skin Flashcards
epidermis structure
squamous stratified epithelium made mainly keratinocytes
* variable thickness according use - species + anatomical location
layers epidermis
- stratum basale = single layer cuboidal cells in contact w BM. stem cells, dividing form new keratinocytes replace lost @ surface
- stratum spinosum = several layers keratinocytes bound tightly by desmosomes (cyt conts tonofilament)
- stratum granulosum = fewer layers, v basophilic, loads keratohyaline granules (only if epi v thick)
- stratum lucidum = dead cells, lost nuclei, translucent, keratinised (only if epi v thick)
- stratum corneum = flattened dead keratinised cells continuously sloughed (v basophilic
deep -> superficial
eosinophilic vs basophilic
pink vs purple
desmosomal prots
- desmoglein 1
- desmocollin 1
- E-cadherin
hemidesmosomal prots
- plakophilin 1
- keratins 5 + 14
- laminin
melanocytes
cells w tenticles to prod melanin + inject it in keratinocytes
* prod pigment (melanin) to reduce damage UV light on DNA
* mel synthed, packed in vesicles -> adjacent keratinocytes = lost when reach skin surface
* nucleus v close basement mem
* amount determines phenotypic characteristic skin pigment
in stratum basale, extensions bet stratum spinosum layers
Langerhans cells
macrophages for immuno surveillance in epidermis => cause rashes
merkel cells
sensory receptors in basal layer, associated w nerve endings
can see on slides
processes occurring in epidermis
- continuous proliferation of keratinocytes in basal layer
- migration, differentiation + keratinisation of keratinocytes
- squamous cells being sloughed off at surface
- protection from UV light
- immunosurveillance
- sensorial perception
==> relatively impermeable protective layer
dermis is
extracellular matrix w collagen etc + vessels + nerves/sensory corpuscles + adnexa (hair follicles, musc)
mols in extracellular matrix of dermis
- collagen
- elastic fibres
- GAG (hyaluronic acid)
- proteoglycan
- water
dividing dermis
- outer papillary - collagen less chunky
- reticular = bigger bottom layer
bv plexi in skin
- superficial plexus just beneath epidermis => nutrients to all epidermis
- mid plexus => supply adnexa
- deep plexus
pacinian corpuscle histology
hypodermis
== subcutis
layer where collagen ends, made adipocytes, connecting skin to musc etc below
* variable in thickness
label
hair follicle where hair grows from
dermal papilla cont bvs to supply whole structure
histology of hair folliclle
simple vs compound hair follicles species
simple = pig, horse, cow
compound = cat, dog, sheep, goat
primary vs secondary hair follicles
primary = may have additional apocrine gland asw
secondary = smaller + go into dermis/hypodermis less deep
life cycle of hair follicle/shaft
- anagen phase = growing
- catagen = regressing
- telogen = resting
- kenogen = latent (hairless)
what affects hair growth cycle
- photoperiod = times of day org exposed to light
- genetics
- age
- hormones
how does photoperiod affect hair growth cycle domestic animals
most shed coat seasonally under influence hormones prolactin + melatonin (proded in dark)
* dogs + cattle change in summer
* cats + rabbits -> winter coat in autumn, summer in spring
how hormones affect hair growth cycle
thyroid:
1. decr anagen (growth)
2. incr telogen (resting)
so hypothyroidism => bilat, symmetrical alopecia
sinus hair
whisker (also in toes)
special bc w/in wall of hair follicle are sinus of blood + nerves to understand environ around
sebaceous glands
exocrine gland prod sebum (oily) as aqueezed by contractions piloerector muscs
* pale staining, flask shaped
* secr by holocrine method
* excretory duct empties into hair follicle
* sebum = lipids: triglycerides, cholesterol esters, waxes (odourless until broken down by bac)
function sebum
oils hairs + forms oily film on skin to:
1. prevent water loss =/ waterproofing
2. lubricate skin
3. inhibit growth certain bac
4. spread sweat
5. territorial marker
skin not v perm water but not waterproof = route drug administration
what increases water resistance skin
- sebaceous gland secretions
- insoluble keratin w/in keratinocytes
regulation sebaceous glands
regged sex steroid hormones (androgens incr activity)
* more active after puberty
* larger + more productive in breeding season
used territorial marking + sexual attraction
sebaceous glands in birds
none w feathers
* in preening, spread secretions from uropygial gland @ base tail
sweat/apocrine/epitrichial glands
exocrine gland prod sweat (ultrafiltrate of blood plasma)
* for thermoreg (evap heat loss), excr, scent signalling
* simple cuboidal epithelium w myoepithelial cells
* symp adrenergic
* oily opaque secr odourless -> smell w bac breakdown
* cont myoepithelial cells
excr duct = 2 layers cuboidal => hair folicle/sweat pore to exit (merocrine)
common in domestics, less in primates
ecrine sweat glands
for evaporative heat loss
* symp cholinergic
* watery NaCl sol modified by aldosterone
* odourless
* cont myoepithelial cells
common primates, less in domestics
sweat glands diff species
- horse, donkey, cattle = abundant
- sheep + goats = moderate, on scrotum + inguinal region -> enhanced heat loss there
- dogs, cats, pigs = sparse, of lil thermoreg importance
pig specialised skin glands
preputial glands @ opening foreskin => sexual attraction initiate mating behaviours sow
sheep specialised skin glands
- infraorbital pouch => territorial marking
- interdigital on all limbs => fatty secr, mark footprints, signal other animals in flock
also in goats, deer
specialised skin glands dog
- anal => fatty secr during pooing => signature on faeces for territorial marking
- tail gland (dorsal tail) => territorial marking
cats have tail gland too; anal = stink gland in skunks for defense
mammary glands
modified sweat glands
v susceptiblle changes due hormones
arrector pili musc
- 45deg to hair follicle
- mostly present in dorsal aspect
- attached follicle wall to raise/lower hairs for thermoreg/social functions
super pink
functions of skin
- protection as boundary
- thermoreg
- secretion
- sensory
- pigmentation
- vit D metabolism
- immunosurveillance
what determines temp
depends on balance bet heat input + heat output
thermoreg defn
organism’s ability to keep body temp w/in certain boundaries, even when surrounding tempv diff
core temp
= brain, thorax, abdom
mammals = endotherms = stable core temp
normal core temp
- range 0.5-1.0° over 24h
- diurnal animals = lowest @ night + 1st thing
- incr in metabolic rate = incr temp: growing, lactating, pregnant
controlling body temp mammals
maintained by hypothalamus
* thermoreceptors on skin (skin temp) or in hypothal (blood temp)
symp ANS both ways, neg feedback control
responses to cold stress
- vasoconstriction
- less sweating
- hairs stand upright = contract erector pili musc to trap thicker layer air insulate
- shivering = thermogenesis
- adrenaline + thyroxine released
- activate brown adipose tiss = thermogenesis
- behaviour
responses to heat stress
- vasodilation
- sweating/panting = evaporative heat loss
- hairs lie flat
- no shivering
- no adrenaline or thyroxine release
- behaviour = decr symp activity
what happens when you relax/contract resistance arterioles
- blood shunted -> dermis thru subcut adipose tiss + blood heats skin
- decr bloodflow in dermis + subcut fat provides insulation from heat loss from vasculature
normal core temp horse
rectal temp 37.5-38.5
normal core temp cow
rectal temp 38.0-38.5
normal core temp pig
rectal temp 38.5-39.0
normal core temp sheep
rectal temp 38.5-39.5
normal core temp cat
rectal temp 38.5-39.5
normal core temp dog
rectal temp 37.5-39.0
evaporative heat loss
evap requires heat E + causes insensible heat loss
* sweating, panting + wetting bod
horses sweat profusely, cattle/sheep moderate, pigs/dogs/cats minimal
-> pigs/dogs/cats reliant panting
panting
rapid shallow breathing
* incr RR 30->300-350/min = natural oscillation frequency so lil E expended
* water to evap mostly from nasal turbs
dogs, cats, pigs, rumis + birds can
what contributes heat input
not working, growing etc all E converted -> heat
60-70% heat prod in heart, brain, liver, kidneys (10% body mass)
thermogenesis
incr basal metabolic rate by
1. shivering as antagonistic muscs contr simultaneously
2. incr secr of symp NS for rapid short-lived incr in metab = ox FAs in BAT
3. incr secr thyroid hormone - slow + prolonged
4. incr appetite
behavioural responses to heat/cold stress
- open/closed posture
- seeking shade/heat
- wallowing for evap heat loss
thermo-neutral zone
TNZ
where additional E not required to maintain core temp (includes thermoreg mechs that use lil/no E
lower critical temp
where animal must start heat prod to maintain body temp
upper critical temp
cutaneous blood flow has reached max + extra E required to lose heat
which homeostatic mechs have E cost
- evaporative heat loss - sweating/panting
- thermogenesis
- some behavioural changes like incr exercise
chem forms of vit D
- vit D2 = constituent of plants
- vit D3 = cholecalcoferol, synthed in skin
vit D synth in skin
7-dehydrocholesterol in dermis -UV-> cholecalciferol
inhibited by dense fur coat, heavy pigmentation
pyrogens
systemic illnesses like viral infections release pyrogens
* incr hypothalamic set pt to higher val than normal => you’re acc really hot but you feel cold
why production of melanin important
- camouflage
- mimicry
- social comms
- protect against harmful solar radiation (can dissipate over 99.9% absorbed UV)
melanin
- eumelanins = black + brown
- pheomelanins = red + yellow
what factors control pigment synth
- genetics
- local factors in skin
- hormones
process of melanin synth control
more MSH binding receptor = more tyrosinase = tyrosin -> eumelanin (derivative)
MSH prod stimmed by:
* UV light
* disease states
* external signals, e.g. for camouflage
controlled MSH-receptor binding
