Structure and Function 1 and 2 Flashcards
What are the two layers of the skin? Which is external and which is internal? When do they come together?
Epidermis (external) and dermis (internal), they come together during embryo development
Which layer is thicker, the dermis or epidermis?
Dermis
What epithelial cell is the epidermis composed of?
Stratified squamous epithelium
What is the dermis composed of?
Leathery, fibrous connective tissue
Where is the epidermis embryologically derived from?
Ectoderm
How is the epidermis embryologically formed?
Forms a single layer periderm which gradually increases in the number of cells until they cast off
Where is the dermis embryologically derived from?
Mesoderm
Where is the mesoderm in relation to the ectoderm?
Below
In relation to skin development, what happens at 4 weeks?
The periderm, basal layer and dermis are formed
When does gastrulation occur?
Days 7-10
In relation to skin development, what happens at 16 weeks?
The layers of the epidermis are formed
In relation to skin development, what happens at 26 weeks?
Skin appendages are formed
What do Blascko’s lines show?
The developmental growth pattern of skin
Do Blascko’s lines follow vessels, nerves or lymphatics?
No
What does it indicate if Blascko’s lines show up on a child?
A congenital fault where something went wrong with the migration of cells during development
What makes up 95% of cells in the epidermis?
Keratinocytes
Describe the differentiation of cells in the epidermis?
Cells move upwards from the basal layer which allows continuous regeneration of the epidermis, with one cycle taking around 28 days
How many layers are there of the epidermis?
4
Give three examples of specialised cells found in the epidermis?
Melanocytes, Merkel cells, Langerhans cells
Are the contents of the epidermis consistent all over the body?
No, they vary depending on the site
How does the epidermis reversibly react to mechanical pressure?
Produces more keratin
What are three things which control epidermal cell turnover?
Growth factors, cell death and hormones
Control of epidermal cell turnover is lost in what diseases?
Psoriasis and skin cancer
How long does epidermal cell turnover take in psoriasis? Problems with differentiation in psoriasis lead to the loss of which epidermal layer?
4-5 days
No granular layer
What are the layers of the epidermis from inner to outer?
- Basal cell
- Prickle cell
- Granular
- Keratin
Which layer of the epidermis is made up essentially of stem cells?
Basal cell layer
Describe the basal cell layer?
Usually one cell thick, small and cuboidal with lots of intermediate filaments. It is highly metabolically active.
Describe the prickle cell layer?
Larger polyhedral cells which contain lots of desmosomes and intermediate filaments to hold the cells together
How many layers of cells does the granular layer have?
2-3 layers of flatter, granular cells
What are the two structural proteins found in the granular layer? What is their function?
Filaggrin and involucrin- important in protecting the water barrier
The water barrier of the epidermis is lost in what disease?
Eczema
What is the lipid content of the granular layer?
Are there nuclei present?
High lipid content
No nuclei
What cells is the keratin layer composted of?
Corneocytes
What are corneocytes?
Terminally differentiated keratinocytes
The keratin layer can also be known as what?
Stratum corneum
Describe the keratin layer?
80% keratin and filaggrin with lamellar granules releasing lipids to form a tight waterproof barrier
HPV infection of keratinocytes causes what?
Viral warts
Which layer of the epidermis looks like flat slabs?
Keratin
Apart from skin, what other structure can be implicated in skin disease?
Mucosal membranes
In the oral mucosa, which of the masticatory/lining mucosa is keratinised?
Masticatory
What three other cells can be found in the epidermis which are not keratinocytes?
- Melanocytes
- Langerhans Cells
- Merkel Cells
Are melanocytes found basal, supra basal or both?
Both
Are Langerhans cells found basal, supra basal or both?
Supra basal
Are Merkel cells found basal, supra basal or both?
Basal
Where are melanocytes embryologically derived from? When do they join up with the epidermis?
Derived from the neural crest, transfer to the epidermis in the first 3 months of foetal development
What type of cells are melanocytes?
Pigment producing dendritic cells
What are the specialised organelles found within melanocytes? What do they do?
Melanosomes- convert tyrosine into melanin
What colour is eumelanin?
Black/brown
What colour is phaeomelanin?
Red/yellow
What happens once melanin has absorbed light?
Melanin granules (full melanosomes) are transferred to adjacent keratinocytes to form a protective cap over the nucleus to protect the DNA and basal stem cells from UV light
What is vitiligo?
An autoimmune disease causing immune destruction of melanocytes
How can vitiligo be treated? What is the risk of this?
UV phototherapy to block the function of the immune cells which are destroying the melanocytes
If the melanocytes are stimulated this can cause melanoma
What is albinism?
Genetic partial loss of pigment production
What is Nelson’s Syndrome?
Melanin stimulating hormone is produced in excess by the pituitary gland, most likely because of a pituitary adenoma
What is a malignant melanoma?
A tumour of the melanocyte cell line
Where do Langerhans cells originate from?
Bone marrow
Where are Langerhans cells found?
Prickle cell layer of the epidermis as well as the dermis and lymph nodes
What is the function of Langerhans cells?
Antigen presenting cells- they pick up the antigen in the skin and then circulate it back to lymph nodes via the lymphatics
What is the specific racket organelle found in Langerhans cells known as? What is its function?
Birbeck granules- they have no known function
Where are Merkel cells found?
Basal, between keratinocytes and nerve fibres
What is the function of Merkel cells?
Mechanoreceptors forming a connection between the skin and brain
Where do Merkel cells originate from embryologically?
Mesoderm
What is Merkel cell cancer?
A neuroendocrine carcinoma which is rare and caused by a viral infection- there is no cure
Are hair follicles in the epidermis, dermis or both?
Both, the papilla is in the dermis
What gland is always associated with hair follicles?
Sebaceous glands
What always comes with a sebaceous gland?
A grease sac
Where does hair pigment come from?
Melanocytes above the dermal papilla
Where is hair embryologically derived from/
Ectoderm
What is the muscle which allows hairs to stand up known as?
Arrector pili muscle
What are the 3 stages of growth of hair follicles?
Anagen- growing
Catagen- involuting
Telogen- resting
What are the lengths of the three periods of growth of hair?
They vary, with the exception of catagen which always lasts 4 weeks
What hormones may influence hair growth?
Thyroxine, androgens
Is it normal for humans hairs to enter the stages of growth at the same time? What is it called if this occurs?
No- telogen effluvium
What is the most common cause of hair loss in humans? Is it reversible?
Telogen effluvium- yes it is reversible
What is alopecia areata?
Autoimmune hair loss condition where the follicles are attacked by the immune system
What is virilisation?
The development of male physical characteristics in a women or precociously in a boy due to excess androgens
What is hirsutism?
Secretion of excess androgens causing excessive male pattern hair growth in females
What is the growth rate of nails?
0.1mm/day
When do nails grow faster, winter or summer?
Summer
If a part of the nail is crumbly what does this mean/
There has been trauma at the matrix under the nail and loss of stem cells
