Skin Structure Skin Structure Skin is made of 3 layers: Skin is made of 3 layers: 1) 1) epidermis epidermis – stratified squamous epithelium stratified squamous epithelium cells cells – constantly replaced from inside out constantly replaced from inside out – entirely from ectoderm entirely from ectoderm 2) 2) dermis dermis – “ “ true skin” true skin” 3) 3) hypodermis – subcutaneous layer hypodermis – subcutaneous layer – last to develop last to develop – immigration of cells from other immigration of cells from other body regions body regions
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Skin StructureSkin StructureSkin is made of 3 layers:Skin is made of 3 layers:1)1) epidermisepidermis
– stratified squamous epithelium cellsstratified squamous epithelium cells– constantly replaced from inside outconstantly replaced from inside out– entirely from ectodermentirely from ectoderm
2)2) dermisdermis– ““true skin”true skin”
3)3) hypodermis – subcutaneous layerhypodermis – subcutaneous layer– last to developlast to develop– immigration of cells from other body immigration of cells from other body
regionsregions
EpidermisEpidermis
squamous cells stacked sequentially squamous cells stacked sequentially by levels of maturityby levels of maturity
older cells on the outsideolder cells on the outside
innermost cells are metabolically innermost cells are metabolically active and constantly undergoing active and constantly undergoing mitosis = mitosis =
stratum basalestratum basale
The stratum basale and any newly The stratum basale and any newly dividing cells immediately above the dividing cells immediately above the stratum basale =stratum basale =
germinativum – part that produces germinativum – part that produces other layersother layers
The cells of the epidermis start out The cells of the epidermis start out from the germinativum as cuboidal from the germinativum as cuboidal or columnar cells, then flattened as or columnar cells, then flattened as they migrate to the surface.they migrate to the surface.
it takes 60-75 days for cells to reach it takes 60-75 days for cells to reach the outermost skin from the the outermost skin from the germinativumgerminativum
mitosis in the germinativum occurs 2 mitosis in the germinativum occurs 2 ways:ways:
1)1) cytokinesis in the horizontal plane cytokinesis in the horizontal plane → an outer and inner cell→ an outer and inner cell– new skin layersnew skin layers– stimulated by vitamin Astimulated by vitamin A– accelerated by continuous pressure or accelerated by continuous pressure or
rubbingrubbing
2)2) cytokinesis in the vertical plane cytokinesis in the vertical plane → → growth of skingrowth of skin– response to growth and stretchingresponse to growth and stretching
Cells of the stratum germinativum Cells of the stratum germinativum are located on ridges called are located on ridges called dermal dermal papillaepapillae
These projections of the underlying These projections of the underlying dermis are bound to the epidermis dermis are bound to the epidermis cells by a thin layer of fibrous cells by a thin layer of fibrous connective tissue = connective tissue =
basement layerbasement layer
Interspersed in and on top of the Interspersed in and on top of the stratum germinativum are the stratum germinativum are the melanocytes in a layer called the melanocytes in a layer called the Malpighian layerMalpighian layer
These cells secrete These cells secrete melaninmelanin – a black – a black to brown colored chemical made of to brown colored chemical made of amino acid building blocksamino acid building blocks
Some people take the amino acid Some people take the amino acid tyrosine in an attempt to enhance tyrosine in an attempt to enhance melanin production during tanningmelanin production during tanning
no proof of effectivenessno proof of effectiveness
As germinativum cells move up they As germinativum cells move up they form the next layer called the form the next layer called the stratum spinosumstratum spinosum (prickly layer)(prickly layer)
many many desmosomesdesmosomes on the outer on the outer surface of these cellssurface of these cells
mixed in with these cells are mixed in with these cells are LangerhansLangerhans cells cells
Stratum spinosum cells give rise to Stratum spinosum cells give rise to the next layer of epidermis called the the next layer of epidermis called the stratum granulosumstratum granulosum– named for granules in the cytoplasmnamed for granules in the cytoplasm
accumulation of yellowish sulfur-rich protein accumulation of yellowish sulfur-rich protein = keratin= keratin
cells = keratocytescells = keratocytes
keratinkeratin
tough proteintough protein
gives strength to skin gives strength to skin
Keratocytes produce a substance Keratocytes produce a substance that acts as a waterproofing to that acts as a waterproofing to prevent the free flow of water into prevent the free flow of water into and out of the skinand out of the skin
Stratum granulosum cells flatten out Stratum granulosum cells flatten out into a layer of waterproof cells =into a layer of waterproof cells =
stratum compactumstratum compactum– dying cells filled with keratindying cells filled with keratin
The uppermost layer of skin = The uppermost layer of skin =
stratum corneumstratum corneum
flattened dead cellsflattened dead cells
shed during desquamationshed during desquamation
DermisDermis
thick layer of connective tissue thick layer of connective tissue attached to the stratum attached to the stratum germinativumgerminativum
majority of dermis is dense, irregular majority of dermis is dense, irregular connective issueconnective issue
the dermis also contains loose the dermis also contains loose connective connective tissue called connective connective tissue called areolar connective tissueareolar connective tissue
used throughout the body to bind used throughout the body to bind blood vessels, membranes, muscles, blood vessels, membranes, muscles, nerves, and skin to other structuresnerves, and skin to other structures
extensive meshwork of protein fibers extensive meshwork of protein fibers secreted by fibroblastssecreted by fibroblasts
thickness and makeup varies thickness and makeup varies throughout the body and form person throughout the body and form person to personto person
very thin or absent in the areas of very thin or absent in the areas of the:the:– eyelidseyelids– penispenis– scrotumscrotum– nipplesnipples
The subcutaneous layer is The subcutaneous layer is responsible for increases in female responsible for increases in female hips and breasts after pubertyhips and breasts after puberty
The subcutaneous layer differs from The subcutaneous layer differs from the dermis in many waysthe dermis in many ways
1)1) composed of loosely arranged composed of loosely arranged elastic fibers that anchor the skin to elastic fibers that anchor the skin to underlying underlying fasciafascia
– sometimes the subcutaneous layer is sometimes the subcutaneous layer is directly attached to bone and joint directly attached to bone and joint surfacessurfaces
2)2) contains large amounts of adipose contains large amounts of adipose tissue (fat cells)tissue (fat cells)
– thickness of the adipose tissue = thickness of the adipose tissue = indirect indicator of body fatindirect indicator of body fat
3)3) contains large blood vessels that contains large blood vessels that branch out into capillaries into the branch out into capillaries into the dermisdermis
lymph vessels are found along with lymph vessels are found along with the blood vessels (part of the the blood vessels (part of the immune system)immune system)
the subcutaneous layer is still the subcutaneous layer is still susceptible to infection = susceptible to infection = fasciitisfasciitis
deep nerves are located in the deep nerves are located in the subcutaneous layersubcutaneous layer
Langerhan cells – Langerhan cells – immune system cells immune system cells that are important in fighting skin that are important in fighting skin infections and healing injured skininfections and healing injured skin
fascia – fascia – a sheet of fibrous tissue that a sheet of fibrous tissue that covers muscle, skull bones, and covers muscle, skull bones, and some organssome organs
fasciitis – fasciitis – an irritation of the an irritation of the subcutaneous layer; can also result subcutaneous layer; can also result from injuries that leave bone from injuries that leave bone fragments or other material in skin fragments or other material in skin that is prone to pressure and that is prone to pressure and stretchingstretching
