Integument

Question 1

Integument

Answer 1

Skin + epidermal derivatives
foot pads, claws
Hooves
horns
glands 
feather etc

Question 2

Skin

Answer 2

Considered the largest organ in the body

Question 3

Skin functions

Answer 3

Protection: barrier against physical, chemical and biological agents
Prevents water and electrolyte loss
Temperature regulation
Sensation
Calcium homeostasis
Energy storage
Immune function

Question 4

Components of skin

Answer 4

Epidermis- stratified squamous keratinized epithelium
Dermis- papillary layer and reticular layer
Hypodermis- loose CT that may be rich in adipocytes

Question 5

Epidermis characteristics

Answer 5

Ectoderm derived
Avascular
Thick barrier
Composed of epithelium

Question 6

Dermis Characteristics

Answer 6

Mesoderm derived
Contains blood vessels + nervous tissue
Supports the epidermis

Question 7

Thick skin

Answer 7

Thick epidermis
Hairless
Contains merocrine sweat glands
Paw pads, muzzle

Question 8

Think skin

Answer 8

Epidermis is thin
Contains hair follicles often with arrestor pills muscle
Sebaceous and sweat glands

Question 9

The demo-epidermal junction

Answer 9

Interface between the dermis and epidermis
Epidermal pegs
-downward projections of the deep epidermis into dermis
Dermal Papillae
-upward projections of superficial dermis
-Increased surface area between both layers
-Brings blood supply closer to the epithelium

Examples: footpads, nasal planum, scrotum
Areas subjected to traction
not seen on haired skin normally

Question 10

Dermis

Answer 10

2 layers:
Papillary layer
-loose connective tissue
-type I and III collagen
-mast cells and macrophages
-vessels and nerves

Reticular layer

• dense irregular CT
• type I collagen
• elastic fibers
• blood vessels and nerves

Question 11

Cells of epidermis

Answer 11

Keratinocytes: most common cell (95% of the total number of cells) in epidermis

Non-keratinocytes

• langerhans cells
• merkel’s cells
• melanocytes
• variable numbers of intraepithelial lymphocytes

Question 12

Basic plan of epidermal layers

Answer 12

Generate constant supply of cells
Facilitate cells adhering
-desmosomes (between cells)
-hemidesmosomes (between basal cells and basal lamina)
Replace cytoplasm with keratin
-waterproof
-flatten cells
-provide many layers of this cellular barrier

Question 13

Layers of the Epidermis

Answer 13

As cells mature and progress to the next layer, they move closer to the surface where they eventually die and slough off
From superficial to Deep
1. Stratum corneum: very dead
2. Stratum lucidum (not always present) : dead
3. Stratum granulosum: non- active, alive
4. Stratum spinosum: active and alive
5. Stratum basale: active and alive

Question 14

Stratum Basale

Answer 14

Deepest layer of the epidermis, located at the epidermal-dermal junction
Single layer of cuboidal to columnar epithelium
Attached to basal lamina via hemidesmisomes
Actively dividing (area of mitotic activity)
Basal keratinocytes are functionally heterogenous. Some act as stem cells, whilst some function to anchor the epidermis
May see melanocytes

Question 15

Hemidesmosomes vs desmosomes

Answer 15

Hemidesmosomes bind cells to basal lamina
Desmosomes bind neighboring cells together
Both connect intermediate filaments

Question 16

Stratum Spinosum

Answer 16

Cuboidal or slightly flattened
-Thin skin: 1-2 layers
-Thick skin: many layers thick
Increased number of monofilaments and desmosomes give spiny appearance
Cells are cohesive and they resist abrasion
Cells in this layer retain some capacity for division if needed

Question 17

Stratum Granulosum

Answer 17

Layer that is 3-5 cells thick
Cells begin to flatten
Contain basophilic Keratohyalin granules–> bind with keratin filaments
Lamellar granules (not visible via LM)- secreted by cells to form waterproof lipid sheets, “Intercellular cement”
No mitotic activity, last living layer, nucleus and organelles soon to be lost

Question 18

Stratum Lucidum

Answer 18

Translucent layer
Present in thick skin only
Many keratin filaments, desmosomes present
Cellular organelles are gone- cells are fully keratinized
Cytoplasmplasm contains eleidin- protein chemically related to keratin

Question 19

Stratum Corneum

Answer 19

Outermost layer
Many (up to 20) layers thick, thickness varies by location
Cells consist entirely of Keratin, a water-resistant protein
No nuclei or organelles
Known as horny cells surrounded by a thicker plasma membrane coated by the exterior lipid matrix “bricks and mortar”
Cells continually shed at surface

Question 20

Keratinization

Answer 20

Process by which keratinocytes differentiate about 21 days in length in dog

Question 21

Cornification

Answer 21

Production of stratum corner by terminal epidermal differentiation

Question 22

Non-Keratinocytes of the epidermis

Answer 22

Langerhan’s Cell- immune system
Merkel’s cells- sensory
Melanocytes- protection

Question 23

Langerhan’s Cell

Answer 23

Located in the stratum basal and spinous
Intra-epidermal macrophages
Derived from bone-marrow monocytes
Role in immunity
-antigen presenting to T-cells
-mediators of tolerance
Not often seen without Hand E

Question 24

Merkel’s cells

Answer 24

Located in stratum basal of thick skin
Connected to adjacent keratinocytes via desmsosomes
Can act as sensory mechanoreceptors for cutaneous sensation
Can also function to attract nerve endings and stimulate growth
Free nerve endings seen at the base of these cells
Fingertips, feet

Question 25

Melanocytes

Answer 25

Present in the stratum basale
Neural crest origin
Produce melanin pigment –> migrates within cytoplasmic extensions –> transferred to keratinocytes of stratum basale and spinosum
Protects cells from effects of UV radiation
Must have tyrosinase for proper function

Question 26

Melanin

Answer 26

Absorbs harmful UV radiation
Transformed the energy into harmless amounts of heat
Keeps the generation of free radicals at a minimum
Eumelanin- most common form of melanin, brown black pigment
Pheolmelanin- a red brown polymer largely responsible for red hair and freckles

Question 27

Sensory nerves of the dermis

Answer 27

Nociceptors- free nerve ending that reach the stratum granulosum. Detect pain, itch, temperature
Encapsulated nerve endings:
-Meissner’s corpuscles: light pressure/touch
-Pacinian corpuscle: deep pressure
-Ruffini corpuscle: senses streatch

Question 28

Epidermal structures/derivatives

Answer 28

Hair follicles
Compound hair follicles
SInus (tactile) hair
Sebaceous glands
Sweat glands-apocrine or merocrine
Udders, mammary glands
Hooves, claws, nails
Footpads (have merocrine sweat glands)
Anal sac glands and anal sacs (paraxial sinuses)
Circumanal glands

Question 29

Functions of hair

Answer 29

Insulation 
Camouflage
Social display
Sense/protect
Sex recognition

Question 30

Anatomy of hair

Answer 30

Produced by hair follicle
Hair shaft is above the surface of the skin
Hair root is within the follicle and ends with bulb
Components:
-medulla: loose cuboidal cells with areas of air
-Cortex: dense compact keratinized cells
-Cuticle- single layer of late keratinized cells

Question 31

Anatomy of hair follicle

Answer 31

Invagination of the epidermis
Basement membrane is thickened (glassy membrane)
Hair root is within the follicle and ends with bulb
Root sheath and dermal papilla

Question 32

Root sheath

Answer 32

External glassy membrane= basal lamina
External root sheath- continuous with epidermis
Internal root sheath- a few layers of squamous cells
Cuticle- internal to internal root sheath; formed by overlapping keratinized cells but in the opposite direction from the hair cuticle

Question 33

Dermal papilla

Answer 33

Carries blood supply to the cells of the hair

Hair matriculates cells comparable to stratum basale

Question 34

Primary hair follicle

Answer 34

Large diameter
Rooted deep in dermis
Sebaceous glands, arrestor pili muscle, sweat glands
Primary or guard hair

Question 35

Secondary hair follicle

Answer 35

Smaller diameter
Rooted nearer the surface
+/- sebaceous gland; no sweat glands, no arrestor pili muscle
Secondary or under hairs

Question 36

Compound follicles

Answer 36

Cluster of several hair follicles
The follicles merge at the level of the sebaceous gland and emerge through one external orifice
Compound follicles usually have one primary and several secondary

Question 37

Arrector pili

Answer 37

Smooth muscle attached to follicle of primary hairs
Contraction causes hair to stand up
Role in insulation

Question 38

Sinus hairs/whiskers

Answer 38

Tactile hairs
Composed of a very large single follicle
Blood filled sinus between inner and outer dermal root sheath (movement of hair moves the blood and is a sensory signal)
Attached to skeletal muscle to allow for voluntary movement

Question 39

Sebaceous glands

Answer 39

Located in the dermis
Produce sebum a mixture of lipid and cell debris
Holocrine secretion
Antibacterial and waterproofing
Ducts empty into a follicle
Can be simple, branched or compound glands

Question 40

Specialized sebaceous glands

Answer 40

Supracaudal glands- dog
Mental glands-cat
Horn glands- buck goat
Circumanal glands-ruminants
Preputial glands- smegma in horse
Tarsal (meibomian) glands- eyelids
Uropygial glands in birds

Question 41

Uropygial gland

Answer 41

Strongly developed in many waterbirds such as ducks

Question 42

Aprocrine sweat glands

Answer 42

Secrete by apical budding/piches
Epithelial cells have apical secretory caps
Simple saccular or tubular glands with coiled secretory portion and straight duct which opens into the distal hair follicle
Contractile myoepithelial cells help express the product
In domestic animals, located throughout most of the ski
Function is mainly communication (attractions, marker)

Question 43

Specialized apocrine sweat glands

Answer 43

Mammary gland
Glands of Moll (in eyelid, make tear film)
Apocrine glands of the anal sac
Ceruminous glands (ear wax)

Question 44

Anal sacs

Answer 44

Are supplied by perianal glands (sebaceous) and apocrine glands, that should be empty to be manually empties

Question 45

Merocrine sweat glands

Answer 45

Excrete via exocytosis
Open directly on to skin surface vs hair follicle
Minor in domestic animals
Thermoregulation and electrolyte balance; secrete fluid onto skin surface when body temperature rises

Question 46

Hooves and claws

Answer 46

Modification of skin
Variation of the stratum corneum
Underlain by highly vascular dermis
Lack stratum granulosum and stratum lucidum

Question 47

Hoof

Answer 47

A highly modified, specialized skin derivative that protects and encloses the end of the digit of an ungulate mammal
Equivalent to a nail or claw
The hoof has two main layers:
-the outer epidermis
-the underlying dermis (corium)

Question 48

Stratum externum (Hoof)

Answer 48

External layer is known as the glass

Continuation of the periodic epidermis

Question 49

Stratum medium (hoof)

Answer 49

Main supportive layer
Tubular and intertubular horn produced by the stratum basale and stratum spinosum of the epidermis of the coronary groove

Question 50

Stratum lamellatum/internum (hoof)

Answer 50

Lamellar horn= insensitive lamellae

Question 51

Laminary corium

Answer 51

Sensitive lamimnae