Structure and Function of the Skin Flashcards
what is the most common cell type in the epidermis?
keratinocytes
name three cells, that aren’t keratinocytes, that are found in the epidermis?
melanocytes
langerhans cells
merkel cells
how do melanocytes reach the epidermis?
they migrate from the neural crest in the first 3 months of foetal development
where are melanocytes found?
in and above the basal layer
what are melanocytes?
pigment producing dendritic cells
what are the organelles found in melanocytes called?
melanosomes
how do melanocytes produce melanin?
they convert tyrosine to melanin pigment
what are the two types of melanin?
eumelanin
pheomelanin
what colour is eumelanin?
brown or black
what colour is phaeomelanin?
red or yellow
what does melanin absorb?
light
it acts as a neutral density filter
where and how are full melanosomes transferred?
to adjacent keratinocytes
via dendrites
what do melanosomes form?
a protective cap over the cell nucleus, to protect the DNA in basal cells
what is vitiligo?
an autoimmune disease where melanocytes are lost
what is involved in albinism?
a genetic partial loss of pigment production
what occurs in nelson’s syndrome?
melanin stimulating hormone is produced in excess by the pituitary
what is a malignant melanoma?
a tumour of melanocytes
where do langerhans cells originate?
bone marrow (mesenchymal)
where are langerhans cells found?
the prickle cell layer of the epidermis
the dermis
lymph nodes
what type of cells are langerhans cells?
antigen presenting cells
where are merkel cells located?
basal layer
between keratinocytes and nerve fibres
what type of cells are merkel cells?
mechanoreceptors
what causes merkel cell cancer?
a viral infection
this is very rare and has a high mortality rate
what causes hair pigmentation?
melanocytes above the dermal papilla
what forms a pilosebaceous unit?
epidermal component
dermal papilla
specialised keratins
adjacent sebaceous gland
what does a sebaceous gland produce?
sebum
what is sebum?
a greasy wax that acts as a natural emollient
where is hair always found?
with a sebaceous gland
what are the three phases of hair growth?
anagen
catagen
telogen
which phase of hair growth is the growing phase?
anagen
which phase of hair growth is the resting phase?
telogen
which phase of hair growth is the involuting phase?
catagen
name two hormonal influences on hair growth?
thyroxine
androgens
name three types of hair
lanugo
vellus
terminal
where is lanugo hair found?
in utero
which phase of hair growth is asynchronous in humans?
telogen
what is alopecia areata?
autoimmune hair loss
what are nails made from?
specialised keratins
what is the growth rate for nails?
0.1mm per day
occurs more on the fingers and in summer
what is the largest vital organ in the body?
the skin
what can skin disease indicate?
underlying disease
what are the two layers of the skin?
epidermis
dermis
what is the outer layer of the skin?
epidermis
what is the epidermis?
a very thin layer of stratified squamous epithelium
what is the epidermis made of?
connective tissue
what is the role of the dermis?
provides mechanical strength
how does the epidermis develop in an embryo?
ectoderm cells form a single layer periderm, which builds up and is eventually cast off, forming the epidermis
what forms the dermis in an embryo?
cells from the mesoderm
what are melanocytes?
pigment producing dendritic cells
where do melanocytes originate in development?
the neural crest
what are the development growth lines of skin called?
blaschko’s lines
what is the sub-cutis predominantly made from?
fat
what is another name for the sub-cutis?
subcutaneous tissue
what is the main cell type in the epidermis, and what do these cells contain?
keratinocytes
contain structural jeratins
how does skin grow?
from the basement layer to the top
what are the four defined layers of the epidermis from bottom to top?
basal layer
prickle cell layer
granular layer
keratin layer
name four cell types found in the epidermis?
keratinocytes
melanocytes
langerhans cells
merkel cells
what type of cells are found in the basal layer?
stem cells
what layer of the epidermis is very thick on the palms and the soles?
the keratin layer
how thick is the granular layer of the skin of the hands and feet normally?
around one cell thick
what three things control epidermal turnover?
growth factors
cell death
hormones
name two conditions that can be caused by loss of regulation of epidermal turnover
skin cancer
psoriasis
what is the majority of the dermis made from?
collagen fibres
what cell type produces collagen fibres?
fibroblasts
how long does it take the skin to regenerate from bottom to top?
28 days
how thick is the basal layer normally?
one cell thick
what are the cells of the basal layer like?
small and cuboidal
what is there lots of in the basal layer?
intermediate filaments such as keratin
which layer of the epidermis is very metabolically active?
the basal layer
describe the cells of the prickle cell layer
large
polyhedral
what cell feature is found in the prickle cell layer?
lots of desmosomes with intermediate filaments attached
describe a normal granular layer
two to three layers of flat cells
name two things found in the granular layer
keratohyalin granules
odland bodies
what do keratohyalin granules contain?
structural proteins i.e. filaggrin and involucrin
describe the masticatory oral mucosa
keratinised
this is to deal with friction
describe the lining mucosa of the oral cavity
non keratinised
what does the mucosa of the tongue contain?
papillae
what does the ocular mucosa contain?
lacrimal glands
eyelashes
sebaceous glands
what is the dermo-epidermal junction (DEJ)?
the interface between the epidermis and the dermis
how does the epidermis receive nutrients?
no blood supply
all nutrients diffuse up from the dermis
where are sweat glands and hair follicles located?
the dermis
what is another name for the upper dermis?
the papillary dermis
what is another name for the DEJ?
the basement membrane
what are the three layers of the DEJ?
lamina lucida
lamina densa
sub lamina densa
name two diseases caused by problems with the DEJ
bullous pemphigoid
EB
what is the dermis made of?
ground substance
cells
fibres
what is ground substance?
a supportive water based substance
what cells are found in the dermis?
fibroblasts macrophages mast cells langerhans cells lymphocytes
what two fibres are found in the dermis?
collagen
elastin
what causes photoaging?
UV exposure
what is the pathological process behind photoaging?
loss of collagen makes skin collapse
loss of elastin means the skin cant bounce back
what supports the vessel walls in the skin?
collagen
muscle fibres
what three things make up the somatic sensory supply of the skin?
free nerve endings
pacinian corpuscles
meissner’s corpuscles
what do pacinian corpuscles sense?
pressure
what do meissner’s corpuscles sense?
vibration
what creates the pigment of hair?
melanocytes
what is acne a disease of?
the pilosebaceous unit
what are the three stages of hair growth?
anagen
catagen
telogen
what are the three skin glands?
sebaceous
appocrine
eccrine
when do sebaceous glands become active?
puberty
what do sebaceous glands secrete?
sebum
where are apocrine sweat glands found?
axillae
perineum
what are the main sweat glands?
eccrine
what is the two way barrier of the skin?
epidermis
what is steroid sulphatase deficiency?
an inherited disorder of steroid sulphates
lipids in the keratin layer are not formed
what two substances are metabolised by the skin?
vitamin D
thyroid hormone
what is the reaction of vitamin D metabolism in the skin?
UVB reactions convert 7-dehydrocholesterol to vitamin D
what is the reaction of thyroid hormone metabolism in the skin?
thyroxine is converted to triiodothyronine
