Skin Structure

Question 1

Function of skin

Answer 1

-protection: mechanical impacts, pressure, variation in temperature, microorganisms, radiation/ chemicals
- physiological regulation: body temperature via sweat and hair, changes in peripheral circulation, fluid balance via sweat, synthesis of vit D
- sensation: network of nerve cells that detect and flat changes in the environment

Question 2

Epidermis

Answer 2

• basement membrane: sheet like layer of extra cellular matrix proteins
• stratum basale: cuboidal/ low columnar cells, mitotically active, constant regeneration of the other layers, connected to BM by hemidesmosomes
• stratum spinosum: polyhedral keratinocytes, rich in desmosomes
• stratum granulosum: cells becoming flattened, contain keratohyalin granules, starting to lose nucleus and cytoplasm
• stratum corneum: large flat plat like envelopes filled with cross linked keratin, lipids

Question 3

dermis

Answer 3

• connective tissue
• collagen type 1 ( provides tensile strength)
• elastin ( allows stretch)
• two layers- papilary layer and reticular layers
• fibroblasts- synthesis collagen, elastin, ground substances

Question 4

sensory organ

Answer 4

Free nerve endings in the skin
-papillary dermis and form attachments with Merkel cells act as mechanoreceptors

-Meissner’s corpuscles:
rapidly acting mechanoreceptors responsible for touch.
Papillary dermis of hands and feet

-Pacinian corpuscles
detect deep pressure and vibration usually in subcutis

Question 5

keratinocyte

Answer 5

location- keratinised stratified squamous epithelium
function- protection and barrier, vitamin D production

Question 6

stem cell

Answer 6

location- stratum basale
function- self reveal and repopulation of epidermal layers

Question 7

merkel cells

Answer 7

location- epidermis (mostly basel layer)
function- sensation

Question 8

langerhans cell

Answer 8

location- epidermis (mostly stratum spinous) and upper dermal layer (papillary)
function- dendritic cells

Question 9

melanocyte

Answer 9

location- basal layer
function- protection from radiation

Question 10

UV light

Answer 10

Chronic UV exposure in humans leads to:
-Loss of skin elasticity / fragility,
-Abnormal pigmentation
-Haemorrhage of blood vessels
-Wrinkles and premature ageing

Question 11

keratins

Answer 11

location- all epidermis layers
function- major structural protein, intermediate filaments

Question 12

keratohylain granules- profilaggrin

Answer 12

-converted to filaggrin which aggregates keratin filaments into tight bundles

Question 13

keratohyalin granules- involucrin

Answer 13

-formation of a cell envelope around cells in the stratum corneum

Question 14

keratohyalin granules- Ioricin

Answer 14

cross links to involucrin

Question 15

polysaccharides, glycoproteins, lipids

Answer 15

location- lamellar granules
function- extrude into intercellular space; form the “cement” that holds together the stratum corneum cells

Question 16

mast cells

Answer 16

-Produce inflammatory mediators (eg, histamine, heparin) & chemotactic factors for eosinophils and neutrophils

Question 17

inflammation/vascular phase

Answer 17

-24-48 hours

-Platelets initiate haemostasis/blood clot and also the healing cascade.

-Attracts other cells to the wound to fight infection and transition from inflammation to repair (neutrophils/macrophages).

 characteristic signs of inflammation: red/swelling
-Neutrophils and macrophages phagocytose dead tissue and microorganisims

Question 18

proliferative phase

Answer 18

1. Re-epithelialisation:

Within 1-2 days of wounding, epithelial cells loosen cell-cell adhesions and migrate to the wound site, cover the granulation tissue, and then meet in the middle.

Once the wound is covered in a single layer of keratinocytes  all keratinocytes start to proliferate.
2. Formation of granulation tissue;
mainly type III collagen
3. Neovascularisation: proliferation and migration of endothelial cells

Question 19

remodelling phase

Answer 19

Granulation tissue becomes mature
scar tissue

Collagen is organised into thick
bundles and extensively
cross-linked to form a mature scar

Switch in type III collagen to
type I collagen

Final strength only 70-80% of
preinjured skin

Scar strength 5% at 1 week,
20% at 3 weeks and
70-80% at 1 year

Question 20

EGF (epidermis growth factor)

Answer 20

-Re-epithelialisation
(keratinocyte proliferation and migration)

Question 21

Platelet- derived growth factors (PDGF)

Answer 21

-Matrix formation (increased numbers and activity of fibroblasts)
-Remodelling (production of proteases)

Question 22

Vascular endothelial growth factors

Answer 22

• angiogenesis (endothelial cell proliferation and migration)

Question 23

IL1/6 and Tumour necrosis factor alpha

Answer 23

function- inflammation

Question 24

factors affecting wound healing- local factors

Answer 24

• infection
• foreign body
• oxygenation
• vascular supply

Question 25

factors affecting wound healing- systemic factors

Answer 25

• age
• disease eg diabetes
• alcohol and smoking
• immunocompromised conditions
• obesity
  -medication