Structure and Function Flashcards
Roughly how many skin diseases are known?
> 2000
Describe the difference between the EPIDERMIS and the DERMIS
Epidermis = outer layer of stratified squamous epithelium
Dermis = below epidermis, made of connective tissue, often described as “leather”
In terms of embryology, where does the epidermis come from?
the ectoderm
In terms of embryology, where does the dermis come from?
The mesoderm
What part of the embryo do melanocytes (pigment cells) come from?
The neural crest
What layers of the skin are present at week 4 of foetal development?
Periderm
Basal Layer
Dermis
What layers of the skin are present at week 16 of foetal development?
Keratin Layer Granular Layer Prickle Cell Layer Basal Layer Dermis
melanocytes also migrate from neural crest
What layers of the skin are present at week 26 of foetal development?
Epidermis Appendages Dermo-epidermal junction Dermis Subcutis (Fat)
Name the appendages found in the epidermis and dermis of the skin
melanocytes
sebaceous gland
hair follicle
arector pili muscle
What is the function of the arector pili muscle in animals?
Controls temperature
Muscle contraction allows animal to stand its fur on end to decrease temp
What are Blaschko’s Lines?
growth patterns of skin that do not follow nerves/vasculature/lymphatics
e.g if a rash were to start at the nipple and progress down the inner arm
If a patient displays a rash in a developmental pattern, what can be assumed about their condition?
It was acquired pre-natally
During what week of foetal development could a mutation occur which causes all cells in a specific section to be affected?
Week 11
What type of epithelium is found at the epidermis and how thick is it?
Stratified squamous epithelium
~ 1.5 mm thick
What type of cell predominantly makes up the epidermis?
95% epidermis = keratinocytes
Name 3 other types of cell found in the epidermis
Melanocytes
Langerhans cells
Merkel cells
What is the function of the thick layer of keratin on the surface of the epidermis?
Thick layer of keratin = dead skin cells from proliferation
Stops water and bacteria penetrating the skin
Describe the epidermal variation between the scalp, the armpit and the palms of hands/sole of the foot
Scalp = hair, normal amount of sweat glands Armpit = hair, extra apocrine sweat gland adjacent to hair follicle (produces smell) Hands/feet = no hair , but extra sweat glands
Give an example of “mechanical trauma” that would cause calluses to develop on the hands
playing guitar
Describe the ratio of epidermis to dermis in the skin of the abdomen
EPIDERMIS = thin
DERMIS - thick
What 3 factors regulate skin growth?
Growth Factors
Cell Death
Hormones
Name conditions where the predominant feature is a loss of control of skin growth
Cancer
Psoriasis
What produces the thick scabs in psoriasis?
Cells multiply too quickly and skin grows too fast
layer of keratin on surface is larger and does not fall off
=> leaving behind scabs
Where do keratinocytes come from?
The basement membrane
How long does it take for cells to migrate from the bottom to top of the epidermis (i.e. regeneration to occur)?
28 days
What type of epithelium does the basal membrane have and what thickness is it?
Usually one cell thick
Small cuboidal
Where do prickle cells arise from and what are they connected to?
Daughter cells of basal cells
Connected to desmosomes
these cells move upwards
Describe the appearance of the granular layer
2-3 layers of flatter cells
What proteins, released in the granules, are responsible for forming the ‘cornified envelope’
structural filaggrin and involucrin proteins
What is the function of the ‘cornified envelope’?
No water OUT (retains moisture in skin)
No bacteria IN (prevents infection)
How do the proteins in the granular layer retain moisture?
Large proteins are not req’d therefore they are split into small amino acids which can bind water.
Without this mechanism our skin dries out
What is the largest component of the keratin layer?
Corneocytes
overlapping non-nucleated cell remnants
Why is the dermis so large in a wart?
The body attempts to proliferate the dermis to push the virus out
Can mucosa also be affected by skin diseases?
Yes
What can you deduct from the oral mucosa being white in colour?
Blood vessels are no longer visible, therefore the epidermis or dermis must have thickened.
What happens when skin appendages are lost?
Scarring
What is scarring made up of?
Collagen
What are melanocytes?
Pigment producing dendritic cells
Where are melanocytes found?
The basal layer and above
What organelles are found inside melanocytes and what is their function?
melanosomes
Convert tyrosine to melanin pigment
How is melanin pigment transferred to keratinocytes?
via dendrites
How does the border of a melanocyte look histologically?
White halo effect
due to water depletion which causes contents of cell to shrink
What is the function of melanin caps?
Protect nuclear DNA of basal cells
What is vitiligo?
autoimmune disease with loss of melanocytes
What stimulates melanin production?
UV Light
Hormones
What is the risk of biochemically stimulating melanocytes?
Melanomas can form
How many people does Albinism affect in the UK?
1:20,000
What is albinism?
a genetic partial loss of pigment production
What hormone is responsible for Nelson’s syndrome?
ACTH
produced in excess by pituitary in this condition
`Where are Langerhans cells found?
Prickle cell level in epidermis
Also found in dermis and lymph nodes
Where do Langerhans cells originate from?
Mesenchymal origin – bone marrow
What role do Langerhans cells play in the immune system?
Antigen presenting cells
They pick up antigens in skin and circulate to lymph nodes via lymphatic system
What organelle and granules are specific to Langerhans cells?
Racket Organelle
Birbeck granules
What is the function of Merkel cells?
mechanoreceptors
=> can sense if something goes over you
Where are merkel cells found?
On the ends of myelinated nerves in the basal layer
What is notable of Merkel Cell cancer?
Rare
Caused by viral infection
High mortality
What is a hair follicle always accompanied by?
Adjacent sebaceous gland
What causes the pigment of hair?
melanocytes above dermal papilla
What is the side effect of retinoids given to treat acne?
They block formation of sebum => can create very dry skin
Name the three phases of hair growth
Anagen = growing Catagen = involuting Telogen = resting
How does the hair follicle develop embryologically?
Buds from the epidermis downwards
What hormones can influence hair growth?
Thyroxine and androgens
What drugs can cause a synchronous Telogen phase? (aka all hair beginning to fall out at the same time)
Chemotherapy & Radiotherapy
What causes alopecia areata?
Autoimmune condition where the hair follicles are attacked by T-lymphocytes
How much do nails grow each day?
Growth rate 0.1mm per day
Fingers > toes
Summer > winter
How are the stem cells which make up our nail, different to that which make up the rest of the skin layers?
They differentiate into keratin which is aligned into a parallel sheath
Which part of the nail is responsible for severe pain during trauma to the nail?
Nail matrix
What is the main function of the dermo-epidermal junction?
Support / anchorage / adhesion
growth and differentiation of basal cells
What can happen if the dermo-epidermal junction is not intact?
skin can slip/blister/fail
What are the layers of the dermo-epidermal junction?
Lamina lucida
Lamina densa
Sub-Lamina densa
Give an example of a condition where failure of the dermo-epidermal junction causes blistering
Bullous Pemphigoid
If a person produces antibodies to their own dermo-epidermal junction, what test can we use to detect these/
Immunofluorescence
Give an example of a condition where there is a structural protein complex mutation in the dermo-epidermal junction
Epidermolysis Bullosa
(in babies)
What symptoms can Epidermolysis Bullosa cause?
Widespread blistered, red and crusted skin
oesophageal strictures => feeding problems
Nailbeds are absorbed
Hands are fused (mitten deformities)
What cells are found in the dermis?
fibroblasts macrophages mast cells lymphocytes Langerhans cells
What do fibroblasts in the dermis make?
Collagen and elastin
What 3 things can give you fewer elastic fibres in your skin?
Ageing
UV light
smoking
Why do we have way more blood vessels in our skin that we require for only nutrition?
Temperature regulation (vasoconstriction/vasodilation)
How are blood vessels in the skin arranged?
Horizontal plexuses
What is an angioma?
a benign overgrowth of blood vessels showing through the epidermis and dermis
How are lymphatic vessels in the skin arranged?
Sub-epidermal horizontal plexus (like blood vessels)
What is cellulitis?
Bacterial infection of lymphatics
What specialised receptors are present in the skin
Pacinian (pressure) and Meissners (vibration) corpuscles
What condition can occur as a result of nerve overgrowth?
Neurofibromatosis
Name the three types of skin glands
Sebaceous
Apocrine
Eccrine
Where are sebaceous glands found and what is their function?
largest glands face and chest
Functions:
control moisture loss
protection from fungal infection
Where are apocrine glands found and what do they produce?
Axillae and perineum
Androgen dependent
Produce oily fluid (odour after bacterial decomposition)
Where are eccrine glands found and what is their function?
Whole skin surface
(palms, soles and axillae in particular)
Functions:
cooling by evaporation
moisten palms / soles to aid grip
What are the main functions of the skin?
Barrier Metabolism & detoxification Temp. reg. Immune defence Sensory
Give 2 examples of acute skin failure
Toxic epidermal necrolysis
Erythroderma
`
What consequences are there if the skin fails and therefore doesnt work as a BARRIER?
Fluid loss => Dehydration
Protein loss => Hypoalbuminaemia
Infection
What consequences are there if the skin fails and therefore deosnt work to regulate heat?
Heat loss => Hypothermia
What consequences are there if the skin fails and cant function as an immune defence?
Spread of infection
What consequences occur if the skin fails metabolically?
Disordered thyroxine metabolism
What consequences can occur if the skin fails and loses its sensory function?
Pain sensation
What 3 categories does the skin protect us from as a BARRIER?
Physical
- Friction, mechanical trauma
- Ultraviolet radiation
Chemical
- Irritants, allergens, toxins
Pathogens
- Bacteria, viruses, fungi
How does the skin not split when you hit your hand off of a table for example?
The subcutaneous layer dissipates the energy
Give examples of everyday items that could be responsible for Cumulative irritant hand dermatitis
Rings
Soap/washing up liquid
If an ulcer were to develop following a compound fracture, what is the patient at risk of now that the compound is exposed?
Osteomyelitis
infection of the bone
Give 2 examples of how the skin is metabolically active
Vitamin D metabolism
Thyroid hormone metabolism
In what ways can our skin regulate our temperature?
Control sweating
shivering
Vasoconstrict/ vasodilate blood supply
How many scabies mites can usually be found on an average infected patient?
12
How many scabies mites can be found if the skin is crusting?
Millions!
Describe the type of inflammation and its location in Tuberculoid leprosy (Hansen’s Disease)
Granulomatous inflammation to wall off an infection in the dermis
What percentage of patients with Chronic discoid lupus erythematosus will progress to having SLE?
10%
What sensory functions can the skin perform?
Touch, pressure, vibration
Pain and itch
Heat and cold
Nerve endings and receptors in skin
What other condition is linked to Neuropathic ulcers(leprosy)?
Diabetes Mellitus
