Unit 5 - Integumentary System Flashcards
Organs of Integumentary System
Skin Hair Oil & Sweat Glands Nails Sensory Receptors
Functions of Integumentary System
Regulates body temp Stores blood Protects body from external environment Detects cutaneous sensations Extremes and absorbs substances Synthesizes vitamin D
Epidermis
Superficial, thin layer
Composed of epithelial tissue
Avascular
Dermis
Deeper, thicker layer
Composed of connective tissue
Contains a blood and nerve supply
Epidermal Cells
Contains 4 types of cells:
- Keratinocytes
- Melanocytes
- Intraepidermal Macrophrages
- Tactile Epithelial Cells
Keratinocytes
-Compose about 90% of epidermal cells
-Arranges in 4-5 layers and produce keratin
-Also produce lamellar granules that release a water-repellant sealant that decreases water entry and loss and inhibits passage of foreign molecules
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Melanocytes
- 8% of epidermal cells
- develop from neural crest of a developing embryo and produce melanin
- have cuboidal cell body with arm-like projections that go between keratinocytes
- 1 melanocyte : 30 keratinocytes
- arm-like projections transfer melanin to keratinocytes
- inside keratinocytes, melanin cluster to form protective veil over nucleus on the side toward the skin surface
- melanocytes themselves are susceptible to damage by UV light
Melanin
-pigment that contributes to skin colour and absorbs damaging UV light
Intraepidermal Macrophage cells/Langerhan Cells
- arise from red bone marrow and migrate to epidermis
- have long projections that go in between keratinocytes
- participate in immune responses mounted against microbes that invade the skin
- easily damaged by UV light
Tactile Epithelial Cells / Merkel Cells
- least numerous cells
- located in deepest layer of the epidermis where they contact the flattened process of a sensory neuron - a tactile disc
- Tactile epithelial cells and tactile discs detect touch sensations
Formation of Epidermis
- Several distinct layers of keratinocytes in various stages of development form epidermis
- Epidermis has 4 layers:
- Stratum Basale
- Stratum spinosum
- Stratum granulosum
- Stratum Lucidem (in thick skin only)
- Stratus Corneum (can be thick or thin depending on skin type)
Stratum Basale
- Deepest layer
- Single row of cuboidal/columnar keratinocytes
- Nuclei of these keratinocytes are large, cytoplasm contains many ribosomes, small Golgi, few mitochondria, and little rough ER.
- Cytoskeleton includes scattered intermediate filaments called keratin intermediate filaments which form keratin.
- Keratin protects deeper level from injury
- Melanocytes and Tactile epithelial cells scattered among keratinocytes
- Sometimes referred to as stratum germinativum due to its role in forming new cells
Stratum Spinosum
- Superficial to stratum Basale
- Contains numerous keratinocytes produced by stem cells in stratum basale, arranged in 8-10 layers
- few tactile epithelial cells
- Cells in more superficial layers become slightly flattened
- At each spinelike projection, bundles of keratin intermediate filaments insert into desmosomes, which tightly join the cells to one another
- This arrangement provides both strength and flexibility to skin
Stratum Granulosum
- Middle of epidermis
- 3-5 layers of flattened keratinocytes that are undergoing apoptosis
- Nuclei and other organelles of these cells being to degenerate as they move further from their source of nutrition (dermal blood vessels)
- keratin intermediate filaments no longer being produced, but they become more abundant because the organelles in the cell are regressing
- distinctive darkly staining protein granules called keratohyalin (involved in assembling keratin intermediate filaments into keratin)
- Lamellar granules also present which fuse with plasma membrane and release lipid-rich secretion
- secretion is deposited in the spaces between cells of 3 superficial epidermal layers.
- lipid rich secretion acts as water-repellant sealant
- Stratum granulosum marks transition between metabolically active strata and dead cells.
Stratum Lucidum
- Present in thick skin of areas such as fingertips, palms, and soles.
- 4-6 layers of clear, flat, dead keratinocytes that contain large amounts of keratin and thickened plasma membrane.
- keratin is more regularly arranged parallel to the skin surface to provide extra toughness.
Stratum Corneum
- most superficial layer
- average of 25-30 layers of flattened, dead keratinocytes, but can range depending on thickness of skin
- thin, flat, plasma membrane enclosed packages of keratin are called corneocytes or squames.
- no longer contain nuclei or organelles
- corneocytes within each layer overlap one another like scales
- neighbouring layers form strong connections also
- plasma membrane of adjacent corneocytes are arranged in complex, wavy folds that fit together like a puzzle to hold layer together
- cells are continuously shed and replaced by cells from deeper strata
- constant exposure of skin to friction stimulates increased keratin production resulting in calluses
Dermis
- Composed of dense, irregular connective tissue
- contains collagen and elastin fibers
- thicker than epidermis
- great tensile strength
- ability to stretch and recoil easily
- cells in dermis are scattered and include fixed cells and wandering cells
- predominant fixed cell = fibroblasts
- wandering cell = macrophages, mast cells, eosinophils, neutrophils and dermal interstitial dendritic cells.
- dermis essential to survival of epidermis
Layers of dermis
- Thin, superficial, papillary region
- Thick, deeper reticular region
Papillary Region
- 20% of thickness of dermal layer
- contains thin collagen fibres and fine elastic fibers
- surface area increased by dermal papillae that project into undersurface of epidermis
- dermal papillae increase contact region between dermis and epidermis
- in thick skin they are longer and more abundant than in think skin
- all dermal papillae contain capillary loops
- some contain corpuscles of touch (sensitive nerve endings to detect touch)
- other dermal papillae contain free nerve endings
- different free nerve endings initiate signals like warmth, coolness, tickling and itching,
Reticular Region
- attached to subcutaneous layer
- contains bundles of thick collagen fibres, scattered fibroblasts and various wandering cells, and some coarse elastic fibres
- presence of some adipose cells in deepest part of layer
- collagen arranged in a netlike manner and more regular that papillary region
- this orientation aligns with the local tensile forces to help skin resist stretching
- blood vessels, nerves, hair follicles, sebaceous glands and sudoriferous glands occupy space between fibres
- in some regions, collagen fibres orient in a certain direction due to natural tension of bony projections, muscles, and joint movements.
- Tension lines indicate predominant directions of underlying collagen
Dermis
- both layers contain dense horizontal networks of small blood vessels
- Collagen and elastic fibres allow skin ability to stretch, elasticity, and ability to return to normal shape after stretching
Epidermal Ridges
- series of ridges and grooves
- straight lines or patterns of loops
- produced during 3rd month of fetal development
- increase surface ares to increase grip by increasing friction
- creates stronger bond between epidermis and dermis in regions of high friction
- increase number or corpuscles of touch increasing tactile sensitivity
Cutaneous Arterial Plexus
-located at junction of dermis and subcutaneous layer and sends branches that supply the sebaceous and sudoriferous glands, deep portion of hair follicles, and adipose tissue
Papillary Arterial Plexus
- formed at level of papillary region
- sends branches that supply the capillary loops in dermal papillae, sebaceous glands and the superficial portion of hair follicles.
- accompanied by venous plexuses that drain blood from dermis into larger subcutaneous veins.