ANATOMY (Skin) Flashcards by Danielle Groenendijk

Function of skin:

-thermal regulation
-sensory
-protection and barrier (pathogens, water)
-metabolic (synthesize vitamin D3)
-sexual signalling (pigmentation and hair)
-mechanical strength
-flies (twitch)
-visually siganlling device
-olfactory signalling device

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skin size

-largest organ in the body
-15-20% of total body weight in humans
-integument or cutaneous layer
-much greater than the liver
-about half the collagen in body
-20% of the body’s protein

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layers of skin

-epidermis
-dermis
-hypodermis

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epidermis

-epithelial layer of ectodermal origin
-outermost part
-epidermal derivatives
-melanin
-epidermal ridges
-lacks vasculature
-keratinized
-limited physical strength
-resistant to friction
-inhibits diffusion
-sustains homeostasis

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epidermal derivatives

-hairs
-nails
-sebaceous and sweat glands

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cells of epidermis

-stratified squarmous keratinized =keratinocytes
>melanocyes
>antigen presenting Langerhaans cells
>tacticle epithelial cells: Merkel cells

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thickness of skin=

-thickness of epidermis
>major distinction between thick (palms and soles) and thin skin

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Dermal papillae:

-irregular junction between epidermis and dermis
-projections that interdigitate with invaginating epidermal ridges=strengthens adhesion of the two layers

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Immune (Langerhans) cell:

-similar to macrophages in rest of body
-sensory cells
-first cells that will encounter incoming pathogens

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Sensory (Merkel) cell:

-case
-nervous system origin

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Melanocyte:

-produce melanin pigment
-they are permeant
-come from neural crest during development
-melanin: injected into cells (why when you get a wound, you lose colour)

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Dermal-epidermal interdigitations:

-peg-and-socket variety in most skin=epidermal ridges-and-dermal papillae
-thick skin (palms and soles): well-formed ridges and grooves=more subject to friction
-different patterns for each person (dermatoglyphs = finger + footprints)

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layers of epidermis (bottom to top)

-stratum basale
-stratum spinosum
-stratum granulosum
-stratum lucidum
-stratum corneum

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Stratum basale

-One cell thick
-Mostly miotic cells (intense mitotic activity)
-Hair follicle sheaths that are continuous with the epidermis
-Hemidesmosomes in basal cell membrane join them to basal lamina
-Desmosomes bind the layer together in the later and upper surfaces

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stratum basale (mitotic activity)

-Progenitor cells for all epidermal layers (also in the deepest part of the next layer): basal stem cells for keratinocytes
-*characteristic cytoskeletal keratins (10nm diameter)

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stratum spinous

-Synthesis of keratin and other proteins (polyhedral cells)
-Thickest layer (epidermal ridges)
-basal layer: stratum germinativum

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stratum germinativum (basal layer of stratum spinous)

-where some cells still divide
-Keratin filaments assemble in tonofibrils
1. These converge and terminate at numerous desmosomes holding the cell layers together
2. Spines or ‘prickles’ at cell surfaces: Cells extend slightly around the tonofibrils on both sides of the desmosomes

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stratum granulosum

-3-5 layers of flattened cells
-Undergoing terminal differentiation process of keratinization
-Cytoplasms filled with keratohyaline granules (basophilic masses)
-Golgi-derived lamellar granules

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keratohyaline granules (stratum granulosum)

-Dense, non-membrane bound masses of filaggrin and other proteins associated with keratin tonofibrils

golgi-derived lamellar granulles (stratum granulosum)

-Many lamellae containing various lipids and glycolipids
-Under exocytosis producing a lipid-rich impermeable layer around the cells
*barrier for skins water loss

Stratum lucidum:

-only in thick skin
-translucent layer of flattened eosinophilic keratinocytes held together by desmosomes
-nuclei and organelles are lost
-cytoplasm consists of packed keratin filaments embedded in an electron-dense matrix

Stratum corneum

-Dead squames composed mostly of keratin
-15-20 layers of squamous cells
-Keratin filaments contain at least 6 different polypeptides
-Continuously sheds at the epidermal surface as desmosomes and lipid-rich cell envelope breaks

Keratinization and production of lipid-rich layer:

-prevents water loss
-also prevents penetration by most foreign materials

As cells move upwards:

-amount and types of keratin filaments increase until they represent about half the total protein in superficial keratinocytes

Friction blisters:

-lymph-filled spaces between epidermis and dermis of thick skin

Thicker skin:

-subject to continuous friction and pressure -thicker stratum spinosum with more abundant tonofibrils and desmosomes -stratum lucidum

Basal cell and squamous cell cancers:

-where 1/3 of cancers originate -both can be diagnosed and excised early

dermis

-Mesodermal connective tissues -Supports epidermis and binds it to subcutaneous tissue (hypodermis) -Thickness varies on region of body -Irregular surface -2 sublayers with indistinct boundaries -Rich network of blood and lymphatic vessels (vascular) -Strong -Collagen rich: runs in random directions (flexibility and strength) -Well innervated -Cannot maintain homeostasis

2 sublayers in dermis

1. Papillary layer 2. Recticular layer

Skin subject to frequent pressure:

-dermis had many dermal papillae to reinforce the dermal-epidermal junction

Thin skin dermis:

-more cellular and well-vascularized -less elastin -less coarse bundles of collagen

Papillary layer (dermis)

-dermal papillae -loose connective tissues (collagen fibers) -fibroblasts -scattered mast cells -dendritic cell -leukocytes -anchoring fibrils into basal lamina to help bind the dermis to epidermis

Reticular layer:

-much thicker -dense irregular connective tissues -more fibers and fewer cells than papillary layer -network of elastic fibers also present

Hypodermis (or subcutaneous tissue)

-Loose connective tissue layer -Contains pads of adipocytes -Binds skin loosely to underlying tissues -Corresponds to superficial fascia of gross anatomy -Appears similar to dermis -Fewer fibers -Layer that allows your skin to move freely (ex. where you inject)

nerve endings in the skin

-tactile (meissner) corpuscles -krause bulb -free nerve endings -root hair plexus -lamellated (picinian) corpuscles

Tactile (Meissner) corpuscles

-Light touch -Consist of sensory axons winding among Schwaan cells -Initiate impulses when light-touch against skin temporarily deform their shape -Numerous in fingertips, palms and soles -Decline during aging after puberty

Krause bulb

-Pressure -Encapsulated structure -Collagenous capsules penetrated by a sensory fiber -Primarily in skin, penis and clitoris -Sense low-frequency vibrations

Free nerve endings

-Temperature -Pain -Itching -Touch

Root hair plexus

-Mechanoreceptors for touch

Lamellated (picinian) corpuscles

-Sustained touch/pressure -Vibrations -Distortion of capsule amplifies a mechanical stimulase to the axonal core -Also found in connective tissue of organs deep in the body (wall of rectum and urinary bladder)

Apocrine sweat glands:

-secrete more protein-rich sweat into follicles of hair in skin -tubular glands -open into a hair follicle -smelly glands -development depends on sex hormones (not complete and functional until puberty) Ex. in humans: only in hairy parts of the body

Eccrine (merocrine) sweat glands:

-not associated with hair follicles -secrete a watery secretion (increase traction) -empty secretion onto skin surface via pores -most numerous on foot soles -myoepithelial cells 1. Light cells: ion pump 2. Dark cells: mucous secretion

light cells: ion pump (eccrine sweat glands)

-produce the sweat -lots of mitochondria and microvilli to provide large SA -interstitial fluid from capillary rich dermis around gland is transported into them

Myoepithelial cells:

-when signalled to released sweat, cell contracts to move watery secretion into duct

Sebaceous (oil) glands:

-associated with hair follicles -oil producing (secrete sebum into short ducts)