Integument Flashcards
Integument
Skin + epidermal derivatives foot pads, claws Hooves horns glands feather etc
Skin
Considered the largest organ in the body
Skin functions
Protection: barrier against physical, chemical and biological agents Prevents water and electrolyte loss Temperature regulation Sensation Calcium homeostasis Energy storage Immune function
Components of skin
Epidermis- stratified squamous keratinized epithelium
Dermis- papillary layer and reticular layer
Hypodermis- loose CT that may be rich in adipocytes
Epidermis characteristics
Ectoderm derived
Avascular
Thick barrier
Composed of epithelium
Dermis Characteristics
Mesoderm derived
Contains blood vessels + nervous tissue
Supports the epidermis
Thick skin
Thick epidermis
Hairless
Contains merocrine sweat glands
Paw pads, muzzle
Think skin
Epidermis is thin
Contains hair follicles often with arrestor pills muscle
Sebaceous and sweat glands
The demo-epidermal junction
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
Dermis
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
Cells of epidermis
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
Basic plan of epidermal layers
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
Layers of the Epidermis
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
Stratum Basale
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
Hemidesmosomes vs desmosomes
Hemidesmosomes bind cells to basal lamina
Desmosomes bind neighboring cells together
Both connect intermediate filaments
Stratum Spinosum
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
Stratum Granulosum
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
Stratum Lucidum
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
Stratum Corneum
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
Keratinization
Process by which keratinocytes differentiate about 21 days in length in dog
Cornification
Production of stratum corner by terminal epidermal differentiation
Non-Keratinocytes of the epidermis
Langerhan’s Cell- immune system
Merkel’s cells- sensory
Melanocytes- protection
Langerhan’s Cell
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
Merkel’s cells
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
Melanocytes
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
Melanin
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
Sensory nerves of the dermis
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
Epidermal structures/derivatives
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
Functions of hair
Insulation Camouflage Social display Sense/protect Sex recognition
Anatomy of hair
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
Anatomy of hair follicle
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
Root sheath
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
Dermal papilla
Carries blood supply to the cells of the hair
Hair matriculates cells comparable to stratum basale
Primary hair follicle
Large diameter
Rooted deep in dermis
Sebaceous glands, arrestor pili muscle, sweat glands
Primary or guard hair
Secondary hair follicle
Smaller diameter
Rooted nearer the surface
+/- sebaceous gland; no sweat glands, no arrestor pili muscle
Secondary or under hairs
Compound follicles
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
Arrector pili
Smooth muscle attached to follicle of primary hairs
Contraction causes hair to stand up
Role in insulation
Sinus hairs/whiskers
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
Sebaceous glands
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
Specialized sebaceous glands
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
Uropygial gland
Strongly developed in many waterbirds such as ducks
Aprocrine sweat glands
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)
Specialized apocrine sweat glands
Mammary gland
Glands of Moll (in eyelid, make tear film)
Apocrine glands of the anal sac
Ceruminous glands (ear wax)
Anal sacs
Are supplied by perianal glands (sebaceous) and apocrine glands, that should be empty to be manually empties
Merocrine sweat glands
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
Hooves and claws
Modification of skin
Variation of the stratum corneum
Underlain by highly vascular dermis
Lack stratum granulosum and stratum lucidum
Hoof
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)
Stratum externum (Hoof)
External layer is known as the glass
Continuation of the periodic epidermis
Stratum medium (hoof)
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 (hoof)
Lamellar horn= insensitive lamellae
Laminary corium
Sensitive lamimnae
