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
