Skin Flashcards
Skin
Largest organ of body, ~ 15-20% of body mass
4 main functions of the skin
- protection
- sensation
- thermoregulation
- metabolic functions
3 main layers of skin
- epidermis
- dermis
- hypodermins = subcutis
epidermis
Consists of keratinized, stratified squamous epithelium
ketatinocytes
Cells of epidermis
thick skin
thick, highly keratinized layer
•Restricted to volar (soles) & palmar (palms) surfaces
•lacks hair (glabrous)
•Most of body covered in “thin skin”, with thin keratinized epidermis
what does the epidermis lack?
blood vessels. Do not penetrate BM
Epidermis role
supplied & nourished by blood vessels in underlying (subjacent) dermis
Dermis composition
Composed of dense, irregular, collagenous connective tissue (Type I collagen), interspersed with elastic fibers
what is the progressive damage to elastic fibers?
- dermis
- “aging”, loss of skin tone
Layers of the dermis
- superficial papillary later
2. reticular layer
Papillary layer
-relatively thin
-interdigitates with epidermis
•Corrugations ↑surface area for attachment, prevent shear & mechanical abrasion
Epidermal ridges (rete ridges)
epidermal projections into dermis
Dermal ridges (dermal paillae)
- dermal projections into epidermis
- finerprints
dermatoglyphs
fingerprints, unique to individual
dermatoglyphics
form basis of study
reticular layer of dermis
- thicker and less cell than papillary layer
- Contains hair follicles, sweat & sebaceous glands
subcutis
Interdigitates with underlying hypodermis
Langer’s lines
- Thick collagen bundles & elastin fibers in reticular layer form lines of tension
- skin incisions parallel to this for less scarring
hypodermis
- Located below dermis
- layer of loose, irregular connective tissue & adipose tissue
panniculus adiposus
= superifical fascia= subcutis
what are the 3 vascular plexi
- subcutaneous
- subpapillary plexus
- cutaneous plexus
Subpapillary plexu
located at junction of papillary & reticular layers
Cutaneous plexus
located at junction of reticular layer & hypodermis
Subcutaneous plexus
-located deep within hypodermis; largest of three
what plexus is used in thermoregulation?
subcutaneous plexus; in fingertips & ears, associated with AV shunts containing glomus bodies
Subcutaneous plexus, contains glomus bodies for thermoregulation. What are glomus bodies?
- Thickened regions of smooth Mm in arterioles, surrounded by connective tissue capsule
Bypass capillary bed, re-route blood from arterial to venous circulation-
Growth of epidermis
- Skin continuously grown & replaced
* Takes ~25-50 days for cells to travel from deep to superficial
psoriasis
keratinocyte maturation only takes ~1 wk => Absence of a granular layer and abnormal keratohyaline & tonofibrils
Stratum basale
=stratum germinativum
- basal layer
hemidesmosomes
How mitotic layer of cuboidal germinal cells bound to basement membrane
what do hemidesmosomes attach to?
Attach to underlying dermis via anchoring filaments& microfibrils
Stratum spinosum
“prickle cell layer”—cells look spiny; thickest layer of epidermis in thin skin
what cells does the stratum spinosum have a lot of?
Polyhedral cells with prominent intercellular bridges (desmosomes), numerous cytoplasmic processes & lateral folding of cell membrane
what is the predominant cell product in desmosomes
Predominant cell product, cytokeratin, forms tonofilaments, aggregate into larger tonofibrils, anchor onto desmosomes
Stratum granulosum
- granular cell layer
- characterized by kertohylaine graules
keratohyaline granules
non-membrane bound, electron dense granules
keratinization of cells
interaction between keratohyaline granules & tonofibrils
how is kertainization initiated?
by release of lysosomal enzymes => rupture of keratohyaline granules & polymerization of their contents
kertain
Forms a matrix for tonofibrils of cytokeratin => amorphous mass of mature kertin
release of lysosomes is known as what?
death of the cell
release of lysosomes is known as what?
death of the cell
what happens when keratinocytes mature?
die and lose nuclei
keratinsomes
Cells of granular layer contain membrane-bound, lamellar structures
what does kertinosomes contain?
contain glycolipids, provide waterproofing coat for skin cells
stratum lucidum
- present on in thick skin
- Homogenous, compact layer of enucleate cells between stratum granulosum & stratum corneum
Stratum corneum
- cornified layer
- most superficial layer
- thickest layer of epidermis in thick skin
squames
- in stratum corenum
- Contains flattened, enucleate, dead cell remnants
what do squames composed?
Composed 1’ of soft keratin—acts as hydrophobic barrier, prevents desiccation
desquamation
Continuously exfoliated
In females, what is routinely examined?
Pap smear, to detect cervical cancer
What are the common skin tumors?
- Squamous cell carcinoma
- Basal cell carcinoma
- Melanoma
what two skin tumors are derived from epithelia cells?
- squamous cell carcinoma
2. basal cell carcinoma
what is melanoma dervied from?
melanocytes
what do all aggressive cancers have a tendency to undergo?
metatstasize
first intention healing
from a clean (surgical), approximated incision
incision
immediately fills with blood & clots
in first intention healing, what happens within 3-24 hrs?
neutrophils infiltrate clot (acute phase)
what occurs within 24-48 hrs in first intention healing?
Epithelial cells of stratum basale begin mitosis => epithelial closure (reapproximation)
what occurs in day 3-7 in would repair?
neutrophils begin to be replaced by M(transition from acute to subacute phase)
In production of granulation tissue, what are the 3 processes
- neovascularization,
2. fibroplasia 3.re-epithelialization
In production of granulation tissue, what are the 3 processes
- neovascularization,
2. fibroplasia 3.re-epithelialization
fibroplasia
(fibroblasts elaborate collagen
re-epithelialization
epithelial proliferation) => production of granulation tissue
what occurs in week 2 of wound repair
continued fibroplasia & collagen accumulation => mature granulation tissue
•Progressive ↓in inflammation
•Presence of inflammatory cells & inflammatory cell products => itching while healing
what occurs in month 2 of wound repair?
connective tissue scar, without inflammation, covered by intact epithelium
•With Vit C deficiency, collagen breaks down; old scars can re-open & bleed
Keloid
excess fibroplasia => raised, thickened
Second intention healing
- occurs with more extensive loss of tissue
- where wound edges do not approximate
what happens following an intial flot formation in second intention healing?
epithelial cells of stratum basale migrate from edges of wound at ~ 0.5 mm/day
In hair skin, what happens to the migration of cells in second intention healing?
migration of cells from external root sheath of hair follicles augments re-epithelialization
overall significance of second intention healing?
Simultaneous proliferation/ maturation of keratinocytes behind migrating front slowly restores multilayered, stratified epidermis
hwo long does keratinization occur in second intention healing?
Takes ~ 25 days for cells to mature from stratum basale to stratum corneum
Keratinazation of new cells will undergo what?
desquamation & lifting of scab from periphery after ~ 3 wks
•Followed by wound contraction due to myofibroblasts
when is grafting generally necessary?
In full thickness abrasion, or third degree burns, re-epithelialization limited by size of wound
what are the burn classifications according to severity?
1st degree
2nd degree
3rd degree
1st degree burn
involves only epidermis
2nd degree burn
involves both epidermis & dermis
3rd degree burns
ivolves all three layers, epidermis, dermis & hypodermis
