Tissues Under Load

Question 1

How is the skin anistropic?

Answer 1

Because it stretches in more then one direction

Question 2

How do we know skin is anistropic?

Answer 2

Due to the difference in the gaping of wounds caused by straight line incisions. Wounds in areas of tension change to ovals.

Question 3

Regions of high tension of the skin are?

Answer 3

Langers Lines.

Question 4

How can Langers Lines be determined?

Answer 4

With the flint circles. This is effective for wound healing and as everyones LL’s are slightly different

Question 5

How are hypertrophic scars formed?

Answer 5

If the incision is made at a RIGHT ANGLE to the Langer’s lines. If made parallel no scar will form

Question 6

Where is a hypertrophic scar formed?

Answer 6

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

Question 7

When PRESSURE is applied to a tendon

eg) sesamoid bone pushing into

Answer 7

• PG content increases, stains blue/green instead of red
• tenocytes to chondrocytes, (turns into fibrocartilage)
• cells become rounder

Question 8

What allows resistance to tensile stress in tendons and ligaments?

Answer 8

Regularly arranged bundles of collagen fibres

Question 9

What allows for resistance to compressive stress in tendons and ligaments?

Answer 9

The PG content. These are hydrophilic and absorb lots of water.

Question 10

Main PG in the peripheral regions next to the pressure bearing region?

Answer 10

Decorin (0.15%)

Question 11

Main PG in the pressure bearing region?

Answer 11

Versican/aggrecan (2-4%)

Question 12

What would you expect to see ten days post tendonectomy and neurectomy (cut of tendon and nerve so no tension is there at all)

Answer 12

• 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

Question 13

In relation to cancer patients, why are Langer’s lines important

Answer 13

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

Question 14

What are the layers of the skin

Answer 14

Epidermis
Dermis - Papillary & Reticular
hypodermis
investing fascia

Question 15

What in the tendon allows for precise movements

Answer 15

The inability of collagen to stretch

Question 16

What do you see under a light microscope (x1000) with massons trichrome

Answer 16

Red, parallel aligned collagen FIBRES under tension,

Question 17

What would you see under an electronmicroscope

Answer 17

Aligned collagen fibrils with long elongated nucleus wedged in between. This regular arrangement shows collagen is a crystal.

Question 18

How much can collagen be stretched and what happens after?

Answer 18

2% then there will be NO MORE stretch, like mild steel

Question 19

Structure of tendons and ligaments

Answer 19

Closely packed collagen fibres, with intervening rows of elongated fibroblasts and a sparse capillary network. There are some elastic fibres, more so in ligaments,

Question 20

Aponeuroses

Answer 20

Flat tendon

Question 21

Purpose and contents of tendon sheath

Answer 21

To allow for gliding and sliding of tendons so they dont fray/ not adhere. This is filled with synovial fluid (high HA)

Question 22

Properties of Hyaline/articular Cartilage

Answer 22

high PG content (10%) mainly aggrecan, especially at weight bearing regions
less PG at periphery
Lots in fetus, less in adult

Question 23

What makes up aggrecan

Answer 23

Chondroitin sulfate
keratin sulfate
protein core

Question 24

Why does aggrecan resist compression

Answer 24

1) Negative GAG charges

2) bound water molecules between branches

Question 25

What does aggrecan bind to

Answer 25

1) Hyaluronan

2) collagen fibres (via + aminoacids)

Question 26

What is the 2 second creep modulus

Answer 26

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

Question 27

What is meant by “the longer its lost, the harder it is to regain”

Answer 27

The longer you remove pressure from a connective tissue, the harder it will be to regain the PG content you lost.

Question 28

What can maintain PG content

Answer 28

Movement and weight bearing.

Question 29

What is fibrocartilage designed to resist?

Answer 29

Both tension and compression

Question 30

What are the epidermal derivatives?

Answer 30

Hair
Sweat glands
Sebaceous glands
Nail

Question 31

What can be used as a source of epithelial cells?

Answer 31

The epidermal derivatives: hair, sebaceous glands and sweat glands

Question 32

What are the two types of skin?

Answer 32

Thick (epidermis 0.4-0.6mm)
Thin (epidermis 75 - 150 micrometres)
butthis only refers to the EPIDERMIS

Question 33

Where is the thickest skin in the body and how thick?

Answer 33

Back (4mm)