Name a disease manifestation of each of the macroscopic features of the skin and how the variations can effect manifestations
- Colour-> Vitiligo-> autoimmune depigmentation-> bigger psychosocial effect in dark-skinned races
- Hair-> Alopecia areata-> autoimmune hair loss-> bigger psychosocial effect depending on site, particularly in women
- UV abnormalities-> increases skin ageing in whites. Increases risk of skin cancer in whites
What are the macroscopic features of skin and how do they vary?
- Colour-> Ethnicity, Site, UV
- Hair-> site, age, sex
- Laxity/wrinkling ->age, site, UV
What are the two microscopic structures of the skin?
- Epidermis
- Dermis
Is the epidermis vascular or avascular?
-Avascular
What are the 4 layers of the epidermis in order from apical to basolateral?
- Stratum corneum
- Stratum granulosum
- Stratum spinosum
- Stratum basale
Name the cells and their features in the stratum corneum
- Keratinised stratified corneocytes
- No nucleus or cytoplasmic organelles
- No plasma membrane as the cells are interlocked with each other
Where is the stratum granulosum?
-Directly below the stratum corneum
How do the cells in the stratum granulosum differ from those in the stratum corneum?
- Known as keratinocytes
- Keratinised stratified squamous
- Retain the nucleus
- Cells loose pm here and begin differentiating into corneocytes
Where is stratum spinosum?
-Below stratum granulosum, just above the protrusions into the dermis
How do the cells in the stratum spinosum differ from those in the stratum granulosum?
- Cells are less squamous in shape
- Not as deeply stained as they contain less keratin
- Cells are joined by intercellular junctions called desmosomes
Where is the stratum basale?
-Base of the epidermis (protrudes into dermis)
Are the cells in the stratum basale keratinised?
-Yes but only with a few keratin filaments
Where does mitotic division occur in the epidermis?
-Stratum basale
When do keratinocytes loose their ability to divide?
-As they enter the stratum spinosum
Where are keratohyalin granules found and what is there function?
- Stratum granulosum
- Contain aggregations of keratins, fibrous proteins and enzymes do degrade the pm and cross-link keratins
Name another two cell types, bar keratinocytes and corneocytes, found in the epidermis
- Melanocytes
- Langerhan cells
Where specifically are langerhan cells found and what is their function?
- Stratum spinosum
- Antigen presenting cells
Where specifically are melanocytes found?
-At intervals along the stratum basale
What do melanocytes produce and what happens to this substance?
- Melanin
- Buds off and taken up into cells, then aggregates on/around the nucleus
What s particular about the epidermis of the palm/sole?
- No hair follicles
- Thick corneum and spinosum
What is the dermo-epithelial junction?
-The point between the dermis and the epidermis
Does the epidermis have a basement membrane?
-Yes, it is just visible with H and E (better with PAS)
What clinical relevance does the dermo-epidermal junction have?
-Malignant melanomas which do not cross this junction are accosiated with good prognosis
Is the dermis vascular or avascular?
-Vascular
What structures does the dermis contain?
- Connective tissue
- Blood vessels
- Nerves
- Glands
- Muscles
- Mast cells
What functional relevance do mast cells being located near blood vessels have?
-Release of histamines increases vascular permeability leading to oedema
What fibres does the dermis contain?
- Collagen
- Elastic
Where are the fibres located in the dermis?
-Scattered throughout in the ECM
What are the two areas of the dermis?
- Papillary
- Reticular
What are the blood vessels like in the two layers of the dermis?
- Papillary-> small
- Reticular-> large
What lies directly below the dermis?
-Subcutaneous layer of fat lobules
What are the four functions of the skin?
- Protective barrier
- Sensory
- Thermoregulation
- Psychosexual communication
How does the skin act as a barrier?
-Prevents percutaneous absorption of exogenous substances
What pharmological relevance does the barrier function of the skin have?
-barrier function must be overcome by percutaneous drugs
How does the skin allow sensation?
-Has many nerve endings
By what two mechanisms does the skin help thermoregulation?
- Vascular-> dilation/contraction of blood vessels
- Eccine sweating-> evaporation of sweat aids cooling
How does the skin allow psychosexual communication?
-Can be manipulated for expression and communication
Name 4 skin appendages
- Hair follicles
- Nails
- Sweat glands
- Sebaceous glands
What makes up a pilosebaceous unit?
- Hair sheath/shaft
- Sebaceous gland
- Arrector pili muscle attached to hair sheath
Where are pilosebaceous units located?
-Predominantly in the dermis with the hair shaft extending into the epidermis
Where to, and what do sebaceous glands secrete into?
- Sebum
- Into ducts which lead to hair follicles
Where are sebaceous glands most abundant?
-Face
How are sebaceous glands linked to acne?
-Sebaceous glands become blocked with sebum due to abnormal differentiation of sebaceous ducts, increased sebum production and infection with normally harmless bacteria
What are the two types of sweat gland?
- Eccrine
- Apocrine
What is the mechanism of secretion of sweat glands?
- Serous apocrine secretions in apocrine
- Serous merocrine secretions in eccrine
Where are sweat glands located in the skin?
-Extend from the dermis to the epidermis
What structure do sweat glands often have?
-Coiled
What condition is characterised by increased sweating, and what areas are usually effected?
-Hyperhidrosis-> predominantly effects palms/soles
Where are apocrine glands located?
- Axilla
- Genital
- Submammary
What causes body odour?
-Secretions from apocrine glands are odourless and protein rich. Digestion of this by subcutaneous flora produces body odour
Name a disease which disrupts the barrier function of the skin
-Psoriasis
What are the consequences of disruption to the barrier function in psoriasis?
- Loss of fluid
- Loss of protein
- Loss of heat
- Potential for excessive absorption of exogenous substances
Why can erythrodermic psoriasis lead to hypothermia?
-Widespread vasodilation due to inability to vasoconstrict in cold environments leads to hypothermia
What is vitiligo?
- An autoimmune disease in which the immune system attacks the melanocytes, usually in symmetrical localised areas of the skin causing depigmentation
- Increased death of melanocytes
- Damage to melanocytes resulting in inability to function
- Symmetry possible under neural control as melanocytes are derived from neural crests
What cells are effected in malignant melanoma?
-Melanocytes or melanocyte-derived cells
