The integumentary
system
S
Skin
S Aka the cutaneous membrane, covers the external surface of the body
S Largest organ of the body in both surface area and weight
S 2square meters and 4.5-5kg
S Integumentary system also includes hair and nails
Structure of skin
S Epidermis
S Superficial, thinner portion
S Dermis
S Deeper thicker portion composed of connective tissue
S Subcutaneous layer (subQ or hypodermis)
S Not part of the skin
S Consists of areolar and adipose tissue
S Functions:
Storage depot for fat
S Large blood vessels to supply the skin
S Contains lamellated (pacinian) corpuscles sensitive to pressue
S
Epidermis
S Composed of keratinized stratified squamous epithelium
S 4 types of cells
S Keratinocytes
4-5 layers produce protein keratin, protects skin and underlying tissue from heat,
microbes, chemicals
S Also produce lamellar granules – release water-repellant sealant
S
S Melanocytes
S Produce pigment melanin – protects skin from UV rays
S Langerhans cells
S Participate in immune response
S Merkel cells
S Contact sensory neuron called a tactile (merkel) disc –detect different aspects of
touch
Continued
S Has 4 layers called thin skin
S Where friction is greatest (fingertips, palms and soles) has 5 layers, called thick skin
S Stratum basale
S Deepest
S Single row of cuboidal/columnar keratinocytes, some skin cells continuously produce new
keratinocytes
S Skin cannot regenerate if this layer is destroyed
S Stratum spinosum
S 8-10 layers of keratinocytes
S Cells in superficial layers become flatter
S Stratum granulosum
S 3-5 layers flattened keratinocytes undergoing apoptosis
S Contains lamellar granules
Continued
S Stratum lucidum
S Only in thick skin
S 3-5 layers flattened keratinocytes
S Stratum corneum
S 25-30 flattened dead keratinocytes
S Continuously shed
S Protect deeper layers
S Constant exposure to friction = callus
S Cells move from the bottom – top layer slowly accumulating more
keratin (keratinization)
S Excessive shedding of of skin = dandruff
Dermis
S Composed of connective tissue containing collagen and elastic fibers
S Superficial portion consists of areolar connective tissue and here the
surface area is < by dermal papillae
S Contains Meissner corpuscles, capillary loops, free nerve endings associated
with warmth, coolness, pain, tickling, itching
S Deeper part is attached to the subcutaneous layer and consists of dense
irregular connective tissue
S Adipose cells, hair follicles, nerves, oil glands, and sweat glands are found
here
S Collagen and elastic fibers provide skin with strength, extensibility, elasticity
S
Extreme stretching may produce small tears in the dermis called striae or stretch
marks
Skin color
S Melanin cause skin color to vary from pale yellow-red-tan-black
S Differences in color are due to the amount of melanin produced
S If melanin accumulates in patches = freckles
S As you age tannish blemishes called liver spots
S Benign localized overgrowth of melanocytes = nevus or mole
S Exposure to UV light stimulates melanin production
S Tan is lost when melanin containing keratinocytes are shed
S Albinism is the inability to produce melanin
S Depending on the amount of blood and oxygen content of the blood light
skinned people can appear pink to red because of hemoglobin
S Carotene is a yellowish-orange pigment that is a precursor of vitamin A ( used
to synthesis pigments needed for vision)
S Accumulates in stratum corneum and fatty areas of the dermis and subQ in
response to excessive dietary intake giving the skin an orange color
Hair (pili)
S On most surfaces of the skin except the palms, palmar surfaces, fingers,
soles, plantar surfaces of the toes
S Each hair is a thread of fused dead keratinized cells that consists of a
shaft and a root
S Root penetrates into the dermis or subQ and is surrounded by a hair follicle
S
It is composed of 2 layers of epidermal cells ( external and internal root sheath)
S
Surrounded by nerve endings (hair root plexuses)
S
Onion shaped structure at its base is the bulb
S Contains a region called the matrix that produces new hair cells
S
Papilla of the hair contains many blood vessels to nourish the growing hair
Continued
S Arrector pili extends from upper dermis to side of hair follicle
S Under stress it is stimulated by nerve endings to contract pulling the hair
shafts perpendicular to the skin and producing goose bumps
S Color is due to melanin synthesized by melanocytes in the matrix of the
bulb
S Blonde and red hair contain variants of melanin with Fe and S
S Grey hair is due to decline in melanin
S White hair is the result of air bubbles in the hair shaft
S At puberty testes secrete androgens = male pattern of hair growth
Sebaceous glands
S Lie in the dermis and open onto hair follicles
S Secrete an oily substance called sebum
S Keeps hair from drying out, prevents excessive evaporation from the skin,
keeps skin soft, inhibits growth of certain bacteria
S When they become enlarged because of accumulated sebum blackheads
develop
S Is nutritive to certain bacteria resulting in pimples or boils
Sudoriferous glands (sweat
glands)
S Eccrine glands
S More common
S Distributed throughout body with exceptions
S Secretory portion is located in the deep dermis, duct projects upward and
ends at a pore on the epidermal surface
S
Consists of water, ions, urea, glucose, lactic acid
S Apocrine sweat glands
S Found in skin of axilla, groin, areolae, bearded region of face
S Secretory portion in the subQ, excretory duct opens onto hair follicles
S Do not function until puberty
S Stimulated during emotional stress, sexual excitement
S Secretions are known as cold sweat
Ceruminous glands
S Present in external auditory canal
S Secretions combine with sebaceous glands creating cerumen
S Provides sticky barrier against foreign bodies
Nails
S Plates of tightly packed, hard, dead, keratinized cells of the epidermis
S Consists of nail body, free edge, nail root
S Whitish area near root = lunula
S Color is because vascular tissue underneath does not show as a result of
thickened stratum basale
S Nail growth occurs by transformation of superficial cells of the nail
matrix into nail cells
S Cuticle consists of stratum corneum
S Help grasp and manipulate small objects, provide protection to ends of
digits, allows us to scratch
Functions of the skin
S Body temperature regulation
S Liberating sweat, adjusting the flow of blood in the dermis
S Protection
S Cutaneous sensations
S Excretion and absorption
S Synthesis of vitamin D
S Exposure to UV rays activate vitamin D which will be converted into its
active form calcitriol which aids in the absorption of Ca and P in the
gastrointestinal tract
Aging and the integumentary
system
S effects begin to be noticeable in late 40’s and occur in the dermis
S Collagen fibers >#, stiffin
S Elastic fibers lose their elasticity
S Further aging Langerhan cells dwindle, sebaceous glands > in size,
production of sweat >, > in # of melanocytes
S Aged skin is thinner and heals porely