Integument

Question 1

T/F: Skin is the largest organ in the body.

Answer 1

True

Question 2

Functions of the skin

Answer 2

• protection
• prevents loss of water and electrolytes
• temperature regulation
• sensation
• elasticity permits movement
• immune function
• excretion
• calcium homeostasis
• energy storage

Question 3

Functions of hair

Answer 3

• insulation
• camouflage
• social display
• sense/protect
• sex recognition

Question 4

What kind of epithelium is found in the epidermis?

Answer 4

Stratified squamous keratizined epithelium

Question 5

Desribe thick skin and give examples

Answer 5

• epidermis is thin
• hairless
• merocrine sweat glands are present
• ex.) digital pads, muzzle

Question 6

Describe thin skin

Answer 6

• epidermis is thin
• hair follicles with arrector pili muscle
• sebaceous and sweat glands

Question 7

Epidermal pegs/ridges

Answer 7

Downward projections of the epidermis into the underling dermis

Question 8

Dermal papillae

Answer 8

Upward projections of the superficial dermis; increase area of contact between epidermis and dermis; bring blood vessels near the epithelium

Question 9

What is the principal component of dermis and describe the two layers?

Answer 9

• connective tissue is principal component
• papillary layer
  
  • loose CT
  • type I, III collagen
  • mast cells, macrophages, vessels, nerves
• reticular layer
  
  • dense irregular CT
  • type I collagen
  • network of elastic fibers
  • blood vessels, nerves

Question 10

What contributes to skin’s elasticity?

Answer 10

A network of elastic fibers in the reticular layer of the dermis

Question 11

Cells of the epidermis

Answer 11

• keratinocytes - most common cell, account for 95% of the total number of cells in the epidermis
• non-keratinocytes
  
  • Langerhans cells
  • Merkel’s cells
  • melanocytes
  • variable numbers of intraepithelial lymphocytes

Question 12

Desmosomes vs. Hemidesmosomes

Answer 12

• desmosomes are found between cells
• hemidesmosomes attach basal cells to the basal lamina

Question 13

Name the layers of epidermis

Answer 13

• Stratum basale
• Stratum spinosum
• Stratum granulosum
• Stratum lucidum (not present at all sites)
• Stratum corneum
• Ball Sacs Get Licked Constantly

Question 14

Stratum basale

Answer 14

• epidermal-dermal junction
• single layer of cuboidal to columnar cells
• rests on basal lamina
  
  • hemidesmosomes bind cells to basal lamina
  • desmosomes bind neighboring cells together
• area of mitotic activity
  
  • stem cells proliferate by mitotic division, new cells move up and keratinize
• may see melanocytes in this layer

Question 15

Stratum spinosum

Answer 15

• cuboidal or slightly flattened
  
  • thin skin: 1-2 cells thick
  • thick skin: many layers thick
• desmosomes and increased number of tonofilaments give spiny appearance –> “prickle cells layer”
• cells are cohesive and they resist abrasion
• cells in this layer retain some capacity for division if needed

Question 16

Stratum granulosum

Answer 16

• 3-5 layers, cells begin to flatten; may be difficult to see in thin skin
• keratohyalin granules –> bind with keratin filaments
• staining appearance: basophilic
• lamellar granules (EM) - secreted by cells to form waterproof lipid sheets, “intercellular cement”
• no mitotic activity, last living layer, nucleus and organelles soon to be lost

Question 17

Stratum lucidum

Answer 17

• translucent layer (present in thick skin only)
• many keratin filaments, desmosomes present
• cellular organelles are gone - cells are fully keratinized
• cytoplasm contains eleidin - protein chemically related to keratin

Question 18

Stratum corneum

Answer 18

• 15-20 layers thick, thickness varies by location
• cells consist of keratin, a water-resistant protein that forms a barrier against the destructive forces of the environment
• 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 19

Keratinization

Answer 19

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

Question 20

Cornification

Answer 20

Production of stratum corneum by terminal epidermal differentiation

Question 21

Langerhans cells

Answer 21

• found in stratum basale, stratum spinosum
• small percentage of total cells, 2-8%
• intra-epidermal macrophages: bone-marrow derived (from monocytes)
• role in immunological skin reactions as
  
  • APCs
  • internalize surface-bound antigen for processing and presenting at its cell surface to T lymphocytes

Question 22

Merkel’s cells

Answer 22

• present in thick skin near stratum basale
• may be sensory mechanoreceptors for cutaneous sensation or diffuse neuroendocrine system
• free nerve endings seen at base of these cells

Question 23

Melanocytes

Answer 23

• present in stratum basale
• neural crest origin
• stable cell, live years
• produce pigment melanin –> migrates within cytoplasmic extensions –> transferred to keratinocytes of stratum basale and spinosum
• protects cell from effects of UV radiation
• must have tyrosinase for proper function

Question 24

Melanin

Answer 24

• absorbs harmful UV-radiation
  
  • transforms 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
• pheomelanin - a red-brown polymer largely responsible for red hair and freckles
• no tyrosinase –> no melanin –> albino!

Question 25

Sensory nerves of dermis

Answer 25

• free nerve endings to stratum granulosum
  
  • nociceptors - pain, itch, temperature
• encapsulated nerve endings
  
  • meissner’s corpuscles
  • pacinian corpuscle
  • ruffini corpuscle - sense stretching

Question 26

Hair follicle

Answer 26

• epidermal invagination
• glassy membrane - a thick basement membrane
• hair
  
  • medulla - loose cuboidal cells; air filled in areas
  • cortex - dense compact keratinized cells parallel to hair shaft
  • cuticle - single layer of flat keratinzied cells
• the pattern of cuticle and medulla is characteristic for each species

Question 27

Layers of hair follicle

Answer 27

• dermal papilla
  
  • carries blood supply to the cells of the hair
  • hair matrix cells comparable to stratum basale
• root sheath
  
  • external glassy membrane - basal lamina; external to external root sheath
  • 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 with free edges oriented in the opposite direction from the hair cuticle, towards the hair bulb

Question 28

Primary hair follicle

Answer 28

• large diameter
• rooted deep in dermis
• sebaceous glands, arrector pili muscle, sweat glands
• primary or guard hair

Question 29

Secondary hair follicle

Answer 29

• smaller diameter
• rooted nearer the surface
• +/- sebaceous gland; no sweat glands, no arrector pili muscle
• secondary or under hairs

Question 30

Compound hair follicle

Answer 30

• clusters 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 follicle and several secondary hair follicles

Question 31

Sebaceous glands

Answer 31

• produce sebum - mixture of lipid and disintegrated cells
• acts as an antibacterial and waterproofing agent
• ducts empty into hair follicle or skin surface
• cells accumulate lipid droplets as they differentiate towards the center of the gland

Question 32

Uropygial/Preen gland

Answer 32

Sebaceous glands that are strongly developed in many waterbirds such as ducks (but not in cormorants which are highly aquatic)

Question 33

Sweat glands

Answer 33

• epithelial cells of apocrine sweat glands with apical secretory caps
• simple saccular or tubular glands with coiled secretory portion and strait duct
• contractile myoepithelial cells surround secretory units and help express the product
• in domestic animals, located throughout most of the skin, in contrast to humans
• function is mainly communication (attraction, marker)

Question 34

Eccrine/Merocrine sweat glands

Answer 34

• open directly onto skin surface vs. hair follicle
• minor in domestic animals
• thermoregulation and electrolyte balance; secrete fluid onto skin surface when body temperature rises
• vs apocrine glands - where hair is, smelly

Question 35

Hooves and claws

Answer 35

• modification of skin
• variation of the stratum corneum
• underlain by highly vascular dermis
• lack stratum granulosum and stratum lucidum

Question 36

Epidermal layers of the hoof wall

Answer 36

• stratum tectorium/externum
  
  • thin orange layer
  • external layer is known as the ‘glaze’
  • continuation of perioplic epidermis
• stratum medium
  
  • yellow
  • the main supportive layer
  • tubular and intertubular horn produced by the stratum basale and stratum spinosum of the epidermis of the coronary groove
  • stratum lamellatum/internum
    
    • blue
    • lamellar horn = insensitive lamellae
• laminar corium/dermis
  
  • laminar corium (red area) = sensitive lamimnae