MNSR 24 - Integument Flashcards
Skin Function
Skin forms integument coating entire body
= Protection
- tough hide of mammals protects against physical trauma
- forms continuous unbroken
- line of defense against invasion by pathogens
= Thermoregulation
- hair provides insulation, major role in temperature regulation
- aids in water regulation in terrestrial animals
= Sensation
- skin appears to have been area of origin of sensory nervous structures
- embryologically nervous system arises in continuity with skin ectoderm
- contains many sensory nerve endings for pressure, temp, pain
- allows interpretation of external environment
= Metabolism
- produces vit D used in calcium & phosphate metabolism
Skin Structure
- Largest body organ
- 12-16% mass
- Tight over palms and feet, loose in other parts
- Variable thickness (thin over eyelids, thick on soles of feet)
- Continuous with digestive tract (mouth anus), and urogenital system (penis/vagina/urethra)
- Not a single structure
- Composed of Outer Epidermis & Inner Dermis (vascular)
- Below dermis is loose connective tissue / fat = Hypodermis
- First line of immunological defence
Epidermis Histology
- Superficial body covering
- 0.06-0.01 mm
- Cellular, Avascular
- Arises from embryonic *ectoderm, gives rise to sweat glands, sebaceous glands, mammary glands
- Keratin protein gives rise to hair, nails, hooves, horns
- Made of stratified squamous epithelium, undergoes keratinization
Epidermis Structure
- Surface layer (corneum) covered with oily secretion *Sebum from sebaceous glands (waterproofing protection)
- 5 layers
- Gradually die and flatten out as reach upper surface
- usually rate of mitosis equals rate of desquamation (skin shedding) = entire epidermal cycle is 27 days
5 Layers of Epidermis
1) Stratum Basale (germinativum
- germinal layer of dark, basophilic columnar/cuboidal cells
2) Stratum Spinosum
- growing cells showing early keratin synthesis
3) Stratum Granulosum
- showing granules within cells
4) Stratum Lucidum
- only in thick skin
- clear homogenous layer of cells without nuclei/organelles
- elongate and flatten
5) Stratum Corneum
- thick outer layer of flattened fused cell remnants composed mostly of keratin
- dead, flattened, keratinized
Skin Pigmentation due to 3 factors:
- Inherent yellowish color derived from *carotene in subcutaneous fat
- Concentration and oxygenation of haemoglobin in dermal capillaries
- Special branched cells scattered through stratum basale
Melanocytes (or melanophores)
Produce pigment melanin, protects skin from UV radiation
Number of melanocytes relatively constant irrespective of racial group
Melanoma
Patch of dark skin (mole)
If it becomes cancerous, invades tissues
= Malignant Melanoma (one of most aggressive skin cancers)
Dermis
- Much thicker than epidermis (bulk of skin tissue)
- Derived from embryonic mesoderm
- Layer of dense fibro-elastic connective tissue (collagen, elastic fibers, fibroblasts, mast cells, macrophages)
- Highly vascular (blood, lymphatic vessels, many nerve endings)
- Supports sweat glands, sebaceous glands, hair follicles which grow down from epidermis
- Main function of dermis to support and protect body
Hypodermis
- Beneath dermis
- Loose connective areolar tissue & adipose tissue
- Provides thermal insulation, energy store, further mechanical protection
Hair
- Elongated rod of keratinized cells (hair shaft) grow from root (hair bulb) in dermal layer
- Hair bulb at the base of a pit sunk in the dermis = hair follicle
- Follicle cells are continuous with overlying epidermal layer
Hair Structure
- Early fetal life, epidermis grows down into dermis to form cellular shaft
- Dead keratinized epidermal cells except at the base (growing germinal matrix)
- Germinal matrix forms cap over vascularized plug of dermal tissue = dermal papilla
- Germinal matrix connected to overlying epidermis by cellular external root sheath
Hair Structure & Growth
- Proliferation of germinal matrix produces hair growth
- Initially cells pushed up center of epidermal downgrowth
- Move further from papilla blood supply, become keratinized, die
- Initial cells transform into hair cortex with outer single layer of cells = hair cuticle
- Arrector pilus muscle, (may be removed by natural selection eventually) important for monkeys living outside, contracts (fight or flight) to make hair stand up to trap air in hair for warmth
- Sebaceous glands to keep hair lubricated
- Sebaceous gland can have white pus, WBCs, pus oozes out
Hair Follicle Structure
- Medulla (seldom seen)
- Cortex (keratinized cells)
- Cuticle (single layer of overlapping keratinized cells)
- Internal Root Sheath (IRS) produced by further division of germinal matrix which pushes between External Root Sheath (ERS) and hair cuticle
- Hair shaft held in position in follicle by ERS and IRS
Hair growth
- Hair grows on cyclical basis (phase of growth/regression)
- Growth phase in young adult 3 years (85% of scalp hair in growth phase)
- Baldness - growth phase does not resume, shaft falls out, followed by degeneration of follicle
- Male Pattern Baldness - hair follicles fell out due to testosterone sensitivity, need treating with testosterone lowering tablets
- Old hair shaft loosens and is pushed out by the new shaft when growth resumes
