Skin Flashcards
Definition
Largest organ in the mammalian body
Comprised of an epithelial covering, it’s derivatives (hair, glands, horns, hooves, etc.), and associated CT
Functions
Protection Regulation of body temperature Secretion Sensory Organ Communication Reflects physiological condition of the animal
Organization
Epidermis & dermis
Epidermal cell types
Keratinocytes
Langerhans cells
Melanocytes
Merkel Cells
Layers of Epidermis
Stratum basale/germinativum Stratum spinosum Stratum granulosum Stratum lucidum Stratum corneum
Keratin - types
Soft keratin
Hard keratin
Keratinization/Formation of Keratin
- Synthesis of filaments in stratum basale - synthesizes 2 of 4 keratin subtypes
- Aggregation of filaments 0 in superficial cells of stratum spinosum
- Stratum spinosum cells form membrane-coating granules that eventually release lipid-rich contents into intercellular space forming a waterproof permeability barrier
- Keratohyalin granules - non membrane bound - appear in close association w/filaments in s. granulosum and non-keratin proteins released by them cause keratin to associate into thicker bundles
Keratohyalin granules also sequester non-keratin proteins (loricrin and filaggrin and keep them separated from other cellular constituents until they are required in stratum lucidum for keratin filaments to form macrofibrils - Degradation of nucleus and loss of cellular organelles - begins in most superficial layer of the stratum granulosum and is completed in stratum lucidum and corneum
- formation of a filament-matrix complex of keratin - in stratum corneum
Layers of Dermis
Papillary layer
Reticular layer
Dermis - definition
= corium
layer of skin immediately deep to epidermis
derived from mesoderm
composed of connective tissue
most accessory structures are embedded in here
Hypodermis
subcutaneous layer/superficial fascia that isn’t part of the skin
consist of looser irregular CT
anchors dermis to underlying CT of deep fascia, perocondrium, etc
Depots of fat are here in animals of good condition
Accessory structures of the skin
Hair, sweat glands, sebaceous glands
derived from epidermis
anchored in dermis or hypodermis
Function - Protection
most important characteristic
barrier between internal and external environments
guards against injury, bacterial invasion, UV damage, desiccation
Function - regulation of body temperature
insulation - mediated by hair coat & adipose tissue
heat dissipation - cutaneous blood supply and sweat glands (in some animals)
Function - secretion
from sweat, sebaceous, and mammary glands
Function - Sensory organ
largest sensory organ of the body
provides pain, touch, pressure, and temperature sensation
Function - communication
gives off odors that govern sexual behavior
helps animals ID each other and their territories
Function - reflects physiological condition of the animal
may reflect internal and external disease processes
endocrine disorders, nutritional problems (i.e. Vitamin A deficiency)
Epidermis
stratified squamous epithelium
ectodermal origin
Keratinocytes
majority of cells
arranged in 5 laters
Melanocytes
derived from neural crest
octopus like
produce pigment melanin from tyrosine
pass melanin to neighboring keratinocytes (don’t retain it) that carry it up thru layers of skin
Langerhans cells
dendritic cells
in stratum spinosum
play a role in induction of cutaneous immune responses
important in allergic responses - interact w/Ag and migrate to lymph nodes and interact w/T cells
Merkel cells
ubiquitously distributed in skin of vertebrates
couple w/axon terminals to form mechanoreceptors
can form malignant tumors in cats, but benign tumors in dogs
Stratum basale/germinivatum
innermost single layer of cuboidal/low columnar keratinocytes
lie against dermo-epidermal boundary
Stratum spinosum
polyhedral cells
comprise majority of epidermis
appear to have spines/”hairs” protruding from them and connecting them to adjacent cells = desmosomes that hold adjacent cells together
Stratum granulosum
thin layer
keratinocytes still retain nucleus and basophilic keratohyalin granules and membrane-coating granules
not uniform in distribution
may not be present in thin skin
Stratum lucidum
clear layer/lightly stained thin layer flattened dead cells no nuclei or organelles that contain densely packed keratin filaments only found in thick, hairless skin
Stratum corneum
outermost layer
keratinized
flattened cells (squamous)
dead cells filled w/keratin filaments embedded in an amorphous matrix
outermost stratum corneum is sloughed off in normal process of wear and tear
Soft keratin
elastic, desquamates (ex: skin)
Hard keratin
more sulfur than soft keratin less elastic more permanent resistant to degradation does not desquamate (ex: nails, horns, hooves)
Papillary layer
Dermal layer
subepithelial loose CT
contains thin collagen and elastic fibers in loose networks
Reticular layer
dermal layer
dense CT
thick type I collagen fibers packaged into large bundles assoc. w/thick elastic fibers
contains epidermally derived hair, sweat, and sebaceous glands
thick in horse and cow
thin in carnivores
Squamous cell carcinoma
neoplasia of cells in stratum spinosum
Accounts for 15% of cutaneous tumors in the cat and 5% of those in the dog
Usually found in unpigmented or lightly pigmented skin
Melanoma
Melanocytic tumor
represents 4-7% of all canine neoplasms
most common malignant tumor of canine oral cavity and digits
Early recognition can lead to more successful attempts at removal and ID of grade/stage of cancer
can metastasize to any area of body, esp. lymph nodes and lungs
cats seem much less susceptible to melanoma tumors than dogs
Hair
dead
produced by living keratinocytes at base of hair (hair bulb)
pigmentation comes from melanocytes
Hair follicle
sac from which a hair grows and into which sebaceous glands open
Function - insulation, camouflage, sex recognition, social purposes
Types: single and compound
Single hair follicle
=simple hair follicle
one hair emerges from a single open
found in horse, cattle, pig, sheep
face, ear, distal portion of limbs
Compound follicle
several hairs emerge from a single opening
cat, dog, sheep (wool growing areas)
consists of a long principle/guard hair and 7-20 soft, smaller, auxiliary (wool) hairs, (undercoat)
Structure of hair follicles
Hair bulb
Hair shaft
Hair Sheath
Arrector pili muscle
Hair bulb
=hair root and dermal papilla
located at the base of hair follicle
comprised of germinal matrix cells - give rise to layers of hair and to internal and external epithelial root sheath
dermal papilla: forms center base of hair bulb - sends chemical signals that induce germinal matrix to proliferate, plays an important role in hair growth
hair root: embedded in a hair follicle. contains epithelial cells that actively divide about dermal papilla. Produces 5 cell layers (hair shaft forms inner 3 layers and hair sheath forms outer 2)
Hair shaft
non-growing portion of a hair that protrudes from skin
consists of inner 3 layers of hair root
characteristics are species specific
Cuticle: hard, thin, outermost layer of hair. comprised of a single layer of flat, keratinized cells w/overlapping edges (interdigitates w/cuticle of internal epithelial root sheath)
Cortex: consists of compact, dead, keratinized cells - form the bulk of hair shaft - pigment may be present
Medulla - central region of shaft - may be absent in some hairs - comprised of flattened cells separated by numerous air spaces
Hair sheath
outer 2 layers from hair root
inner epithelial root sheath - forms from periphery of germinal matrix - surrounds hair root and ends somewhere around the point of input of sebaceous glands
external epithelial root sheath - adjacent to internal root sheath - similar in structure and continuous with stratum germinativum - upper part keratinized, lower part not
Arrector pili muscle
smooth muscle origin at epidermal/dermal junction inserts onto the outside of the follicle contraction --> erection of hair (piloerection) response to cold, anger, fear innervated by the sympathetic nervous system most evolved in furry animals increases insulation against heat loss
Sweat glands - definition and types
=sudoriferous glands simple, coiled tubular glands hollow or more or less circular walls composed of low cuboidal epithelium Types: eccrine and apocrine
Eccrine sweat glands
small widely distributed produce a watery secretion mainly a mechanism for cooling restricted to foot pads of carnivores, frog of ungulates, and nasolabial region of ruminants and swine
Apocrine sweat glands
larger
cuboidal epithelium
produce oily and foamy secretions
most common in the grown, axilla and scrotum of dogs and cats
most numerous and extensive in horses
most common type found in domestic animals
pheromones are produced and emitted by these
Sebaceous glands
simple, often branched
acinar glands
open into a hair follicle about halfway up the shaft
secrete sebum = lysed cells and accumulated lipids containing precursors of vitamin D; gives hair it’s sheen and acts as a lubricant for skin and hair
