Describe the layers of the epidermis
- Germinative (basal) - single layer
- Spinous(prickle) - thickest, spinous become desosomes have mucin, also contains langerhan’s cells (immune system)
- Granular - narrow with keratohyaline, granules in cytoplasm
- dead layer - anucleate cells, dead keratinised squames, thickness depends on location and abrasion
The epidermis has no vasculature supply to relies on nutrients from the dermis
Describe the layers of the dermis
- Rich in collagen (close to surface)
- Deep fatty layer
RETE ridge separates the layers
-develops from the mesoderm, contains elastic fibres (stretch) and collagen fibres (strength)
What are the functions of the skin
Sensory organ Immune system Temp regulation Mechanical layer water proof UV protection Vit D
How does keratinised epithelium form?
The germinative layer contains keratinocytes - from stem cells
- these cells mature and move up the epithelial layer when new cells are made
- the most superficial layer of the epidermis is made up of flattened keratinising dead cells
- abrasion flakes these cells off of the skin
- the rate of cell division and thicks of this layer depends on area of the body and the amount of abrasion it experiences
What are melanocytes
Melanocytes secrete melanin, this is transferred to keratinocytes of the basal and prickle cell layers, the amount of melanin present is proportional to skin colour
What is in the spinous layer?
- Also known as the prickle layer
- Joined by desmosomes so that the skin can stretch, preventing it from splitting
- If the skin shrinks the desmosomes become obvious and the cells appear spiny
- Contains Langerhan’s cells (these have a pale cytoplasm and irregular shaped nucleus)
- Basal layer contains Merkel’s cells - these are difficult t resolve and synapse with nerve fibres at the dermis to transmit fine touch
Describe the structure of hair roots
In hairy skin the hair root originates in the epidermis and project to the dermis, the downgrowth terminates in an expanded end that becomes invaginated by a mesodermal papilla. The central cells of the downgrowth become keratinized to form a hair, which then grows outward to reach the surface
(melanocytes result in hair colour)
What do sebaceous glands produce?
Lubricating oily matter
In hairy skin is flows from hair to the skin surface oiling the hair and keratinising the skin = waterproof and stops cracking/dehydration
Describe the structure of nails
Compacted keratin
- arise from nail matrix cell under a fold of skin called the eponychium/cuticle
- The nail lengthens across the nail bed
Describe the structure of sweat glands
Eccrine sweat glands are lined by glycogen rich cells
- MOST COMMON SWEAT GLAND
- tightly coiled knot of fluid secreting cells and straight duct with simple cuboidal epithelium
- contain a duct to the surface of the skin
- the coiled section is surrounded by myoepithelium cells, this contain actin to secrete sweat
(apocrine sweat glands are found at armpits and anus) and ear wax!
What are Merkel’s cells?
- Basal layer contains Merkel’s cells - these are difficult t resolve and synapse with nerve fibres at the dermis to transmit fine touch
- Merkel cells are slowly adapting touch receptors in the basal epidermis
What do fibroblasts do?
Produce and secrete collagen - growth/repair
What do mast cells do?
Granules packed with histamine and other chemicals - these are released when the cell is disturbed (inflammation)
What do apocrine glands produce?
They accompany hair follicles in the armpits and groins
- they secrete apocrine secretions eg pheromones ( territorial marker, and warning signal)
- sensitive to adrenaline
Describe the junctions and adhesion molecules of the dermis and epidermis
Dermis = anchoring fibrils Epidermis = anchoring filaments of hermidesmosomes link cells together
What cells anchor cells together
Desomsomes and conea desmosomes
- this means that the skin is impervious to pathogens
- lipid lamellae protects the cells lower down
Difference between adult and baby’s skin
Adult’s is much thicker - so irritants pass through baby’s skin easier - eyelids and cheeks
What are filagrins
Filagrins are proteins that bind to keratin fibres in epidermal cells
This increases the structure of the cells
When there is a loss of filagrin there is an increase in adhesion as more foreign material can pass through
How does pH affect skin?
An increase in pH encourages serine protease activity, this means that the proteins that hold the cell together in the epidermis can be digested = breaks in the skin and irritation
What is the function of serine proteases?
Digest proteins at surface of skin so they don’t get too thick
What causes red skin
Red skin is caused by inflammation and the dilation of blood vessels
What causes itchy skin
-Rash, hypersensitive skin, decreased sweating, allegens
-due to neural pathway
-itching can damage skin
(NERVE STIMULATION)
What causes dry skin
- Lack of moisture in the stratum corneum - leads to cracks due to reduction of lipids in barrier/proliferation of keratinocytes
- retention of corneocytes and reduced water holding capacity (LEAKAGE)
What causes acne
- narrowing of hair follicle
- increase in sebum production from sebaceous gland
- more sebum gets blocked and starts to stagnate since no oxygen
- causes ‘propioni bacterium acnes’ to multiply in the sebum
- this ‘propioni bacterium acnes’ causes the breakdown of triglycerides to free fatty acids
- these cause irritation, inflammation, and attracts neutrophils
- leads to pus development
