10. Skin Flashcards
What are the 8 functions of skin?
Protection against injury Protection against pathogenic organisms Waterproofing and fluid conservation Thermoregulation Protection against radiation, absorption of ultra violet radiation and vitamin D production Surface for grip Sensory organ Cosmetic
Describe the structure of skin
Stratum cornea Epidermis Papillary dermis Reticular dermis Hypodermis
Appendageal structures
Pilo-sebaceous unit (follicle, hair shaft, sebaceous gland and pilo erecti muscle) Sweat glands (apocrine and eccrine).
Describe the structure of the epidermis
Consists of keratinocytes arranged in 4 layers
What are the 4 layers of the epidermis?
Stratum basale
Stratum spinosum
Stratum granulosum (cells have keratin granules)
Stratus corneum (cells have no nucleus)
Name 3 cell types found in the epidermis and their functions
Melanocytes: produce melanin
Langerhans cells: antigen presenting cells
Merkel cells: sensation
What is the main purpose of the epidermis and what forms this?
Barrier
Much of the barrier is formed by Keratin
What happens as a keratinocyte progresses up through the epidermis?
It transforms at stratum granulosum into a nonviable corneocyte before being shed in the normal epidermal turnover process
Structure of stratum corneum
Corneocytes/keratinocytes produce layers of skin, stuck together by lipids to create a seal
Protective
No nucleus as dead
What is the result of a mutation in filagrin gene?
“Glue” between corneocytes in epidermis is not normal
Leads to eczema
Palmar hyper-linearity is a sign
What are the dendritic cells within the epidermis?
Langerhans
Melanocytes
Where are melanocytes found?
Basement membrane of epidermis
In which organelle is the pigment melanin produced?
Melanosomes
How are melanosomes packaged?
Into granules which move down dendritic processes and are transferred by phagocytosis to adjacent keratinocytes
What do melanin granules do?
Form a protective cap around the keratinocyte nuclei
Protect DNA within nucleus from UV induced damage and lead to skin pigmentation
What stimulates melanocytes to produce more melanin?
UV radiation (mainly within 290-320 nm spectrum)
What causes variation in racial pigmentation?
Number and size of melanosomes produced
What is Vitamin D deficiency in children called?
Rickets
When is Vitamin D produced in skin?
After sun exposure
What may rickets lead to?
Problems with immune system
Predisposition to certain cancers
What is Vitamin D deficiency in adults called?
Osteomalacia
What is the basement membrane zone?
Region where epidermis is attached to dermis via semi-desmosomes, anchoring plaques and a multitude of proteins
What happens if there is a mutation in a protein in the basement membrane zone?
Layers aren’t connected properly
Gives rise to blisters
Epidermolysis bullosa (Bullous Pemphigoid)
What does the dermis contain?
Collagen Elastin Glycosaminoglycans (GAGs) Fibroblasts Immune cells
What is the function of fibroblasts in the dermis?
To synthesise:
Collagen
Elastin
Glycosaminoglycans
Give examples proving variation in thickness of dermis
0.1mm Eyelids
3mm Back
What does the subcutaneous layer consist of?
Connective tissue
Fat
How is a body temperature of 36.8 maintained?
Regulation of skin blood flow
Sweating
Shivering
Behaviour
Discuss regulation of skin blood flow
Skin temp responsive to blood flow (vasoconstriction and vasodilation)
1 – 100ml / min per 100g skin
Under sympathetic control
Discuss sweating
Cools skin through evaporation
Minimum 0.5L per day
Max 10L per day
Produced by eccrine and apocrine sweat glands
2 types of sweat glands
Eccrine = all over body, salty sweat Apocrine = under hair follicle, viscous sweat can be metabolised by bacteria
Embryology of epidermis, dermis and melanocytes
Epidermis = ectoderm Dermis = mesoderm Melanocytes = neural crest
