Uploaded by JESSICA CAVALLA

Integumentary System

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Integumentary System
 The integumentary system is the organ system that
protects the body from various kinds of damage,
such as loss of water or abrasion from outside.
 The system comprises the skin and its appendages
(including hair, scales, feathers, hooves, and nails).
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Skin
 Skin is the largest organ of the human body
 The skin is several layers deep of tissues and
comprised of a number of different type of cells.
 The three major layers of skin, that are comprised of
smaller layers, are the epidermis, dermis, and
hypodermis.
 The hypodermis is also known as the subcutaneous,
or subcutis layer
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Layers of Skin
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Epidermis
 The epidermis is the outermost layer of the skin
 It contains stratified, squamous epithelial cells
 Stratified- layers
 Squamous- flattened
 Epithelial- cells that line cavities, blood vessels, and
organs
 Epidermis is avascular
 This means it does not have a blood supply of its own
 Oxygen and nutrients diffuse up from the underlying
dermis
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Epidermis
 The epidermis is composed of 5 different layers
(from outer to innermost):
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Stratum corneum
Stratum lucidum
Stratum granulosum
Stratum spinosum
Stratum basale
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Layers of the Epidermis
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Stratum corneum
 Outermost layer, about 15 to 30 cell layers thick
 Nuclei no longer exist in these cells
 Completely composed of dead cells – this is the furthest
layer from the dermal blood supply
 Very flat, compacted cells – gives skin its protective
property
 In between the cells, the spaces have been filled with lipids
 Closest to the surface, cells appear loosely dense, due to
their constant shedding
 These cells have been keratinized
 Layers below release a tough protein, called keratin, that
become deposited into these cells
 Keratin is responsible for hardening and flattening the cells
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Stratum lucidum
 2nd layer from the skin surface, composed of several
layers of flattened, dead cells
 Nuclei are degenerated (broken down); only a few
nuclei, if any, can be seen under the microscope
 Thin layer of the epidermis,
 Extremely difficult to identify in thin skin, almost
appears translucent
 This transLUCent property gave rise to its name
 A precursor to keratin can be found in these cells
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Stratum granulosum
 3rd layer from the skin surface
 Thin layer of the epidermis
 A few layers deep in thick skin, one layer in thin skin
 Cells in this layer contain Lamellar granules
 These granules release lipids and proteins into the
space above, causing the cells above to start losing
their nuclei and organelles
 These granules also gives rise to a hydrophobic
envelope that serves as the skins’ barrier
 The name for this layer came from these granules
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Stratum spinosum
 4th layer from the skin surface
 Thickest layer of living keratinocyte cells
 Cells are irregular, polygons in shape
 Cells have tiny spine-like extensions protruding off
the cell – giving this layer its name ‘spine’-osum
 Cells here are switching over from mitotic roles
(dividing) into keratin production
 These are the cells that begin the formation of keratin
precursors
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Stratum basale
 Deepest layer of the epidermis, found closest to the
dermal blood supply
 Contains a single, continuous layer of cuboidal
keratinocyte cells that sit on top of the basement
membrane
 Serve as the stem cells of the epidermis
 Stem cells- early cells that can become other types of cells
(called differentiation)
 Cells go through mitosis to continually replenish the
layers of cells above
 The further the cells get away from this layer, the sooner
they die
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Stratum basale
cont’d
 Besides keratinocytes, this layer contains
 Melanocytes
 These are cells that create melanin, the protein pigment
that gives skin its color
 These pigments also serve as protection for DNA from UV
rays
 Merkel Cells
 Touch receptors- nervous system
 Immune Cells
 Helps against infection
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Basement membrane
 This is a thin, non-cellular region that separates the
epidermis from the dermis
 Mostly composed of collagen fibers
 Anchors the epidermis to the dermis
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Dermis
 Is not composed of epithelial tissue, but connective
tissue
 Thicker than the epidermis
 Composed of two separate layers
 Dermal Papillary region
 Contains
 terminal blood capillaries
 Meissener’s corpuscles – receptors of touch
 Reticular Dermis
 Contains collagenous, elastic, and reticular protein fibers
 Gives skin its strength, extensibility, and elasticity
 also contains hair roots, glands, blood vessels
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Hypodermis
 Also known as the subcutaneous tissue
 Deepest, lowermost layer of the integumentary
system
 Anchors the skin to the deep fascia below it
 Composed of
 Fibrous bands- for anchoring
 Adipose cells- for fat storing
 Macrophages- for protection
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Accessory Structures
 Besides epithelial and connective tissue, the skin
contains a few other important structures:
 Hair
 Exocrine Glands
 Nails
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Hair
 Majority of skin is covered in hair
 Although humans appear to not have as much hair as
other mammals, they actually do
 Most of the hair is short, fine, and lightly pigmented
 Truly hairless body parts include palms of hands, soles of
feet, distal phalanges, sides of fingers and toes, and parts
of external genitalia
 The hair that we see is actually the terminal endings of
hair, called the shaft
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Hair Structure
 Root of the hair is anchored in a tubular invagination of
the epidermis
 A hair follicle surrounds the root of the hair and extends
down into the dermis, and sometimes the hypodermis
 The follicle is the only living, growing part of the hair
structure
 The follicle is at the same level blood vessels are
 As the cells divide and push the cells outward (hair
growing out) the cells begin to become keratinized and
die
 The arrector pili muscle is responsible for making your
hair stand up on its end
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Exocrine Glands
 There are two different types of sweat glands
 Apocrine- found mainly in the skin of the armpits, of the
anogenital areas, and of the areola of the breasts. Their
secretory portion is located in the dermis or hypodermis.
Their ducts open into hair follicles. Their secretion is more
viscous than that of the eccrine glands. They start secreting
at puberty and may be analogous to the sexual scent glands
of other animals (creating pheromones)
 Eccrine- are more common. Their secretory portion is
located in the dermis or hypodermis. They produce sweat, a
watery mixture of salts, antibodies and metabolic wastes.
Sweat prevents overheating of the body and thus helps
regulate body temperature.
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Exocrine Glands
 Ceruminous glands (or ear wax glands) and mammary
glands are modified apocrine sweat glands.
 Sebaceous glands- secrete the sebum (seb = oil) an oily
product. Sebum is usually secreted into a hair follicle.
Sebum is a natural skin cream:
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helps hair from becoming brittle
prevents excessive evaporation of water from the skin
Keeps skin soft
inhibits the growth of certain bacteria.
 Sebaceous glands are scattered all over the surface of
the skin except in the palms, soles and the side of the
feet.
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Nails
 Plates of stratified, squamous epithelial cells with
hard keratin
 Protects the distal ends of phalanges- replaces the
epidermis of the portion it covers
 Nail growth occurs in the lunula (the white crescent
part of your nail, visible in the thumb)
 Cuticle is a fold of stratum corneum on the proximal
end of nail
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Physiology
 The different layers of skin serve many important
purposes for the body
 Thermoregulation – sweat glands are distributed
throughout the integumentary system to assist in
cooling the body off in homeostasis
 Vitamin D Synthesis – using sunlight, the skin is
capable of creating Vitamin D for the body
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Physiology
 Protection – provides a barrier to fluid loss from the
body; intact skin prevents the entry of microorganisms into the body; melanin absorbs UV,
preventing harm to layers below
 Absorption – the skin can absorb topical
medications
 Sensation – working with the nervous system, skin
can sense pain, touch, temperature, vibration, and
pressure
 Secretion – water, oil, salt, and small amounts of
waste can leave via the skin
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