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?
Is the epidermis vascular or 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?
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
- 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?
- 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?
What structures does the dermis contain?
- Connective tissue
- Blood vessels
- 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?
Where are the fibres located in the dermis?
-Scattered throughout in the ECM
What are the two areas of the dermis?
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
- 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
- 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?
- Into ducts which lead to hair follicles
Where are sebaceous glands most abundant?
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?
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?
What condition is characterised by increased sweating, and what areas are usually effected?
-Hyperhidrosis-> predominantly effects palms/soles
Where are apocrine glands located?
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
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