Functional Anatomy and Physiology of the Skin Flashcards
Name the 4 layers of the Epidermis
Basal Layer, Granular Layer, Prickle cell layer and Keratin layer
What cell type makes up 95% of the epidermis?
Keratinocytes
What is the main proliferative compartment within the epidermis?
The basal layer
What happens at the basal layer of the epidermis?
The keratinocytes migrate from the basal layer to the top later. They differentiate, producing a variety of protein and lipid products
What is the normal time for differentiation from the basal layer to the keratin layer of the epidermis?
28 days
What are the main features of the Prickle cell layer?
Larger Polyhedral cells and lots of Desmosomes
What happens to the keratinocytes at the Granular layer of the Epidermis?
They undergo apoptosis
What are the main features of the Granular Layer?
Cell nuclei lost, 2-3 layers of flatter cells, high lipid content
What layer can you not see in psoriasis?
Granular layer
Where does terminal differentiation occur?
At the Keratin layer
How does terminal differentiation take place?
Filaggrin aggregates keratin filaments and causes terminal differentiation
What are the features of the keratin layer of the Epidermis?
Flattened corneocytes with no nucleus and overlapping cells which creates a tight waterproof barrier
What is psoriasis?
Ongoing, non stop phase of a wound reaction, increased production of skin cells
What is the difference in time for normal differentiation and psoriasis?
Normal: 28 days
Psoriasis: 4-5 days
How does intraepidermal blisters arise?
Lots of hydrostatic water pushes apart the desmosomes within the Prickle cell layer, forming a huge dome
How is the regulation of epidermal turnover controlled?
By growth factors, cell death and hormones
or Loss in control in: skin cancer and psoriasis
What are the skin appendages?
Nails, hair, mucosae, glands
Name 3 other major types of cell within the epidermal layer
Melanocytes, Langerhans cells, Merkel cells
What happens at the melanocytes?
The Melanin pigment is synthesised from Tyrosine–> Melanin absorbs light–> Full Melanocomes are transferred to adjacent keratinocytes via dendrites
Name two of the melanin pigments in the Melanocytes
Euchelanin (brown or black)
Phaeomelanin (red or yellow)
What is the function of melanin caps?
To protect the nuclear DNA in the basal cells
What is the role of the Langerhans cells in the Epidermal layer?
They are involved in the skin immune system, in the antigen presentation to lymphocytes
They circulate between the epidermis and the lymph nodes
What are Birbeck granules?
Organelles within the Langerhans cells with an unknown function
Where are Langerhans cells found in the epidermis?
Dispersed at the prickel cell level, very densely packed together
What are Merkel cells?
Mechanoreceptors which are found in the basal layer
What happens to Merkel cells in diabetes patients?
Merkel cells are myelinated–>
Diabetes affects the myelin sheaths, glucose disrupts the protein arrangement and the sheath no longer conducts–>
This causes paraethesia or itchiness
What can affect the Merkel cells?
A specific viral infection which has a high mortality rate
Where are the Merkel cells?
In the basal layer
What is Vitiligo?
An autoimmune disease with loss of melanocytes
- “white spot disease:
- constant and active loss of melanocytes
What is Albinism?
Genetic partial loss of pigment production
What is Nelson’s syndrome?
Melanin stimulating hormone is produced in excess by the pituitary
What is Virilisation?
Excess hair on women (facial hair etc) due to excess androgen from a tumour
What is Alopecia Areata?
An autoimmune condition which caused hair loss. Can be triggered by massive psychosocial stress such as bereavement or pregnancy
What can you look at as a sign of internal inflammation?
Nails
During the hair cycle what do these phases refer to, and for how long dot they last?:
- Anagen
- Catagen
- Telogen
- Anagen: growing (years)
- Catagen: transitional (a few days)
- Telogen: resting phase (3 months)
What is the difference between lanugo hair and vellum hair?
Lanugo: newborns and non pigmented
Vellus: similar to lanugo but pigmented
Why do we have lots of hair?
To reduce the need to have melanin and melanocytes
What are the three layers of the Dermo-epidermal junction?
- Lamina lucida
- Lamina densa
- Sublamina densa
What are some of the components of the dermis?
- 75% collagen
- 1% elastin
- mast cells, langerhans, blood vessels, lymphatics, ground substance, T lymphocytes
What is the function of the basement membrane?
allows the movement of cells and nutrients between the dermis and epidermis
How are the cell membrane of the epidermal basal cell and the basement membrane attached?
By hemi-desmosomes
What is present at the DEJ?
Proteins, fibrils and keratins
What happens to the DEJ during old age?
Becomes flatter
-wrinkles are caused by tired elastic
What does smoking and UV do to the DEJ?
depletes the collagen
What happens in inherited diseases of the DEJ?
Skin fragility due to a mutation in one of the proteins
Give examples of inherited diseases of the DEJ
Epidermolysis bullosa simplex or dystrophic
Give an examples of an acquired disease of the DEJ
Bullous Permohigoid
- Type 2 hypersenstivity reaction
- formation of anti-hemidesmosome antibodies
- treated with steroids
What is Meissner’s corpuscle?
- Dermis nerves
- Touch receptors in the fingertips
What is Pacinian Corposcle?
- Dermis nerves
- Pressure receptors
What can chronic lymphoedema be seen as?
“Elephantism”
What is the function of the lymphatic vessels of the dermis?
Continual drainage of plasma proteins, extravasated cells and excess interstitial fluid
What are the three main skin glands in the dermis?
- Sebaceous
- Eccrine
- Apocrine
What do Eccine glands do?
- Whole body sweat glands
- None in groin and mouth
- Cools by evaporation
What do Apocrine glands do?
- In axillary and groin
- Produce oily fluid
- Odour
What do Sebaceous glands do?
- Produces sebum
- Activated during puberty
- Moisture control
- Opens onto hair follicle
- High concentration on face and back
Name the main functions of the skin
Barrier function, metabolism and detoxification, thermoregulation, immune defence, communication, sensory functions
What is Toxic Epidermal Necrolysis?
Acute skin failure, usually caused by a reaction to drugs
-rare and life threatening
What is erthyroderma?
Another type of acute skin failure, red skin all over 80-90% of the body
- skin peeling off in layers
- can be due to a number of conditions such as dermatitis, psoriasis and T cell lymphoma
How can statins cause dry skin?
- Lowers cholesterol
- skin is made up of “brick and mortar” with brick being keratin and mortar cholesterol
In dermatitis, if the skin between the fingertips is affected what is it more likely to be?
Irritancy
What is the function of melanocytes?
Absorb UV rays
How is vitamin D3 produced?
By photosynthesis
How is vitamin D stored and converted?
D3 is stored as hydroxycholecalciferol in liver
This is converted to 1,25-dihydroxycholecaliferol in the kidney
What vitamin do kidney failure patients need?
Vitamin D
Where is T4 metabolised to T3?
- 20% conversion occurs in thyroid gland
- 80% conversion in the peripheral tissues including skin
What is more abundant T3 or T4?
T4 is more abundant but less active
What happens when body temperature decreases?
Blood flows from the superficial plexus
What is Hansen’s disease?
TB Leprosy
Granuloma formation around peripheral nerves, causing damage due to immune response
Name some autoimmune diseases
Eczema herpeticum, chronic discoid lupus erythmatous, squamous cell carcinoma
How does the epidermis form in embryology?
- Ectoderm cells form single layer periderm
- There is a gradual increase in layer of cells
- Periderm casts off
How does the dermis form in embryology?
Formed from mesoderm below ectoderm
How does the melanocytes form in embryology?
Pigment producing cells from the neural crest
What does the foetal skin look like at 4 weeks?
Periderm, Basal layer and dermis
What happens in the foetal skin at 16 weeks?
Melanocytes migrate from neural crest
What are Blascho’s lines?
Developmental growth pattern of skin which doesn’t follow vessels or lymphatics
