Structure & Function of Skin Flashcards
1
Q
skin layers
A
epidermis
dermis
2
Q
epidermis
A
outer layer, stratified squamous epithelium (skin proper)
3
Q
demis
A
beneath epidermis, connective tissue
4
Q
which granular layer does epidermis come from & how?
A
ectoderm cells form single layer periderm, gradual increase in layers of cells & periderm cells are cast off
5
Q
which granular layer does dermis come from?
A
formed from mesoderm below ectoderm
6
Q
where do melanocytes come from and what is their function?
A
pigment producing cells from neural crest
7
Q
if there is a defect in one stem cell, how will the lesion appear?
A
it will follow Blaschko’s lines & will be asymmetrical
8
Q
what does the skin consist of?
A
epidermis, appendages, derma-epidermal junction, dermis & sub-cutis
9
Q
which cells make up the epidermis?
A
mostly keratinocytes
melanocytes
Langerhans cells
Merkel cells
10
Q
how many layers does the epidermis have?
A
4 defined layers: keratin layer granular layer prickle cell layer basal layer
11
Q
how do the epidermal stem cells divide?
A
divide at bottom & migrate to the top
12
Q
palms & soles skin
A
thick coat of keratin over normal layer
13
Q
abdominal skin
A
very thin epidermis, glands & hair follicles more pronounced
14
Q
what is epidermal turnover?
A
how fast keratinocytes travel upwards
15
Q
how is epidermal controlled?
A
growth factors
cell death
hormones
16
Q
what happens if control of epidermal turnover is lost?
A
skin cancer
psoriasis
17
Q
how long does migration of keratinocytes usually take?
A
28 days from bottom to top
18
Q
how long does migration of keratinocytes take in psoriasis?
A
45 days
19
Q
describe the basal layer
A
usually one small cuboidal cell thick, lots of intermediate filaments (keratin), highly metabolically active
20
Q
describe the prickle cell layer
A
larger polyhedral cells, lots of desmosomes which intermediate filaments connect to
21
Q
how does intra-epidermal blistering occur?
A
a build up of hydrostatic pressure which busts apart the relatively delicate cells (desmosomes detach) within the epidermis, more water gets pumped in & a fragile roof is formed on top which will eventually pop with any change of pressure. e.g. baby nappy rash
22
Q
describe the granular layer?
A
very thin layer of 2-3 flattened cells, large keratohyalin granules contain flaggrin & involcurin proteins, has a high lipid content & Odland bodies. no cell nuclei.
23
Q
where do cells die?
A
the granular layer where they spit out material which will be used to seal off & prevent water loss
the main component of this material is flaggrin
24
Q
what is missing from the skin in eczema?
A
flaggrin
25
describe the keratin layer?
final top layer. Has an insoluble cornified envelope. mostly keratin and some filaggrin. lamellar granules release lipids. creates a tight waterproof barrier.
26
what are corneocytes?
overlapping non-nucleated cell remnants
27
describe the oral mucosa
masticatory - keratinised to deal with friction and pressure
lining mucosa - non-keratinised
specialied mucosa (tongue papillae) - taste
28
describe the ocular mucosa
has lacrimal glands & sebaceous glands and eye lashes for specialist functions
29
white lesions in skin (nail beds & mucosal membranes) is what?
thickening of normally thin epidermis so that you can't see blood vessels anymore
30
what's the difference between skin & scar tissue?
scar tissue has no appendages (hair follicles/nails)
31
is the dermis or epidermis thicker?
dermis is thicker
32
what are the majority of epidermal cells?
keratinocytes
33
what are the other epidermal cells?
melanocytes
Langerhans cells
merkel cells
34
which epidermal layer are melanocytes found in?
basal & suprabasal
35
which epidermal layer are Langerhans cells found in?
suprabasal
36
which epidermal layers are Merkel cells found in?
basal
37
when do melanocytes migrate & where during foetal development?
in the first 3 months
| from the epidermis to neural crest
38
what are melanocytes?
pigment producing dendritic cells
39
how do melanocytes produce pigment?
convert tyrosine to melanin pigment;
- eumelanin (brown or black)
- phaeomelanin (red or yellow)
40
what are melanin organelles/granules called?
melanosomes
41
Full melanocytes are transferred where and how from epidermal cells?
to adjacent keratinocytes via dendrites
42
what do melanocytes form a protective cap over?
the nucleus
43
what cell type are melanocytes?
neuronal as they are evolved from the neural crest.
| similar properties to astrocytes
44
what is vitiligo?
an autoimmune disease with loss of melanocytes, can be seen in both black/white people but more obvious in black people.
45
what is albinism?
the partial loss of pigment production
46
what is Nelson's syndrome?
a melanin stimulating hormone is produce in excess by the pituitary causing an overproduction of eumelanin.
47
where do Langerhans cells originate from?
mesenchymal origin - bone marrow
48
where are langerhans cells found?
strategically dispersed in prickle cell level in epidermis. Also found in dermis & lymph nodes.
49
what do Langerhans cells do?
involved in skin immune system;
- Ag presenting cells
- pick up Ag in skin & circulate to lymph nodes via lymphatics.
50
which granules are present in Langerhans cells & why?
birbeck granules but we don't know why
51
what are Merkel cells for?
responsible for sense of touch - mechanoreceptors
52
where are Merkel cells found?
in the basal layer between keritanocytes & nerve fibres
53
where do Merkel cells synapse?
directly with free nerve endings
54
what part of the free nerve endings does diabetes affect?
diabetes affects the myelin sheath which causes reduced/no/funny feeling.
55
is Merkel cell carcinoma more common the melanomas?
no but is more deadly than melanoma.
56
what is a pilosebaceous unit?
a hair follicle;
- epidermal component + dermal papilla
- specialised keratins
- adjacent sebaceous gland
57
how is hair pigmented?
via melanocytes above the dermal papilla of a pilosebaceous unit which melanise the matrix of a hair
58
name some functions of a pilosebaceous unit
- sensory
- reduces need for melanocytes
- is the origin of the gland which supplies moisture to the skin surface
59
where are the stem cells of a pilosebaceous unit?
in the dermal root sheath
60
what are the phases of growth of hair?
anagen, catagen & telogen
61
what happens during anagen?
hair grows
| over 1-8 years
62
what happens during catagen?
the hair involutes
63
what happens during telogen?
shedding phase
64
what can affect the speed of hair growth?
hormones but hair will usually go through phases like clockwork
65
how is a hair shed?
through dermal papilla dissociation which always takes about 4 weeks
66
what is virilisation?
excessive & rapid hair growth
| e.g. due to excess androgen from a tumour
67
what is alopecia areata?
autoimmune hair loss
| normal hair -> grey hair -> hair loss
68
what are nails?
specialised keratins
69
which part of a nail is a hair bulb similar to?
nail matrix/root
70
where is the nail matrix found?
just below the skin surface proximal to the cuticle
71
what can a crumbly nail be due to?
- fungus
| - repeated small traumas
72
what is the cannula of a nail?
the thick layer which creates a white semi circle at the base of the nail
73
what is the derma-epidermal junction?
the interface between epidermis & dermis, complicated structure
74
what does the DEJ have a key role in?
epithelial-mesenchymal interactions:
- support, anchorage, adhesion, growth & differentiation of epidermal cells
- semi-permeable membrane acts as a filter & barrier
75
where does the epidermis get it's blood supply?
the dermis
| also brings nutrients & takes away waste
76
name the two layers of the DEJ
lamina densa & lamina lucida
77
where are hemidsemosomes found?
in basal cells of epidermis
78
what are hemidesmosomes?
filaments that attach to proteins in the lamina lucida
79
what happens in an inherited disease of the DEJ?
a mutation in one of the proteins in the DEJ causes skin fragility
80
what happens in an acquired disease of the DEJ?
auto-antibodies against proteins in the DEJ are formed
81
describe epidermolysis bullosa simplex
caused by inherited defect of DEJ
lots of blistering, very fragile skin, mum can’t hold it properly, tearing of skin, can become severe enough to cause webbing of toes & fingers
82
describe bullous pemphigoid
can come on at any point in life (acquired)
defect in skin tethering, not stuck together very well causing blistering & a severe itch
controlled by steroids
83
What are the components of the Dermis?
- cells
- fibres
- ground substance
blood vessels, lymphatics, nerves
84
which cells are found in the dermis?
```
mainly fibroblasts
macrophages
mast cells
lymphocytes
Langerhans cells
```
85
which fibres are found in the dermis?
collagen - more common
| elastin - less common but very important
86
what is ground substance?
a jelly like mass of mucopolysaccharides & glycosaminoglycans
87
what do fibroblasts do?
make collagen;
| pro-collagen is made first which is cleaved by enzymes to make collagen
88
what does collagen do?
becomes fixed in the dermal layer & gives strength to it
89
what does elastin do?
gives the skin elasticity
90
what do macrophages do?
they are immune scavengers & Ag presenters
91
what do Langerhans cells of?
Ag presentation
92
what are mast cells?
chemical messengers
93
what happens to skin in ageing?
- elastin fibres become less well formed
- collagen gets depleted
- fibroblasts & DEJ become much flatter
- there are less nutrients being delivered to the epidermis
94
what makes ageing worse?
UV light & smoking
95
how is blood transported to the skin?
arteriole-> precapillary sphincters -> arterial capillaries -> venous capillaries -> post capillary venules -> collecting venules
(more blood delivered than metabolic need)
96
why is the surface of the epidermis undulating?
for a greater surface area
97
what does a localised overgrowth of blood vessels cause?
port wine stain, "stork marks"
often on face
can be liked to epilepsy
pretty harmless
98
how is lymph drained from the skin?
through sub-epidermal meshed networks from smaller non-contractile vessels to larger contractile lymphatic trunks
99
what are the important immune functions of the lymphatics?
- immune surveillance by circulating lymphocytes and Langerhans cells
- channelling of micro-organisms / toxins
100
how do lymphatics run?
they mirror the blood supply
101
how is chronic lymphoedema caused & treated?
caused by a variety of things e.g. blockage/lack of lymph nodes or infection damaging lymph vessels
squeeze leg with bandages but skin is irreversibly damaged for life
102
which somatic sensory nerves are found in the skin?
- free nerve endings
| - special receptors: pacinian (pressure) & meissners (vibration) copuscles
103
describe messiness' corpuscles
sense light touch
| found in fingertips & lips
104
what do free nerve endings detect?
pain
105
what do motor nerves do in the skin?
innervate sweat glands
106
describe pacinian corpuscles
onion shaped nerve ends that detect deep pressure
107
what is neurofibromatosis?
overgrowth of nerve ending which are abnormally thickened
| benign growths unless affecting brain or spine
108
name the 3 types of skin glands
eccrine
sebaceous
apocrine
109
when are eccrine glands stimulated & where are they?
stimulated when the body is working hard
| found over the whole skin surface, particularly on palms, soles & axillae
110
where are sebaceous glands usually found?
often found linked to hair follicles, widely distributed across body mostly on face & chest
are hormone sensitive
111
what does the over stimulation of a sebaceous gland cause?
acne
112
where are apocrine glands found & what do they do?
found in the perineum & axillae
| secrete odours containing pheremones
113
what do sebaceous glands produce?
sebum: squalene, wax esters, triglycerides & free fatty acids
114
what are the functions of a sebaceous gland?
control moisture loss & protect against bacterial & fungal infection
115
what can hair follicles do if the skin is damaged?
they can repopulate the top part of the skin using the epithelium in the hair follicle
116
how do apocrine sweat glands develop?
as part of the pilosebaceous unit
117
how are apocrine glands stimulated?
by androgen
118
how are eccrine glands controlled?
by sympathetic cholinergic nerve supply in response to mental, thermal & gustatory stimulation
119
what functions do eccrine glands have?
can perform ultrafiltration
cooling by evaporation
moisten palms & soles to aid grip
120
where do eccrine glands secrete to?
directly onto skin surface
121
name some of the functions of the skin (at least 3)
- barrier function
- metabolism & detoxification
- thermoregulation
- immune defence
- social communication
- sensory functions
122
give an example of acute skin failure
toxic epidermal necrolysis
123
what can cause erythoderma?
dermatitis
psoriasis
drug reaction
T cell problmes
124
what is erythoderma?
inflammatory skin disease with erythema and scaling that affects nearly the entire cutaneous surface. causes a loss of water from the skin.
125
what does skin failure do in terms of the barrier function?
fluid loss -> dehydration
protein loss -> hypoalbuminaemia
infection
126
what does skin failure do in terms of thermoregulation?
heat loss -> hypothermia
127
what does skin failure do in terms of immune defence function?
spread of infection
128
what does skin failure do in terms of the metabolic function?
disordered thyroxine metabolism
129
what does skin failure do in terms of the communication function?
inability to display healthy skin -> stigma
130
what does skin failure do in terms of the sensation function?
pain sensation working -> pain
131
what is the skin a barrier to?
physical factors: friction, mechanical trauma UV radiation
chemical factors: irritants, allergens, toxins
pathogens: bacteria, viruses, fungi
132
name the 4 stratum layers of the skin, top to bottom
stratum corneum
stratum granulosum
stratym spinosum
stratum basale
133
how does our skin protect us from UV radiation?
melanin pigment formed in basal cells absorbs UV rays to protect DNA in the cell's nuclei
134
how is the skin metabolically active?
Vit. D metabolism
| Thyroid hormone metabolism
135
what is the detoxification function of the skin?
defence against chemicals, drugs, pollutants & sunlight
136
where is Vit. D3 stored?
as hydroxycholecalciferol in the liver
137
what is hydroxycholcalciferolconverted to?
1,25-dihydroxycholecaliferol in the kidney
138
how is Vit. D metabolised?
UV light stimulates the conversion of cholecalciferol to Vit. D3
139
how is thyroid hormone metabolised?
thyroxine to triiodothyronine
140
where does thyroid hormone metabolism occur?
mostly in the peripheral to the thyroid tissues including skin
some occurs in thyroid glands
141
how is temperature sensed?
through thermoreceptors
142
describe how the superficial & deep plexuses of blood vessels help with temperature control
depending on how much going through each decides how much heat you lose from the skin
e.g. central body temp too high, more blood flow through superficial plexus
143
what is eczema herpeticum?
disseminated herpes simplex virus infection
144
what are the sensory functions of the skin?
touch, pressure, vibration, pain, itch, heat, cold
