Skin Structure and Function Flashcards
What are the 2 main layers of skin?
The epidermis (outer) and the dermis
Which germ layer is the epidermis derived from?
ectoderm
How does the epidermis form in the fetus?
Ectoderm cells form a single layer periderm which gradually increase in layers and before birth the periderm cells are cast off
What germ layer is the dermis derived from?
mesoderm
What are melanocytes derived from?
the neural crest
What are the 6 layers in skin?
Keratin layer Granular layer Prickle cell layer basal layer dermis sub-cutis
what are blaschkos lines?
developmental growth patterns of skin, which don’t follow vessels, nerves or lympathics
What does the skin consist of?
epidermis; appendages (hair, nails, glands, mucosae) ; dermo-epidermal junction; dermis and the sub-cutis
What does the basal layer do?
Divides in order to replenish the upper layers
How does the prickle cell layer become the granular layer?
It differentiates and produces lots of protein (granular- lots of proteins)
How does the granular layer becoem the keratin layer?
Releases protein in order to become flat
What type of epithelium is the epidermis
stratified squamous epithelium
What are the majority of the cells found in the epidermis?
Keratinocytes which contain structural keratins
What other cells are found within the epidermis?
Melanocytes; langerhan cells and merkel cells
How is epidermal turnover regulated?
growth factors; cell death and hormones
How long does it take for a keratinocytes to migrates from the basmement membrane to the top?
28 days
Describe the basal layer
usually one cell thick
small cuboidal
lots of intermediate filaments (keratin)
highly metabolically active
Describe the prickle cell layer
larger polyhedral cells
lots of desmosomes
intermediate filaments connect to desmosomes
(named after prickly pear appearance)
Describe the granular layer
2-3 layers of flatter cells large keratohyalin granules- contain structural filaggrin and involucrin proteins odland bodies ( lamellar bodies) high lipid content origin of "cornified envelope" cell nuclei lost
What is the cornified envelope?
A layer of ceramides which become covalently bonded to an envelope of structural proteins. This replaces the cell membrane during a process called cornification in which live keratinocytes become non-living corneocytes. The complex surrounds the cells and contributes to the barrier function of the skin.
Describe the keratin layer
Made up of the corneocytes- overlapping non-nucleated cell remnants insoluble cornified envelope 80% keratin and filagrin lamellar granuels release lipid TIGHT WATRETPROOF BARRIER
What are melanocytes?
pigment producing dendritic cells
Where are melanocytes found?
in the basal layer and above
What happens in the melanosomes?
tyrosine is converted to melanin pigment
What happens to full melanosomes (melanin granules)?
they are transferred to adjacent keratinocyte via dendrites
What is the function of melanin granules?
form a protective cap over nucleus as they absorb light and prevent UV ray messing with the DNA in basal cells
What is vitiligo?
an autoimmune disease where there is loss of melanocytes
What is the origin of langerhan cells?
mesenchymal origin (bone marrow)
Where are Langerhan cells found in the skin?
prickle cell level in the epidermis and in dermis (also in lymph nodes)
What is the function of langerhan cells?
APCs - pick up Ag in skin and circulate to lymph nodes via lymphatics
What is the special organelle found in langerhan cells?
birbeck granules/ racket organelle (looks like a tennis racket)
Where are Merkel cells found?
in the basal layer between keratinocytes and nerve fibres
What are merkel cells?
mechanoreceptors
Look at picture of hair follicle and be able to name different parts of it
\:) sebaceous unit (grease bag that sits on top of muscle) pili arrector muscle dermal papilla matrix cortex medulla interal and external root sheaths
What are the 3 phases of growth in a hair follicel
anagen- growing
catagen- involuting
telogen- resting
What is telogen effluvium?
when stress pushes more hair follicles prematurely into the telogen phase (meaning more fall out)
When does telogen effluvium most commonly occur?
postpartum
How is the nail plate and the matrix of a nail connected?
The 3 partsof the nail plate- dorsal; intermediate and ventral all grow from the same corresponding subdivision of the matrix
What are the functions of the dermo-epithelial junction?
- support; anchorage; adhesion; growth and differentiation of basal cells
- semi-permeable membrane acting as a barrier and filter between the epithelium and mesenchyme
What cells are found in the dermis?
fibroblasts, macrohpages, mast cells, lymphocytes and langerhan cells
what fibres are found in the dermis?
collagen and elastin
Describe the blood vessels found within the dermis
The supply is greater than metabolic need
vessel walls are well spported
plexuses are horizontal
What is an angioma?
localised overgrowth of blood vessels
What is the somatic sensory supply of the dermis like?
there are:
free nerve endings
speical receptors for pressure-pacinian corpuscles and for vibration- meissners corpuscles
Where does the pigmentation of the hair follicles take place?
In the melanocytes above the dermal papilla
What are the 3 types of skin glands?
sebaceous; apocrine and eccrine
Describe sebaceous glands
widely distrbuted but the largest glands are in the face and chest produce sebum hormone sensitive (dont do anything before puberty)
what are the functions of sebaceous glands?
control moisture loss and protect from fungal infections
what is sebum made from?
squalene, wax esters, triglycerides and free FAs
Decribe apocrine sweat glands
develop as part of pilo-sebaceous unit
found in axillae and perineum
androgen dependent
produce oily fliud- odour after bacterial decomp
Describe eccrine sweat glands
whole skin surface- especailly skin, soles and axillae
sympathetic cholienrgic nerve supply
function of eccrine sweat glands?
cooling by evap
moisten palms/soles to aid grip
Why would you describe the skin as metabolically active?
takes part in vitamin D metabolism and thyroid hormone metabolism (which also occurs in thyroid gland-20%)
What are the sensory functions of the skin
touch, pressure, vibration, pain and itch, heat and cold
What cells carry out vitamin D metabolism?
keratinocytes
Where are hemi-desmosomes found?
In the DEJ
What are commonest sweat glands in the face?
eccrine glands
Which hormone stimulates the sebaceous glands production of sebum?
androgen
Which glands play a role in temperature regulation?
eccrine glands
Which glands play a role in scent?
apocrine glands
