Download Integumentary System

INTEGUMENTARY SYSTEM
Produced by asistant lecturer:
zahraa ahmed
Definition:
The skin or integument is the largest organ in
the mammalian body and is comprised of an
epithelial covering, its derivatives (including hair,
nails ,and several types of sweat and sebaceous
glands) and its associated connective tissue.
the surface of body are covered either by thin
skin or thick skin
Layers Of The Skin
 Skin consist of two distinct regions
1. Epidermis – outer
Is non vascular and is lined by keratinized stratified
squamous epithelium
2. Dermis – inner
Characterized by dense irregular connective
tissue,blood vessels,nerves,and different gland
Beneath the dermis is the hypodermis or
subcutaneous layer of connective tissue and
adipose tissue that forms the superficial fascia
seen in gross anatomy
Epidermis
Composed of stratified squamous epithelium
Avascular as it has no blood supply of its own
Oxygen and nutrients diffuse from the underlying
dermis
The most abundant epithelial cells, the keratinocytes
form different layers.
Thick skin (5) and thin skin (4)-refer only to the
epidermis.
Five structurally different layers can be identified:
EPIDERMAL LAYERS
 Stratum basale .
 Stratum Spinosum
Stratum Granulosum
 Stratum Lucidum
 Stratum Corneum
The stratum basale(First Layer)
is the deepest layer of the
epidermis .It consists of a single
layer of columnar or cuboidal cells
which rest on the basement
membrane
Basal cells serve as stem cells for
the epidermis.
Stratum Spinosum(second layer)
 This consists of 4-6 rows of cells
 Cells synthesize keratin filaments that become assembled
into tonofilaments.
 Also contain Langerhans cells, part of the immune system
(defense against microorganisms and cancers).
The stratum granulosum(Third Layer)
 Consists of 3-5 cell layers of flattened cells.
 Cells filled with dense keratohylaine granules(
hence the name of the layer). and membranebound lamellar granules.
 Dendritic cells found throughout this stratum
 Nuclei already begin to degenerate in the
outer part of the stratum granulosum.
stratum lucidum (fourth Layer)
lucidum can usually not be identified in thin skin
is translucent and barely visible (in thick skin of the
palms and soles.)
The tightly packed cells lack nuclei or organelles and are
dead .
The flatted cells contain densely packed keratin filaments
Stratum corneum (the fifth layer)
All nuclei and organelles have disappeared from the
cells .
Consist of flatted , dead cells filled with soft keratin
filaments
Superficial cell from this layer are continually shed
or replaced by new cells arising from the deep
stratum basale.
The protection of the body by the epidermis is due to
the functional features of the stratum corneum
Dermis
can recognize a division into two structully distinct layers .
The papillary layer
1. Basement membrane separate the dermis from the epidermis
2. Is the superficial layer in the dermis and contain loose
irregular C.T.
3. Dermal papillae and epidermal ridges form evagination and
interdigitations .
4. Connective tissue filled with fiber ,capillaries,blood vessels
,fibroblasts , macrophages ,and another loose C.T.
5. Senseory receptor are resent in the dermal papillae .
6. dermal papillae, that project into the under surface of the
epidermis .When it contain a blood vessel then called vascular
papillae, but when it contain a nerve ending (Meissner
corpuscle) .
.
The reticular layer
 lies deep to the papillary layer; it characterized by
thick , irregular bundles of collagen and elastic fibers.
 less cellular than papillary layer.
 No distinct boundary between the papillae and
reticular layers.
 Accessory organs of epidermal origin, such as hair
follicles and sweat glands extend into the dermis.
 contain Sensory receptors_ Meissner’s and Pacinian
corpuscles
 The hypodermis contains variable amounts of
adipose tissue.
Other skin cells
Keratinocytes:represent the majority of cells
Melanocytes:derived from neural crest cells,have long
,irregular cytoplasmic or extension that branch into the
epidermis ,located between the stratum basal and stratum
spinosum of epidermis ,and synthesize melanin which
transferred from cytoplasmic extension to Keratinocytes in
basal cell layer,and melanin darkens skin color and
protects it from u.v.radation .
Langerhans cells (dendritic cells ):originated from bone
marrow ,migrate via blood stream to the skin in stratum
spinosum , are- part of immune system of skin ,and are
antigen-presenting cells of the skin.
Merkel cells:found in stratum basal layer of epidermis and
function as mechanoreceptor for sensation.
Thick versus Thin Skin:
 The terms thick and thin refer to the thickness of the epidermis.
 Most of the body is covered by thin skin.
 thin skin contains hair follicles, sebaceous glands, and arrector
pili muscles.
 The epidermis in thick skin may be six times thicker than the
epidermis that covers the general body surface.
 Thick skin does not have hair, smooth muscles, or sebaceous
glands but contains sweat glands .
 Thick skin on the palms of the hands, the fingertips, and soles
of the feet may be covered by many layers of keratinized cells
that have cornified.
Major function of skin
1. Protection through the keratinized epidermis from abrasion
and the entrance of pathogen
2. Impermeable to water ,owing to lipid layer in the epidermis
3. Body temperature regulation as a result of sweating and
changes in the vessel diameters.
4. Sensory perception of touch ,pain ,pressure ,and temperature
changes because of nerve endings
5. Excretions through sweat of water ,sodium salts,urea,and
nitrogenous waste .
6. Formtion of vitamine D from precursore molecules produced
in the epidermis when exposed to the sun
Skin derivatives
Hair
 Developed from the epithelium of the epidermis and
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reside deep in the dermis
Are hard cylindrical structure that arise from hair
follicles
Surrounded by external and internal root sheaths
Grow from the expanded hair bulb of the hair follicle .
Hair bulb indented by connective tissue(dermis) papilla
that is highly vascularized
Functions of Hair
 Prevents heat loss,
 Decreases sunburn,
 Eyelashes help protect eyes
 Touch receptors senses light touch,
Skin derivatives
sebaceous glands
Numerous sebaceous associated with each hair follicle
Cells in sebaceous glands grow ,accumlate secretion
,die and become oily secretion sebum .
Smooth muscles arrector pili attach to the papillary
layer of the dermis and to the sheath of the hair
follicle
Contraction of the arrector pili muscle stands hair
up and for forces sebum into the lumen of the hair
follicle
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