6 - Skin, scars and invisible lines of force Flashcards
3 functions of skin
Protection against: UV, injury, dehydration, invasion by micro-organisms
Sensation: Receptors for touch/pressure and pain/temperature
Thermoregulation: sweat glands, hair, adipose tissue
What are dermal papillae?
They act like tread to give the epidermis and dermis grip so the skin doesn’t slide of and increases the surface area allowing nutrients from down below to get up to the skin
What are some epidermal derivatives/appendages and what are they important for?
- hair, nail, sweat glands, sebaceous glands
- intrinsic to skin and important in healing as source of epithelial cells to migrate to wounds
Describe the dermis
- thickest skin layer
- collagen for tensile strength and elastin for elasticity made by fibroblasts
- has a weave pattern not uniform in all directions
What does it mean that skin is anisotropic?
- skin has different physical properties in different directions meaning it can stretch more in one direction than another
Why is the skin anisotropic?
- the collagen is in a 3d weave in many directions
- a fibril of collagen is, at rest, more stretched out compared to its structure in the other direction i.e. the fibril is already drawn out/extended/there is already tension in the skin so it is limited compared to the fibre being less drawn out in direction 90 degrees to that
4 ways the skin can be damaged?
- thermal injury
- abrasions
- lacerations and puncture wounds
- surgical incisions
What does how skin is repaired depend on?
- depends on the degree of tissue loss and depth of the wound
- superficial wounds can heal with little or no scarring (through epidermis or partly through dermis)
- wounds of a certain depth inevitably heal with scarring and or contraction
- there is a wide range of possibilities of colour or texture change
- skin is a renewable source for skin graphs. Can harvest from same place multiple places
- usually not the same as normal skin can tell was damaged
How long does wound healing take?
A long time at least 12 -24 months before activity stops
What are the 6 steps of wound healing?
- Bleeding control and clot (haematoma) formation
- Inflammation (redness/erythema, swelling/oedema, heat and pain)
- Matrix formation
- fibroblast migration producing collagen and elastin - Neovascularisation (new BV formation)
- Re-epithelialisation
- epithelial cell migration/growing over of skin - Wound contraction and remodelling
Describe wound healing very briefly
- piece of tissue missing with the area filled with RBCs platelets etc. that release signals to get help
- then get an advancing layer of squamous epithelium over the top of the wound which is covered by a scab (dried blood products) that acts as a cap/plug on top of the epithelial cells
- it is a very complicated and lengthy biological process
What is the wound strength at 5 days, 21 days and a year?
5 days - 10% (wouldn’t take much to be disrupted)
21 days - 45%
1 year - 90%
Never get the area of skin back to full strength
Helps to decide when you should take sutures out
What is a scar?
- it is a patch as the skin is not able to return to the same state it was before and restore complete structural integrity
- during scar formation the collagen becomes ALIGNED along the lines of stress
Why does a hypertrophic or keloid scar occur?
- for some unknown reason sometimes excessive or disorganised connective tissue is produced during healing leading to these abnormal scars
- they are histologically the same as normal scars but behave differently
What are hypertrophic scars?
- red, raised and itchy
- remain within the confines of the original wound
- many scars have an ELEMENT of hypertrophy but usually regresses in 2-6 months
- hypertrophic scars remain for an indefinite amount of time and then MAY regree
- they may contract
What is a hypertrophic scar like under the microscope?
- in the reticular layer of the dermis of the scar is lots of disorganised collagen surrounded by collagen bands caused by tension in the skin which causes the collagen to align
- after burns patients wear tight garments to apply pressure to change the nature of the scar and improve it
What are keloid scars?
- keloid scars are equivalent to benign tumours and are only found in humans
- they too are red, itchy and raised but unlike hypertrophic scars they can invade surrounding tissues
- they DO NOT contract or regress like hypertrophic scars
- they may occur months/years after initial injury and often reoccur even if cut out
- often on earlobes, shoulders, trunk, face and after cardiac surgery
Dupuytren’s contracture?
Fibrous band on palm of hand meaning fingers can flex greatly into palm
Dupuytren
- Noticed someone who stabbed themselves with a circular cross section awl had slit like puncture wounds.
- Discovered the distortion on puncture wounds was due to some relationship with the innate, natural tension of the skin
How advanced Dupuytren’s ideas?
- Langer. Stabbed cadavers and found the slit like wounds followed a pattern
What was causing misinterpretation on Langer’s work?
- he had stabbed a child’s abdomen but adults on the other side
- meant the lines were transverse on one side but oblique on the other
- Langer’s lines were misinterpreted and inaccurately reproduced in pristigous surgical textbooks
- UOA professor discovered
McBurney’s Incision?
- the inaccurate reproduction of Langer’s Lines had unfortunate consequences for generations of patients undergoing surgery for appendicitis
- showed where you should cut to go along the lines of tensions
Cox?
- also stabbed cadavers 20 000
- more elegant lines of skin tension
- in the abdomen the lines were pretty much transverse unlike what was used in the Mcburneys incision
- other researchers found differences especially in the head
- M. Flint at UOA did a paper on this
- today what is called Langer’s Lines is actually Cox’s work
What did M. Flint discover?
- that the lines of skin tension could be visualised by using a rubber circular flint stamp on the patient in the flexed fetal position
- when they then straighten into the anatomical position the circles deform into ellipses
- the long axis of the ellipses align with the skin tension lines (Langer’s Lines)
How are the skin tension lines used clinically?
- if you make a cut INLINE with the skin tension lines there is a natural tendency for the wound to stay together (like pulling 2 pieces of string next to each other tight and the 2 middle pieces come together UNDER THE TENSION)
- if you make an incision at right angles to the skin tension lines the tension tends to bring the wound apart, not heal nicely, and more likely to lead to a hypertrophic scar
What is another clinical relevance of the skin tension lines?
- given the nature of the lines you can often find redundant skin to use and this enables you to cut something large out and sew it together without a skin graft
