Vet Micro Anatomy Skin

Front 1

fxns of skin

Back 1

Protection
– UV light, mechanical, thermal, chemical insults, and microorganisms
– Keeps fluid in – prevents dehydration

Sensation
– Touch, pressure, pain, temperature

Temperature regulation
– Via hairs, subcutaneous fat, blood flow

Secretion/Excretion
– Sebum, ‘sweat’, cerumen, milk

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

Front 2

epidermis

Back 2

Most superficial layer

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

Sits on top of the dermis

Front 3

components of skin

Back 3

Epidermis

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

Hypodermis (subcutis)

Front 4

layers of epidermis

Back 4

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

Front 5

non-epithelial cells in epidermis

Back 5

Melanocytes
– 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

Front 6

the epidermis lacks

Back 6

blood vessels

nerves

lymphatics

Front 7

inflammatory cells in the epidermis comes from

Back 7

dermis

Front 8

Where are dermal scales found?

Back 8

reptiles

non-feathered skin of birds

Front 9

What are dermal scales?

Back 9

extensions of stratum corneum

Front 10

fxns of the dermis

Back 10

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.

Front 11

Describe the epidermal/ dermal junction in high friction areas

Back 11

Downward projections of epidermis (rete pegs) interdigitate with upward projections of dermis (dermal papillae)

Front 12

the dermis is composed of

Back 12

collagen, reticular, and elastic fibers

Ground or interstitial substance
- Proteoglycans & electrolytes

Blood & lymphatic vessels

Nerves

Mixed other cells
- melanocytes, macrophages, lymphocytes & mast cells

Front 13

What are dermal scales?

Back 13

bony scales arising from dermis

Front 14

Name the parts of hair follicles

Back 14

1.Hair shaft
2.Epidermis
3.Sebaceous gland
4.Arrector pili muscle
5.Adventitial sheath
6.Outer root sheath
7.Inner root sheath
8.Matrix
9.Dermal papilla
10.Apocrine glands

Front 15

How are wool hairs unique

Back 15

they lack a medulla

Front 16

Back 16

1.Hair shaft
2.Epidermis
3.Sebaceous gland
4.Arrector pili muscle
5.Adventitial sheath
6.Outer root sheath
7.Inner root sheath
8.Matrix
9.Dermal papilla
10.Apocrine glands (not shown)

Front 17

Know the parts of a hair shaft

Back 17

Front 18

Know the layers of the epidermis

Back 18

Front 19

Back 19

epidermis
- notice stratum corneum (top)

Front 20

Back 20

foot pad
- large stratum corneum (top)
- light stratum lucidum
- stratum granulosum beneath that

Front 21

Back 21

stratum corneum

(orthokeratosis)

Front 22

Back 22

stratum lucidum

(foot pad)

Front 23

Back 23

foot pad

Stratum lucidum

Stratum granulosum

Stratum spinosum

Stratum basale

Front 24

Back 24

stratum granulosum

Front 25

Back 25

stratum spinosum

Front 26

Back 26

stratum spinosum

Front 27

Back 27

epidermis

- stratum corneum (top)
- stratum granulosum (next)
- stratum spinosum (next)
- stratum basale (notice melanin)
- bottom right is mast cell

Front 28

Back 28

epidermal scales

Front 29

Back 29

Epidermal Scales

Front 30

Back 30

epidermal dermal junction

Front 31

Back 31

epidermal dermal junction in high friction area (rete pegs & dermal papilla)

Front 32

Back 32

dermis

notice blood vessels on right and few mast cells between the vessels.

Front 33

Back 33

dermal scales (bony)

Front 34

Back 34

dermal scale

notice that it is bone

Front 35

Back 35

arrector pili muscles

Front 36

What part of the hair follicle is involved in making hair?

Back 36

Adventitial sheath
Outer root sheath
Inner root sheath
Matrix
Dermal papilla

Front 37

segments of the hair follicle

Back 37

Infundibulum
- Granular layer
- Flaky keratin
- hair shaft, epidermis

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

Suprabulbar & bulbar
- Small dark cells (matrical)
- adventitial sheath, outer root sheath, matrix, dermal papilla

Front 38

classification of hair follicles

Back 38

Primary
- Large diameter; Deeply rooted in the dermis
- Have sebaceous & apocrine glands, & arrector pili muscle

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

Simple
- single hair comes out

Compound
- multiple hairs come out

Front 39

Name 3 ways to classify hair follicles

Back 39

Layers
- Inner & Outer root sheaths etc

Segments
- Infundibular, Isthmus, Suprabulbar/Bulbar

Types
- Primary vs. Secondary
- Simple vs. Compound

Front 40

species differences in hair follicles

Back 40

Horses, Pigs & Cows
- Simple hair follicles

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

Goats
- Primary & Secondary follicles

Dogs & Cats
- Primary (simple) follicles and Secondary (compound) follicles

Front 41

hair cycle

Back 41

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

Front 42

know the hair cycle

Back 42

Front 43

know the hair cycle :)

Back 43

Front 44

Back 44

sinus hair

(whisker)

Front 45

describe sinus hair

Back 45

(whisker)

The adventitial sheath (#5) is thickened by connective tissue trabeculae which are filled with blood

Front 46

Back 46

feather follicle

Front 47

describe a feather follicle

Back 47

Front 48

feather anatomy

Back 48

Front 49

types of feathers

Back 49

Front 50

Apocrine sweat glands

Back 50

(epitrichial)

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

Front 51

all mammals have _______ sweat glands

Back 51

apocrine & eccrine

Front 52

Eccrine sweat glands

Back 52

(atrichial)

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…

Front 53

both types of sweat glands have what shape

Back 53

simple coiled tubular

lined by cuboidal cells and myoepithelium

Apocrine (epitrichial) in the skin

Eccrine (atrichial) in the foot pad

Front 54

sebaceous glands use what type of secretion

Back 54

Holocrine secretion

The entire cell becomes the secretory product

Front 55

Back 55

hair follicles

notice associated apocrine glands

Front 56

Back 56

eccrine (atrichial) glands

Front 57

Back 57

sebaceous glands

holocrine secretion

Front 58

Back 58

sebaceous glands

holocrine secretion

notice reserve cells along periphery

Front 59

Where are sebaceous glands found

Back 59

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)

Front 60

perianal (hepatoid) glands

Back 60

Modified sebaceous glands

Hair follicle associated

Resemble hepatocytes (liver cells) = hepatoid

Territorial marking...

Front 61

Back 61

top- epidermis

next- dermis

notice follicle in the dermis

bottom- perianal (hepatoid) gland

Front 62

Back 62

perianal (hepatoid) gland

Front 63

Back 63

perianal (hepatoid) gland

Front 64

Back 64

liver (no reserve cells)

Front 65

anal glands

Back 65

NOT PERIANAL (HEPATOID)

Specialized apocrine glands

Open directly onto anal skin

OR

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

Front 66

Back 66

anal glands (bottom)

anal sac (top)

Front 67

mammary glands

Back 67

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

Front 68

mammary gland secretion pathway

Back 68

Alveolus -> Secretory tubule -> intralobular duct -> lobular duct -> lobar duct -> gland sinus -> teat sinus -> teat canal

Front 69

Mammary gland

inactive vs. active lactating

Back 69

inactive
- cuboidal

active
- columnar

Front 70

Back 70

Mammary gland

acini surrounding duct

Front 71

Back 71

mammary gland lactating

(pink stuff is milk)

Front 72

which species don't have teats?

do they have mammary tissue?

Back 72

Rats & horses the males don’t have teats – but they DO have mammary tissue

Front 73

subcutis (hypodermis)

Back 73

Deepest layer of skin

Thickest layer of skin (in some animals)

Site of injections…

Absent in some locations:
- Lip
- Cheek
- Eyelid
- Ear canal
- Anus

Front 74

functions of subcutis

Back 74

Energy storage (fat)

Thermoregulation/Insulation

Protective padding

Maintains surface contours

Front 75

subcutis is composed of

Back 75

Primarily white adipose tissue

NO lymphatics

Blood vessels

Nerves

Panniculus muscle

Attached to underlying muscle & bone (periosteum)

Front 76

Back 76

chicken feather and subcutis

Front 77

nose

Back 77

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

Front 78

Back 78

planum nasale (dog)

parakeratosis top

Front 79

foot pads

Back 79

Epidermis
- 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

Dermis
- No hair follicles
- Eccrine glands

Hypodermis with lots of adipose tissue (digital cushion)

Front 80

carnivore toenail

Back 80

Very well developed keratin layer

Supported by bone
- Ungual process

Front 81

equine foot

Back 81

Hoof:
Insensitive keratinized layer

Hoof wall:
Epidermis that makes the hoof

The epidermis at the junction of skin and hoof is called the periploic epidermis

Front 82

periploic epidermis

Back 82

The epidermis at the junction of skin and hoof

Front 83

Equine Foot Laminae

Back 83

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

SDL
PDL
SEL
PEL – keratinize centrally to make the hoof

Front 84

ruminant & porcine claws

Back 84

Similar to the horse...

NO secondary laminae

More primary laminae