Skin Structure & Function (1-4) Flashcards
What is the epidermis?
Outer layer
Wafer thin
What cell type is the epidermis composed of?
Stratified squamous epithelium
What is the dermis?
Beneath the epidermis
Connective tissue
The “leather skin”
From which embryological structure does the EPIDERMIS arise?
ECTODERM
Ectoderm cells form single layer periderm
Increase in layers of cells
Periderm cells cast off
From which embryological structure does the DERMIS arise?
MESODERM
below ectoderm
Melanocytes (what are they & embryological origin)
Originate from the NEURAL CREST
Pigment producing cells
What is the term for “cellular organisation into germ layers”?
Gastrulation
What are the layers of the EPIDERMIS?
BPGK
Basal –> Prickle –> Granular –> Keratin (or C for Cornified envelope)
Are epidermal cells dynamic?
Yes.
Constantly being replaced.
Differentiation
Many different cel types
Which layer of the epidermis is moving the most?
Prickle/spinous layer
What structure connects the prickle layer together?
Desmosomes (??? not sure at m will update)
Where would you find Apocrine glands? (grossly)
AXILLAE (main one at present time)
Additional ones//
areola and nipples of the breast, ear canal, eyelids, wings of the nostril, perianal region, and some parts of the external genitalia
(wikipedia)
What are APOCRINE glands? (later)
Function in humans still not largely known
What are ECCRINE/MEROCRINE glands? (later)
Glands
Make you sweat
Autonomc system
Thermoregulation
Whole skin surface - palms, soles and axillae in particular.
SYMPATHETIC cholinergic nerve supply
Ultrafiltration can be more than 10L per day.
Hypotonic fluid
Colling; moisten palms/soles to aid grip
Skin is able to reversible react to mechanical pressure by forming?
What does this mean?
Keratin
Callouses forming
Playing guitar a lot = thicker callous
Play it less = callous is not as thick
– hence “reversible”
How is turnover of skin regulated?
Controlled by:
Growth factors
Cell death
Hormones
What happens if there is a loss of control in skin regulation?
Skin cancer
Psoriasis
In normal skin, how long does it take for prickly cells to move up to the “top”?
In psoriasis?
28 days
5 days or so when someone has psoriasis
extremely rapid turnover
In psoriasis, cells have difficulty with?
Differentiation
In psoriasis, keratinous cells do not…
Slough off as easily as normal cells
Gives a “scaly” look
Where do keratinocytes migrate from?
The basement membrane
The basal layer is composed of what type of cell?
Small cuboidal with intermediate keratin filaments
Prickle cell layer is composed of?
Larger polyhedral cells
Desmosomes
Intermediate filaments connecting to desmosomes
In what direction does the prickle cell layer move in general?
Upwards towards apical
Granular layer
2-3 layers of flatter cells Lamellar bodies High lipid content Origin of cornified envelope Cell nuclei lost Keratohyalin granules (contain filaggrin & involucrin)
What are lamellar bodies?
lamellar bodies are secreted from keratinocytes, resulting in the formation of an impermeable, lipid-containing membrane that serves as a water barrier and is required for correct skin barrier function
Filaggrin (needs work)
is a filament-associated protein that binds to keratin fibers in epithelial cells
Involucrin
In binding the protein loricrin, involucrin contributes to the formation of a cell envelope that protects corneocytes in the skin.
Keratin layer
- composed of
Corneocytes (overlapping non-nucleated cell remnants) held together by filaggrin products (?)
NO NUCLEI
What kind of barrier does the keratin layer provide?
Tight waterproof barrier
Does the keratin layer have nuclei?
NO
What does HPV infection affect?
Keratinocytes
Causing warts
Mucosal membranes
make more concise, just guide at moment
Highly specialised for function
Eyes, mouth, nose, genito-urinary & GI tracts
Oral mucosa
Masticatory – keratinised to deal with friction/pressure
Lining mucosa – non-keratinised
Specialised mucosa - tongue papillae – taste
Ocular mucosa
Lacrimal glands, eye lashes, sebaceous glands
Why are the insides of our mouths red?
You can see straight through into the upper dermal vascular plexus
What does white indicate on the inside of the mouth?
Thickened skin
The boundary between the dermis and epidermis is not flat because…
The skin can withstand pressure and sideways displacement
Majority of epidermal cells are…
What are the 3 (main) others?
Keratinocytes
3 others:
- melanocytes
- Langerhans cells
- Merkel cells
Melanocytes
- where they originate embryologically
- what they are
Migrate from neural crest to epidermis (during first 3 months of development)
They are PIGMENT-producing dendritic cells
What are melanocytes related to?
Neuronal dendritic cells
What organelle do melanocytes contain?
Melanosomes
Melanosomes do what?
Convert tyrosine –> melanin pigment
What are the 2 types of melanin pigment?
- Eumelanin (brown/black)
2. Phaeomelanin (red, yellow)
What is the function of melanin?
Absorbs light
neutral density filter
What happens to full melanin granules?
They are transferred to adjacent keratinocytes via dendrites
What does the melanin form? (hat/cap)
Protective cap over the nucleus
What do these “melanin caps” protect?
The nuclear DNA in basal cells
Are basal cells STEM cells?
YES
Vitiligo
Melanocytes are attacked by the immune system
Autoimmune disease
Albinism
Genetic partial loss of pigment production
Missing enzymes in enzymatic cascade
Nelson’s syndrome
Melanin stimulating hormone (MSH) is produced in excess by the pituitary gland
Hyperpigmentation of the skin
What is MSH
Melanin stimulating hormone
Malignant melanoma
Tumour of the melanocyte cell line
Langerhans cells
- origin
- where found
- function
Origin - bone marrow
Found in prickle cell layer and dermis and lymph noes
Skin immune system
- antigen presenting cells
- pick up antigen in skin and circulate to lymph nodes via lymphatics
Langerhans cells are the outermost line of…
detecting cells
human burglar alarm
Racket organelle/ Birbeck granules***
Specific to langerhans cells
No one knows what they do.
Merkel cells
Basal membrane
Between keratinocytes and nerve fibres
Mechanoreceptors
Cushion-like –> provide touch sensation
Merkel Cell cancer
- cause
- mortality
Rare
VIRAL infection - merkel cell polyomavirus
High mortality
Hair follicles/ Pilosebaceous Unit
Epidermal component + dermal papilla
Specialised keratins
Adjacent sebaceous gland
Hair pigmentation via melanocytes above dermal papilla
The hair follicle is an invagination of epidermal tissue.
The papilla is dermal.
What do SEBACEOUS glands secrete?
Sebum
Lubricates the hair follicle
Hair follicles - stages of growth
There are 3 stages
Anagen = growing (3-7 yrs)
Catagen = involuting (preparing for resting phase) (3-4 wks)
Telogen = resting (each day)
Regional variations in growth patterns
Hormonal influences e.g. thyroxine, androgens
Types of hair follicle (3)
Lanugo (in utero)
Vellus
Terminal
Why can some of your come out when you put your hand through your hair?
Some of your hair is in Telogen phase (shedding)
Telogen effluvium
When many hairs enter cycle at the same time – therefore hairs will enter telogen phase at the same time and will fall out
Most common cause of hair loss
Where does pigmentation of a hair occur?
In the hair matrix
Hypertrichosis
Too much hair at androgen receptor controlled regions - chin/chest
Female patient
Alopecia areata
Autoimune hair loss
How a nail is formed (basic, expand later)
Stem cells differentiate and become flat
filled with keratin
cross link - forming the nail
Nails are sensitive to
Chemical or mechanical trauma
Normal nail that becomes thick and crumbly in one area …
Tells you that patient has had a trauma on the nail matrix which has led to stem cells losing ability to differentiate properly
Subungual mole
Under the nail
sharp brown line
What occurs in Bullous Pemphigoid
Autoantibodies are attacking the hemidesmosomes within the skin.
Requirements for healthy skin
Intact epidermis - protective barrier Keratin Good blood supply Melanocytes Langerhans cells Need the keratin to slough off properly Moisture Vitamin D Functioning immune system
What are the 3 stages of wound healing
- Inflammation
- Proliferation
- Tissue remodelling
What is Primary intention wound healing?
Healthy edges are brought together by sutures
Surgical
e.g. suturing, skin grafts
What is Secondary intention wound healing?
Wound is left to heal on its own
What is a CHRONIC wound?
A wound that hasn’t healed within 3 months
What factors must be considered in the assessment of a chronic wound?
- Infection
- Poor arterial blood supply
- Poor nutrition/ nutrition status
- Impaired venous return
- Repeated trauma/pressure
- Systemic disease present – diabetes?
How could pressure sores be prevented?
Moving about regularly
Physiotherapy
Clean sheets
Special mattress
What is the Dermal-Epidermal junction?
What is its role?
Interface between the epidermis and the dermis
Key role in epithelial-mesenchymal interactions//
- support, anchorage, adhesion, growth and differentiation of basal cells.
- Semi-permeable membrane acting as barrier and filter
What kind of membrane is the derma-epidermal junction?
Semi-permeable membrane.
What layers does the Dermo-epidermal junction consist of?
Lamina lucida
Lamina densa
Sub-lamina densa zone
Proteins that link and hook together
What occurs in bullous pemphigoid?
An autoantibody attacks the proteins in the DEJ
Skin slips and breaks up –> blistering and itching
Among whom is bullous pemphigoid common?
Stroke and parkinson’s patients.
Epidermolysis Bullosa is….
- type of condition
- presentation
- seriousness
Inherited genetic condition.
Fragile skin
Friction sites slough and sheath off
Constant sloughing of skin causes some skin to merge together - leading to loss of features on the fingers.
Can be deadly in children/young babies.
What does the dermis contain?
mainly fibroblasts, macrophages, mast cells, lymphocytes, Langerhans cells
collagen, elastin
Muscles, blood vessels, lymphatics, nerves
What do fibroblasts manufacture?
Collagen
What is the majority of the dermis composed of?
Collagen
What occurs in photo aging?
is elastin involved( will add later)
Collagen have broken down
Saggier, more wrinkled
Leathery skin
Where are the larger blood vessels in the skin located?
In subcutaneous fat
Angioma
Overgrowth of blood vessel structure
Can dilate and can bleed
Type of angioma in babies?
Strawberry nevi
What is dermographism?
Dermographism is an exaggerated wealing tendency when the skin is stroked. Physical urticaria
i.e. you can “draw” on the skin with very little effort.
Skin lymphatics
What is circulating?
Are vessels contractile?
Sub-epidermal
Small non-contractile vessels -> larger contractile vessels
Continual drainage of extra fluuid, extravasated cells, debris, foreign bodies
Circulating lymphocytes and langerhans cells
Channeling of micro organisms and toxins
Chronic lymphoedema
Lots of swelling
Skin thickens
COBBLESTONING
SCALING
Skin breakdown
Nerves of the Skin
- Somatic Sensory (dermatomes)
a) Free nerve endings
b) Special receptors:
i) Pacinian (pressure) corpuscles
ii) Meissners (vibration) corpuscles
2. Autonomic Nerve supply
- blood vessels
- nerves
- Glands
Where are meissners corpuscles located?
Quite high up in the dermis
Fingerpads
Where are pacinian corpuscles located?
In the subcutaneous fat (?)
They look like the cross section of an onion under the microscope.
Neurofibromatosis
Overgrowth of the nerve endings
Can become cancerous
Soft to the touch/ squidgy
Hirsutism
Male hair growth patterns on a female.
e.g. on the chin and face
Sebaceous Glands
Function
Holocrine secretion opening into pilar canal
Largest glands on the face and chest
Hormone sensitive
- quiescent pre-puberty
Control moisture loss
Protection from fungal infection
What is Sebum composed of?
Composed of : squalene, wax esters, Triglycerides and Free Fatty Acids
Main functions of the skin
Barrier function Metabolism & detoxification Thermoregulation Immune defence Communication Sensory functions
Toxic epidermal necrolysis
Acute skin failure
Failure of the barrier function leads to…
Fluid loss –> dehydration
Protein loss -> hypoalbuminaemia
Infection
Dermatitis
Ulcers
Failure of Thermoregulation
Heat loss –> Hypothermia
Immune defence failure
Spread of infection
Metabolic failure
Disordered thyroxine metabolism
Sensation failure
Pain sensation working -> pain
Skin communication failure
Inability to display healthy skin –> stigma
What temperatures are good for patients whose thermoregulation has failed?
Warmer rooms.
Less heat loss to the environment.
Barrier function
Physical
Chemical
Pathogens
Two way barrier
Physical barrier //
- friction, mechanical trauma
- UV radiation
Chemical//
- irritants, allergens and toxins
Pathogens//
- bacteria, viruse, fungi
Steroid -sulphatase deficiency X linked ichthyosis
Fish scales
Lack of formation of lipids in the dermiss
Cholesterol is produced properly but cannot be broken down into the lipids required for epidermal barrier to function properly
Function of melanin?
It absorbs UV rays to protect DNA in the cells’ nuclei
What metabolic processes go on in the skin?
Vitamin d metabolism
Thyroid hormone metabolism
Defence against chemicals, drugs, pollutants and sunlight
Which wavelengths of light are needed for vitamin D formation?
290-320nm UV (i.e. UVB)
Cholecalciferol –> VitaminD3
Where does thyroid hormone metabolism take place?
20% in thyroid glands
80% peripherally including skin
Thyroxine (T4) –> Triiodothyronine (T3)
Thermoregulation
- function
Protects against being too hot or cold
Warm/cold-sensitive thermoreceptorrs
- behavioural changes
- control sweating/shivering/ blood supply
Immune defence is important in…
cells important i the skin
Protection against infection
Sunlight responses
Allergic reactions (to chemicals/drugs)
Langerhans & T cells
Crusted scabies
severe form of scabies
thousands of scabies mites as opposed to a dozen in “normal” scabies
Chronic discoid lupus erythematosus
Autoimmune disease
Sores with inflammation and scarring favouring the face, ears, and scalp and at times on other body areas. These lesions develop as a red, inflamed patch with a scaling and crusty appearance.
