skin structure and function Flashcards
what is the largest organ
skin
how many skin diseases are there
> 2000
what percentage of the population suffers from a skin condition
25%
1:5
describe the epithelium of the dermis
stratified squamous epithelium-1.5mm
where did the epidermis come from
it came from the Ectoderm cells form single layer periderm
what is the biggest component of the epidermis
keratinocytes
what other cells are present in the epidermis
o Melanocytes (basal & suprabasal)
o Langerhans cells (suprabasal)
o Merkel cells (basal)
what are the 4 layers of the epidermis
Keratin layer
Granular layer
prickle cell layer
basal layer
where did the dermis come from
mesoderm bellow ectoderm
what is the dermis
connective tissue
what are the cells present in the dermis
fibroblasts, macrophages, mast cells, lymphocytes, Langerhans cells
what are the fibres in the dermis
collagen
fibrin
^ produced by the fibroblast
elastin
what other parts are present in the dermis
Muscles,
blood vessels,
lymphatics,
nerves
what skin type is the stronger
dark skin
what is the basal layer for
stem cells
true or false: keratinocytes have no nucleus
TRUE
what are Appendages
nails hair glands muscles nerves blood vessels ect
what junctions are present in the prickle cell layer
desmosomes that attach and un attach
* they contain intermediate filament
what are the Blaschko’s lines
the developmental pattern of skin
describe skin conditions that follow the Blaschko’s lines
congenital conditions
mosaic
what are the layers of the skin
• Epidermis • Appendages o Nails o Hair o Glands o Mucosae • Dermo-epidermal junction • Dermis: connective tissue, less cellular • Sub-cutis: predominantly fat
what is the name of the muscle that lifts the hair shaft
Arrector pili muscle
what is the regulation of skin turnover
• Balance between cells in/out
what is the skin turnover controlled by
- Growth factors
- Cell death
- Hormones
what happens when the regulation of the skin is lost
- Skin cancer
* Psoriasis
what are the steps of differentiation
- Keratinocytes migrate from basement membrane
- Continuous regeneration of epidermis
- 28 days from bottom to top
- This period can change in disease
describe the thickness of the basal layer
one cell thick
describe the cell types in the basal layer
small cuboidal
true or false: there are Lots of intermediate filaments (keratin) in the basal layer
TRUE
true or false the basal layer is Highly metabolically active
TRUE
describe the cell types in the Prickle cell layer
Larger polyhedral cells
describe the cell types in the Granular layer
2-3 layers of flatter(squamous) cells
what does the Granular layer contain
• Large keratohyalin granules – contain structural filaggrin & involucrin proteins
How do you retain the water in your skin
- the granular cells rupture and release granules. containing filaggrin.
- Enzymes take the filaggrin protein and snip it into short pieces. So you have groups of 2 or 3 amino acids. These amino acids bind water molecules therefore they are hydroscopic.
- This means that there is a sudden massive accumulation of tinny substances that bind water (emollient- it prevent water from leaving the body).
- If we don’t have the filaggrin mechanism the skin gets very dry and this for example leads to eczema in atopic dermatitis
what are Corneocytes
Corneocytes are terminally differentiated keratinocytes and compose most if not all of the stratum corneum, the outermost part of the epidermis. They are regularly replaced through desquamation and renewal from lower epidermal layers, making them an essential part of the skin barrier property.
true or falses keratine layer contains non-overlaping nucleated cells
false
• overlapping non-nucleated cell remnants
true or falses keratine layer contains Insoluble cornified envelope
true
true or falses Lamellar granules in keratine layer release ions
false they release lipids
give an example of viral infection affecting keratinocyte
Human papillomavirus infection of keratinocytes causes warts.
• HPV thrives in the keratin and epidermis layers as they can’t handle the heat in the dermis
explain why keratinocytes are waterproof
- Tight waterproof barrier
- Mechanical protection
- They bind fatty acids and cross-link them. This is why water doesn’t enter your body.
how do Viral warts change the epidermis
the epidermis thickens and becomes round and inflamed. They are not transmitted to other people unless they have a breached barrier.
true or false Mucosal membranes varies depending on the area
true
Masticatory Mucosal
keratinised to deal with friction/pressure
Lining mucosa
non-keratinised
Specialised mucosa
- tongue papillae – taste
Ocular mucosa
Lacrimal glands, eye lashes, sebaceous glands
why is the oral mucosa red
In the mouth because the keratin layer is so thin the vascular plexus shines through giving it the red layers. If we have thickening it look white and that is bad news
what does the Hypodermis (subcutaneous) consist of
it mostly consist of fat lobules and droplets each with a membrane.
why is the Hypodermis important
This is important as it allows all of the dermis and all of the epidermis to move across
what happens if you block the Spacious glands
skin becomes dry
how does acne occur
bacteria feeds on the oil produced by spacious glands.
it breaks down the fatty acid causing inflation.
These break down lipids trigger inflammation and the buildup of pus
what is the commonest side effect of acne treatment
to treat acne you have to dry the oil, this results in the skin becoming dry and can cause eczema.
what are milia
oil trapped underneath the skin due to a block in the skin follicle.
describe Melanocyte migration
• Migrate from the neural crest to the epidermis in the first 3 months of foetal development.
why do melanocytes look like brain cells
they migrate from the same neural crest
true or false melanocytes have synapse and synaptic functions.
True
where are melanocytes present
basal layer
what are melanocytes described as
They are described as pigment-producing dendritic cells
what are melanosomes’
melanocyte organelles that contain pigments
• Full melanosomes (‘melanin granules’) transferred to adjacent keratinocytes via dendrites
melanocytes convert tyrosine to what
to melanin pigment
what colour is Eumelanin
brown or black
what colour is Phaeomelanin
red, yellow
why is Melanin described as a neutral density filter
as it absorbs light
true or false melanocytes Form a protective cap over the nucleus
TRUE
Melanin caps protect the nuclear DNA in basal cells
how do melanocytes transport melanin
melanin gets transported through the axon of the melanocyte to the keratinocyte
what is the other name for the keratine layer
stratum corneum
true or false Hair does some protections against sunlight
true
For examples animals who have lots of hair tend to not have lots of melanin in their skin
Describe VITILIGO
- Vitiligo represents an autoimmune disease with loss of melanocytes
- Melanocytes are being attacked by cytotoxic lymph cells
- Self-limited
Describe ALBINISM
In this disorder, there is a genetic partial loss of pigment production.
Describe NELSON’S SYNDROME
In this disorder, melanin production stimulating hormones are produced in excess by the pituitary glands.
what are Langerhans cells
Tissue-resident macrophages
what is the origin of Langerhans cells
Mesenchymal origin – bone marrow
where are Langerhans cells resident
Prickle cell level in epidermis
• Also found in dermis and lymph nodes
what appearance do Langerhans cells have
- Tennis racket appearance
* Antigen-presenting cells
where are Merkel cells found
- basal
* between keratinocytes & nerve fibres
what type of receptors are Merkel cells
• mechanoreceptors
what is the function of Merkel cells
- connects 2 nerve endings
- direct entry point to the central nervous system.
- Sense of feeling
what is the cause of Merkel cell cancer
• caused by viral infection (polyomavirus)
describe Hair follicles “Pilosebaceous unit”
• Epidermal component plus dermal papilla
where does hair pigment come from
• Hair pigmentation via melanocytes above the dermal papilla
where does the hair follicle grow from
- Hair branches out from the epidermis and becomes a bud
- Then at the same time, something else also buds out to the side and becomes the sebaceous gland.
- The papilla comes in from the dermis (comes from the mesoderm)
- The stem cells come from the bulge on the side
Phases of growth
Anagen = growing Catagen = involuting (around a month) Telogen = resting
which hormones influence the growth of haiur
thyroxine, androgens
types of hair growth
Lanugo (in utero),
vellus, childhood
terminal, adult
true or false • In humans the telogen phase is asynchronous
true
it doesn’t occur at the same time unlike animals
what is Telogen effluvium
Telogen effluvium occurs when there is a marked increase in the number of hairs shed each day.
eg during chemotherapy
it grows back afterwards
it usually occurs because of a sharp drastic change in the levels of hormones
After Childbirth is an example or a contraceptive. Stress is also a cause.
Describe Virilisation
is a condition in which a female develops characteristics associated with male hormones (androgens), or when a new-born has characteristics of male hormone exposure at birth. due to excess androgen from a tumour
Nails
• Specialised keratins • Nail matrix / root similar to hair bulb • Growth rate 0.1mm per day – Fingers > toes – Summer > winter • Some drugs increase nail / hair growth • Hyponychium–secures the free nail edge
what is the function of Dermo- epidermal Junction
• Interface between epidermis and dermis
• Key role in epithelial–mesenchymal interactions:
– Support, anchorage, adhesion, growth and differentiation of basal cells
– Semi-permeable membrane acting as barrier and filter
– Important in terms of structure and what can go wrong in diseases
– Complex structure filled with protein desmosomes and collagen.
what are the layers of Dermo- epidermal Junction
Lamina lucida
lamina densa
sub-lamina densa zone
describe Bullous Pemphigoid
- Occurs in older patients
- It occurs when an antibody is created by immune cells against the junction
- Its an inflammatory response causing Bulli
how can we treat Bullous Pemphigoid
steroids
describe Epidermolysis Bullosa
- Rare
- Children usually
- No cure
- Inheritance where there is a defect in the proteins that make the junction
- Can be life threatening
- Causes deformities and scarring
Describe Intrinsic ageing
Happens to everyone and everywhere
Describe Extrinsic ageing
caused by UV light, smoking, pollution, heat
Describe Hypertrophic photoaging
this is characterised by deep furrows and a leathery appearance
Describe Atrophic photoaging
this is characterised by telangiectasia, a smooth, relatively unwrinkled appearance, and the development of a variety of benign and malignant skin lesions.
what are the 2 types of Extrinsic ageing
Hypertrophic photoaging
Atrophic photoaging
what type of plexuses of blood vessels are present in the dermis
Horizontal plexuses
describe angioma
- When the blood vessels go wrong in the dermis.
- Its benign dilatation of the blood vessels
- Can bleed easy and hard to stop
what are the treatments of Angioma
laser -for large areas
surgery -for small areas
topical beta blockers
true or false lymphatic vessels follow vertical plexus
false they follow the horizontal plexus of the blood vessels.
what is the function of the lymphatics
• Smaller non-contractile vessels drain into larger contractile lymphatic trunks.
• Continual drainage of plasma proteins, extravasated cells and excess interstitial fluid
• Have no muscle so they require external help to pump fluid around.
• Important immune functions:
- immune surveillance by circulating
o lymphocytes and Langerhans cells
- channelling of micro-organisms / toxins
