9/30/2013
Integumentary System
9/30/2013
Basics of Epithelial Tissue
• Sheet of cells that covers a body surface or lines a
body cavity
– Covering and Lining: outer layer of skin, inner and
outer lining of most organs and body cavities
– Glandular: creates the glands; one or more cells that
make and secrete an aqueous fluid
• Barrier that most substances received by or given
off from the body must pass through
• Rest upon and supported by connective tissue
• Avascular (no blood supply), but innervated (has
supplied by nerve fibers)
– Nourished by blood vessels in the underlying
connective tissue
Functions of Epithelial Tissue
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Protection
Absorption
Filtration
Excretion
Secretion
Sensory Reception
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Coverings and Linings
• Continuous multicellular sheets composed of at least 2
primary tissue types
– Epithelium bound to underlying connective tissue proper
• Cutaneous Membrane: skin
– Organ system consisting of keratinized epithelium
(epidermis) attached to a layer of dense irregular
connective tissue (dermis)
• Mucous Membranes: line body cavities that open to
the exterior
– Moist membranes bathed in secertions (or urine)
• Serous Membranes: found in closed body cavities
– Thin, clear serous fluid that lubricates the membranes and
surrounding organs
Overview
• Skin is the largest organ in the body
• Accounts for about 7% of total body weight in
adult
• Aka, Integument = “covering”
• Composed of two distinct regions: epidermis
and dermis ( 3rd hypodermis)
– Each region of epidermis consists of several layers;
each layer is called a stratum
Integumentary System: Functions
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Protection
Body Temperature Regulation
Cutaneous Sensation
Metabolic Functions
Blood Reservoir
Excretion
Absorption
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Functions: Protection
• Chemical Barriers
– Skin secretions—low pH (aka, acid mantle); natural
antibiotics
– Melanin—barrier preventing UV damage
• Physical/Mechanical Barriers
– Continuity of skin
– Keratinized cells—hard, “shell-like” barrier
• Biological Barriers
– Immune cells in both epidermis and dermis; i.e.,
dendritic cells in epidermis, macrophages in dermis
Functions: Body Temperature Regulation
• Body Temperature Rises
– Nervous system stimulates dermal blood vessels to dilate
– Sweat glands are stimulated into vigorous secretory
activity
– Visible output of sweat is called sensible perspiration
• Body Temperature Falls
– Dermal blood vessels constrict
– Warm blood bypasses skin temporarily
– Skin temperature drops to external environment
temperature
– Passive heat loss from body is slowed, conserving body
heat
Functions Continued
• Cutaneous Sensation
– Receptors part of the nervous system located in skin that respond
to stimuli arising outside the body (touch, pain)
• Metabolic Functions
– Vitamin D production when exposed to UV from the sun
– Keratinocyte enzymes can “disarm” many cancer-causing
chemicals that penetrate epidermis
• Blood Reservoir
– Dermal vascular supply can hold about 5% of the body’s entire
blood volume
• Excretion
– Nitrogen-containing wastes (i.e., ammonia, urea, and uric acid) are
eliminated from the body in sweat
• Absorption
– Oxygen, Nitrogen, Carbon Dioxide, Nicotine, anything lipid soluble
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Epidermis
• Outer part of skin
• Composed of four to five strata depending on
location (i.e., thickness of skin)
• Deep to Superficial
– Stratum Basale
– Stratum Spinosum
– Stratum Granulosum
– Stratum Lucidum
– Stratum Corneum
Stratum Basale (Basal Layer)—
• aka, Stratum Germinativum- deepest layer of
epidermis
– In this layer the cells of the epidermis “germinate”
or are formed
• Cells undergo rapid division
• Consists of a single row of the youngest
Keratinocytes
• Located at the junction between the
epidermis and dermis
Stratum Spinosum (Prickly Layer)—
• Between the Stratum Basale and Stratum
Granulosum
• Cells start to round up like little balls
– cells change shape, dehydrate, and protrude into the
other layers from here—hence the name from the
spiny architecture of this layer
• Melanin granules and Langerhans’ cells (nonfixed) are abundant in this layer
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Stratum Granulosum (Granular Layer)
• Between Stratum Spinosum and Stratum
Corneum
• Here is where keratin production occurs
– stratum gets its name from granules of keratin found
there
– Keratin - a tough, durable protein that is secreted and
fills this stratum for protection
• holds up to lots of wear-and-tear and waterproofs the body
• actual protective mechanism in the epidermis
• 3-5 cell layers in which drastic changes in
keratinocyte appearance occurs
Stratum Lucidum (Clear Layer)—
• Between Stratum Granulosum and Stratum
Corneum in THICK skin only
• Protects soles of feet and palms of hands from
abrasion
– Occurs in reposne to pressure
• Thin transparent band that contains no pigment
– A few rows of flat, dead keratinocytes
Stratum Corneum (Horny Layer)
• Outermost layer of keratinized cells
– dead cells that have flattened out
• Varying ages of cells are found in this layer with
oldest near the surface and youngest closest to
the layer below.
– cells will remain there for two to four weeks until
they are lost or washed off.
• These cells are held together by very strong
cellular connections called tight junctions and
desmosomes
– Peel off in sheets when you get sunburned.
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Dermis
• The inner subdivision of skin
– Contains strong, flexible connective tissue
• Serves several functions
– Makes Sweat (Sudoriferous Glands)
– Secretes Oils (Sebaceous Glands)
– Gives rise to Hair & Nails
– Contains many sensory receptors and blood
vessels
Dermis
• Contains two types of connective tissue fibers
– Collagen
• Gives skin strength and resistance to stretching
– Elastin
• Allows your skin to stretch and then recoil back to normal
length
Dermis
• Two Layers
• Papillary Layer—forms projections into the
epidermis
– Contains sweat and oil glands, hair follicles, blood
vessels, lymph vessels, and the sensory nerves that
sense changes on the surface of the epidermis
• Reticular Layer—innermost layer of dermis
– Contains the network of collagen and elastic fibers
that gives skin its properties of strength and flexibility
– 80% of the thickness of skin
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Hypodermis
• Subcutaneous tissue just deep to the skin;
aka, superficial fascia
• Adipose tissue and areolar connective tissue
• Anchors skin to the underlying structures
– mostly muscles
• Strictly speaking, this is not part of the skin,
but it shares some of the skin’s protective
functions.
Skin Color
• Determined by the amount of melanin produced
– darker skin = more melanin production
• Melanocytes produce melanin
– located between the epidermis and dermis.
• Brown pigment serves two important purposes
– Primary way skin gets its color
– Protects from harmful UV rays
• 2 Additional Pigments
– Carotene: yellow to orange pigment (palms and
soles)
– Hemoglobin: reddish pigment yields pinkish hues
Glands Associated with Skin: Sweat
• Exocrine Glands = glands that secrete through a
tube/duct onto the surface; generally, have a local
effect.
• Sweat (Sudoriferous) Glands
– Sweat is composed mostly of water (99%); 1% =
potassium ions, lactic acid, ammonia, and sodium chloride
(making sweat taste salty)
• Types of sweat glands
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Merocrine: thin sweat
Apocrine: thick sweat
Ceruminous: cerumen (ear wax)
Mammary: milk during lactation
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Merocrine Glands
• Most numerous on the skin
• Produce watery perspiration that cools your
body temperature and aids in excretion
• Most abundant on the soles, palms, and
forehead
• On average, you will sweat five hundred
milliliters per day without realizing it
– With heavy exercise, you could lose up to one liter
of sweat per hour.
Apocrine
• Associated with hair follicles
– Help reduce friction between the hair follicle and the
surrounding skin.
• Anogenital and axillary regions, areola, beard
region of men
• Scents associated with body odor
– particularly active with stress and sexual stimulation
Sebaceous (oil) Glands
• Produce an oily secretion called sebum
– keeps the skin and hair supple and prevents it from
becoming dry, brittle, and scaly
• Acne is a condition in which the sebaceous
glands ducts become blocked
– secretions accumulate, and a bacterium colonizes
the area
– genetic predisposition, or by hormone fluctuations
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Hair
• One hair is called a pilus; many hairs are called pili
• Filamentaous strands of dead keratinized cells
produced by hair follicles
– hard keratin- tougher and more durable than the soft
keratin of the skin
• Hair originates in the dermis of the skin at the bulb
• Composed of three layers – core called a medulla,
cortex, outermost cuticle
• Pigmented by melanocytes at the base of the hair
and transferred to the cells of the cortex
– Yellow, brown, black
– Red hair also has an iron-containing pigment called
trichosiderin.
Hair Function and Distribution
• Functions
– Maintain warmth
– Alert body to insects on skin
– Guarding scalp against heat loss, sunlight and physical
trauma
• Hair is distributed over the entire skin surface
except
– Palm, soles, lips, nipple and portions of external
genitalia
Nails
• Scale-like modification of the epidermis
• Forms a clear protective covering
• Changes in nail appearance may help diagnose
certain conditions
– Yellow-tinged nails = respiratory or thyroid gland
disorders
– Yellow-tinged and thickened nails = fungal infection
– Outwardly concave nail (spoon nail) = iron deficiency
– Horizontal lines (Beau’s Lines) = malnutrition
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Skin Cancer
• 3 Major Types of Skin Cancer
– Basal Cell Carcinoma: cells of Stratum Basale
proliferate and invade the dermis and hypodermis
• Least malignant, most common
– Squamous Cell Carcinoma: arises from keratinocytes of
the Stratum Spinosum
• Scalp, ears, lower lip
– Melanoma: cancer of melanocytes
• Most dangerous – highly metastatic
Melanoma ABCD (E) Rule
• Asymmetry: two sides of pigmented area don’t
match
• Border: irregular and exhibits indentations
• Color: pigmented area is black, brown, tan and
sometimes red or blue
• Diameter: larger than 6mm (pencil eraser)
• Elevation: raised
Burns
• Critical if…
– 25% of the body has second degree burns
– 10% of the body has third degree burns
– Third degree burns on face, hands, feet
• First Degree: only the epidermis
• Second Degree: epidermis and upper regions of
the dermis
• Third Degree: entire thickness of the skin is
damaged
– Painless because the nerves have been damaged
– Dehydration, infection
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Integumentary System
Picture Slides
3 Layers Become the 4 Tissues
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Epithelial Tissue - Covering
Connective Tissue - Support
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Skin: More Than Epithelial Cells
Squamous Cell Epithelium
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Layers of Epidermis
Layers of the Dermis
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Hypodermis
Sweat Glands
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Sebaceous Glands
Hair
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Nail
Skin Cancer
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