Dermatology - Development and Structure of Epidermis

Question 1

2 main layers of skin and tissue types of both?

Answer 1

Epidermis (outer layer) - stratified cellular epithelium

Dermis (beneath epidermis) - connective tissue

Question 2

Formation of the epidermis layers?

Answer 2

Ectoderm cells form a single layer periderm (replaces the epidermis); the layers of cells are increased until periderm cells are cast off

Question 3

Formation of the dermis layers?

Answer 3

Formed from mesoderm below ectoderm

Question 4

Melanocytes and their formation?

Answer 4

Pigment-producing cells from neural crest

Question 5

Gastrulation and period of time during which it occurs?

Answer 5

Cellular organisation into germ layers takes place during days 7-10

Question 6

Foetal skin layers at 4 weeks?

Answer 6

From superficial to deep:
Periderm
Basal layer
Dermis

Question 7

Foetal skin layers at 16 weeks?

Answer 7

Keratin layer
Granular layer
Prickle cell layer
Basal cell layer
Dermis

Question 8

Foetal skin development at 26 weeks?

Answer 8

Hair follicles have formed, along with arector pili muscles and sebaceous glands; hairs extend through the epidermis

Question 9

What is the dermo-epidermal junction

Answer 9

Interface between the dermis and epidermis

Question 10

Cells of the epidermis?

Answer 10

95% of the epidermis consists of keratinocytes; the rest are stratified squamous epithelial cells, Merkel cells, Langerhan cells and melanocytes

Question 11

Describe the epidermal variation at different body sites

Answer 11

On the soles of the feet, there is no hair, as opposed to the armpit and scalp; also, in some regions, there are more sweat glands

Question 12

Dermatological conditions where there is a loss of regulation of epidermal turnover?

Answer 12

Skin cancer

Psoriasis

Question 13

Process of differentiation of keratinocytes?

Answer 13

Migrate from the basement membrane, over 28 days from the bottom to the top, to continuously regenerate the epidermis

Question 14

Structure of the basal cell layer?

Answer 14

One cell thick (small and cuboidal); there are many intermediate filaments/keratin The basal cell layer is curved to supply rigidity

Question 15

Structure of prickle cell layer?

Answer 15

Consists of larger polyhedral cells and many desmosomes, which are connected to intermediate filaments

Question 16

Structure of the granular layer?

Answer 16

2-3 layers of flatter cells along with:
Large keratohyalin granules (contain proteins)
LAMELLAR BODIES (Odland bodies)

Question 17

Features of the granular layer?

Answer 17

Cell nuclei are lost and the layer has a high lipid content

Question 18

What is the cornified envelope?

Answer 18

Cornified envelope replaces the plasma membrane of differentiating keratinocytes and consists of keratins that are enclosed within an insoluble amalgam of proteins and a lipid envelope

This originates in the granular layer

Question 19

Structure of the keratin layer?

Answer 19

Mostly consists of keratin and fillagrin (links keratin to epithelial cells) but also corneocytes (overlapping non-nucleated cell remnants)

This layer forms a waterproof barrier

Question 20

What happens when the keratin layer thickens?

Answer 20

A transparent layer becomes less so, e.g: thickened nails and white patches on mucosal surface of mouth, and the skin can thicken