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ENI 2 > 1. Skin structure and function 1-3 > Flashcards

1. Skin structure and function 1-3 Flashcards

1
Q

What are the 3 main layers of the skin

A
  • epidermis
  • dermis
  • subcutis
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2
Q

what is a keratonocyte? describe its function

A

the building block of the skin (over 90% of skin cells)
- provide the principle protection of the skin
- form intermediat efilaments to provide mechanical support
- like cell’s nuclear membrane to the plasma membrane at desmosomes
- anchored together by desmosomes that fit together like a zipper so they cant float apart (also provide intercellular signal)
- anchored to the dermis by hemidesmosomes (link between keratin intermediate filaments and interstitial collagen in the dermis
- large cells of epithelial origin with complex internal cytoskeletons
- immunologically active (produce extracellular lipids

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3
Q

what 3 things do karatinocytes need to be able to do to functionally create protective skin

A
  • strength
  • attachment to eachother
  • attachment to the underlying dermis (otherwise will peel off)
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4
Q

how do epidermal cells get nutrients

A

diffusion from dermal vessels etc.

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5
Q

Label

A
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6
Q

name the layers of the epidermis

A
  • stratum corneum
  • stratum granulosum
  • spinous spinosum
  • stratum basale
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7
Q

Discuss features of the stratum basale

A
  • single layer of cuboidal cells (both proliferative and anchoring)
  • have a structural role (attaching to the dermis via hemidesmosomes and keratinocyte to keratinocyte via desmosomes)
  • proliferative cells are mitotically active to produce daughter cells)
  • influenced by growth factors and hormones (epidermal growth factor, insulin like growth factor, karatinocyte growth factor, corisol and thyroid hormones), inflammatory mediators and drugs/viatmins
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8
Q

discuss the features of the stratum spinosum

A
  • 1-20 cells thick
  • polyhedral cells
  • prominent intracellular bridges (desmosomes)
  • upper layer produces involucrin (part of cornified layer)
  • appears spikey on histo
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9
Q

discuss features of stratum granulosum

A
  • variably present in haired skin
  • slightly flattened cells, shrunken nuclei with inracellular keratohyaline granules containing profilaggrin (glue)
  • various lipids and enzymes secreted extracellularly (creates a watertight seal)
  • desmosomes express corneodesmosin (slightly different desmosome)
  • sometimes not visible on histology but essential to forming stratum corneum
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10
Q

discuss features of the stratum lucidum

A
  • not present in haired skin!
  • variable present in hairless, thickened skin (nasal planum)
  • slightly flattened cells with shrunken nuclei
  • intracellular keratohyalin
  • increased intracellular lipids
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11
Q

discuss features of the stratum corneum

A
  • composed of anucleate flattened cells (squames) of variable thickeness (depends on location and species)
  • plasma membrane is replaced by cornified envelope comprising intracellular proteins (involucrin, loricin, peripalkin)
  • extensively cross linked with the aid of filaggrin and keratins
  • hydrophilic bonging of lipids forms organised mortar between squames
  • desmosomes now called corneodesmosomes due to addition of corneodesmosin
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12
Q

discuss the formation of the cornified envelope

A
  1. in the basal and spinous layers the cell membrane is a typical lipid bilayer
  2. in the upper granular layer, envoplakin and periplakin are laid on the cytoplasmic side of the cell membrane, under the influence of increased calcium.
  3. to this, involucrin anf transglutimase 1 are added.
  4. the contents of the lamella bodies are released into the cell membrane. ceramides are incorporated into the wall and fatty acids and cholesterol are released into the intercellular space
  5. the cell membrane is replaced by a ceramind and fatty acid complex. loricin, SPRPs and other proteins provide a strong stratum corneum
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13
Q

what is desquamation

A
  • the final part of terminal development
  • homeostatic process (continual loss of cells)
  • in part mediated by proteinases and glycosidases in which a variety of intracellular and intercellualr macromolecules are degraded
  • destructuion of the corneodesmosome
  • invisible rafts of attached corneocytes fall off
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14
Q

what is the dermis

A

connective tissue of mesenchymal origin containing insoluble fibres (collagen and elastin for tensile strength) and soluble polymers (proteoglycans and hyaluronan to resist and absorb compressive forces)
- thickeness of dermis determines the thickness of the skin
- divided into deep and superficial dermis
- contains epidermal appendages, arrector pili muscles, blood and lymph vessels and verves
- cells present include perivascular lymphocytes, dermal dendritic cells, mast cells and fibroblasts

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15
Q

name and describe the 2 different nerve types in the dermis

A

sensory nerves
- respond to touch, pressure, temp, nociception, pruritis
- has mechanoreceptors (free nerve endings, meissneners and pacinian corpuscles and tylotrich hairs, merkel cells, ruffini corpuscles, sinus hairs and tylotrich pads)

motor nerves
- has adrenergic and cholinergic fibres
- control arterioles, artichial and epitrichial sweat glands

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16
Q

name and describe the 3 layers of blood supply in the dermis

A

deep dermal vascular plexus
- interface of dermis and subcutis
- supply lower hair follicle and epitrichial sweat glands

mid-dermal vascular plexus
- level of the sebaceous glands
- supply arrector pili muscles, mid hair follicle and sebaceous glands

superficial dermal vascular plexus
- just below epidermis
- capillary loops supply epidermis and upper hail follicle

17
Q

discuss sebaceous glands

A
  • basal layer of germinative cells divide and differentiate to form large polygonal cells abundant with vacuolated cytoplasm
  • holocrine secretion of sebum containing triglycerides and other lipids, transferrin, IgA, IgG
  • function of sebum is to lubricate the hair and skin. it is required for normal hair shaft separation
  • sebum is secreted via the squamous duct to the hair follicle
18
Q

name some specialised sebaceous glands

A
  • meibomian gland (eyelid)
  • circumanal (hepatoid) gland
  • supracaudal gland of dogs and cats
  • submental glands in cats
  • preputial glands in horses
  • infraorbital, inguinal and interdigital glands in sheep
19
Q

name the 2 types of sweat glands and discuss characteristics of both

A

epitrichial
- associated with a hair follicle
- single layer of flattened cuboidal cells surrounded by myoepithelial cells
- coiled and saccular or tubular structures
- distributed throughout haired skin
- located below the sebaceous gland
- excrete sweat into piliary canal just above the sebaceous gland opening
- not innervated
- pheremonal and antimicrobial properties

atrichial
- not associated with hair follicles
- single layer of flattened cuboidal cells surrounded by myoepithelial cells (merocrine secretion, contract to produce sweat)
- small tightly coiled glands
- innervated by cholinergic nerve fibres
- restricted to non-haired areas (nose and footpas in carnivores)
- also carpus of pigs, frog of ungulates and nasolabial region of ruminants and pigs

20
Q

list some specialised atrichial glands

A
  • mammary glands
  • interdigital glands of small ruminants
  • external ear canal
  • nasolacrimal glands
  • apocrine glands of the anal sac
21
Q

what is hair

A
  • a specialised keratinised tubular structure
  • 2 types: primary (guard hairs) secondary (downy hairs)
  • important for insulation, signalling anf physical protection
22
Q

what type of hair follicles do omnivores and herbivores have

A

simple follicles: each infundibulum contains a single hair shaft of approximately the same size (except sheep)

23
Q

what type of hair follicle do carnivores have

A

compound follicles: multiple hair shafts per follicle

24
Q

define the term anagen

A

actively growing hair

25
Q

what is meant by catagen hair

A

a period of rapid change in which the lower portion undergoes apoptosis in a short period of time

26
Q

what is telogen hair

A

the resting hair

27
Q

what is the difference between primary and secondary hair

A
  • primary hairs are deep in the dermis because they are growing and are bound in connective tissue
  • secondary hairs are soft, shorter and sit more superficial in the dermis
28
Q

discuss the hair cycle

A
  1. anagen: growth phase, new hair produced under previous hair in deep dermis. distinctive hair bulb containing collicular dermal papilla present. duration determines hair length
  2. *catagen. rarely seen in normal skin. transitional phase
  3. telogen: resting phase
  4. exogen: the process of the hair being lost

ACTE

29
Q

what is the difference between anagenic and telogenic growth patterns and give examples of animals that have these patterns

A

anagenic: hair grows and grows (humans, angora rabbit, mohair goat, poodles)
telogenic growth: hair grows to a length then stops (dogs, cats, horses, hedgehogs)

30
Q

how is the hair cycle regulated

A
  • photoperiod (meletonin)
  • temp
  • hormones (thyroid and growth hormone increase, oestrogen and corticosteroids decrease)
  • nutritional status and general health
  • growth factors
  • drugs
31
Q

what are the 6 layers of the anagen hair inner to outer

A
  • medulla
  • cortex
  • cuticle
  • inner root sheath
  • outer root sheath (continuous with epidermis)
  • glassy membrane (basement membrane, holds it all together)
32
Q

discuss the appearance of the telogen hair

A
  • located in mid to upper dermis
  • conical bulb at the level of the attachment of the arrector pili muscle
  • hair surrounded by the external root sheath, which terminates at sebaceous gland level
  • hair bulb separated from the dermal papilla by thick basement membrane
  • original bulb is dormant
  • new bulb and papilla form beneath old follicle
  • when stimulated, new bulb forms a new hair and old hair is lost
33
Q

what is vibrissae

A
  • simple follicles with blood filled sinus between the inner and outer layers of the dermal sheath
  • located on nose, above eyes, lips etc
  • have mechanoreceptors for sensing touch
34
Q

what are tylotrich hairs

A
  • simple folliclles in amongst body hairs
  • have mechanoreceptors (fast adapting)
  • associated with tylotrich pads (slow adapting)
35
Q

what is the subcutis and what are its functions

A
  • connective tissue of mesenchymal origin
  • deepest and thickest layer of the skin
  • variably present
  • projects into the dermis (papillae adiposae) to pretect hair follicles, weat glands and vessels
  • predominant cell type = lipocyte
  • energy reserve
  • thermogenesis and insulation
  • protective padding and support
  • maintaining surface contour/shape
  • has small blood flow and is therefore susceptible to disease
36
Q

what are melanocytes

A
  • derived from the neural crest
  • cell immersed in the epidermis with close contact with a defined number of karatinocytes
  • melanin is composed of two types (eumalanin black or brown, phaeomelanin reddish yellow)
  • melaocytes produce pigment in melanosomes which are membrane bound structures derived from golig involved in the transfer of pigment to keratinocytes
  • melanocytes have photoprotection and immune function
37
Q

what are langerhans cells

A
  • professional antigen presenting cells in the epidermis
  • seen as clear cells on H&E hisopath
  • distinctive tennis racket shape on electron microscopy
  • migrate to the dermis and regional lymph nodes on activation to activate T lymphocytes
  • markedly reduced in UV light (increases infection risk on white legs of horses, increases melanoma/squamous cell carcinoma in plae skin)
38
Q

what are the functions of the skin

A
  • protective barrier via hair, stratum corneum, sebum, sweat)
  • chemical barrier via inorganic acids, proteins and fatty acids
  • normal flora inhibits infectious agents via coagulase negative spp breaking down lipids to form antibacterial free fatty acids, making the environment hostile for bacteria
  • temp regulation via blood flow, sweat, hair
  • exrectory organ via small amounts of urea, uric acid, ammonia and lactic acid
  • sensory organ via sensory nerve endings in the dermis and epidermis sensitive to pain, temp and touch
  • photoreception via urocanic acid and melanin that absorb UVA and UVB, as well as nuclear capping by melanin and skin thickness
  • immunosurveillance
  • BP regulation via storing Na in skin
  • produces Vitamin D
  • stores nutrients (particularly in subcutis)
  • absorptive surface (esp of drugs)
39
Q

how can external fctors influence skin and hair

A

skin is largest organ in body therefore normal function of other organs paramount to healthy skin environment
- nutritional deficiencies (proteins, fatty acids, vitamins and minerals, hepatic dysfunction, pancreatic dysfunction, bowel disease and genetics)
- endocrine influences
-

ENI 2 (81 decks)

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