Skin Pharmacology Flashcards
State the functions of the skin:
Protective barrier
Involved in mechanical support
Prevents loss of moisture
Reduces harmful effects of UV radiation
Sensory organ- touch, temp, pressure etc
Helps regulate body temp
Immune organ to detect infections
Involved in production of vitamin D
Excretion of waste products through sweat
Describe how the skin is a protective barrier:
Physical- cells tightly packed together
Chemical- antimicrobial peptides and oils
Describe how the skin reduces the harmful effects of UV radiation:
Melanin production- a pigment adapted from tyrosine
Describe how the skin helps regulate body temperature:
Vascular rich region-many capillaries
Name and briefly describe the layers of the skin:
Epidermis- outer layer of epithelial cells, no blood supply, nutrients come from nearby capillaries, replace every 2-3 days
Dermis- middle, vascular rich, hair follicles, glands (receptors), connective tissue
Hypodermis- adipose tissue
Name the 5 layers of the epidermis:
1) stratum basale (closest to dermis)
2) stratum spinosum
3) stratum granulosum (dark layer)
4) stratum lucidim
5) stratum corneum (dead keratinocytes)
Name the main cell types in the epidermis:
Keratinocytes
Merkel cells
Melanocytes
Langerhan cells
T cells
Describe the keratinocytes in the epidermis:
Main cell type
Numerous layers, starts off in the basal layer as cuboid cells but as move up to surface begin to flatten out and die
Stem cells
Describe Merkel cells in the epidermis:
Present in stratum basal
Pressure/light attached to sensory neurones
Different locations in skin
Describe melanocytes in the epidermis:
Near basal layers- stratum spinosum
Produce melanin, protect from UV
Describe Langerhans cells in the epidermis:
Immune/ dendritic cells - detect self and non self
All layers in epidermis
Describe T cells in the epidermis:
CD8+ T cells- dendritic cells can present to T cells
What is another name for keratinocytes?
Corneocytes
Describe the lifetime of a keratinocyte:
In stratum basal- have stem cells which self renew and rapidly proliferate and differentiate into any other cell types in the area
Cuboidle cells which have nuclei once in granules layer, start to flatten and lose nuclei and then in stratum lucidium fully flattened and eventually die in the corneum, where they are enriched with lipids and keratin
What is the function of keratinocytes?
Secrete IL1-B important in maintaining homeostasis and if cells become damaged
Describe the dermis:
Middle layer, 1-6mm fibrous and elastic tissue
Made of connective tissue
Has 2 layers
Name the 2 layers of the dermis:
Papillary layer 20%- next to the epidermis
Reticular layer
Describe the papillary layer of the dermis:
Vascular rich region, lots of capillaries which release O and nutrients near epidermis to provide for epidermis, that’s why the keratinocytes become flattened further up (dead)
Supportive and cushioning tissue composed mainly of collagen (70%), elastin and fibrillin which allows more exchange of oxygen and nutrients
Describe the reticular layer of the dermis:
Majority of dermis
Dense irregular connective tissue- elastin and fibirillin
Immune cells, several types
Number of structures found
Name the structures found in the reticular layer of the dermis:
Skin appendages
Meissner’s corpuscle
Pacinian corpuscle
Hair shaft
Eccrine sweat glands
Apocrine sweat glands
Describe the function of the Meissner’s corpuscle:
Sense receptors for light or discriminative touch (epidermal layer)
Describe the function of the Pacinian corpuscle:
Detects vibration in the skin
Describe the function the hair shaft:
Hypodermis
Root hair plexus- detects fine touch
Sebaceous (oil) gland- keeps skin and hair moist
Describe the function of the eccrine sweat gland:
Watery sweat- urea/CO2 etc
Describe the function of the apocrine sweat gland:
Present in armpit/ pubic
Protein rich sweat bacteria
Describe the diversity of the skin on the face:
Sebaceous
High density of sebaceous glands
Hair and eccrine glands
Evironmentally exposed
Describe the diversity of the skin on the palm:
Dry
Thick stratum corneus
Hairless
High density of eccrine glands
Describe the diversity of the skin on the axilla:
Moist
Apocrine glands present
High density of hair
Occluded, humid environment
Describe the subcutaneous tissue in the hypodermis:
Fat layer acts as a:
-mechanical protector
-thermal insulator
-energy store
Thickness depends whole body adiposity but need a minimal amount for skeletal and organ protection
Heat regulation uses SC fat and blood supply
Name the components of the skins immune system in the dermis:
Dendritic (dermal/plasmacytoid)
CD4 T cell (Th1,Th2,Th17)
NK cells
g ∂ T cells
Macrophages
Mast cells
Fibroblasts- remodels skin like collagen if damaged
What factors can cause signal mediated responses to cellular insult?
Infectious agents- bacteria, fungi, viruses, parasites
Toxins- chemical, radiation, biological etc
Physical stresses- mechanical, burns, trauma
Describe the skin microbiome:
1cm2 human skin has up to 1 billion MOs e.g bacteria, fungi, viruses, mites
What are the advantages of the skins microbiome?
Inhibit pathogen growth
Educate and prime adaptive immunity
Enhance host innate immunity
What are the detrimental/ disadvantages of the skins microbiome?
In acne, this bacteria clogs sebaceous glands
Exacerbation skin lesions
Promote disease
Delay wound healing
How does the skin microbiome interact with the hosts immune system?
Bi-directional
We provide the bacteria with nutrients and space and they protect us
What type of bacteria is majorly found in the upper body?
Actinobacteria
What type of bacteria is majorly found in the limbs/middle body?
Proteobacteria
What type of bacteria is majorly found in the foot/leg?
Firmicutes
How does the skin resident microbiome inhibit pathogen growth?
Occupy space and nutrients
Produce AMPs/ bactericidal compounds- antimicrobial peptide
Inhibit S aureus biofilm formation
How does the skin resident microbiome educate and prime adaptive immunity?
Tune local cytokine production
Epigenetically prime APCs to educate adaptive immunity
Influence T regs in epidermis
How does the skin resident microbiome enhance host innate immunity?
Increase AMP production
Decrease inflammation after injury
Strengthen epidermal barrier
How can the microbial communities on the skin cause things to go wrong?
Shift in community composition e.g infection
Altered host immune response release pro-inflammatory cytokines
Impaired barrier homeostasis- immune infiltration- disrupted physical barrier
Microbes escape typical niches/ overgrow into sterile tissues
How can the hosts biology/ pathology cause things to go wrong for the skin microbiome?
Alterations in the skin barrier/immune functions e.g genetic predisposition (filigrin gene)/chronic condition
Changes in distribution of microbes causes overgrowth of potential pathogens into sterile tissues
Altered/inappropriate immune responses increase inflammation, opportunistic infections, impaired wound healing
Name the different types of wound:
Superficial
Partial thickness
Full thickness
What is a superficial wound?
Epidermal layer
Heals rapidly through regeneration of epithelial cells- no bleeding as no vascular system, keratinocytes
What is a partial thickness wound?
Involves dermal layer
Vascular damage
What is a full thickness wound?
Involves the SC fat and deeper
Longest time to heal, new connective tissue required
Contraction during healing
Name the 4 stages of wound healing:
- Bleeding
- Inflammatory
- Proliferative
- Remodelling
Describe the bleeding stage of wound healing and how long does this occur?
Injury to skin, haemostasis, blood clot to stop bleeding
Takes less than a day- platelet/ complement activation
Describe the inflammatory stage of wound healing and how long does this occur?
Linked with bleeding
Stop infection, lots of immune cells e.g fibroblasts
Framework for new bv growth- scab
Within 72 hours
Anything between 1-10 days
Peak after a day- neutrophils (granulocytes)
2-3 days after- macrophages
Describe the proliferative stage of wound healing and how long does this occur?
Fibroblasts proliferating- more connective tissue to replace damages, new dermal layer (delicate)
After 3 days:
-deposit matrix, fibroplasia, angiogenesis, collagen, proteoglycans, extraceullar matrix synthesis, epitheliaization
Describe the remodelling stage of wound healing and how long does this occur?
Freshly healed dermis/epidermis- avascular scar
Month- extracellular matrix synthesis, degradation and remodelling
Increase tensile strength, decrease cells, decrease vascularity
- can take up to a year
Describe the steps in haemostasis:
Microvascular injury- blood seeps in wound
BVs contract-limits blood in wound
Coagulation cascade activated by tissue factor
Clot formation and platelet aggregation
Platelets trapped in clot release PDGF,IGF,EGF,TGFb which attract and activate fibroblasts, macrophages and endothelial cells
Also release serotonin, which increases vascular permeability, BVs relax so immune cells can come into area
Describe early inflammatory phase:
Activation of complement
Infiltration of neutrophils (within 24-48hrs)
Diapedesis into wound and phagocytosis of bacteria and foreign particles with ROS and degrading enzymes- prevent infection
Dying cells cleared by macrophages extrusion to would surface
Describe late inflammatory phase:
Blood monocytes arrive and become macrophages (48-72hrs)
Key cell type for repair
Cytokines and GFs to recruit fibroblasts, keratinocytes and endothelial cells to repair damage
Collagenases to degrade tissue
Lymphocytes enter wound (72hrs) and are involved in remodelling
Name the processes that occur in the proliferative phase:
Fibroblast migration
Angiogenesis
Granulation tissue formation
Epithelialisation
Describe fibroblast migration:
Produce fibronectin, hyaluronan, collagen, proteoglycans
Proliferate and construct new ECM
Collagen synthesis- strength and integrity
Describe angiogenesis:
TGFB and PDGF from platelets, TNF and BFGF from macrophage
Capillary sprouts invade fibrin/fibronectin rich wound clot and organise microvascular network
Describe granulation tissue formation:
Mainly proliferating fibroblasts, capillaries, macrophages in matrix of collagen GAGs (glycosaminoglycans) and fibronectin and tenascin (ecm GP)
Describe epithelialisation:
Single layer of epidermal cells migrate from wound edges to form delicate covering
Basal cells increase proliferation, new basement membrane
EGF stimulates epithelial mitogenesis and chemotaxis
BFGF and KGF stimulate proliferation
How can chronic wound and impaired healing occur?
When normal processes of healing disrupted at one of the stages, usually inflammatory or proliferative
Disturbances in GF, cytokines, proteases
Describe which cells and how are involved in the matrix maturing and remodelling stage:
Fibronectin and HA broken down
Collagen bundles increases in diameter and strength 80% of strength of original
Collagen synthesis and breakdown by TGFb and MMPs
Collagen becomes more organised and shrink to bring wound margins closer together
Fibroblasts and macrophages apoptose
Capillary outgrowth halted and blood flow reduces
Acellular, avascular, scar
What are the local factors which affect wound healing?
Pressure
Mechanical injury/ trauma
Infection/ foreign substances
Oedema
Necrosis
Topical agents
Lack of oxygen delivery (ischemia)
Desiccation and dehydration
What are the systemic factors which affect wound healing?
Old age
Obesity
Chronic diseases e.g diabetes
Connective tissue disorders
Immunosuppression
Smoking
Malnutrition
Vascular insufficiency
Stress
Radiation/ chemo
Name and describe some causes of chronic wounds:
Neuropathy e.g DM, spinal injuries
Ischemia e.g atherosclerosis
Peripheral oedema e.g DVT
Pressure e.g poor mobility
Describe some clinical features of chronic wounds:
Presence of necrotic and unhealthy tissue
Excess exudate and slough
Lack of adequate blood supply
Absence of healthy granulation tissue
Failure of re-epitheliasation
Cyclical or persistent pain
Recurrent wound breakdown
Clinical or sub clinical infection
How does motor neuropathy cause diabetic ulcers?
Muscle atrophy/ bone changes- deformed foot- changes in gait- new pressure distribution- ulcer- infection- gangrene
How does sensory neuropathy cause diabetic ulcers?
Painless trauma leads to ulcers and infection/ gangrene
How does autonomic neuropathy cause diabetic ulcers?
Decreases sweating- dry skin cracks- chronic ulcer which leads to infection and ischamiea
What is the difference between eczema and dermatitis?
Eczema= inflammation of the epidermis
Dermatitis= inflammation of the dermis
Name the different types of dermatitis:
Atopic
Contact
Seborrhoeic
Dyshidrotic
Nummular
Neurodermatitis
Stasis
Describe atopic dermatitis:
Chronic disorder with flare ups and remissions- may clear up for long periods
Type IV hypersensitivity
Often occurs with asthma/ hayfever (atopic triad)
Commonly affects knees, elbows, wrists, neck and face
What population does atopic dermatitis commonly affect?
1-2% adults- hand eczema
15-20% school children- flexural eczema
Males and females equally affected
Describe the aetiology of atopic dermatitis:
Genetic predisposition
Defect in the filaggrin gene- important for maintaining the skin barrier
Defects in the skin barrier
Lack of anti-microbial peptides
Abnormalities in the normal inflammatory and allergy response
Barrier defects makes the skin in affected patients much more susceptible to infection and to irritation and allows allergy- inducing substances to enter skin, causing an itch and inflammation
Describe the pathophysiology of atopic dermatitis:
Allergen- dendritic cell- T cell- change in balance of the Th1/2 and so expansion of Th2 which secretes IL4- activates B cells causing class switching of antibodies so produced IgE- blood to mast cells, so allergen can be taken up (adaptive IR)- pro inflammatory mediators
What are the clinical features of atopic dermatitis?
Dry skin
Itching may be severe, especially at night
Red to brownish grey patches on affected areas become lichenified
Raw sensitive swollen skin from scratching
Skin infections and sores can occur when scratching due to breaks in the skin
What could be the causes of flare ups of atopic dermatitis?
Heat, dust, smoke, irritants, soaps, stress
What would be the preventions of flare ups for atopic dermatitis?
Moisterisers
Identify and avoid triggers if possible
Mild soaps and short showers/ baths
What are the first line treatments for atopic dermatitis flare ups?
Emollients
Topical corticosteroids
Antibiotics if eczema infected
Phototherapy
What are the second line treatments for atopic dermatitis flare ups if first line not sufficient?
Systemic corticosteroids
Topical calcineurin inhibitors (TCIs)
What is the third line treatment for atopic dermatitis flare ups if first line not sufficient?
Immunosuppresents -ciclosporin, azathioprine
Dupilimumab- MAB inhibiting IL4/IL13 signalling
What would be the treatment for eczema on the hands in adults?
Last treatment option
Alitretinoin- for chronic hand eczema refracory to steroids
Name some topical calcinerin inhibitors and how do they work?
Pimecrolimus and Tacrolimus
Inhibit T cell response so no IL4
Describe contact dermatitis:
Mainly substances responsible
2 types:
-irritant
-allergic
More common in adults than children as associated with workplace
Common in network
Atopic dermatitis pts have increase susceptibility