Structure & Function 1- embryology + epidermis

Question 1

why is skin important (3)

Answer 1

largest vital organ

25% pop have skin condition

indicator of underlying disease

Question 2

skin - epidermis (5)

Answer 2

epidermis =
-outer layer
-stratified cellular epithelium

ectoderm forms cells from single layer periderm

gradual increase in layers of cells

periderm cells cast off

Question 3

skin- dermis (3)

Answer 3

dermis =
-beneath epidermis
-connective tissue

formed from mesoderm below ectoderm

Question 4

skin- subcutis (2)

Answer 4

subcutis=
-fat layer beneath dermis

melanocytes- pigment producing cells from neural crest

Question 5

foetal skin development - w4 (3)

Answer 5

P- periderm
B- basal layer
D- dermis

Question 6

foetal skin development - w16 (5)

Answer 6

KL- keratin layer
GL- granular layer
PL- prickle cell layer
BL- basal layer
D- dermis

Question 7

foetal skin development - w26 (5)

Answer 7

epidermis

-melanocyte
-sebaceous gland
-arector pili muscle
-hair follicle

Question 8

blaschko’s lines

Answer 8

developmental growth pattern of skin – not following vessels, nerves or lymphatics. Thought to represent pathways of cell migration during foetal development

Question 9

What does the skin consist of? (5)

Answer 9

Epidermis​
Dermo-epidermal junction​
Dermis: connective tissue, less cellular​
Appendages​- Nails​, Hair​, Glands, Mucosae​
Sub-cutis: predominantly fat

Question 10

Epidermis​ (5)

Answer 10

Stratified squamous epithelium​- 1.5 mm thick​

95% epidermis = keratinocytes - contain structural keratins​

Movement from basement membrane​

Four defined layers​

Other cells​- Melanocytes​, Langerhans cells​, Merkel cells​

Question 11

Epidermal layers (4)

Answer 11

Keratin layer
Granular layer
Pickle cell layer
Basal layer

Question 12

Regulation of epidermal turnover (3)

Answer 12

Balance between cells in/out​

Control by:​
-Growth factors​
-Cell death​
-Hormones​

Loss of control in:​
-Skin cancer​
-Psoriasis​
​

Question 13

Differentiation (3)

Answer 13

Keratinocytes migrate from basement membrane​

Continuous regeneration of epidermis​

28 days from bottom to top

Question 14

Basal layer (4)

Answer 14

Usually one cell thick​

Small cuboidal​

Lots of intermediate filaments (keratin)
​
Highly metabolically active​

Question 15

Prickle cell layer (3)

Answer 15

Larger polyhedral cells​

Lots of desmosomes (connections)​

Intermediate filaments connect to desmosomes

Question 16

Granular layer (6)

Answer 16

2-3 layers of flatter cells​

Large keratohyalin granules – contain structural filaggrin & involucrin proteins ​
Odland bodies (lamellar bodies) – secretory organelles that contribute to skin barrier​

High lipid content​

Origin of “cornified envelope”​

Cell nuclei lost​

Question 17

Keratin layer ​(6)

Answer 17

Corneocytes​= overlapping non-nucleated cell remnants​

Insoluble cornified envelope​

80% keratin & filaggrin​

Lamellar granules release lipid​

Tight waterproof barrier​

Human papilloma virus infection of keratinocytes causes warts​

Question 18

Melanocytes (3)

Answer 18

Migrate from the neural crest to the epidermis in first 3 months of foetal development​

basal layer and above ​

pigment producing dendritic cells

Question 19

Skin types (5)

Answer 19

Same number of melanocytes ​

Darker skin has larger melanosomes containing more melanin​

Fairer skin – smaller amounts of melanin, degrades more quickly​

More eumelanin + less phaeomelanin in dark skin​

Unexposed fairer skin, melanosomes confined to basal layer. Darker skin - exist throughout epidermis. ​

Question 20

Langerhans cells​ (6)

Answer 20

Mesenchymal origin – bone marrow​

Prickle cell level in epidermis​

Also found in dermis and lymph nodes​

Involved in the skin immune system​=
-Antigen presenting cells​
-Pick up antigen in skin and circulate to lymph nodes via lymphatic system​
​

Question 21

Merkel cells​ (3)

Answer 21

basal

between keratinocytes + nerve fibres

mechanoreceptor

Question 22

Mucosal membranes​ (8)

Answer 22

Highly specialised for function​
=Eyes, mouth, nose, genito-urinary & GI tracts​

Oral mucosa​
=Masticatory – keratinised to deal with friction/pressure​
=Lining mucosa – non-keratinised​
=Specialised mucosa - tongue papillae – taste​

Ocular mucosa​
=Lacrimal glands, eye lashes, sebaceous glands​