Integumentary System Flashcards
What is integument?
Skin and epidermal derivatives
T/F: The largest organ in the body is skin
True
What are skins functions?
- protection; barrier against physical, chemical, and biological agents
- prevents water and electrolyte loss
- temperature regulation
- sensation
- calcium homeostasis
- energy storage
- immune function
What are the layers of skin? What are their characteristics?
- epidermis (ectoderm derived, avascular, thick barrier, composed of stratified squamous keratinized epithelium)
- dermis aka corium (mesoderm derived, vascular and nervous tissues, connective tissue composition, supports epidermis)
- **hypodermis aka subcutis (mesoderm derived, loose connective tissue,rich in adipocytes (panniculus adiposus))
** not really a layer of skin -> superficial fascia
What are the characteristics of thick vs thin skin?
Thick
- thick epidermis, hairless, merocrine sweat glands (ex: paw pads)
Thin
- thin epidermis, hair follicles (often w arrector pili), sebaceous and sweat (apocrine) gland
What is the dermo-epidermal junction? What are some of its features?
- interface between dermis and epidermis
- epidermal pegs/ridges (downward projections of deep epidermis into the dermis)
- dermal papillae (upward projections of the superficial dermis that increase surface area between the layers and bring blood supply closer to the epithelium)
- ex: footpads, nasal planum, scrotum, areas subject to traction
What are the two layers of the dermis?
Papillary and reticular
What are features of the papillary layer?
- LOOSE connective tissue
- type i + iii collagen
- mast cells + macrophages
- vessels + nerves
What are features of the reticular layer?
- DENSE IRREGULAR connective tissue
- type i collagen
- elastic fibers
- blood vessels + nerves
What cell types are in skin?
- keratinocytes (most common, 95 %of cells in epidermis)
- non-keratinocytes
- langerhams cells (immunity/tissue macrophage)
- merkel’s cells (mechanoreception)
- melanocytes
- variable #s of intraepithelial lymphocytes
What are the layers of the epidermis, in order from deepest to most superficial?
Stratum basale, stratum spinosum, stratum granulsum, stratum lucidum, stratum corneum
What layer of the epidermis is this? What are its features?
- stratum basale
- deepest layer, at epidermal-dermal junction
- single layer of cuboidal columnar epithelium
- attached to basal lamina via hemidesmosomes
- actively dividing via mitotic activity
- basal keratinocytes (functionally heterogenous, some are stem cells, some anchor epidermis)
- melanocytes sometimes
What layer of the epidermis is this? What are its features?
- stratum spinosum
- cuboidal/slightly flattened (thin skin 1-2 cells thick, thick skin many layers)
- increased # of tonofilaments and desmosomes give “spiny” appearance
- cells are cohesive and resist abrasion
- cells retain some capacity for division
What do hemidesmosomes do?
Bind cells to basal lamina
What is shown in these structures? What do they do?
Desmosomes. Bind cells to cells
What do both desmosomes and hemidesmosomes do?
Connect intermediate filaments
What layer of the epidermis is this? What are its features?
- stratum granulosum
- 3-5 cells thick
- somewhat flattened cells
- contains basophilic keratohyalin granules (bind w keratin filaments)
- lamellar granules (secreted by cells to form waterproof lipid sheets “intracellular cement”)
- last living layer, no mitotic activity
What layer of the epidermis is this? What are its features?
- stratum lucidum
- translucent layer
- thick skin only
- many keratin filaments, desmosomes present
- cell organelles gone, fully keratinized
- cytoplasm contains eleidin (protein related to keratin)
What layer of the epidermis is this? What are its features?
- stratum corneum
- outermost layer
- many (up to 20) layers thick, location dependent
- cells consist entirely of keratin (water-resistant)
- no nuclei or organelles
- known as horny cells surrounded by a thicker plasma membrane coated by the exterior lipid matrix “bricks + mortar”
- cells continually shed at surface
What is keratinization? Cornification?
- process by which keratinocytes differentiate (~21 days)
- production of stratum corneum by terminal epidermal differentiation
What is this structure? What are it’s characteristics?
- langerhans cells
- located in stratum basale and spinosum
- intra-epidermal macrophages
- derived from bone-marrow monocytes
- role in immunity (antigen presenting to t-cells, mediators of tolerance)
- not usually seen with H+E stain
What is this structure? What are it’s characteristics?
- merkel’s cells
- located in stratum basale of thick skin
- connected to adjacent keratinocytes via desmosomes
- can act as sensory mechanoreceptors for cutaneous sensation
- can also function to attract nerve endings and stimulate growth
- free nerve endings at the base of the cells
What is this structure? What are it’s characteristics?
- melanocytes
- present in stratum basale
- neural crest origin
- produce melanin pigment (migrates within cytoplasm extensions, transferred to keratinocytes of stratum basale/spinosum)
- protects cells from effects of UV radiation
- must have tyrosine for proper function
What is this pigment? What purposes does it serve?
- melanin
- absorbs harmful UV radiation
- transforms radiation energy into harmless heat
- keeps the generation of free radicals at a minimum
What are the sensory nerves of the dermis?
Free nerve endings:
- nociceptors: detect pain, itch, temperature
Encapsulated nerve endings:
- meissner’s corpuscles: detect light pressure/touch
- pacinian corpuscle: detect deep pressure
- ruffini corpuscle: senses stretch
What are some epidermal derivatives?
- hair follicles
- compound hair follicles
- sinus (tactile) hairs
- sebaceous glands
- sweat glands (apocrine/merocrine)
- udders/mammary glands
- hooves/claws/nails
- footpads
- anal sac glands/anal sacs
- circumanal glands
Identify the following:
Epidermis, dermis, hair shaft, hair follicle, hair bulb, sebaceous gland, apocrine sweat gland
What are functions of hair and feathers?
- insulation
- camouflage
- social display
- sense/protect
- sex recognition
What are the components of hair?
- medulla: loose cuboidal cells w/ areas of air
- cortex: dense compact keratinized cells
- cuticle: single layer of flat keratinized cells
What is the difference between the hair shaft and hair root?
Hair shaft - above the surface of the skin
Hair root - within the follicle and ends with the bulb
What are features of the root sheath?
- external glassy membrane = basal lamina
- external root sheath: continuous with the epidermis
- internal root sheath: few squamous layers
- cuticle: internal to external root sheath formed by overlapping keratinized cells but in the opposite direction from the hair cuticle
What carried blood supply to the cells of the hair?
Dermal papilla
What are the phases of the hair cycle?
Anagen, catagen, telogen
What happens during anagen?
Period when hair bulb cells are mitotically active
Describe catagen
Regressive stage when metabolic activity slows down and the base of the follicle migrates towards the surface. Detachment of the dermal papilla occurs.
What phase is the resting or quiescent phase when growth stops and the base of the bulb is at the level of the sebaceous canal?
Telogen
What are the types of hair follicles? What are their features?
Primary hair follicle
- large diameter
- rooted deep in dermis
- sebaceous glands, arrector pili muscle, sweat glands
- primary or guard hair
Secondary hair follicle
- smaller diameter
- rooted nearer the surface
- +/- sebaceous glands, no arrector pili or sweat glands
- secondary or under hairs
**follicles can be arranged as individuals or clusters and can vary in the number of hairs per cluster
What are features of compound follicles?
- cluster of several hair follicles
- follicles merge at the level of sebaceous gland and emerge through on external orifice
- compound follicles usually have one primary follicle (hf) and several secondary hair follicles (s)
- most common in carnivores
What is smooth muscle attached to the follicle of primary hairs?
Arrector pili, contraction causes hair to stand up (role in insulation)
What are tactile hairs composed of a single very large follicle, a blood filled sinus between the inner and outer dermal root sheet, and attachments to skeletal muscle that allow for voluntary movements called?
Sinus hairs aka whiskers
What is this epidermal derivative? What are it features?
- Sebaceous gland
- located in dermis
- produce sebum (mix of lipids and cell debris)
- holocrene secretion
- antibacterial and waterproofing
- ducts empty in a folllicle
- can be simple, branched, or compound glands
What is this epidermal derivative? What are it features?
What is this epidermal derivative? What are it features?
- Apocrine sweat glands
- secretion by apical budding
- epithelial cells have apical secretory caps (a)
- simple saccular or tubular glands with coiled secretory portion and straight duct that opens into distal hair follicle
- contractile myoepithelial cells (m) help express product
- in domestic animals, located throughout most of the skin
- function is mainly communication (attraction, markers)
What are the following examples of:
- supracaudal glands : dog
- mental glands : cat
- horn glands : buck goat
- preputial glands : smegma in horse
- tarsal (meibomian) glands : eyelids
- uropygial gland (preen gland) - birds
Specialized sebaceous glands
What are the following examples of:
- mammary gland
- glands of mal : eyelid, tear film
- ceruminous glands : ear wax
- mental organ and planum rostiale
Specialized apocrine sweat glands
What is this structure?
Mammary gland
What are some features of merocrine/eccrine sweat glands
- merocrine : excrete via exocytosis
- open directly to skin surface via hair follicle
- minor in domestic animals
- thermoregulation and electrolyte balance; secrete fluid onto skin surface when body temperature rises
What are some features of hooves and claws?
- modification of skin
- variation of stratum corneum
- underlain by highly vascular dermis
- lack stratum granulosum and stratum lucidum
What is a highly modified, specialized skin derivative that protects and encloses the end of the digit of an ungulate animal?
the hoof
What are the two main layers of the hoof?
- outer epidermis
- underlying dermis (aka CORIUM)
What are the layers of the hoof wall superficial to deep?
- stratum externum
- stratum medium
- stratum lamellatum/internum
- laminar corium ** (not hoof wall)
What hoof wall layer is called the “glaze” and is a continuation of the perioplic epidermis?
Stratum externum
What is the main supportive layer of the hoof wall and its features?
- Stratum medium
- tubular and intertubular horn produced by the stratum basale and stratum spinosum of the epidermis of the coronary groove
What layer of the hoof wall has insensitive lamellae (lamellar horn)?
Stratum lamellatum/internum
What feature of the hoof is this?
Interlocking dermal and epidermal laminae
What is the white line?
- interdigitation of the non-pigmented wall laminae with the pigmented tubular and intertublar horn of the sole
What is the laminar corium?
- the sensitive laminae, the innermost portion of the hoof structure before bone
What are features of the uropygial/preen gland?
- strongly developed in many waterbirds
- rest of bird skin is aglandular
- function: involved in chemical protection, water-proofing, and maintenance of plumage brightness
