Skin Structure and function Flashcards
What are the three main functions of skin?
Protection, regulation/physiological & sensation.
What things does the skin protect from?
- Mechanical impacts
- Pressure
- Variations in temperature
- micro-organisms
- radiation/chemicals
What is the skin’s physiological role?
- body temperature regulation via sweat and hair.
- changes in peripheral circulation.
- Fluid balance via sweat
- synthesis of Vitamin D
What is the skin’ role in sensation?
- Network of nerve cells that detect and relay changes in the environment
- heat, cold, touch and pain
- reflexes
What are the three layers of the skin?
- Epidermis
- Dermis
- subcuteus or hypodermis
What does the arrector pili muscle do in the skin?
It contracts to cause the hair to stand on end to warm the body
- goosebumps
What are the name of the epithelial cells in the Epidermis that make up its layers?
Keratinocytes
What structure does the epidermis sit on?
The basement membrane
What is the role of the basement membrane?
It seperates the Epidermis from the Dermis.
What are the names of the different layers in the Epidermis and their positions?
- Stratum Basale (basal layer)
- Stratum Spinosum (2nd layer)
- Stratum Granulosum (3rd layer)
- Stratum Corneum (top layer)
What is the role of Stratum Basale?
- cuboidal/low columnar cells.
- mitotically active, constant regeneration of other layers.
- contains skin cells
What connects the Stratum Basale to the Basement membrane?
Hemidesmosomes
What is the Stratum Spinosum made up of?
- Made up of Polyhedral Keratinocytes held together by Desmosomes (strong cell junctions).
What are the Stratum Granulosum features?
- Cells become flattened
- Contain Keratohyalin granules
- start to lose nucleus and cytoplasm
What are the features of the Stratum Corneum?
- large flat plate like cells filled with keratin
- lost their nucleus
- filled with lipids between cells that provide a water barrier.
What do some parts of the skin have?
An extra layer called the Stratum Lucidum (only in thick skin)
What process are the cells in the Stratum Basale responsible for?
They differentiate upwards to replace the dead skin cells.
Skin cells are constantly dying and being replaces with a complete replacement happening within a month.
How long does it take for skin cells to migrate from the basal layer to the top of the granular layer?
arorund 14 days
How many days for the cell to cross the stratum corneum to the surface to be shed?
another 14 days
What occurs as cells travel to the surface and differentiate?
They change in the amount and type of keratin they produce.
What is keratin?
- 30 different types
- intermediate filaments that provide strong mechanical resilience to cells.
What are the features of the Dermis?
- Connective tissue: collagen type I, Elastin & ground substance.
- Fibroblasts
- immune role
- blood supply (contains BVs)
- Tensile strength (collagen fibres)
- Allows stretch (elastin Fibres)
What are the two layers of the Dermis?
- Papillary layer
2. reticular layer
What are features of the papillary layer of the dermis?
- loose
- contains very fine insulated collagen fibres.
- where most BVs are found
What are features of the reticular layer of the dermis?
- stronger collagen bundles
- more elastic fibres and larger
- contains BVs and nerves but not as much as the papillary layer.
What attaches the Dermis and Epidermis together?
Dermo-Epidermal junction
What are the functions of the Dermo-Epidermal junction?
- a regulated barrier for movement from and into Epidermis
- attachment site of Dermis and Epiderdmis
- Aligns cells of the Epidermis
- Serves as a base for wound healing through reepithelialisation.
What attach the Epidermis and Dermis together at the Dermo-Epidermal junction?
Hemidesmosomes
What is the subcutis (hypodermis) mainly composed of?
Adipose tissue
What are the functions of the Subcutis?
- Energy source
- insulation
- Shock absorption
What physiological aspects of the skin allow it to act as a sensory organ?
- Free nerve endings in the skin
- Meissner’s corpuscles
- Pacinian Corpuscles
Where are the free nerve endings in the skin?
- in the papillary dermis and form attachments with Merkel cells to act as mechanoreceptors (touch and pressure)
What are Meissner’s corpuscles and where are they?
- Rapidly acting mechanoreceptors responsible for touch
- Papillary dermis of hand and feet.
What are Pacinian Corpsucles and where are they?
- Detect deep pressure and vibration
- usually in Subcutis
What are adnexal strucutres (structures associated with) the skin?
- Hair and nails
What types of glands are found in the skin?
- Eccrine gland
- Apocrine gland
- Sebaceous gland
What are Eccrine glands and where are they found?
- These are temperature control glands -> excrete sweat
- everywhere on skin apart from nail beds, lips, external auditory canal and some parts of genetalia.
- mostly found on palms, soles, and axillae
What are Apocrine glands and where are they found?
- Scent glands. Role unclear in humans.
- found in axillae and genitals.
What are Sebaceous glands and where are they found?
- Formed from hair follicle
- everywhere except palms and soles
- greantly enlarge at puperty in response to androgens
- produces sebum (oily, waxy substance to moisturise skin).
Which cell layer increases its proliferative activity in Psoriasis as the number of epidermal cells is increased?
Stratum Basale
What are the types of cells in the Epidermis?
- Langerhans cell
- Melanocyte
- Merkel cell
- Keratinocyte
- stem cell
What is the location and function of the Keratinocyte?
Location: Keratinised Stratified Squamous Epithelium
Function: protection & barrier; Vitamin D production
What is the location and function of the stem cell?
Location: Stratum Basale
Function: self renewal and repopulation of the epidermal layers.
What is the location and function of the Merkel Cell?
Location: Epidermis (mostly basal)
Function: sensation
What is the location and function of the Langerhans cell?
Location: Epidermis (mostly Stratum Spinosum) and upper dermal layer.
Function: Dendritic cell; antigen presentation Phagocytosis. Part of immune system. long cytoplasm to detect antigens.
What is the location and function of the Melanocyte?
Location: Basal layer
Function: Protection from Radiation. UV light.
What amino acid does the melanocyte produce?
Melanin - skin pigmentation to protect from UV light.
What does chronic UV exposure lead to in humans?
- loss of skin elasticity
- abnormal pigmentation
= haemorrhage of BVs - Wrinkles
- malanoma and non melanoms skin cancers
What are melanosomes?
Organelles of pigment cells in which melanins are synthesized and stored.
How do melanosomes protect keratinocytes?
melanosomes are transferred to the keratinocytes through the melanocytes cytoplasmic processes and create a protective layer over DNA.
What are the different molecules in the Epidermis?
- Keratins
- Profilaggrin
- involucrin
- loricrin
- polysaccharides glycoproteins lipids
What are the location and function of Keratins?
Location: all epidermal layers
Function: major structural proteins; intermediate filaments
What are the location and function of Profilaggrin?
Location: Keratohyalin granules
function: converted to filaggrin which aggregates keratin filaments into tight bundles
What are the location and function of involucrin?
Location: keratohyalin granules
Function: Formation of a cell envelope around cells in the Stratum corneum
What are the location and function of Loricrin?
Location: keratohyalin granules
Function: cross-links to involucrin
What are the location and function of polysaccharides glycoproteins lipids?
Location: Lamellar granules
Function: extrude into intercellular space, form the cement that holds the stratum corneum cells.
What molecules are found in the Keratohyalin granules in the Epidermis?
- Profilaggrin
- involucrin
- loricrin
What are the names of the cells found in the Dermis?
- Fibroblast
- lymphocytes
- Dermal dendritic cells
- mast cells
What are the function of fibroblasts?
Synthesis (collagen, elastin & other extracellular matrix components)
Growth factors
What are the function of Lymphocytes?
immunosurveillance
What are the function of Dermal dendritic cells?
phagocytosis
antigen presentation
What are the function of mast cells?
Produce inflammatory mediators (histamine, heparin) & chemotactic factors for eosinophils and neutrophils
What are the types of molecules in the Dermis?
- Collagen Type I
- Elastin
- Proteoglycans
- Glycosaminoglycans
What is the role of collagen type I?
Major structural fibrous proteins
What is the role of Elastin?
Confer elasticity and recoil
What is te role of Proteoglycans and Glycosaminoglycans?
Hydration
Which cellular specialisation is found in a fibroblast?
Rough Endoplasmic Reticulum.
What change in skin accounts for the collagen content in the dermis decreasing by 1% each year in adult life?
Decrease in Fibroblasts
Which cell type is defective in albinism?
Melanocyte
What is albinism?
An autosomal recessive condition where the skin is white or pink, hair white and pigmentation is lacking in the eye.
What is a wound?
- A breakdown in the protective function of the skin
- a loss of continuity in the epitheliun with ot wirhout loss od underlying CT
- depth of injury affects ability to heal
What are the different depths of injury for a wound?
- Erosion
- ulceration
- partial thickness
- full thickness
What depth is erosion?
Only epidermis lost
What depth is ulceration?
Structures deep to epidermis.
What depth is partial thickness?
Epidermis + varying parts of dermis.
Adnexal structures act as a reservoir of epithelial cells to repopulate wound + cells from wound edge.
What depth is full thickness?
Epidermis + all of dermis + deeper structures.
wound edge only
Define wound healing.
a highly coordinated and orderly process that requires the activities of a number of different cell types, including inflammatory cells, keratinocytes, fibroblasts and endothelial cells.
What are the three overlapping phases of wound healing?
- inflammatory
- proliferative
- remodelling.
What are the features of the inflammatory phase of healing?
- 24/48 hours
- platelets intiate haemostasis/blood clot and healing cascade.
- other cells attracted to wound to fight infection and transition from inflammation to repair (neutrophils/macrophages)
- signs of inflammation
- neutrophils and macrophages phagocytose (eat) dead tissue and microorganisms.
What are the features of the proliferative phase of healing?
- Re-epithelialisation
- Within 1-2 days of wounding, epithelial cells loosen cell-cell adhesions and migrate to the wound site, cover the granulation tissue, and then meet in the middle.
- Once the wound is covered in a single layer of keratinocytes -> all keratinocytes proliferate. - Formation of granulation tissue; mainly type III collagen.
- Neovascularisation: proliferation and migration of endothelial cells. `
What is neovascularisation?
Formation of new blood vessels.
What needs to occur to close the wound?
Keratinocyte migration.
What are the 2 methods of keratinocyte migration?
- Leap frog method = leap frog over eachother
2. Train method = pull eachother along
What do fibroblasts produce to form granulation tissue?
Type III collagen.
What are the features of th remodelling phase?
- Switch in type III collagen to type I collagen
- granulation tissue becomes mature scar tissue.
- collagen is organised into thick bundles and extensively cross-linked to form a mature scar.
- final strength is only 70-80% of preinjured skin.
What do myofibroblasts do in the remodelling phase?
These are fibroblasts that develop into myofibroblasts. These contract to pull the edges of the wound together.
How do the cells involved in the healing process know what to do?
Signalling molecules released from one cell to another.
What types of signalling molecules are involved in wound healing?
- Epidermal Growth Factor (EGF)
- Platelet-derived Growth Factor (PDGF)
- Vascular Endothelial Growth Factor (VEGF)
- Interleukin-1
- Interleukin-6
- Tumour necorosis factor
What is the function of Epidermal Growth Factor (EGF) as a signalling molecule?
Re-epithelisation (Keratinocyte proliferation and migration)
What is the function of PDGF as a signalling molecule?
matrix formation (increased numbers and activity of fibroblasts) remodelling
What is the function of VEGF as a signalling molecule?
Angiogenesis (endothelial cell proliferation and migration)
What is the function of Interleukin-1, interleukin-6, tumour necrosis factor as a signalling molecule?
inflammation
What factors affect wound healing?
- infection
- forreign body
- oxygenation
- vascular supply
- age
- diseases
- alcohol & smoking
- immunocompromised conditions
- obesity
- medications
If someone has a skin abbrasion what needs replaced in the skin?
the keratinocytes.
Which part of the keratinocyte would detect an EGF signal telling it to move?
A trans-membrane protein on the plasma membrane
