Integumentary System Flashcards
Skins consists of what two distinct regions?
- Epidermis- superficial region
Keratinized stratified squamous epithelial tissue
- Dermis- underlies epidermis
Loose areolar and dense irregular connective tissue
What are the five layers of the epidermis?
1) Stratum corneum: 20-30 rows of dead, flat, enucleate keratinized membranous sacs.
Protects from abrasion and penetration, protects deeper cells from environment and water loss, barrier against biological, physical, and chemical assaults
2) Stratum lucidum: Only in thick skin. A few rows of flat, dead keratinocytes. Thin, translucent band superficial to the stratum granulosum.
3) Stratum granulosum: Thin, four to six layers. Cells above this layer die. Cytoplasm full of lamellar granules (release lipids; their water resistant glycolipids slow water loss) and keratoyhalin granules (form keratin in upper layers).
4) Stratum spinosum: Several layers thick, several layers of keratinocytes unified by desmosomes.
5) Stratum basale: Single row of stem cells, actively mitotic (produce daughter cells). One cell journeys from basal layer to surface (takes 25-45 days, dies as it reaches surface) and one remains in basal layer as a stem cell.
Keratinocytes
-Most cells of epidermis
-Produce fibrous protein keratin
-Tightly connected by desmosomes
Melanocytes
-Located at stratum basale
-Produce pigment melanin, which protects keratinocyte nucleus from the UV damage
Dendritic (Langerhan) cells
-Located in the stratum spinosum
-Macrophages- key activators of the immune system
Tactile (Merkel) cells
-Located at stratum basale
-Sensory touch receptors
Compare and contrast the possible variations in the layers of the epidermis.
Thick skin
* 5 layers in epidermis
– Has stratum lucidum
* Found in palms of hands and soles
of feet
* Epidermis is 0.4–0.6 mm thick
* No hair follicles or sebaceous
glands
Thin skin
* 4 layers in epidermis
– No stratum lucidum
* Covers most of body
* Epidermis is 0.075–0.150 mm thick
Is the epidermis vascular or avascular?
Avascular
Describe the dermis
-Strong, flexible connective tissue
-Fibroblasts, macrophages, and occasionally mast cells and white blood cells
-Fibers in matrix bind body together. “Hide” used to make leather
Contains:
– nerve fibers
– blood and lymphatic vessels
– epidermal hair follicles
– oil and sweat glands
- Two layers
– Papillary
– Reticular
Papillary layer of the dermis
- Superficial layer
- Loose areolar connective tissue
- Dermal papillae
– Superficial peg-like projections
– Connect to epidermal ridges
– Most contain capillary loops
– Some contain Meissner’s corpuscles (touch receptors)
– Some contain free nerve endings (pain receptors)
Reticular layer of the dermis
-80% of the dermis
-Dense irregular fibrous connective tissue
Why do we have fingerprints?
They are formed from large folds and valleys of both dermis and epidermis. They are found in the fingers, palms, soles, and toes.
They enhance gripping ability and contribute to sense and touch.
Lines of cleavage
Most collagen and elastic fibers are parallel to skin surface
– Externally invisible
– Important to surgeons
– Incisions parallel to cleavage lines gap less and heal more readily
What are the functions of skin?
-Protection
-Prevention of water loss and gain
-Temperature regulation
-Metabolic regulation
-Sensory regulation
-Secretion
The skin is selectively permeable with chemical, physical, and biological barriers
Chemical barriers:
Skin secretions
– Sebum and defensins kill bacteria
– Low pH retards bacterial multiplication
– Melanin- defense against UV radiation damage
Physical barriers:
The outermost layer of the epidermis is composed of flat, dead cells surrounded by lipids
- Limited penetration of skin:
- Lipid-soluble substances
- Plant oleoresins (e.g., Poison ivy)
- Salts of heavy metals (e.g., Mercury)
- Some drugs
- Drug agents
Biological barriers:
– Dendritic cells of epidermis
* Phagocytize pathogens and cancer cells
* Present foreign antigens to white blood cells
– Macrophages of dermis
* Similar functions
Subcutaneous layer
Superficial fascia deep to skin
– Not part of integument, but shares some functions
– Mostly adipose tissue that absorbs shock & insulates
– Anchors skin to underlying structures – mostly muscles
– Vascular networks make for good drug delivery
- Injections
What are the derivatives of the epidermis?
-Nails
-Hair
-Exocrine glands
Nails
-Scalelike modifications of epidermis
-Protective cover for distal, dorsal
surface of fingers and toes
-Contain hard keratin
-Nail matrix