Physiology of skin Flashcards
Which type of skin cells are formed from the neural crest?
Melanocytes
How is the epidermis formed embyologically?
Ectoderm cells form single layer periderm
Gradual increase in layers of cells
Periderm cells cast off
Which embryological layer is the dermis formed from?
Mesoderm
At which stage of development are the four epidermis layers and dermis formed?
16 weeks
At which stage of embyrological development is the skin formed to look like this?
26 weeks
What are Blaschko’s lines?
Lines of skin development
What is the epidermis?
The outermost layer of skin, stratified squamous epithelium
What does most of the epidermis consist of?
Keratinocytes (95%)
What are the four epidermal layers?
Keratin layer
Granular layer
Prickle cell layer
Basal cell layer
How do keratinocytes allow constant regeneration of the epidermis and how long does it take to do this?
Keratinocytes migrate from basement membrane to the keratin layer
28 days
How thick is the basement layer of epidermis usually and what shape are the cells?
1 cell thick
Small cuboidal cells
What does the prickle layer consist of?
Larger polyhedral cells with lots of desmosomes, with connecting intermediate filaments
What does the granular layer consist of?
2-3 layers of flatter cells
Large keratohyalin granules – contain structural filaggrin & involucrin proteins
Which layer of epidermis contains Odland bodies?
Granular layer
What does the keratin layer consist of?
Corneocytes - overlapping, non-nucleated cell remnants
Keratin
Fillagrin
What are melanocytes?
Pigment producing dendritic cells
Where are melanocytes found?
In the basal layer and above
What do melanosomes do?
Convert tyrosine to melanin pigment
–Eumelanin (brown or black)
–Phaeomelanin (red, yellow)
What does melanin do?
Absorbs/filters light
Forms protective cap over nucleus
What does this diagram show?
Melanin caps are protecting nuclear DNA
Which cells are of mesenchymal origin?
Langerhans cells
Where are Langerhans cells found?
Prickle cell layer
Dermis
Lymph nodes
What is the function of Langerhans cells?
Antigen presenting cell in the skin’s immune system
Pick up antigen in skin and circulate to lymph nodes via lymphatic system
Where are Merkel cells found?
Basal layer
Between keratinocytes and nerve fibres
What are Merkel cells?
Mechanoreceptors
What are the phases of hair growth?
Anagen = growing
Catagen = involuting
Telogen = resting
What is the dermo-epidermal junction?
Interface between epidermis and dermis
What are the functions of the dermo-epidermal junction?
Support, anchorage, adhesion, growth and differentiation of epidermal cells
Semi-permeable membrane acting as barrier and filter
What is the dermis composed of?
Cells - mainly fibroblasts, macrophages, mast cells, lymphocytes, Langerhans cells
Fibres – collagen, elastin
Blood vessels, lymphatics, nerves
What is the function of fibroblasts?
Secrete collagen
What is an angioma?
A localised overgrowth of blood vessels in the skin
Which special nerve sensors detect pressure and vibration in the skin?
Pacinian (pressure) and Meissners (vibration) corpuscles
What are apocrine sweat glands and where are they found?
Scent sweat glands
Found in axillae and perineum
Where are the largest sebacous glands found?
Face and chest
What are the functions of the sebaceous glands?
Control moisture loss
Protection from bacterial and fungal infection
What is control of apocrine sweat glands dependant on?
Androgen
Where are eccrine glands found?
All over skin
Palms, soles of feet and and axillae particularly
How is secretion from eccrine glands controlled?
Parasympathetic cholingeric transmission
How does the epidermis function as a barrier?
Physical: friction, mechanical trauma, ultraviolet radiation
Chemical: irritants, allergens, toxins
Pathogens: bacteria, viruses, fungi
What metabolism takes place in the skin?
Vitamin D metabolism
Thyroid hormone metabolism
Defence against chemicals, drugs, pollutants & sunlight
What role does the skin play in Vitamin D metabolism?
Uses UV light to synthesise vitamin D3 from cholecalciferol to be stored in the liver
What role does the skin play in thyroid hormone metabolism?
Converts T4 to T3
What role does the skin have in thermoregulation?
Protects against being too hot or too cold
Warm/cold-sensitive thermoreceptors cause:
Behavioural changes
Control sweating/shivering/blood supply
What are the functions of the skin?
Barrier function
Thermoregulation
Immune defence
Metabolism & detoxification
Communication
Sensory functions
