Lecture 6 Flashcards
functions of the skin (5)
- protects underlying structures
- first line of defense from external factors
- insulation / T regulation
- sensation (touch, pain, …)
- production of Vitamin D
most outer layer of skin : main cells, vascularized?
Epidermis.
Keratinocytes (also melanocytes and langerhans cells)
No blood vessels.
layers of the epidermis ?
differently differentiated keratonicytes : on top, dead cells filled with keratin
second layer of skin : function, main cells, vascularized ?
Dermis.
Cushions body from stress and strain (ECM).
Fibroblasts (and immune cells).
Contains blood vessels .
third layer : role, main cells
Subcutaneous tissue (NOT part of skin).
Attaches skin to muscle / bone and supplies skin with vessels and nerves.
Main cells are adipocytes (also fibroblasts and macrophages)
classification of wounds
superificial, partial thickness, full thickness, deep wound, complex wound, penetrating wound
differences between regeneration, repair, and fibrosis
1) regeneration : complete restoration of original tissue, function and structure (minor injuries) -> goal of surgical procedures
2) repair : tissues don’t return to original architecture (scar tissue)
3) fibrosis : after chronic tissue damage -> loss of function
first phase of skin wound healing : name, 3 steps, cells involved
Hemostasis.
i) vasoconstriction : cell membrane releases factors that cause vessels to constrict + recruit cells
ii) platelet plug formation : platelets activate (change shape, adhere to collagen and express receptors that creates an aggregation)
iii) clot formation : prothrombin becomes thrombin -> causes fibrinogen to become fibrin -> fibrin matrix that stabilizes the wound and provides a scaffold, clot fills with red blood cells and seals the wound (protection)
second stage of wound healing : name, steps (3), cells involved
Inflammation.
Mast cells release granules (with histamine) that causes vasodilation -> redness, heat, swelling, pain.
Early : neutrophils ; only stay a couple days, remove dead tissue and bacteria, replaced by macrophages
Late : macrophages ; phagocytosis -> wound decontamination, regulation of tissue repair, remain until healing complete
what is it called when neutrophils migrate to the wound site ? 4 steps
Neutrohil extravasation.
Margination, pavementing, rolling and adhesion, transmigration
5 phases of phagocytosis
1) attachment : receptors recognize bacterial cell wall
2) engulfment : phagosome
3) degranulation : phagolysosome
4) degradation : lysosome digests bacteria
5) exocytosis : of digestion products
third stage of wound healing : name, type of tissue, 3 key processes
Proliferation.
Granulation tissue if formed : fragile connective tissue (collagen type III) and microscopic blood vessels (angiogenesis)
Fibroplasia : proliferation of fibroblasts that produce matrix and differentiate into myofibroblasts (contract and close the wound)
Epithelialization : proliferation of outer-lining epithelial cells
fourth phase of wound healing : name, 2 steps, result
Maturation
1) remodeling : reorganization, degradation and resynthesis of ECM (collagen III -> collagen I).
Formation of scar tissue.
2) cross-linking : covalent bonds between collagen fibrils.
Result is increases tensile strength (80% of unwounded skin).
How is the healing process different in bone ?
Maturation stage is different : soft (fibroblasts, chondroblasts) and hard (osteoblasts) callus formation.
3 wound healing complications
1) chronic non-healing wounds (chronic inflammation) : ex diabetic ulcer
2) excessive formation of repair components : hypertrophic scar (collagen I), keloid (collagen III)
3) excessive proliferation of fibroblasts / other connective tissue elements
