Skin Structure and Function

Question 1

where are the epidermis and dermis derived from? when does this begin?

Answer 1

epidermis = ectoderm
dermis = mesoderm (below ectoderm)
gastrulation begins 7-10 days into development

Question 2

what are melanocytes?

Answer 2

pigment producing cells from neural crest

Question 3

how does skin progress from 4 weeks to 16 weeks to 26 weeks?

Answer 3

4 weeks = 3 layers - periderm, basal layer and dermis
16 weeks = 5 layers - keratin layer, granular layer, prickle cell layer, basal layer, dermis
26 weeks = same as 16 but with appendages (hair follicles, glands etc)

Question 4

what are Blaschko’s lines?

Answer 4

developmental growth pattern of skin/lines of tension

skin drawn out to make room for limbs as they develop

Question 5

how can blaschko’s lines be used clinically?

Answer 5

if a rash/malformation follows blaschko’s line this would show that it is a developmental problem

Question 6

what are the components of skin?

Answer 6

epidermis
appendages (hair, nails, glands, mucosae)
dermo-epidermal junction
dermis
sub-cutis

Question 7

what is the sub-cutis responsible for?

Answer 7

elasticity/malleability

predominantly fat

Question 8

where in the skin are blood vessels found?

Answer 8

dermis

Question 9

where do sweat glands descend into?

Answer 9

sub-cutis

Question 10

where are sebaceous glands found?

Answer 10

dermis

Question 11

where does hair follicle begin?

Answer 11

sub-cutis

Question 12

what type of epithelium covers the epidermis?

Answer 12

stratified squamous epithelium

Question 13

what cells are present in the epidermis?

Answer 13

keratinocytes (95%)
melanocytes
Langerhans cells
merkel cells

Question 14

how does the epidermis grow and how long does this take from start to finish?

Answer 14

moves and grows up from the basement membrane

takes 28 days to get to the top

Question 15

what is the basal layer?

Answer 15

embryological ectoderm that keeps dividing constantly

like stem cells of the skin

Question 16

is the epidermis the same everywhere?

Answer 16

no
varies at different body sites - e.g more hair on scalp, more sweat glands on soles of feet etc
thickness can also vary

Question 17

how is the constant production of epidermis controlled?

Answer 17

growth factors, cell death, hormones

rate can also be affected by genetics, temperature etc

Question 18

what happens when the regulation of epidermis turnover fails?

Answer 18

skin cancer

psoriasis

Question 19

what causes the red and white parts of psoriasis?

Answer 19

red = blood vessels shine through thin parts of prickle layer as it varies in thickness in psoriasis
white = thickened keratin does not fall away

Question 20

how does epidermis turnover vary in psoriasis?

Answer 20

takes 28 days in normal people

takes 5 days in psoriasis

Question 21

describe the basal layer structure

Answer 21

usually one cell thick layer of cuboidal cells with lots of intermediate filaments (keratin)

Question 22

why are prickle cells called such?

Answer 22

large polyhedral cells briefly connected by many desmosomes

Question 23

what is the function of the prickle cell layer?

Answer 23

produce keratin

organise cells as they move upwards towards epidermis

Question 24

what is the function of the granular layer?

Answer 24

thin layer of cells with large keratohyalin granules containing filaggrin and involucrin proteins
high lipid content

Question 25

what do the granular cells become and how?

Answer 25

origin of the cornified envelope
cells shrink in size and loose nuclei and burst open as they use last resources to overproduce proteins and left overs combine to form envolope

Question 26

what are the components of the keratin layer?

Answer 26

corneocytes
cornified envelope
80% keratin and filaggrin
lamellar granules which release lipids
forms tight waterproof barrier

Question 27

what is the function of filaggrin and keratin?

Answer 27

broken down into amino acids which allow skin to retain water

Question 28

give an example of a disease which affects keratinocytes?

Answer 28

HPV (causes warts)

Question 29

describe wart histology

Answer 29

very thick dermis

very few blood vessels hence why warts aren’t red

Question 30

where are mucosal membranes found?

Answer 30

anywhere the skin stops (e.g - eyes, nose, genital tracts, mouth etc)

Question 31

are all mucosal membranes the same?

Answer 31

no, specialised for function

Question 32

how is oral mucosa specialised for function?

Answer 32

masticatory = keratinised
lining = non-keratinised
specialised (tongue papillae)

Question 33

how is ocular mucosae specialised?

Answer 33

lacrimal glands
eye lashes
sebaceous glands