Skin Flashcards
What is the function of the skin?
-Protective barrier
-Mechanical support - skeleton
-Prevents loss of moisture
-Reduces UV radiation - melanin
-Sensory organ - detect and protect environmental fators
-Body temp regulation
-Immune organ to detect infections
-Vitamin D Synthesis
-Excretes waste - sweat
How often do the epithelial cells in the epidermis replace?
Every 2-3 days
Do epithelial cells have a blood supply?
No
What cells are within the epidermis?
Langerhans dendritic cells, Keratinocyte, Corneocyte, CD8+ T Cells, Melanocytes
Describe the Dermis?
Has two layers.
Vascular rich layer with specialised nerve endings which detect pressure and temperature changes, there is glands within the dermis layer.
What is the papillary layer of the dermis?
-20% of it, vascular rich oxygen is released in the bottom layers to retain the nuclei, there is lots of connective tissue which is rich in collagen, there is more exchange of nutrients and oxygen.
What is the Reticular layer of the dermis?
The remainder of the dermis, this is a dense irregular connective tissue, rich in elastin, fibrin and lots of immune cells.
Describe the Hypodermis?
This layer is composed of adipose tissue which acts as a physical, thermal and energy store.
How is heat regulated within the skin?
Heat regulation uses subcutaneous fat and skin blood supply, this thickness depends on the whole body adiposity and needs little for skeletal and organ protection.
What do Keratinocyte’s do?
At the beginning they have a nucleus and at the top layer they become dead and flaky. When they are dead they flake off, these are enriched with lipids and Keratin, this secreted IL-1B, which is important in homeostasis and inflammation.
What do Merkel cells do?
These are attached to sensory neurons and respond to pressure, they can be found in different locations in the skin.
What do Melanocytes do?
These are found in the basal region and produce melanin and protect the skin from UV light.
What do Langerhan cells do?
Immune dendritic cells, which are within all layers of the epidermis and act by sampling bacteria and determining self vs non-self.
What is the skin like at the face?
High density of sebaceous glands, hair and eccrine glands and is exposed to the diagram - sebaceous!
What is the skin at the palms of the hands like?
Thick stratum corneum, hairless and high density of eccrine glands (dry)
What is the skin like at the Axilla (Armpits)
Apocrine glands are present, high density of hair, this is an occluded humid environment.
Where is the skin microbiome and simply what does it do?
There is lots of this on the skin, it protects use against disease but can exacerbate skin lesions, promote disease and delay wound healing. They interact with the host immune system (bi-directional), this can be affected by our lifestyle.
What does skin microbiome do?
1) Directly inhibits pathogen growth by occupying space and nutrients therefore pathogens have no space for food. They produce AMPs and bactericidal compounds to kill pathogens and inhibit the formation of S.Aureus biofilm formation.
2) Educate and prime adaptive immunity by local cytokine production epigenetically prime APCs to educate adaptive immunity and influence regulatory T cells in the epidermis.
3) Enhance host innate immunity which increases AMP production, decreases inflammation after injury and strengthens epidermal barriers.
A wound which is damage to the epithelium, heals rapidly through regeneration of epithelial cells and is not bleeding, what wound is this?
Superficial
A wound which is damage to the dermal layer, and there is vascular damage - is bleeding. What wound is this?
Partial thickness
A wound which involves subcutaneous fat and deeper tissues, takes a long time to heal and new connective tissue is required, also causes a scar to form, is what type of wound?
Full Thickness
What are the four stages of wound healing?
1) Bleeding
-Injury, -haemostasis blood clot forms to stop bleeding.
2) Inflammatory
-Stops infection, immune cells come in. New blood vessels are formed.
3) Proliferative
-More connective tissue to replace damaged tissue and close a wound, there is a new delicate epithelial layer
4) Remodelling
-Normal, decrease in immune cells and a vascular scar is formed
How many days is a wound in the inflammation phase?
1-10 days
What day is the wound in the cell proliferation and matrix deposition?
Day 3
What day is there Matrix remodelling?
Day 10-14
-After 1 month, the area is strengthened can take up to one year to fully repair
What cells are involved in the Inflammation state of wound healing?
Neutrophils, Macrophages make MMPs, ROS, Hydrogen peroxide, IL, TNF, VEGF, TGFb, FGFm PDGF - Proinflammatory cytokines made and growth factors
What cells are involved in the granulation and neo-angiogenesis stage of wound healing?
Fibroblasts, Macrophages, Endothelial cells, MMPs, Prolyl hydroxylase, IL, TNF, TGFb, VEGf, PDGF, KGF
What cells are involve in the re-epithelisation stage of wound healing?
Keretinocytes, MMPs, EGF, KGF
What cells are involved in the tissue remodelling stage of wound healing?
Fibroblasts, Collagen fibre cross-linking, MMPs, TGFb
What are the steps of Haemostasis? (stopping of blood flow)
1) Injury, blood seeps into the wound
2) Injured vessels contract - limiting blood supply
3) Coagulation cascade is activated by tissue factor, this limits blood loss
4) Clot formation and platelet aggregation
5) Platelets trapped in clot release PDGF, IGF, EGF, TGF-b, which attract and activate fibroblasts, macrophages and endothelial cells.
6) Also serotonin is released which increases vascular permeability - cells are relaxed and this allows immune cells into the area.
What happens in the early inflammatory phase?
-Complement system activated
-Neutrophils infiltrate into the area within 24-48 hours
-Diapedesis (blood to capillary) into the wound and phagocytosis of bacteria and foreign particles, with ROS and degrading enzymes - this prevents infection
-Dying cells are cleared by macrophages or extrusion to wound surface
What happens in the late inflammatory phase?
-Blood monocytes arrive and become macrophages within 48-72 hours.
*Key cell type for repair
*Cytokines and growth factors to recruit fibroblasts, keratinocytes and endothelial cells to repair damage
*Collagenases to degrade tissue
*Poor wound healing when inadequate monocytes/macrophages
-Lymphocytes enter the wound within 72 hours and are involved in remodelling
What do fibroblasts do in the proliferative phase of wound healing?
Rebuild
-Produce fibronectin, hyaluronan, collagen, proteoglycans,
-Proliferate and construct new ECM
What does collagen do in the proliferative phase of wound healing?
Collagen synthesis - provides strength and integrity
What happens in angiogenesis in the proliferative phase of wound healing?
TGF beta and PDGF from platelets, TNF and bFGF from macrophages
-Capillary sprouts invade fibrin/fibronectin-rich wound clot and organise microvascular network
What does granulation tissue formation mean in the proliferative stage of wound healing?
Mainly proliferating fibroblasts, capillaries, macrophages in the matrix of collagen GAGs and fibronectin and tenascin.