Name the three layers in skin.
Epidermis (100-150microm), dermis and sub-cutis.
From what does the epidermis develop?
Ectoderm
From what does the dermis develop?
Mesoderm
What cells are found in the epidermis?
Stratified squamous epithelium: Keratinocytes Melanocytes Langerhans cells Nerves
What are the four layers in the epidermis.
Basal layer
Prickle cell layer
Granular layer
Keratin layer
How long does it take a cell to migrate from top to bottom?
~28 days
Describe the basal layer
Once cell thick, skin stem cells, small and cuboidal, lots of intermediate filaments and highly metabolically active.
Describe the prickle cell layer
Large polyhedral cells that don’t touch each other but with lots of desmosomes to move them. Differing thickness throughout layer.
Describe the granular layer
2-3 layers of flattened cells that produce proteins such as filaggrin and involucrin. They shrink in size and lose their nucli. Have a high lipid content.
Describe the keratin layer
Consists of corneocytes (overlapping cell remnants full of keratin and filaggrin) to form an insoluble cornified envelope. Intracellular space filled with lipids for waterproofing.
What role does the filaggrin protein play?
Chopped up to AA which bind H2O to hydrate skin.
Where does skin end?
Where mucosal membranes begin.
What are skin appendages?
Additional non-keratinocyte things that are added into skin.
Give examples of skin appendages.
Hair, nails, melanocytes, Langerhans cells, neuronal cells.
Where do melanocytes originate from and where are they found?
Neural crest and found in basal and prickle cell layers.
What do melanocytes do?
Convert tyrosine to melanin pigment to protect from UV radiation.
What are the two kinds of melanin produced?
Eumelanin- Brown or black
Phaeomelanin- Red or yellow
Once produced what happens to melanin?
Transferred to keratinocytes in melanosomes to form a protective cap over nucli.
Where do Langerhans cells originate from and where are they found?
Mesenchymal cells (bone) and found in prickle cell layer, dermis and lymph nodes.
What do Langerhans cells do?
Detect infection upon which they migrate to the lymph system and present the antigens to immune system. Antigen Presenting Cells.
What is found in Langerhans cells?
Birbeck granules (look like tennis rackets).
What is a pilosebaceous unit?
Hair and sebaceous gland.
What are the three phases of hair growth and how long do they last for?
Anagen- growth. 3-7 years
Catagen- involuting. 3-4 weeks
Telogen- resting/falling out. 50-100 fall out a day.
What can affect hair growth rates?
Hormones such as androgen increase it.
Autoimmune attack can cause alopecia.
How do nails differ from normal skin?
Instead of forming a prickle cell layer cells form a huge layer of keratin.
Where does nail grow from?
Nail matrix and bed.
What is the role of the cuticle?
To prevent infection.
What is the lunula?
The part of the nail matrix visible under the nail.
What is the dermo-epidermal junction?
The interface between dermis and epidermis.
What are the three layers of the dermo-epidermal junction?
Lamina lucida
Lamina densa
Sub-lamina densa zone
What is the dermis made up of?
Ground substance
Fibroblasts, macrophages, mast cells, lymphocytes, Langerhans cells.
Collagen and elastin
Muscles, blood vessels, lymphatics and nerves.
List three factors that can decrease elastic fibres?
Age, smoking and UV light.
Why is the blood supply far greater than its metabolic needs?
For thermal regulation.
List three ways in which the skin can regulate heat.
Radiation
Evaporation
Behavioural changes
What kind of structures do small lymphatic vessels form?
Mesh
Describe the flow of lymphatic vessels.
Along the same route as blood vessels.
What are the two nerve types found in the skin?
Somatic sensory (give rise to dermatomes) Autonomic (supply blood vessels etc)
What do Pacinian corpuscles sense?
Pressure
What do Meissners corpuscles sense?
Vibration
What are the three kinds of gland found in the skin?
Apocrine
Eccrine
Sebaceous
Describe sebaceous glands
Found in face and chest.
Very hormone sensitive therefore active in puberty.
Produce sebum to protect from fungal infection and control water loss.
Acne occurs here.
Describe apocrine glands
Part of the pilosebaceous unit and produce an oily fluid. Function unclear.
Found in axillae and perineum.
Regulated by androgen.
Describe eccrine sweat glands
Found all over skin.
Supplied by sympathetic nerves.
Cool down the body by evaporation.
List the functions of the skin (6 points)
Barrier Met and detox Thermoreg Immune defence Comms Sensory
What happens if the physical barrier is breached?
Infection
Water loss
Protein loss
List two things the skin is involved in metabolising.
VD and thyroid hormone
What can the skin detoxify?
Chemicals, drugs and pollutants.
What are the major cells involved in the skins immune response?
Langerhans, T cells, mast cells and macrophages.
Is the skin an innate or adaptive immune response?
Innate
List a number of ways that the skin can be used in communication.
Visual such as flushing, pigmentation etc
Odour
Pheromones.
What can the skin sense?
Touch, vibration and pressure.
Pain and itch
Temperature