bacteria feed off it and make
odor
• Functional from puberty onward
– Specialized “sweat” glands:
• Ceruminous glands—in external ear canal; secretes
cerumen or wax
• Mammary glands—secrete milk
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Sebaceous (Oil) Glands
•
•
•
•
Widely distributed
Typically located near hair follicles-keep hair moist
Made up of branched alveolar glands
Become active at puberty
– Secrete an oily secretion called sebum
– Bactericidal
– Softens hair and skin
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Specialized Receptors:
• Pressure:
– Meissner corpuscles—light touch
• In Papillary layer
– Pacinian Corpuscles—deep touch
• In Reticular layer
Nails
• Scalelike modification of epidermis on distal,
dorsal surface of fingers and toes
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Hair
• Consists of dead keratinized cells
• Contains keratin which is tougher and more
durable than soft keratin of skin
• Root is in skin, shaft projects from the skin
• Hair pigments: melanins (yellow, rust, brown,
black)
– Gray/white hair: decreased melanin production,
increased air bubbles in shaft
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Hair
• Functions
– Alerts body to presence of insects on skin
– Helps to keep us warm
– Guards scalp against physical trauma, heat loss,
and sunlight
• Distribution
– Entire surface except palms, soles, lips, nipples,
and portions of external genitalia
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Hair Follicle
• Extends from epidermal surface into dermis
• Two-layered wall: outer--connective tissue,
inner--epithelial tissue
• Deep end expands to form hair bulb
• Sensory nerve endings wrap around each hair
bulb or root
• Bending of hair stimulates these nerve
endings; hair functions as a very sensitive
touch receptor
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Hair Follicle
• Arrector pili muscle
– Smooth muscle attached to follicle
– Responsible for “goose bumps”
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Hypodermis or superficial fascia (because it is superficial
to the fascia which wraps the skeletal muscles)
Not technically part of skin
• Subcutaneous tissue deep to dermis
• Consists mostly of adipose tissue
– This area gets thicker with weight gain
• What surgical procedure do some people have to get
rid of this fat?
• Anchors skin to underlying structures
• Is shock absorber
• Is an insulator
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LABWORK
1. List, identify, and describe the major regions of the
skin.
2. List, identify, and describe the layers of the epidermis
(Pacinian and Meissner’s Corpuscle slides may work
best).
3. List, identify, and describe the structures found in the
dermis (scalp and corpuscle slides may be best).
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