PBL 1 Flashcards
What are the three layers of skin?
Epidermis, Dermis, Subcutis
Where are the epidermal cells found?
On top of the dermis and subcutis
What is the thin layer of extracellular proteins on the bottom called?
Basement membrane
What comes after the Basement membrane?
Stratum basale
What is the stratum basale?
a thin layer of mitotically active cells
What type of junction connects the stratum basale to the basement membrane?
Hemidesmosomes
What are hemidesmosomes (desmosomes)?
strong junctions
What comes on top of the stratum basale?
stratum spinosum
What is the stratum spinosum?
A layer of keratinocytes
What are keratinocytes?
keratin producing cells
what are the functions of keratin?
Waterproofing skin
What holds the stratum spinosum (keratinocytes) together?
Desmosomes
what is on top of the stratum spinosum?
Stratum granulosum
What happens in the stratum granulosum?
Cells become flattened and are starting to lose nuclei and cytoplasm
What is the top layer of the epidermis?
Stratum corneum
What is the stratum corneum?
Large plate - like envelopes filled with keratin and are all linked together. It also contains some lipids
What are the layers of the epidermis?
Basement membrane, Stratum basale, Stratum spinosum, Stratum granulosum and the Stratum corneum.
what happens as cells move up the epidermis?
They become keratinised and begin to die as they can’t get enough nutrients
Is the epidermis vascular or avascular?
Avascular
How many layers of keratin are there?
20-30 layers
How does the epidermis get its nutrients?
Supplied by the dermis
What are the layers of the dermis?
The papillary and the reticular layer
Where is the papillary layer?
The upper portion of the epidermis
What is in the papillary layer?
Connective tissue
What is connective tissue?
Tissue that connects, supports, binds or separates other tissues or organs
Where is the reticular layer found?
The lower portion of the dermis
What is the reticular layer made of?
Highly dense connective tissue
What is the connective tissue in the reticular layer made up of?
Collagen type 1 and elastin fibers
What property does collagen give the skin?
Strength
What property does elastin give the skin?
Stretchiness
What are some additional feature of the dermis?
Blood vessels, Glands, Hair follicles, receptors and muscles.
Where is the subcutis?
Below the dermis and the epidermis. It is the lowest layer of the skin.
What does the subcutis contain?
Cells such as macrophages and fat cells and a network of protein fibers.
What are some functions of skin?
Protection - the skin forms a barrier
Thermoregulation - 80% of body heat is lost through the skin
Cutaneous sensation - including touch and pressure
Excretion - metabolic waste products can be released in the sweat
Absorption - lipid - soluble substances enter the body via the skin
Vit. D synthesis - starts in the skin triggered by uv light
Where are keratinocytes found?
In the epidermis - Aprox. 90% of epidermal cells are keratinocytes
What is keratin?
A tough fibrous protein
What else (apart from keratin) do keratinocytes produce?
Lamellar granules
What is the function of Lamellar granules?
To help waterproof the skin
Where are melanocytes found?
In the epidermis - Aprox. 8% of epidermal cells are melanocytes
What do melanocytes produce?
Melanin granules
What is the function of melanin?
To absorb UV radiation so protects the skin from sun damage
It is also partly responsible for skin colour
What are Langerhans cells?
They are part of the immune system that originate in the bone marrow and move to the epidermis
What are the functions of Langerhans cells?
To recognise foreign microbes and engulf them.
They can then present antigens to the immune system for further action.
Where are merkel cells found?
At the border of the epidermis
What feature do merkel cells possess?
Small dendrites that pass in between nearby keratinocytes
What is each merkel cell associated with?
A nerve ending called a merkel disc.
What does the combination of the merkel disc and the merkel cell function as?
A slow adapting touch receptor
What are the functions of fibroblasts?
To synthesise collagen, elastin and other extracellular components.
They also play a critical role in wound healing as a connective tissue.
Where can most of the lymphocytes in the skin be found?
The dermis
What are the functions of the lymphocytes?
Part of the immune response
Carry out immuno-surveillance
What are the functions of mast cells?
Producing substances that cause inflammation e.g. histamine
How often does the skin renew?
Every 24hrs the skin sheds a layer of dead cells with the skin renewing completely every 28 days
How does renewal of the skin benefit the immune system?
It removes any potentially harmful pathogens from the surface of the skin
What happens as epidermal skin cells move up towards the surface of the epidermis?
They become keratinised - becoming flatter and gradually losing their nucleus and cytoplasm. They eventually die
What is another reason for the death of cells as they move towards the surface?
There is a lack of nutrients and oxygen they receive as they get higher up since the epidermis is receiving its nutrients from the dermis
What are the three overlapping stages of wound healing?
Inflammatory, proliferative, and remodelling
How are clots formed?
Fibrin and platelets combine to seal the wound from the external environment
What is the formation of the clot known as?
Haemostasis
What is inflammation triggered by?
The changes in microvasculature.
when does inflammation resolve?
after the neutrophils have finished clearing out the dead tissue
What are the main purposes of inflammation?
- expel any foreign bodies
- isolate the damaged area
- mobilise cells and molecules
- promote healing and tissue repair
What happens during the proliferative phase?
A lot of cell proliferation and the movement of epithelial cells to the injury site
How do fibroblasts move to the injury site?
Along fibrin threads
How do the fibroblasts contribute to clotting?
They secrete collagen which strengthens the clot
What is granulation tissue?
Delicate tissue that grows under the scab
How is the collagen deposited?
In a random arrangement
What is the change in type of collagen in the remodelling phase?
Type 3 to Type 1
What happens when the collagen changes?
The granulation tissue becomes scar tissue
What does the amount of scarring depend on?
The severity/depth of the wound.
Does scar tissue or normal tissue have more collagen fibers?
Scar tissue
Does scar tissue or normal tissue have reduced elasticity/stretchiness?
Scar tissue
Why are scars sometimes a lighter colour than normal tissue?
The way blood vessels arrange themselves
What is an incised wound?
Caused by a clean cut from a sharp edged object.
What treatment is required for an incised wound?
If the wound is deep, stitches may be required.
They may be healed by primary intention as there is usually little or no tissue loss
What is a laceration?
These wounds occur when there is a blunt/ripping force
They may bleed less but there is likely to be more tissue damage
It is also more susceptible to infection due to the increased surface area
What treatment is required for an laceration?
These wounds require a lot of cleaning.
Even if they are repaired very neatly by primary intention they often leave a lot of scarring
What is an abrasion (graze)?
A superficial wound in which the topmost layers of skin are scraped off. They can often contain lots of foreign particles meaning a high risk of infection
What is a contusion (bruise)?
A blunt blow can cause the rupture of capillaries below the skin
What is a puncture wound?
A deep wound with a small entry site
How should a puncture wound be treated?
It’s often best to leave this type of wound open so that if there is any infection the wound can drain.
What is healing by primary intention?
- A clean, uninfected wound
- not much loss of tissue/cells
- The edges of the wound are approximated by sutures
What is healing by secondary intention?
- a wound with large tissue defects
- potentially infected
- the wound would not be approximated but is left open
At what age is a young person presumed to have capacity?
16
What are the laws in Scotland for 16/17 year olds who do not have capacity?
They are treated as an adult who doesn’t have capacity and treatment may be given where required.
What is the law in Scotland to do with parents overriding consent?
In Scotland parents cannot override the competent consent of a young person to treatment that the doctor believes is in the patients best interests
What is the law in Scotland to do with parents authorising treatment a young person has refused?
Parents cannot authorise treatment that a competent young person has refused
