ANATOMY (Skin) Flashcards
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
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
layers of skin
-epidermis
-dermis
-hypodermis
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
epidermal derivatives
-hairs
-nails
-sebaceous and sweat glands
cells of epidermis
-stratified squarmous keratinized =keratinocytes
>melanocyes
>antigen presenting Langerhaans cells
>tacticle epithelial cells: Merkel cells
thickness of skin=
-thickness of epidermis
>major distinction between thick (palms and soles) and thin skin
Dermal papillae:
-irregular junction between epidermis and dermis
-projections that interdigitate with invaginating epidermal ridges=strengthens adhesion of the two layers
Immune (Langerhans) cell:
-similar to macrophages in rest of body
-sensory cells
-first cells that will encounter incoming pathogens
Sensory (Merkel) cell:
-case
-nervous system origin
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)
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)
layers of epidermis (bottom to top)
-stratum basale
-stratum spinosum
-stratum granulosum
-stratum lucidum
-stratum corneum
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
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)
stratum spinous
-Synthesis of keratin and other proteins (polyhedral cells)
-Thickest layer (epidermal ridges)
-basal layer: stratum germinativum
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
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
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
- Papillary layer
- 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)
