Structure & Function Of The Skin - Epidermis Flashcards
What are the three layers of the skin
Epidermis - stratified cellular epithelium (outer layer)
Dermis - connective tissue under the epidermis
Subcutis - fat layer beneath the dermis
Where do the layers of the skin come from embryologically
Epidermis - ectoderm
Dermis - mesoderm
What are melanocytes
Pigment producing cells from neural crest
What are blaschko’s lines
A pattern of lines that indicate normal cell development in the skin
Usually invisible, but can be seen in people with certain skin conditions
Describe the embryological development of the epidermis
The ectoderm forms a single layer called the periderm
The periderm gradually increases in layers of cells
This forms the layers of the dermis
The periderm cells then cast off
What are the four layers of the skin
Keratin layer
Granular layer
Prickle cell layer
Basal layer
Describe the keratin layer of the epidermis
Non-nucleated, tightly bound together cells
Contain corneocytes (mature keratinocytes)
Is a protective, water proof layer
Describe the basal layer of the epidermis
Usually one cell thick
Cuboidal, epidermal stem cells
Are highly metabolically active cells & form keratinocytes
Describe the granular layer of the epidermis
Contain keratohyalin granules, high lipid content & lamellar bodies (secretory organelles)
Secrete lipids, keratin & proteins that create skin barrier
Is where keratinocytes gain keratin & lose their nuclei
Is the origin of the ‘cornfield envelope’
Describe the prickle cell layer of the epidermis
Large polyhedral cells with lots of desmosomes,
Contain langerhans cells (immune response)
Provides structural support
What is the main cell type found in the epidermis
Keratinocytes
What other cells, other than keratinocytes, are found in the epidermis & state which layer they are mainly in
Melanocytes (basal layer & above),
langerhans cells (prickle cell layer),
merkel cells (basal layer)
What regulates epidermal turnover
Growth factors, (programmed) cell death, certain hormones
Describe the production of keratinocytes in the epidermis
Keratinocytes are formed from the differentiation of stem cells in the basal layer. They then migrate up to the more superficial layers. They gain keratin, lose their nucleus and then die in the granular layer
Describe the cells of the basal layer
Small cuboidal stem cells that are highly metabolically active and contain lots of intermediate filaments (keratin)
Describe the cells of the prickle cell layer
Large, polyhedral cells with lots of desmosomes. Also contain langerhans cells
Describe the cells of the granular layer
Cells with high lipid content, large keratohyalin granules & lamellar bodies (secretory organelles)
What are corneocytes
Mature (dead) keratinocytes found in the keratin layer
Describe the embryological development of melanocytes
Migrate from the neural crest to the epidermis in first 3 months of foetal development
What important organelles do melanocytes contain
Melanosomes
What do melanosomes do
Convert tyrosine to melanin pigment
What are the two types of melanin pigment
Eumelanin (brown or black)
Phaeomelanin (red, yellow)
What is the function of melanin & importance of melanin caps
Melanin absorbs light
The melanin cap in melanocytes forms a protective cap over the nucleus
How do melanocytes transfer melanin to keratinocytes
They transfer the melanosomes (melanin granules) to adjacent keratinocytes via dendrites
How does the epidermis change depending on skin types
Darker skin
- larger melanosomes containing more melanin
- melanosomes exist throughout the epidermis
Fairer skin
- smaller amounts of melanin & so degrades more quickly
- melanosomes are confined to basal layer (when unexposed)
Where do Langerhans cells originate
They are mesenchymal in origin
& form from cells in the bone marrow
Where are Langerhans cells found
Prickle cell layer of epidermis
(& dermis & lymph nodes)
What is the role of Langerhans cells
Involved in the skin immune system
– Antigen presenting cells
– Pick up antigen in skin and circulate to lymph nodes via lymphatic system
What organelle is found in Langerhans cells
Racket organelle (Birbeck granules)
What are merkel cells & where are they found in the epidermis
They are mechanoreceptors
They are found between keratinocytes & nerve fibres in the basal layer
Where are mucosal membranes found in the body
Eyes, mouth, nose, genito-urinary & GI tracts
Describe the oral mucosa
Masticatory – keratinised to deal with friction/pressure
Lining mucosa – non-keratinised
Specialised mucosa - tongue papillae – taste
Describe the ocular mucosa
Lacrimal glands, eye lashes, sebaceous glands
What are melanocytes
Pigment (melanin) producing dendritic cells
What is melanin produced from
Tyrosine
Where is melanin produced
In the melanosomes of melanocytes
What three layers of the epidermis are formed from the periderm
Keratin layer
Granular layer
Prickle cell layer
What provides movement of the epidermis
The basement membrane below
What is the cornified envelope
The cornified envelope replaces the plasma membrane of differentiating keratinocytes
It consists of keratins that are enclosed within an insoluble amalgam of proteins (filaggrin etc), which are crosslinked by transglutaminases and surrounded by a lipid envelope.
It originates in the granular layer.
What two proteins are contained in keratohyaline granules & what is their function
Filaggrin & Involucrin
- strengthens & flattens the corneocytes
- key component of the cornified envelope,
- help keratin filaments bind together
=> skin barrier
Summarise the cells of the epidermis
Summarise the 4 layers of the epidermis
