Layers and Cells of the Skin Flashcards
what are the 4 layers of the epidermis (and the 5th layer that is sometimes found)?
(external -> internal)
1 - stratum basale (basal cell layer)
2 - stratum spinosum (prickle cell layer)
3 - stratum granulosum (granular cell layer)
( stratum lucidum - clear layer)
4 - stratum corneum
what type of epithelium is found in the skin epidermis
stratified squamous epithelium
what is the structure of the basal cell layer? (2)
- row of columnar keratinocytes
* attached to the basement membrane by hemidesmosomes
why is the basal cell layer very mitotically active?
small proportion of keratinocytes are stem cells that continuously divide
what cytoplasmic structure is found in basal cells? where do they converge?
- tonofilaments
* hemidesmosomes
what 3 cells are found in the basal layer?
- keratinocytes
- melanocytes
- Merkel cells
what is the structure of the prickle cell layer? (3)
- polyhedral keratinocytes
- interconnected with desmosomes
- give cells a spiny appearance (ie. prickle)
what cytoplasmic structure is found in cells of the prickle layer? where do they converge?
- tonofilaments bundled together forming supportive tonofibres
- desmosomes
what 2 cells are found in the prickle layer?
- keratinocytes
* Langerhans cell
what is the structure of the granular layer?
flattened cells containing important granular structures
what 2 cell processes begin to happen in the granular layer?
- removal of nuclei
* expulsion of lipids and liquid from the cytoplasm
what is the structure of the horny layer?
sheets of cornified cells with no nuclei, stuck together by lipid glue
where on the body is the horny layer thickest? - these areas also have a stratum lucidium
palms of hands and soles of feet
what is the cytoplasm replaced with in the cells of the horny layer?
keratin fibrils
why are cells of the horny layer stuck together with lipids?
makes the skin surface water tight
what is the top layer of their dermis and what are 2 of its features?
• papillary layer
- interdiginates with epidermis
- composed of of loosely woven collagen
what is the lower layer of the dermis and what is a feature of it?
- reticular layer
* coarse, horizontally running bundles of collagen
what material makes up 70% of the dermis, and what quality does this provide the dermis?
- collagen
* toughness and strength
what fibre is incorporated into the collagen network in the dermis? what quality does this provide?
- elastin
* elasticity
what is the ground substance in the dermis and what is its purpose?
- semi-solid matrix
* allows dermal structures some movement
what cells are present in the dermis?
- fibroblasts
- dermal dendritic cells
- mast cells
- lymphocytes
- macrophages
what it is the structure of the hypodermis?
adipose tissue with supporting fibrous bands
why is skin regenerating important? (2)
- horny layer is important for preventing microorganisms, water etc. from entering the skin
- epidermis prevents fluids from getting out
what is the keratinocyte maturation sequence? (7)
1 - stem cells continuously divide into 1 new stem cell and a transit amplifying cell
2 - transit amplifying cells proliferate briefly before progressing upwards for terminal differentiation
3 - in prickle cell layer, cell changes shape from columnar to polygonal
4 - differentiating keratinocytes synthesise keratins
5 - in granular layer, enzymes induce degradation of nuclei and organelles
6 - in horny layer, dead and flattened corneocytes have developed cornified envelopes
7 - corneocytes eventually shed from skin surface after degradation of the lipid glue and loss of desmosomes intercellular connections
what are 2 functions of membrane-coating granules? what is another name for these granules?
- release lipid glue to increase cell adhesion
- provide a water-tight barrier to epidermis
• lamellar bodies
how often do dividing basal cells replicate?
every 200 - 400 hours (8 - 16 days)
how long does it take skin cells to shed?
52 - 75 days (7-12 weeks)
what disorder reduced the maturation time of skin cells?
psoriasis
what are the name of 4 wound depths?
- erosion - epidermis only
- ulceration - structures deep in epidermis
- partial thickness - epidermis + parts of dermis (adnexal structures serve as reservoir of epithelial cells to repopulate)
- full thickness - epidermis + all of dermis + deeper structures (only wound edge heals)
how long does the inflammatory phase of wound healing last?
24 - 28 hrs
what are the 3 processes occurring in the inflammatory phase of wound healing?
- haemostasis - vasoconstriction and primary platelet plug
- activation of coagulation pathway
- inflammation response
what cells are involved in the inflammatory phase of wound healing and what are their roles? (2)
- neutrophils - remove bacteria and necrotic tissue (non-programmed cells death), contribute to cytokine release
- macrophages - phagocytosis, synthesise cytokines and growth factors
what are the 5 processes occurring in the proliferative phase of wound healing?
1 - re-epithelialisation - epithelial cells loosen cell-cell adhesions and migrate towards wound site to cover granulation tissue
2 - once a single later established, keratinocytes proliferate
3 - granulation tissue forms
4 - re-angiogenesis (nourish and support fibroblasts)
5 - fibroblasts activate
what is the role of fibroblasts in the proliferative phase of wound healing? (2)
- scar formation
* collagen deposition
what type of collagen is deposited in wound healing? what happens to collagen during the remodelling phase? (2)
• collagen III
- switches to collagen I
- organised into thick bundles and cross-link -> mature scar
what happens to granulation tissue in the remodelling phase of wound healing?
matures into scar tissue - connective tissue with few cells
what happens to some fibroblasts in the remodelling phase of wound healing?
differentiate into myofibroblasts - produce contractile tissue to close wound
what is EGF? what does it signal?
- epidermal growth factor
* re-epithelialisation - keratinocyte proliferation and migration
what is PDGF? what 2 processes does it signal?
• platelet-derived growth factor
- matrix formation - increases fibroblast number and activity
- remodelling - formation of proteases
what is VEGF? what process does it signal?
- vascular endothelial growth factor
* angiogenesis
what are 3 inflammation signally molecules?
- interleukin-1
- interleukin-6
- activated tumour necrosis factor (TNFa)
what 4 local factors effect wound healing?
- infection
- foreign body
- oxygenation (highly active process)
- vascular supply
what 6 systemic factors effect wound healing?
- age
- disease (eg. diabetes - non-healing ulcers)
- alcohol / smoking
- immunocompromised conditions
- obesity
- medication (anti-inflammatories)
