Integumentary notes for lecture PDF

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Summary

Integumentary summary notesQuick summary: The integument or skin is the largest organ in the body, both in weight and surface area. It is composed of two layers and contains many types of appendages, including hair, nails, and several glands. The layers of skin include: (1) an outer layer of stratif...

Description

1" " Integumentary summary notes

Quick summary: The integument or skin is the largest organ in the body, both in weight and surface area. It is composed of two layers and contains many types of appendages, including hair, nails, and several glands. The layers of skin include: (1) an outer layer of stratified keratinized epithelium, the epidermis and (2) an inner layer of dense irregular connective tissue, the dermis. These two layers sit upon the subcutaneous tissue, which is composed of loose connective tissue, adipose tissue, and dense connective tissue. Skin is classified into two types based on the thickness of the epidermis and keratin layer. Thick skin is found on the palms of the hands and soles of the feet. Thin skin covers the rest of the body. Functions of skin • Protection from UV light, chemical, thermal and mechanical sources, barrier against wetting, bacteria and fungus • Sensation - receptors for touch, pressure, pain and temperature • Thermoregulation – body heating thru insulation (adipose tissue) and cooling (sweating) • Metabolic functions- synthesis of Vitamin D (D3), adipose tissue for storage of TRIGS

The"integument"interacts"with"the"circulatory"system"through"blood"vessels"in"the"dermis,"and"with" the"nervous"system"through"sensory"receptors"for"pain,"touch,"temperature"etc." Parts&of&the&skin& • Consist"of"two"principal"parts"(epidermis"and"dermis)"and"underlying"layer"of"fatty"tissue" • Skin"appendages" " Epidermis@"the"outer"thinner"portion"composed"of"the"epithelium&& • 5"layers:"stratum"basale,"s."spinosum,"s."granulosum,"s."lucidum,"and"s."corneum" • Bound"by"underlying"dermis"by"a"basement&membrane" • Cells"@Stratified"squamous"keratinizing"epithelium" o The"most"abundant"cells"in"the"epidermis"are"the"keratinocytes" o Highly"specialized"self@regenerating"stratified"squamous"epithelium"which"produces" keratin& " • Keratin"(K)"is"tough,"protective"and"partially"water"resistant" • Non@epithelial"cells"in"epidermis"include:"melanocytes"(melanin"producing)," Langerhans&cells"(recognize"external"antigens)"and"merkel"cells"(touch"receptors)" • Does¬&contain&blood&vessels&or&nerves"@avascular" o Relies"on"diffusion"of"nutrients"and"oxygen"from"capillaries"of"the"dermis" • Additional"resistance"to"frictional"shearing"force"is"provided"by"rete&ridges"(a"series" of"epidermal"down"growths"(penetrate"the"upper"dermis"to"provide"tethering)" Basement membrane separated epidermis and dermis

2" " Dermis- the inner thicker portion composed of connective tissue to which the epidermis is attached o Tough layer of collagen and elastic fibres with fibroblasts responsible for the tone and texture of the skin o With blood vessels, nerves and sensory receptors o Exposure to sunlight and the aging process disrupts the skin’s texture causing it to loose elasticity and start to wrinkle • The layer in the upper dermis directly under the epidermis is least dense and contains many small blood vessels, many skin appendages and sensory nerve endings

Subcutis – subcutaneous layer (also called hypodermis) o A layer of adipose tissue often compartmentalised by downwards extensions of dermal collagen • Acts as a shock absorber and thermal insulator, and holds fat stores • Contains the lower parts of the hair follicles, apocrine glands and eccrine glands The dermis and Subcutis contain hair follicles, and many glands (sebaceous, eccrine and apocrine). Skin appendages – specialized structures – e.g. hair follicles, sweat glands, sebaceous glands in mainly the dermis and occasionally the upper Subcutis

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The"accessory"structures"generally"originate"in"the"dermis"and"extend"through"the"epidermis"to" the"skin’s"surface.""

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Epidermis -Layers of epidermis 5"layers"of"epidermis"@" top"to"bottom" o

Stratum"corneum"

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Stratum"lucidum" Stratum"

It"takes"about"15@30"days"fo a"cell"to"move"up"from"s." basale"to"s."corneum"

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granulosum" Stratum"spinosum" Stratum"basale"or" germinativium"

3" " Layer (top to bottom) Stratum corneum

Stratum lucidum

Stratum granulosum

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Stratum spinosum

Stratum basale

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Characteristics • Exposed surface of the skin, layer of dead protective cells filed with keratin • Occurs on all skin surfaces but the eyes • Consist of 15 - 30 rows of flat, dead cells of keratin • No nuclei • Typically dry - Coated with an anti-wetting agent synthesized by the cells of the granular layer • Water resistant, but not waterproof • Permits slow water loss by insensible perspiration • Lasts about two weeks before it is shed and replaced • Clear “glassy” layer (found only in thick skin) • Consists of about five layers of clear flat dead cells. • Tightly packed cells lack nuclei or organelles and are dead and just contain densely packed keratin filaments • “Grainy” layer - About five layers of cells with darkly stained granules. • The cells begin to lose their polyhedral shape and become progressively more flattened nearer the surface • Keratinocytes produce keratohyalin and keratin here • Gradually the cell membranes thicken, the organelles disintegrate, and the cells die • Keratin fibers develop as cells become thinner and flatter • At the surface the granular layer cells lose their nuclei and cytoplasm, leaving keratin only • “Spiny” layer consists of cells produced by the division of the stem cells of the stratum basale • Have about 8-10 rows of polyhedral shaped keratinocytes with spine like projections. • Called the spiny or prickle cell layer because of the presence of cells with spiny arms diverging outward and interconnecting (by desmosomes) with other prickle cells. • Langerhans cells and melanocytes are often present • Innermost, basal layer –germinal layer – attached to basement membrane by hemidesmosomes – forming a strong bond between the epidermis and dermis • Single layer of cuboidal or low columnar cells • Layer responsible for the constant regeneration of the other layers of the epidermis • The cells multiply to produce keratinocytes and contains epidermal stem cells, melanocytes and Merkel cells

4" " What is the difference between thick and thin skin?????? Know this

Thick"skin"(5"layers"of"epidermis),"more" keratin,"only"certain"areas"in"body"(e.g." palms,"soles)","no"hair"

Thin"skin,"4"epidermal"layers"seen"(no" stratum"lucidum),"thinner"layers,"less" keratin,"often"see"hair"follicles"

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Thickness"ranges"from"0.1"–"1.0"mm,"depending"on"location" o The"terms"“thin”"and"“thick”"skin"refer"to"the"thickness"of"the"epidermis" o Thin%skin"="hairy"skin"(most"of"the"body)"–"eyes"thinnest" o Thick%skin"="hairless"skin"(skin"on"palmar/plantar"surfaces,"i.e."palms/soles)" Basement membrane: between basal layer and dermis, three layers 1. Lamina lucida 2. Lamina densa 3. Fibro-reticular lamina • The basal cells of the stratum basale are tethered to the lamina densa by hemidesmosomes A word about epidermal ridges and dermal papillae (epidermal junction – EDJ) • The"EDJ"forms"an"undulating"interface"visible"by"routine"light"microscopy"as"downward"projections"of"

the"epidermis"(epidermal"ridges"or"rete"ridges"or"epidermal"pegs"or"interpapillary"pegs)"and" corresponding"upward"projections"of"the"papillary"dermis"(dermal"ridges"or"dermal"papillae)" o These"projections"interdigitate"to"increase"surface"area"and"to"reinforce"the"connection"(i.e." promote"adhesion)"between"epidermis"and"dermis" o Fingerprints"(only"present"in"thick"skin)"are"caused"by"prominent"dermal"ridges"but"are"not" recognizable"as"distinct"entities"by"light"microscopy"

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Epidermal&Cells& Melanocytes:"& • Responsible"for"melanin" • Present"as"scattered"cells"in"the"basal"layer"and"are"more"numerous"in"areas"which"are"exposed" to"light"(e.g."face)" • Round"cells"with"clear"cytoplasm" • Melanin"pigment"appears"as"a"brown"granules"on"H&E"" Langerhans&cells&–&are"intraepidermal"antigen@recognition"and"processing"cells,"and"are"present"in"all" layers"of"the"epidermis"but"are"most"easily"seen"in"the"prickle"cell"layer"(stratum"spinosum)" • Also"present"in"the"upper"dermis,"particularly"around"small"blood"vessels" • Langerhans"cells"express"a"large"number"of"lymphocyte"and"macrophage"surface"markers" • They"constantly"monitor"the"environment"on"the"skin"surface"and"in"between"epidermal"cells" with"their"dentritic"cytoplasmic"processes"and"are"potent"stimulators"of"cell@mediated" immunological"responses"in"the"skin" • Present"in"huge"numbers"in"epidermis"and"upper"dermis"in"many"inflammatory"skin"diseases" such"as"contact"dermatitis" " Merkel&cells@"intra@epidermal"touch"receptors"that"contain"neuroendocrine@type"membrane@bound" vesicles"(dense"core"granules)"in"their"cytoplasm" • merkel's"cells"–"synapse"site"for"nerve"fibers,"key"mediator"of"sensation" • Scanty"in"adult"skin"and"are"difficult"to"find" • Rounded"cells"with"pale@staining"cytoplasm"and"round"pale@staining"nuclei" "

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& DERMIS The dermis is composed of muscle, nervous, and connective tissue containing collagen and elastic fibers. @ Very vascular @ Dermis contains hair follicles, sensory nerves, glands, muscles and blood vessels @ Two regions - the Papillary and Reticular layers. 1. Papillary layer - is loose areolar connective tissue containing fine elastic fibers o Contains small capillaries, lymphatics and sensory neurons o Dermal papillae are areas in papillary layer that connect to the epidermis and form ridges that make up the fingerprints and toe prints. 2. Reticular layer - is dense irregular connective tissue containing collagen and elastic fibers, adipose tissue, hair follicles, nerve, glands, and sensory nerves. o Contains larger blood vessels, lymph vessels and nerve fibers Epidermal accessory structures (hair follicles, sweat glands) extend into the dermis o The reticular dermis is thickest on the back and thinnest in the eyelids o Strength, extensibility, and elasticity are provided to the skin by the combination of collagen and elastin fibers. @

SUBCUTIS – subcutaneous layer • Composed of loose connective tissue - areolar and adipose • Acts as a shock absorber and thermal insulator, and holds fat stores • Stabilizes skin position o Loosely attached to dermis o Loosely attached to muscle • Contains the lower parts of the hair follicles, apocrine glands and eccrine glands • Also called hypodermis

Epidermal skin derivatives and appendages= hair follicles, sebaceous glands, eccrine sweat glands, apocrine gland Hair– the human body is covered with hair, except for the palms, soles, lips, and portions of external sex organs (functions – protect and insulate, sensitive to light touch) Hair follicles - produce long thin hair shafts composed of keratin surrounded by a cortex, with a surface cuticle composed of a single layer of flattened scales o The follicle is wrapped in a dense connective tissue sheath • The bases of the follicle is surrounded by sensory nerves

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Attached to hair follicle is a strip of smooth muscle called arrector pili o The muscle inserts one end into the hair follicle sheath and at the other end into the dermal papillary area The lower part of the hair follicle is attached to the integument by the hair root The upper part of the hair, not attached to the integument, is the hair shaft Each follicle has a sebaceous gland attached to it, which lubricated the hair Each hair begins in the hair bulb

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The"hair"has"three"layers"@from"outer"to"inner"–"cuticle,"cortex,"medulla"

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Cross@section"hair" Hair"bulb"

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Glands in the skin – two types of exocrine glands – sebaceous (oil) glands and sweat glands Sebaceous glands Majority associated with hair follicles and develop lateral protrusions from the hair follicle at the junction between its upper third and lower two-thirds • Secrete sebum (lipids) which provide some waterproofing of the skin surface

Sweat glands - Two"types"of"sweat"glands"exist:"small"eccrine"sweat"glands"that"produce"a"watery"

secretion,"and"larger"apocrine"sweat"glands"whose"secretions"are"more"oily"and"foamy. Eccrine (merocrine) sweat glands – widespread thru-out skin especially palms, soles, forehead and axillae • Located around the dermis/Subcutis junction and synthesize sweat which is passed along the eccrine ducts and to the skin surface • Two main components – the main secretory component is a coiled secretory gland situated in the deep reticular dermis or upper Subcutis • The secretory gland component has an inner layer of columnar cells

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Serve several function – cooling skin surface, excreting water and electrolyte, flushing microorganisms or harmful chemicals from the skin surface

Eccrine"glands"

Apocrine glands – confined to a few localized areas mainly in the axillary (armpit) and groin regions -like sweat glands the secretory component is located in the lower reticular dermis or subcutis and the duct system carries the secretion thru the hair follicle above the sebaceous duct and out to the skin surface • Associated with hair follicles • Apocrine gland more of use in animals for territory marking and as a sexual attractant • Are large glands which always secrete into the adjacent hair follicle via a duct

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Modified apocrine glands • Ceruminous glands – outer ear – secrete ear wax • Mammary glands – milk Nails – packed with keratin, produced in a deep epidermal fold near the bone called the nail root o The"visible"portion"of"the"nail,"the"nail"body,"covers"a"portion"of"the"epidermis"called"the"nail"bed." Nerves and nerve endings in the skin • the skin is an important sensory organ and is richly innervated and supplied with many nerve endings • afferent nervous system – myelinated and non-myelinated fibres and is responsible for transmitting the impulses from the various nerve endings and the perception of cutaneous sensation • efferent nervous system – non-myelinated fibres from the sympathetic component of the autonomic nervous system, responsible for vessel diameter and blood flow Skin circulation • the arteries which supply the skin are located deep in the subcutis and branch upwards...