Tissues Under Load Flashcards
How is the skin anistropic?
Because it stretches in more then one direction
How do we know skin is anistropic?
Due to the difference in the gaping of wounds caused by straight line incisions. Wounds in areas of tension change to ovals.
Regions of high tension of the skin are?
Langers Lines.
How can Langers Lines be determined?
With the flint circles. This is effective for wound healing and as everyones LL’s are slightly different
How are hypertrophic scars formed?
If the incision is made at a RIGHT ANGLE to the Langer’s lines. If made parallel no scar will form
Where is a hypertrophic scar formed?
In the reticular layer of the dermis, by extra accumulation of collagen fibres. Above and below there are tight collagenous bands that are under tension, and compress whats in between. the increase in pressure leads to cartilage trying to be formed
When PRESSURE is applied to a tendon
eg) sesamoid bone pushing into
- PG content increases, stains blue/green instead of red
- tenocytes to chondrocytes, (turns into fibrocartilage)
- cells become rounder
What allows resistance to tensile stress in tendons and ligaments?
Regularly arranged bundles of collagen fibres
What allows for resistance to compressive stress in tendons and ligaments?
The PG content. These are hydrophilic and absorb lots of water.
Main PG in the peripheral regions next to the pressure bearing region?
Decorin (0.15%)
Main PG in the pressure bearing region?
Versican/aggrecan (2-4%)
What would you expect to see ten days post tendonectomy and neurectomy (cut of tendon and nerve so no tension is there at all)
- From red to green fibres
- cells shorten/rounden
- collagen fibres are less aligned
- PG content increase as seen by the increasing white space
- Tissue becomes ‘puffy’ PG attract water
In relation to cancer patients, why are Langer’s lines important
You can map out a tumor, and find the angle (parrallel to LL) to cut around it that will cause the least scar formation. This will also have the most excessive/slack skin either side so can be stitched up
What are the layers of the skin
Epidermis
Dermis - Papillary & Reticular
hypodermis
investing fascia
What in the tendon allows for precise movements
The inability of collagen to stretch
What do you see under a light microscope (x1000) with massons trichrome
Red, parallel aligned collagen FIBRES under tension,
What would you see under an electronmicroscope
Aligned collagen fibrils with long elongated nucleus wedged in between. This regular arrangement shows collagen is a crystal.
How much can collagen be stretched and what happens after?
2% then there will be NO MORE stretch, like mild steel
Structure of tendons and ligaments
Closely packed collagen fibres, with intervening rows of elongated fibroblasts and a sparse capillary network. There are some elastic fibres, more so in ligaments,
Aponeuroses
Flat tendon
Purpose and contents of tendon sheath
To allow for gliding and sliding of tendons so they dont fray/ not adhere. This is filled with synovial fluid (high HA)
Properties of Hyaline/articular Cartilage
high PG content (10%) mainly aggrecan, especially at weight bearing regions
less PG at periphery
Lots in fetus, less in adult
What makes up aggrecan
Chondroitin sulfate
keratin sulfate
protein core
Why does aggrecan resist compression
1) Negative GAG charges
2) bound water molecules between branches
What does aggrecan bind to
1) Hyaluronan
2) collagen fibres (via + aminoacids)
What is the 2 second creep modulus
If you probe cartilage for 2 seconds and then measure how much deformation you get in the cartilage. shows the straight line relationship between resistance to compression and PG content
What is meant by “the longer its lost, the harder it is to regain”
The longer you remove pressure from a connective tissue, the harder it will be to regain the PG content you lost.
What can maintain PG content
Movement and weight bearing.
What is fibrocartilage designed to resist?
Both tension and compression
What are the epidermal derivatives?
Hair
Sweat glands
Sebaceous glands
Nail
What can be used as a source of epithelial cells?
The epidermal derivatives: hair, sebaceous glands and sweat glands
What are the two types of skin?
Thick (epidermis 0.4-0.6mm)
Thin (epidermis 75 - 150 micrometres)
butthis only refers to the EPIDERMIS
Where is the thickest skin in the body and how thick?
Back (4mm)
