Skin :( Flashcards
What are the functions of the skin?
- Acts as a protective barrier- physical via cells being packed together and chemical due to its oils and antimicrobial peptides
- mechanical suppirt
- Prevents water/moisture loss
- Decrease effects of uv radiation
- sensory organ- has receptors for temp, touch, pressure
- Regulates body temperature
- Excretion of waste products e.g. sweat
What are the 3 layers of the skin?
Epidermis- epithelial cell layers, no blood supply- replaced every 2-3 days
Dermis- Middle layer- vascular-rich, hair follicles. Has a lot of connective tissue (collagen, fibrin and elastin) and nerve endings
Hypodermis- Made up of adipose tissue. Has a fat layer which aids mechanical protection, insulation and an energy store.
What are the 5 layers of the epidermis?
Stratum basale
Stratum spinosum
Stratum granulosum
Stratum lucidum
Stratum corneum
What cell types are found in the epidermis?
- Keratinocytes- basal areas as cuboidal cells- as you reach the surface of the skin, these flatten (work up to surface over 3-4 days and flatten, they then die and flake off due to no access to blood supply near the surface). They are stem cells that can rapidly proliferate and differentiate allowing skin to constantly be renewed. They make keratin which is a component of skin, nails and hair. can also produce cytokines e.g IL-1 AND 6.
- Merkel cells- In startup basal- have receptors that detect light or discriminative touch and is connected to sensory neurones. Protects us from harm as we can feel pain
-Melanocytes- near the basal layers- they produce melanin- to protect the skin from UV and decrease number of DNA mutations (and gives our skin its colour). Melanin is produced by tyrosine and catalysed by tyrosinase
- Langerhans cells- are dendritic cells they detect self and non-self by sampling bacteria on the skin and presenting antigens to cd8+ t-cells
- T-cells- CD8+ t-cells are ready to react in case of foreign organism
What are the 2 corpuscles in the skin and their roles?
- Meissner’s corpuscle- has receptors for light and discriminative touch
- Pacinian corpuscle- detect vibrations
What do the sebaceous glands do?
Produce and secrete sebum which is an oily substance that keeps the hair and skin moisturised. (oil flows to surface to protect hair and skin)
What are the difference between the eccrine and apocrine sweat glands?
- Appocrine glands- only found in the armpit, breast and pubic regions. differ from eccrine glands in that they are larger and open into hair follicles instead of onto the skin surface. Produces a thicker sweat, with the typical ‘sweat’ smell
- Eccrine sweat glands- are found over most of the body (most numerous on the feet and palms of the hands) (only not found on the lips, ear canal, nail beds and genital areas). They. open directly onto the skin’s surface and secrete a clear, thin watery sweat that cools the body.
Discuss the appendages found on the skin (like an exam q)
- Appocrine glands- only found in the armpit, breast and pubic regions. differ from eccrine glands in that they are larger and open into hair follicles instead of onto the skin surface. Produces a thicker sweat, with the typical ‘sweat’ smell
- Eccrine sweat glands- are found over most of the body (most numerous on the feet and palms of the hands) (only not found on the lips, ear canal, nail beds and genital areas). They. open directly onto the skin’s surface and secrete a clear, thin watery sweat that cools the body.
- Sebaceous glands - Produce and secrete sebum which is an oily substance that keeps the hair and skin moisturised. (oil flows to surface to protect hair and skin)
Hair follicles- the hair shaft is the part that is above the skin that sits in the hair follicle. It is important to keep the body warm and regulating body temperature and also has a sensory function and mechanical protection.
Also nails- made of keratin . They allow us to grip, protect the fingertips which are rich in blood vessels and nerve endings and judge how to hold things, detecting pressure changes and increasing the sensitivity of our fingertips.
How does the skin vary throughout the body?
FACE
- High density of sebaceous glands and hair and eccrine glands
- Is exposed to the environment
Palm of hand
- is hairless
- Has a thick stratum corneum which provides protection
- High density of eccrine glands
Axilla (armpits)
- lots of apocrine glands
- High hair density
- Has a humid environment
What cells are involved in the immune system of the skin?
In the Epidermis:
- Langerhans (dendritic cells)- these are antigen-presenting cells and present foreign antigens to CD8+ t-cells
- Keratinocytes- Produce cytokines e.g. IL-1 and IL-6
In the dermis:
- CD4 helper t-cells
- NK cells
- macrophages
- mast cells
- fibroblasts
- neutrophils
Melanocytes- produce melanin which protects the skin against uv damage and decrease number of DNA mutations.
Merkel cells- sensory- prevents ongoing harm due to us being able to feel pain
What causes acne?
When bacteria blocks sebaceous glands
What does it mean that the skin microbiome is bi-directional?
The large skin microbiome is beneficial to us and we are beneficial to them. As we provide the bacteria etc with nutrients and space and they protect us from foreign organisms.
- They inhibit pathogen growth by taking up the space and nutrients an react with innate immune system= local cytokine production, priming antigen presenting cells
- exhausts host innate immunity- train to recognise self and foreign organisms by priming antigen presenting cells
What are the four stages of acute wound healing?
Haemostasis- microvascular injury occurs = blood seeps into the wound:
- Injured vessels contract
- Coagulation cascade activated by tissue factor = clot formation and platelet aggregation
- platelets trapped in the clot release PDGF, IGF which attract fibroblasts, macrophages, endothelial cells and serotonin (increases vascular permeability)
= stops bleeding
INFLAMMATORY PHASE: split into early and late
- Activation of complement system
- Infiltration of neutrophils occurs within 24-48 hours
- Diapedesis into wound and phagocytosis of bacteria and foreign particles with ROS (reactive oxygen species) and degrading enzymes = prevent infection
late:
- Monocytes arrive and become macrophages within 48-72 hours and these are very key for repair!
- pro-inflammatory Cytokines and growth factors e.g. TNF, MMPs recruit other immune cells to repair the damage
collegenases degrade tissue
Lymphpocytes enter around 72 hours and are involved in remodelling
PROLIFERATIVE:
- occurs over 72-hours to 2 weeks
- Fibroblasts migrate to the area= produce collagen, fibronectin, proteoglycans = proliferate and construct a new ECM
- Collagen synthesis also increases strength and integrity
- Angiogenesis occurs- formation of new blood vessels to provide oxygen and nutrients to aid repair. Capillary sprouts invade the fibrin-rich clot and organise a microvascular network
- Epithelialisation occurs- a thin, single layer of epidermal cells migrate from wound edges to form a delicate covering over the wound.
- REMODELLING: takes a long time
- The matrix matures and remodels
- Fibronectin and hylauronic acid breakdown
- Increased collagen synthesis- more organised and shrinks the margins closer together
- Fibroblasts and macrophages apoptose
- least to formation of an acellular and avascular scar
IN CHRONIC WOUNDS (e.g. caused by neuropathy in DM, connective tissue disorders, peripheral oedema, ischaemia) - these normal phases are disrupted- usually at inflammatory or proliferative
- leads to disturbance in growth factors, cytokines, cells
= Necrotic and unealthy tissue, excess exudate, lack of adequate blood supply, failure or re-epithelialisation, persistant pain, recurrent wound breakdown, infection
What happens during haemostasis during wound injury?
- Microvascular injury causes blood to seep into the wound
- the injured vessels contract to try and limit blood loss
- coagulation cascade activated by tissue factor = formation of clots and platelets to aggregate
- Platelets are trapped in the clot and released PDGF, IGF, EGF, TGFB = these attract and activate fibroblasts, macrophages, neutrophils
- Also releases serotonin- this increases vascular permeability to easily allow immune cells through
What factors affect wound healing e.g. post surgery?
LOCAL
- pressure e.g. bed sores
- mechanical injury
- infection
- oedema
- necrosis
- lack of oxygen and nutrients- ischaemia
- dehydration of skin
SYSTEMIC
- old age
- obesity
- chrons
- immunosupression
- smoking
- malnutrition
- stress
- radiotherapy or chemotherapy
What are the symptoms of eczema/dermatitis?
Dry, irritated, inflamed skin
red
oedema
ooszing
papules
crustiness
scaring
itchiness
dry skin
- often flexural - knees, elbows, wrists
