Structure & Function 1- embryology + epidermis Flashcards
why is skin important (3)
largest vital organ
25% pop have skin condition
indicator of underlying disease
skin - epidermis (5)
epidermis =
-outer layer
-stratified cellular epithelium
ectoderm forms cells from single layer periderm
gradual increase in layers of cells
periderm cells cast off
skin- dermis (3)
dermis =
-beneath epidermis
-connective tissue
formed from mesoderm below ectoderm
skin- subcutis (2)
subcutis=
-fat layer beneath dermis
melanocytes- pigment producing cells from neural crest
foetal skin development - w4 (3)
P- periderm
B- basal layer
D- dermis
foetal skin development - w16 (5)
KL- keratin layer
GL- granular layer
PL- prickle cell layer
BL- basal layer
D- dermis
foetal skin development - w26 (5)
epidermis
-melanocyte
-sebaceous gland
-arector pili muscle
-hair follicle
blaschko’s lines
developmental growth pattern of skin – not following vessels, nerves or lymphatics. Thought to represent pathways of cell migration during foetal development
What does the skin consist of? (5)
Epidermis
Dermo-epidermal junction
Dermis: connective tissue, less cellular
Appendages- Nails, Hair, Glands, Mucosae
Sub-cutis: predominantly fat
Epidermis (5)
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
Epidermal layers (4)
Keratin layer
Granular layer
Pickle cell layer
Basal layer
Regulation of epidermal turnover (3)
Balance between cells in/out
Control by:
-Growth factors
-Cell death
-Hormones
Loss of control in:
-Skin cancer
-Psoriasis
Differentiation (3)
Keratinocytes migrate from basement membrane
Continuous regeneration of epidermis
28 days from bottom to top
Basal layer (4)
Usually one cell thick
Small cuboidal
Lots of intermediate filaments (keratin)
Highly metabolically active
Prickle cell layer (3)
Larger polyhedral cells
Lots of desmosomes (connections)
Intermediate filaments connect to desmosomes
Granular layer (6)
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
Keratin layer (6)
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
Melanocytes (3)
Migrate from the neural crest to the epidermis in first 3 months of foetal development
basal layer and above
pigment producing dendritic cells
Skin types (5)
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.
Langerhans cells (6)
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
Merkel cells (3)
basal
between keratinocytes + nerve fibres
mechanoreceptor
Mucosal membranes (8)
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
