Skin Structure + Function

Question 1

functions of the skin

Answer 1

protection (mechanical impacts, temp, microorganisms..)
physiological regulation ( temp homeostasis, peripheral circulation, synthesis of Vit D)
sensation

Question 2

three layers

Answer 2

epidermis, dermis, subcutis/hypodermis

Question 3

layers of epidermis

Answer 3

stratum corneum, (stratum lucidum), stratum granulosum, stratum spinosum, stratum Basale, basement membrane

Question 4

stratum corneum

Answer 4

dead + enuclear cells
stratified squamous keratinised epithelium
keratin provides structure
plasma membrane thickly coated with lipids

Question 5

stratum lucidum

Answer 5

only found in thick skin, such as the soles or palms

Question 6

stratum granulosum

Answer 6

cells start to lose nucleus and cytoplasm
cells contain keratohyalin granules
- these contain proteins that aggregate the keratin filaments
- lipid tich lamella bodies - secreted + form lipid layer for water loss/proofing

Question 6

stratum spinosum

Answer 6

polyhedral keratinocytes
rich in desmosomes
keratinocytes in this layer have strong intercellular connection through desmosomes (cytoplasm filled with keratin bundles)

Question 6

stratum basale

Answer 6

cuboidal/ low columnar cells
mitotically active cells
contains stem cells which differentiate to populate all layers of epidermis
connected to BM by hemidesmosomes

Question 7

cells found in epithelium (list)

Answer 7

melanocyte; Langerhans cell; Merkel cell; keratinocyte; stem cells; mast cells

Question 7

melanocyte

Answer 7

morphology: long cytoplasmic processes
protect skin cells from UV light damage; prevent skin cancer and aging
produces melanin is melanosomes (specialised organelle) and transfers it to keratinocytes
- therefore important in vit D synthesis

Question 7

keratinocytes

Answer 7

protection + barrier; vit D synthesis here
uses melanin to form a protective layer over the nucleus to protect DNA from UV radiation
UVB converts 7-dehydrocholesterol in the plasma membrane of keratinocytes into previtamin D3 (basal and suprabasal keratinocytes)

Question 8

Langerhans cell

Answer 8

located in stratum spinosum/ basal cell layer
dendritic cell (antigen presenting)

Question 9

Merkel cell

Answer 9

mostly basal layer
sensation

Question 10

dermis layers

Answer 10

papillary, reticular

Question 11

connective tissue composition

Answer 11

collagen 1, elastin, immune cells, blood vessels + nerves

Question 12

papillary (superficial) layer

Answer 12

is loose and contains fine interlacing collagen fibres and the majority of blood vessels + nerves

Question 13

reticular layer

Answer 13

collagen stronger and the elastin fibres are much larger

Question 14

cells of the dermis

Answer 14

fibroblast, lymphocytes, dermal dendritic cells, mast cells

Question 15

fibroblast

Answer 15

synthesis (collagen, elastin + other), growth factors

Question 16

lymphocytes

Answer 16

immunosurveillance

Question 17

dermal dendritic cells

Answer 17

phagocytosis, antigen presentation

Question 18

mast cells

Answer 18

produce inflammatory mediators + chemotactic factors for eosinophils and neutrophils

Question 19

subcutis/ hypodermis

Answer 19

mostly adipose cells
energy source; insulation; shock absorber`

Question 20

skin as a sensory organ

Answer 20

free nerve endings in the skin - papillary dermis form attachments with Merkel cells - work as mechanoreceptors
Meissner’s corpuscles - rapidly acting mechanoreceptors (touch); found in papillary dermis of hands and feet
Pacinian corpuscles - detect deep pressure or vibration; found in subcutis

Question 21

adnexal structures

Answer 21

hair - invaginations in epidrmis (follicles) that contain mitotically active (matrix) cells; melanocytes
nails - distal phalanx of each finger and toe; plates of heavily compacted; highly keratinised epithelial cells that originate from the nail plate; epidermis + occupies space of stratum corneum
glands -
eccrine glands - excrete sweat for temp control; located everywhere on human skin apart from: nail beds, lips, external auditory canal and some parts of genitalia
apocrine glands - scent glands (role unclear in humans); axillae and genitalia
sebaceous glands - formed from hair follicle; present everywhere except palms and soles; produces sebum

Question 22

phases of wound healing

Answer 22

inflammatory, proliferative, remodelling

Question 23

inflammatory phase

Answer 23

platelets initiate homeostasis/ blood clotting and also the healing cascade
attracts other cells to the wound to fight infection (neutrophils/ macrophages)

Question 24

proliferative phase

Answer 24

1- re-epithelialisation
- epithelial cells loosen all adhesions and migrate to the wound site, cover granulation tissue and meet in the middle
2- once wound is covered in single layer of keratinocytes they start to proliferate
3- formation of granulation tissue; mainly type III by fibroblasts
4- neovascularisation: proliferation and migration of endothelial cells (blood vessel formation)

Question 25

remodelling phase

Answer 25

longest phase
collagen II switched to collagen I, which is stronger and organised into thick bundles
some fibroblasts transfer t myofibroblasts - contractile force to pull edges of wound together
remaining granulation tissue matures into connective scar tissue - skin regains up to 80% of strength

Question 26

factors affecting wound healing

Answer 26

infection; foreign bodies; oxygenation; vascular disruption; age; diseases (diabetes); alcohol + smoking; immunocompromised condition; obesity; medications (glucocorticoid steroids (anti-inflammatory)

Question 27

depth of injury

Answer 27

erosion - only epidermis
ulceration - structures deep in epidermis
partial thickness - epidermis + varying parts of dermis. adnexal structures serve as a reservoir of epithelial cells to repopulate the wound + cells from wound edge
full thickness - epidermis + dermis + deeper structure