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Charis & Ellie vs Dermatology > Physiology of the Skin > Flashcards

Physiology of the Skin Flashcards

1
Q

what are the components of skin?

A 
epidermis 
appendages (nails, hair, glands and mucosae)
dermo-epidermal junction 
dermis 
subcutis (mainly fat)
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2
Q

where does the epidermis come from embryologically?

A

periderm - starts at 4 weeks, fully developed by 26 weeks

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3
Q

where does the dermis come from embryologically?

A

mesoderm - below the ectoderm

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4
Q

where do the melanoblasts come from embryologically?

A

the neural crest - within 1st 3 months

they then go to the skin and once they are settled in the skin they for melnocytes in the basal layer

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5
Q

What are Blaschko’s lines

A

the developmental growth pattern of skin - it doesn’t follow the vessels/nerves/lymphatics

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6
Q

what is the epidermis?

A

the outer layer of stratified cellular squamous epithelium - 95% keratinocytes

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7
Q

what are the 4 layers of the epidermis - from top to bottom?

A

keratin layer
granular layer
prickle cell layer
basal layer

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8
Q

development of keratinocytes

A

formed in the basal layer and then move to the surface (takes around 28 days)
where they then shed into the environment as dead skin cells [known as epidermal turnover, this happens a lot quicker (loss of control) in psoriasis/skin cancer] - regulated by growth factors, cell death and hormones

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9
Q

What is the function of the keratin layer?

A

the keratinocytes is where vitamin D metabolism occurs

acts as a tight waterproof barrier, sole of foot/palm of hand etc. tend to have thicker keratin layers

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10
Q

what is the keratin layer composed of?

A

keratin
filaggrin and involucrin, corneocytes (type of keratinocyte, overlapping non-nucleated cell remnants)
insoluble cornified envelope and lamellar granules which release lipids

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11
Q

what is the function of the granular layer?

A

acts like glue to prevent things from coming in, (this layer is often deficient in eczema/psoriasis)
these cells lose their nuclei,
they are the origin of the cornified envelope, composed of: 2-3 layers of flatter cells, large keratohyalin granules (which contain structural filaggrin and involucrin proteins), odland [lamellar] bodies, high lipid content

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12
Q

what is the composition of the prickle cell layer?

A

larger polyhedral cells,
lots of desmosomes (connections, these are what give the spiky appearance),
intermediate filaments which connect to the desmosomes

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13
Q

what is the composition of the basal layer?

A

one cell thick
small cuboidal basal cells
highly metabolically active
composed of lots of intermediate filaments (keratins)

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14
Q

what are melanocytes?

A

pigment-producing dendritic cells - they convert tyrosine to melanin pigment
melanin absorbs light so acts as a natural density filter
absorbs UV rays to protect the DNA in the cells’ nuclei

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15
Q

types of melanin

A

eumelanin - brown/black

phaeomelanin - red/yellow

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16
Q

what are melanosomes

A

they are organelles in melanocytes

full melanosomes - melanin granules, are transferred to adjacent keratinocytes via dendrites

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17
Q

how many melanocytes do people have?

A

everyone has the same number regardless of skin tone

the melanocyte ratio = melanocyte: basal keratinocyte = 1:5 - 1:10

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18
Q

what is the MC1R gene?

A

encodes a protein which determines the balance of pigment in the hair and skin
if MC1R has 1 defective copy - freckling and if 2 defective copies - red hair and freckling

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19
Q

what are langerhan cells?

A

In the prickle cell layer of the epidermis, they are also found in the dermis and lymph nodes
They are dendritic cells, involved in the skin immune system, they are antigen-presenting cells so they pick up antigen in the skin and circulate them to lymph nodes via the lymphatic system
They have a mesenchymal origin (bone marrow)
Racket organelle (Birbeck granules) are found in Langerhans cells
There can be tumours of the Langerhans cells.

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20
Q

what are merkel cells?

A

They are found in the basal layer of the epidermis, between the keratinocytes and nerve fibres
They are mechanoreceptors (i.e. they respond to touch/sound etc.)
Merkel cell cancer is rare but very fatal (worse than melanoma), caused by viral infections.

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21
Q

What is the pilosebaceous unit?

A

a structure consisting of hair, hair follicle, arrector pili muscle and sebaceous gland

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22
Q

What are the phases of hair follicles?

A

Anagen - growing (3-7 yrs)
Catagen - involuting (3-4 weeks)
Telogen - resting (the hair that’s fallen out can be aggravated by psycho-social stress)

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23
Q

What are the types of hair?

A

lanugo - in utero
vellus - soft, fine hair, barely noticeable
terminal - thick hair e.g. armpits

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24
Q

What is telogen effluvium?

A

temporary hair loss usually after stress e.g. pregnancy/trauma and usually is lost from the top of the scalp

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25
What is virilisation?
the development of physical male characteristics in a female - hair caused by excess androgen
26
What is alopecia?
hair loss, there are different types - alopecia aerate = autoimmune
27
What happens to skin appendages when there is a scar?
There is a permanent loss of the skin appendages
28
What is a nail made up of?
specialised keratins
29
What are the mucosal membranes?
usually not keratinised highly specialised membranes for function (eyes, mouth, nose, GU and GI tracts)
30
What is keratinised mucosal membranes a sign of?
skin disease
31
functions of the dermo-epidermal junction
support anchorage adhesion growth and differentiation of basal cells semi-permeable membrane acts as a barrier and filter
32
What is the dermo-epidermal junction made of?
lamina lucida - electron sparse area lamina densa - electron dense area sub-lamina densa zone
33
diseases of the dermo-epidermal junction
bullous pemphigoid - autoimmune epidermolysis bullosa - genetic the diseases are characterised by blisters
34
What is the dermis?
a connective tissue which allows movement - basically keeps the skin together
35
What is the dermis made of?
``` ground substance fibroblasts macrophages mast cells lymphocytes langerhans cells fibres (collagen and elastin) muscles glycoaminoglycans (GAGs) blood vessels lymphatics nerves ```
36
Photo-ageing
when light breaks down the collagen and elastin in the dermis - causes those wrinkles
37
what is the blood vessel supply?
greater than metabolic need, horizontal plexus - too many can cause angioma (benign)
38
What is the order of vessels?
``` arteriole to precapillary sphincters to capillary to postcapillary venules to collecting venules ```
39
lymphatic vessels function
meshed network, drain waste, have important immune functions (immune surveillance by circulating lymphocytes and langerhans cells) also channel micro-organisms/ toxins
40
Chronic lymphoedema
may cause damaged/burst vessels - can potentially be caused by obesity
41
Nerve supply
``` somatic sensory (dermatomes) - free nerve endings special receptors = Pacinian (pressure) and Meissner (vibration) corpuscles ```
42
what is neurofibromatosis?
a genetic condition which can cause the development of benign tumours of nerve endings due to genetic defects in the chromosomes
43
what are the 3 types of skin glands?
sebaceous glands apocrine glands eccrine glands
44
what are the sweat glands?
apocrine and eccrine
45
Characteristics of the sebaceous glands
cause acne largest in the face and chest hormone sensitive (glands are more active during/after puberty) develops as part of pilosebaceous unit
46
functions of the sebaceous gland
controls moisture loss protects against fungal infection holocrine secretion into pilary canal they produce - sebum, squalene, wax, esters, triacylglycerol (TG) and free fatty acids (FFA)
47
characteristics of apocrine glands
in the axillae and perineum | androgen dependent
48
function of the apocrine glands
produces oily fluid | odour after bacterial decomposition
49
location of the eccrine glands
whole skin surface - mainly palms soles and axillae, most commonly on the face cooling by evaporation, moistens palms and soles to aid grip
50
nerve supply to eccrine glands
sympathetic cholinergic nerve supply - mental, thermal and gustatory (taste) stimulation
51
Functions of the eccrine glands
thermoregulation works like a kidney (ultrafiltration) 2-4 million glands, NaCl + HCO3 (bicarbonate) are reabsorbed resulting in hypotonic fluid
52
functions of skin
``` barrier thermoregulation immune defence metabolism and detoxification communication sensation ```
53
what happens when there is failure of the barrier function?
fluid loss = dehydration protein loss = hypoalbuminaemia infection
54
What is the purpose of the barrier function?
Physical - friction, mechanical trauma, UV radiation Chemical - irritants, allergens and toxins Pathogens - bacteria, viruses and fungi
55
Examples of diseases of the barrier finction
steroid-sulphatase deficiency X linked ichthyosis cumulative irritant hand dermatitis Ulcer following compound fracture
56
What happens when there is failure of the thermoregulation function?
heat loss = hypothermia
57
How is the thermoregulation achieved?
warm/cold-sensitive thermoreceptors behavioural changes controls sweating/shivering/ blood supply (too hot - blood flow increases so heat is lost, too cold - opposite)
58
Diseases of the thermoregulation function
frostbite
59
What happens when there is failure of the metabolism and detoxification function?
disordered thyroxine metabolism
60
vitamin D metabolism is by what UV light
290 to 320 nm ultraviolet
61
vitamin D3 converted from what by UV light
cholecalciferol (7-dehydrocholesterol) to Vitamin D3
62
how is vitamin D3 stored?
As hydroxycholecaiferol in the liver
63
What is hydroxycholecaiferol converted to
1,25-dihydroxycholecalciferol in the kidney
64
Thyroid hormone metabolism
thyroxine (T4) - triiodothyronine (T3)
65
which is the more active thyroid hormone?
T3 - more active than T4
66
where does T4-T3 conversion occur
20% conversion occurs in the thyroid gland | 80% occurs in the peripheral (to thyroid) tissues including the skin
67
What does failure of the immune defence function do?
allows spread of infection
68
what is the immune defence of the skin involved in?
protection against infection - specific and non-specific (induces immunity responses) sunlight responses allergic reactions
69
What cells are involved in the immune defence?
langerhans cells and T cells
70
What does a failure in the communication function cause?
inability to display healthy skin = stigma
71
What does the failure in the sensation function cause?
pain
72
What are the sensory functions of the skin?
``` touch pressure vibration pain itch heat cold nerve endings and receptors in skin ```
73
Examples of a disease of the sensory function of skin
neuropathic ulcer (leprosy)
74
Immune responses of the skin
normal - infection is controlled hypersensitivity - overreaction to antigen immunodeficiency -infection not controlled, tumours may form autoimmunity - reaction to host tissue, chronic inflammation
75
what do keratinocytes (KC) do?
sense pathogens and help mediate an immune response Produce AMPs - antimicrobial peptides - directly kill pathogens, high levels of AMPs in patients with psoriasis Produce cytokines (proteins secreted from 1 cell and bind to another cell) and chemokines - recruit and regulate cells in the immune system
76
Where are keratinocytes found?
the epidermis
77
what do langerhan's cells do?
the main skin resident immune cell they process lipid antigens (Ag) and microbial fragments and present them to effector T cells they help activate T cells
78
where are langerhans cells found?
the epidermis
79
where are the T cells found?
the epidermis and dermis CD8+ cells - in the epidermis mainly CD4+ and CD8+ cells - in the dermis large number in healthy skin
80
3 examples of CD8+ cells associated with inflammation
Th1 - psoriasis Th2 - atopic dermatitis Th17 - psoriasis and atopic dermatitis
81
How are T cells developed and activated?
produced in the bone marrow and sensitised in the thymus | T cell receptor (TCR) and major histocompatibility complex (MHC) are involved in Ag recognition and T cell activation
82
What enhances Ag recognition and T cell activation?
CD4 + Th1 = activates macrophages to destroy microorganisms produces IL2 and IFNy Th2 = helps B cells make antibody, produces IL4, IL5 and IL6 CD8 + can kill infected cells directly, important in protection against viruses and cancer
83
What are the types of dendritic cells?
``` dermal DC = involved in Ag presenting and secreting cytokines and chemokines Plasmocytoid DC (pDC) = produce IFN--alpha, found in diseased skin ```
84
What immune cells are found in the dermis?
dendritic cells macrophages neutrophils (circulating leukocytes attracted to tissue by chemokines) mast cells
85
What do activated mast cells release?
Preformed (really quick) - tryptase, chymase, TNF, histamine Newly synthesised - IL, TNF, IFNy
86
What activates mast cells?
IgE binding - allergy physical trauma certain drugs micro-organisms
87
What is a MHC?
a bunch of genes located on chromosome 6 Class 1 - found on almost all cells, they present (endogenous) Ag to Th cells Class 2 - found on APC (B cells, macrophages), they present exogenous Ag to Th cells very important in self and non-self recognition
88
What types of immunodeficiency are there?
primary (genetic) secondary (acquired) main sign is getting lots of infections
89
What is type 1 hypersensitivity?
antibody mediated (IgE)
90
Early exposure to antigen in type 1 hypersensitivity
production of IgE, IgE binds to the FceR1 receptor on mast cells very rapid, minutes, wheal and flare
91
Late exposure to the antigen in type 1 hypersensitivity?
rapid cross linking of the receptors, signal transduction and degranulation of the mast cell hours, cellular infiltration, nodule
92
what is type 2 hypersensitivity?
``` antibody mediated (IgG, IgM) mechanisms are important in autoimmunity and transplantation, haemolytic disease of the newborn and blood transfusion recipients ```
93
what is type 3 hypersensitivity?
``` antibody mediated (IgG, IgM) arthus reaction - slower than type 1, faster than type IV skin response involved in certain drug reactions ```
94
What is type 4 hypersensitivity?
cell mediated (Th1 cells) delayed response T cell mediated response which then recruits other cells to the site involved in tuberculin reaction and contact allergies

Charis & Ellie vs Dermatology (26 decks)

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