• Consists of skin and accessory structures
• Such as hair, nails, and glands
• Covers the outside of the body
• Forms the boundary between body and external
environment
• Protects the body from the outside world
• Protection : Skin protects against abrasion, UV light,
reduce water loss, prevent microorganism entry
• Sensation: Has sensory receptors, detect heat,
cold, touch, pressure, pain
• Temperature regulation: By control of blood flow
through skin, sweat glands
• Vitamin D production: Skin produce Vitamin D – UV
light
• Excretion: Excrete through skin
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Covers the entire outer surface of the body
Consists of two layers:
Epidermis
Dermis
Epidermis: Superficial layer of
epithelial tissue
– Resists abrasion
– Reduces water loss
• Dermis: Deep layer of
connective tissue
– Structural strength
• Hypodermis:
– Loose connective tissue that connects
skin to underlying structures (muscle or bone)
– Not part of skin
 Made up of stratified
squamous epithelial cells
 Separated from dermis by
basement membrane
 Avascular
 Nourished by diffusion from
capillaries of the dermis
 Composed of cells arranged
into layers or strata
Cell types
– Keratinocytes: most cells are keratinocytes
– Produce keratin (protein mixture) for strength
– Keratinocytes resist abrasion and reduce water loss
– Melanocytes: contribute to skin color
– Langerhans’ cells: part of the immune system
– Merkel’s cells: detect light, touch, and superficial
pressure
• Desquamate: cells of the deeper layers undergo mitosis;
as they move toward the surface, older cells slough off
• Keratinization: as cells move outward through the layers
they fill with keratin, die, and serve as a layer that resists
abrasion and forms permeability layer
 Epidermis is divided into different
regions or strata
 Stratum basale (germinitivum)
– Deepest portion of epidermis, single
layer of cuboidal or columnar cells
– Desmosomes & hemi-desmosomes
hold cell together
– High mitotic activity
– One daughter cell becomes the part
of stratum basale & other cell is pushed
towards the surface & keratinized
– Takes 40-56 days for cells to reach
epidermal surface & desquamate
Stratum spinosum
– Consists of 8-10 layers of
irregular shape cells
– Formation of lamellar bodies
(lipid-filled, membrane-bound
orgenelles) and additional
keratin fibers takes place
– Limited cell division
 Stratum granulosum
– Consists of 2-5 layers of diamondshaped cells
– Cytoplasm of cells contains
keratohyalin and lamellar granules
– Keratohyalin are non -membrane
bound protein granules
– Lamellar granules move to plasma
membrane & release lipids into
intercellular space & generate
water proof barrier
– In superficial layers nucleus and other
organelles degenerate and cell dies
Stratum lucidum
– Appears as thin, clear zone
– consists of several layers of
flattened dead cells
– Keratin fibers are present
– Found only in palms and
soles
Stratum corneum
– Most superficial layer, consists of 25 or
more dead squamous cell layers
– Consists of keratin and lamellar bodies
– Keratin – mixture of keratin fibers &
keratohyalin
– Gives structural strength
– Lamellar bodies – release lipids,
responsible for permeability
– Excessive desquamation from dry skin –
dandruff
 Thick skin
– Has all 5 epithelial strata
– Found in areas subject to
pressure or friction
Palms of hands, fingertips,
soles of feet
– Outermost layer of epidermis is
thick
– Contains numerous sweat
glands, lack sebaceous glands,
hair follicle, smooth muscle
fibers
 Thin skin
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–
–
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More flexible than thick skin
Covers rest of body
Hair grows here
Contains sweat glands,
sebaceous glands and hair
follicle
 Skin color is determined by 3
factors:
 Pigments
 blood circulating through the
skin
 thickness of stratum corneum
• Melanin
• Group of pigments responsible for skin,
hair and eye color
• Provides protection against UV light
• Two forms of melanin
• Pheomelanin: which is red to yellow in color,
found in light color skin
• Eumelanin: which is dark brown to black,
found in dark color skin
• Amino acid Tyrosine tyrosinase dopaquinone →
pheomelanin or eumelanin
• Melanin is produced at the base of the
epidermis ( stratum basale & spinosum) by
specialized cells called melanocytes
• Albinism:
• Absence of pigment in skin, hair and eyes
• Recessive genetic trait cause inability to produce
enzyme tyrosinase
• Melanin production is determined by genetic factors,
exposure to light and hormones
 Blood circulating through the skin
– Erythema: Increase in blood flow, gives reddish
color to skin
– Eg. blushing, anger, inflammation
– Cyanosis: blue color caused by decrease in blood
oxygen content
– Shock: Decrease in blood flow, Pale color skin
Thickness of stratum corneum
 Carotene, yellow pigment found in plants, such as
carrots, corn
• Source of Vitamin A
• Excess of carotene accumulates in stratum
corneum,
• in adipose cells of dermis, and in hypodermis
• Cause the skin to develop yellowish tint
• Disappears when carotene intake is reduced
• Gives structural strength
• Main C.T. fiber is collagen, but elastin
& reticular fiber is also present
• Dermis contains C.T. with fibroblasts,
macrophages and some adipocytes &
blood vessels
• Also contains Nerve endings, hair
follicles, smooth muscles, glands, and
lymphatic vessels
Function of nerve endings:
• Free nerve endings: pain, itch, tickle, &
temperature sensations
• Hair follicle receptors: light touch
• Pacinian corpuscles: deep pressure
• Meissner corpuscles: two-point
discrimination
• Ruffini end organs: continuous touch or
pressure
 Dermis is divided into two layers
– Papillary layer: Superficial (outer) 1/5
– Composed of loose areolar C.T. with
thin collagen and elastin fibers
– Contains fingerlike projections, called
dermal papillae, extend towards
epidermis
– In the palms, fingers, soles, and toes
papillae forms friction ridges which
improves the grip of hand and feet
– Friction ridges occur in patterns – use
in fingerprinting
– Reticular layer: Deep (inner)
4/5
– Main layer of dermis
composed of dense irregular
C.T.
– And contains dense conc. of
collagen, elastic and reticular
fibers
– Contains hair follicles,
sebaceous glands, sweat
glands, receptors, and blood
vessels
 Cleavage (tension) lines
 In reticular layer, elastin and
collagen fibers are oriented more
in some directions than in others
and produce cleavage or tension
lines
 Important in surgery
– If incision parallel to lines, there is
less gapping, faster healing, less
scar tissue
 If skin is overstretched, striae
(stretch marks) occur – Can
develop during pregnancy in
women`s abdomen and breasts
• Deep to skin
• Consists of loose connective tissue
with collagen and elastic fibers
• Main types of cells in hypodermis are:
– Fibroblasts
– Adipose cells
– Macrophages
• Hypodermis is also called
– Subcutaneous tissue
– Superficial fascia
• Contains about one-half of body’s fat.
Functions as
– Energy source
– Insulation
– Padding
• Found everywhere on
human body except palms,
soles, lips, nipples, parts of
external genitalia, and distal
segments of fingers and
toes
• Hair is divided into
• Shaft
• Root
• Shaft- protrudes above skin
surface
• Root- located below skin surface;
base of root is the hair bulb
• Root & shaft of hair are
composed of dead keratinized
epithelial cells & has 3 concentric
layers
– Medulla: Central axis
– Cortex: Forms bulk of hair
– Cuticle: Forms hair surface
• Hair follicle: Contains the hair and
consists of
– Dermal root sheath
– Epithelial root sheath
– Dermal root sheath: part of dermis
that surrounds the epithelial root
sheath
– Epithelial root sheath: Divided into
an internal and external parts
• Contains all epithelial strata
• When approach hair bulb,
contains only stratum basale
• Supply a source of new
epidermis after injury
• Hair bulb
– Hair bulb is the base of hair root
– Consists of matrix – mass of
undifferentiated epithelial cells
– Matrix produces hair and
internal epithelial root sheath
– Dermis of skin projects into hair
bulb as hair papilla
– Hair papilla contains blood
vessels & provide nourishment
to matrix
Hair Growth
 Hair is produced in cycles and involve
• Growth and resting stages
– Growth stage:
– Hair is formed by matrix cells, cells added at
base and hair elongates
– Resting stage:
– Hair growth stops then hair falls out of follicle.
New hair begins.
– Regular hair loss normally means hair is being
replaced
Hair Color
 Caused by varying amounts and types of melanin
 Melanin can be black-brown and red
 Major skin glands are:
- Sweat glands
- Sebaceous glands
 Sebaceous Glands
– Located in the dermis
– Simple or compound alveolar
glands produce sebum
– Sebum – oily, rich in lipids, release
by lysis of secretary cells
– S. glands are classified as Holocrine
– Connected to hair follicle by duct
– And sebum oils the hair & skin
surface
– Prevents drying and may inhibit
bacteria
Sweat (Sudoriferous) Glands:
 Two types:
 Merocrine, or eccrine
sweat glands
 Apocrine sweat glands
(may secrete in merocrine
or holocrine fashion)
Merocrine or eccrine sweat
glands:
– Most common
– Simple coiled tubular glands
– Open to surface of skin through
sweat pores
– Contains two parts
– Coiled part is located in dermis,
and duct passes to skin surface
Merocrine or eccrine sweat
glands:
– Coiled part of gland produce isotonic
fluid, mostly water some salts like NaCl
and small amount of ammonia, urea,
uric acid and lactic acid
– As fluid moves through duct, NaCl is
moved by active transport back into the
body and conserve salts
– Resulting hypertonic fluid that leaves the
duct is called Sweat
– Sweat glands regulate body temp
– Numerous in palms and soles
 Apocrine
– Simple, coiled, tubular glands open
into hair follicles
– Found in axillae, genitalia and
around anus
– Active at puberty
– Secretions contain organic
compounds such as 3-methyl-2hexenoic acid that are odorless but,
when acted by bacteria, may
become odiferous – known as body
odor
• Ceruminous glands: modified merocrine sweat
glands located at external auditory meatus
– Earwax (cerumen): Combined secretion of ceruminous
gland and sebaceous glands
– Function:
– Cerumen in combination with hairs, prevent dirt and
insects from entry in ear canal and protect eardrum
• Mammary glands: modified apocrine sweat
glands located in the breasts
• Produce milk
 Nail is protecting covering of distal part of
finger or toe
 Tool for pick up small objects, scratching
 Nail contains a hard keratin
 Each nail has a
– free edge
– a body (visible portion)
– proximal root (embedded in the skin)
 Nail bed : Deeper layers of
epidermis below the nail
 Nail matrix: Proximal portion of nail bed
– Responsible for nail growth
 Nails normally appears pink – because
capillaries are present in dermis
 Lunula – Region over thick nail matrix,
appears as white crescent-shaped
 Nail folds – Lateral and proximal
edges of nail are covered by skin
 Nail groove – Edges are held in place
by groove
 Eponychium or cuticle – Proximal nail fold
projects into the nail body
 Hyponychium – Region beneath the free
edge of the nail
 Growth
– Fingernails grow 0.51.2 mm/day; faster
than toenails
– Grow continuously
unlike hair
– Do not have resting
phase
• Protection
• Skin protects underneath structure from mechanical
damage
• Dermis provides structural strength
• Stratified epithelium protects against abrasion
• Protect against microorganisms & other foreign
substances
• Melanin protect against UV radiation
• Protection from hair
• Nails protect ends of digits
• Skin reduces water loss
•
Sensation:
•
Sensory receptors are present in integumentary
system and body feels : Pressure, temperature,
pain, heat, cold, touch, movement of hairs
•
Temperature Regulation:
– Regulated by Sweat
– Blood flow through skin
– constriction of vessels – reduce the rate of heat loss
– dilation of blood vessels – increase the rate of heat
loss
Vitamin D Production
• Vitamin D (calcitriol): functions as hormone
– Stimulates uptake of Ca2+ and PO42– Necessary for bone formation, growth, nerve & muscle function
•
Vitamin D synthesis takes place in skin exposed to UV light
• When Precursor molecule 7-dehydrocholesterol exposed to UV light
and converted into cholecalciferol
• And Cholecalciferol modified to form calcitriol (active vitamin D)
•
Other sources are dairy, liver, egg yolks, supplements
• Excretion
• Removal of waste products from the
body
– Sweat: Water, salt, urea, ammonia, uric
acid.
• With age skin is easily damaged because epidermis
gets thinner & collagen amount decreases in dermis
• More skin infections, repair is slow
• Skin wrinkle due to decrease in elastic fibers
• Skin becomes drier – sebaceous gland activity
decreases
• Decrease in sweat gland activity and blood supply
causes poor ability to regulate body temperature
• With age skin is easily damaged because epidermis
gets thinner & collagen amount decreases in dermis
• More skin infections, repair is slow
• Skin wrinkle due to decrease in elastic fibers
• Skin becomes drier – sebaceous gland activity
decreases
• Decrease in sweat gland activity and blood supply
causes poor ability to regulate body temperature
• Functioning melanocytes decreases or increases
• No. of melanocytes increases on hands & face, eg. age
spots
• Melanocytes decreases in hair, eg. Grey hair
• Sunlight ages skin more rapidly