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84 Cards in this Set

  • Front
  • Back
fxns of skin
– UV light, mechanical, thermal, chemical insults, and microorganisms
– Keeps fluid in – prevents dehydration

– Touch, pressure, pain, temperature

Temperature regulation
– Via hairs, subcutaneous fat, blood flow

– Sebum, ‘sweat’, cerumen, milk

Metabolic functions
– Vitamin D synthesis from UV light
– Energy stored in subcutaneous fat
Most superficial layer

Keratinizing stratified squamous epithelium
– Keratinocytes (cells w/in epidermis)

Sits on top of the dermis
components of skin

– Adnexa
• Hair follicles
• Glands
– Sweat glands
– Sebaceous glands
– Anal glands
– Mammary glands

Hypodermis (subcutis)
layers of epidermis
Stratum corneum (keratin layer)
– Cornified cells
• Dead, flattened, eosinophilic cells (squames)
• Ortho- or Para-keratosis
• Continually shed & replaced
– Thickness varies by location
Thickest in non-haired regions (footpads, nasal planum)
• Thin in inguinal region

(Stratum lucidum)
– Several layers of translucent, homogenous, dead, squamous cells
– Lack nuclei

Except in areas with parakeratosis
– Primarily foot pads

Stratum granulosum
– Intracellular purple (keratohyaline) granules
– 1-2 cells thick in haired skin
– 4-8 cells in non-haired skin or in hair follicles
– This is where keratinization begins...
– Still composed of dead cells
– Only seen in foot pad

Stratum spinosum (prickle cell layer)
– Can see the desmosomes (intercellular bridges) attaching the cells to each other (spiny/prickly)
– Thicker in non-haired skin

Stratum basale
– Deepest layer
– Single layer of cuboidal cells attached to underlying basement membrane
– Continually dividing
– Provides replacement for layers above it
non-epithelial cells in epidermis
– Present in the stratum basale
• 1 per 10-20 keratinocytes
– Hard to identify with light microscopy
– Pass melanin on to adjacent keratinocytes
• Not all pigmented cells in the epidermis are melanocytes!

Langerhans cells
– Present in stratum basale & stratum spinosum
– Similar to macrophages
• Present antigens to other immune cells to incite an inflammatory response etc
– Can’t see with light microscopy

Merkel cells
– Origin unknown
– Clear cells in stratum basale
– ‘neuroendocrine’ effects
• Hair cycle control
– Associated with nerves
• Mechanoreceptors
the epidermis lacks
blood vessels


inflammatory cells in the epidermis comes from
Where are dermal scales found?

non-feathered skin of birds
What are dermal scales?
extensions of stratum corneum
fxns of the dermis
provides tensile strength and elasticity

supports epidermis

nourish epidermis
– The epidermis has NO blood vessels, so oxygen and inflammatory cells etc come from dermal blood vessels.
Describe the epidermal/ dermal junction in high friction areas
Downward projections of epidermis (rete pegs) interdigitate with upward projections of dermis (dermal papillae)
the dermis is composed of
collagen, reticular, and elastic fibers

Ground or interstitial substance
- Proteoglycans & electrolytes

Blood & lymphatic vessels


Mixed other cells
- melanocytes, macrophages, lymphocytes & mast cells
What are dermal scales?
bony scales arising from dermis
Name the parts of hair follicles
1.Hair shaft
3.Sebaceous gland
4.Arrector pili muscle
5.Adventitial sheath
6.Outer root sheath
7.Inner root sheath
9.Dermal papilla
10.Apocrine glands
How are wool hairs unique
they lack a medulla
1.Hair shaft
3.Sebaceous gland
4.Arrector pili muscle
5.Adventitial sheath
6.Outer root sheath
7.Inner root sheath
9.Dermal papilla
10.Apocrine glands (not shown)
Know the parts of a hair shaft
Know the layers of the epidermis
- notice stratum corneum (top)
foot pad
- large stratum corneum (top)
- light stratum lucidum
- stratum granulosum beneath that
stratum corneum

stratum lucidum

(foot pad)
foot pad

Stratum lucidum

Stratum granulosum

Stratum spinosum

Stratum basale
stratum granulosum
stratum spinosum
stratum spinosum

- stratum corneum (top)
- stratum granulosum (next)
- stratum spinosum (next)
- stratum basale (notice melanin)
- bottom right is mast cell
epidermal scales
Epidermal Scales
epidermal dermal junction
epidermal dermal junction in high friction area (rete pegs & dermal papilla)

notice blood vessels on right and few mast cells between the vessels.
dermal scales (bony)
dermal scale

notice that it is bone
arrector pili muscles
What part of the hair follicle is involved in making hair?
Adventitial sheath
Outer root sheath
Inner root sheath
Dermal papilla
segments of the hair follicle
- Granular layer
- Flaky keratin
- hair shaft, epidermis

- Glassy cells
- Homogenous keratin
- sebaceous gland, arrector pili muscle

Suprabulbar & bulbar
- Small dark cells (matrical)
- adventitial sheath, outer root sheath, matrix, dermal papilla
classification of hair follicles
- Large diameter; Deeply rooted in the dermis
- Have sebaceous & apocrine glands, & arrector pili muscle

- Smaller diameter; Rooted more superficially
- May have a sebaceous gland
LACK apocrine glands & arrector pili muscles

- single hair comes out

- multiple hairs come out
Name 3 ways to classify hair follicles
- Inner & Outer root sheaths etc

- Infundibular, Isthmus, Suprabulbar/Bulbar

- Primary vs. Secondary
- Simple vs. Compound
species differences in hair follicles
Horses, Pigs & Cows
- Simple hair follicles

- Wool-growing areas: Compound follicles (both primary & secondary)
- Hair-growing areas: Simple follicles

- Primary & Secondary follicles

Dogs & Cats
- Primary (simple) follicles and Secondary (compound) follicles
hair cycle
Anagen: Growth phase

Catagen: Transitional or involuting phase

Telogen: Resting phase

The inferior segment (suprabulbar & bulbar) portions are temporary and lost during catagen and telogen

The infundibular & isthmus segments of the follicle are permanent
know the hair cycle
know the hair cycle :)
sinus hair

describe sinus hair

The adventitial sheath (#5) is thickened by connective tissue trabeculae which are filled with blood
feather follicle
describe a feather follicle
feather anatomy
types of feathers
Apocrine sweat glands

ONLY found on primary follicles NOT secondary follicles

Secretory portion: single layer of cuboidal cells surrounded by a layer of myoepithelial cells

Secretions mix with sebum for ‘scent’

Thermoregulation in horses and cows only
all mammals have _______ sweat glands
apocrine & eccrine
Eccrine sweat glands

NOT associated with hair follicles

Footpads of dogs & cats
‘frog’ of ungulates (ruminants, camelids)

Snout of pigs

Medial surface of carpus of pigs

Nasal planum of cows

Some role in thermoregulation…
both types of sweat glands have what shape
simple coiled tubular

lined by cuboidal cells and myoepithelium

Apocrine (epitrichial) in the skin

Eccrine (atrichial) in the foot pad
sebaceous glands use what type of secretion
Holocrine secretion

The entire cell becomes the secretory product
hair follicles

notice associated apocrine glands
eccrine (atrichial) glands
sebaceous glands

holocrine secretion
sebaceous glands

holocrine secretion

notice reserve cells along periphery
Where are sebaceous glands found
Associated with hair follicles (1o or 2o)

Higher density in some areas
- Cats: Chin
- Dogs & Cats: Dorsal tail (tail gland)
- Goats: Base of horn
- Sheep: Infraorbital, inguinal, interdigital

NOT on footpads or nasal planum

Associated with eyelids (Meibomian glands)
perianal (hepatoid) glands
Modified sebaceous glands

Hair follicle associated

Resemble hepatocytes (liver cells) = hepatoid

Territorial marking...
top- epidermis

next- dermis

notice follicle in the dermis

bottom- perianal (hepatoid) gland
perianal (hepatoid) gland
perianal (hepatoid) gland
liver (no reserve cells)
anal glands

Specialized apocrine glands

Open directly onto anal skin


Dump into the anal sacs (storage)
- Lined by stratified squamous keratinizing epithelium

Territorial marking...

Found in...
- Domestic & wild felids
- Ferrets, mink (mustelids)
- Raccoons
- canids
- pigs
- rodents
anal glands (bottom)

anal sac (top)
mammary glands
Modified sweat glands

Apocrine method of secretion
- A piece of the apical (top) cytoplasm pinches off

Compound tubuloacinar
- Sort of like a bunch of grapes...
- Lined by cuboidal to columnar epithelium
- Myoepithelium
mammary gland secretion pathway
Alveolus -> Secretory tubule -> intralobular duct -> lobular duct -> lobar duct -> gland sinus -> teat sinus -> teat canal
Mammary gland

inactive vs. active lactating
- cuboidal

- columnar
Mammary gland

acini surrounding duct
mammary gland lactating

(pink stuff is milk)
which species don't have teats?

do they have mammary tissue?
Rats & horses the males don’t have teats – but they DO have mammary tissue
subcutis (hypodermis)
Deepest layer of skin

Thickest layer of skin (in some animals)

Site of injections…

Absent in some locations:
- Lip
- Cheek
- Eyelid
- Ear canal
- Anus
functions of subcutis
Energy storage (fat)


Protective padding

Maintains surface contours
subcutis is composed of
Primarily white adipose tissue

NO lymphatics

Blood vessels


Panniculus muscle

Attached to underlying muscle & bone (periosteum)
chicken feather and subcutis
Carnivores: Planum Nasale
- Keratinizing stratified squamous epithelium
- Thick keratin layer
- No hair follicles or adnexa

Cows/Small ruminants: Planum nasolabiale/ Planum nasale
- Keratinizing stratified squamous epithelium
- Thick keratin layer
- No hair follicles
- Eccrine glands to moisten the surface
planum nasale (dog)

parakeratosis top
foot pads
- Thick keratin layer
- Smooth in cats
- Papillated in dogs
- Thickest epidermis on the body
- Highly pigmented
- Prominent dermal papillae interdigitate with epidermal rete pegs
- Common feature of high-friction sites

- No hair follicles
- Eccrine glands

Hypodermis with lots of adipose tissue (digital cushion)
carnivore toenail
Very well developed keratin layer

Supported by bone
- Ungual process
equine foot
Insensitive keratinized layer

Hoof wall:
Epidermis that makes the hoof

The epidermis at the junction of skin and hoof is called the periploic epidermis
periploic epidermis
The epidermis at the junction of skin and hoof
Equine Foot Laminae
Epidermal rete pegs and dermal papillae form elongate ridges oriented perpendicular to the ground

There are epidermal and dermal laminae
- The epidermal ones are insensitive
- The dermal ones are sensitive

There are primary and secondary laminae
- Primary laminae are the main rete pegs/dermal papillae
- Secondary laminae branch off the primary laminae at an acute angle

These can be epidermal or dermal

PEL – keratinize centrally to make the hoof
ruminant & porcine claws
Similar to the horse...

NO secondary laminae

More primary laminae