Wound Healing Flashcards
Define Parenchyma
Organ specific cells related to function
Define Stroma
‘Background’ tissue - provides the structure, mechanical and nutritional support to the organ
Name some functions of epithelia
Protection
Containment of body fluids
Absorption
Secretion
Name some functions of connective tissue
Mechanical reinforcement
Immune surveillance
Diffusion of nutrients and waste
Cells are not in close contact - embedded in the ECM
Vascularised
Name some functions of muscle
Specialised for gross movement through cellular contraction
Name some functions of nervous tissue
Responsible for rapid, long-distance signalling
Name 2 areas where connective tissue does not have to be vsacularised
Cartilage
Cornea
What 3 things make up the ECM?
Not the only 3 things in the ECM; lymphocytes, adipose and other cells found there also
Fibrous components - collagen and elastin
GAGs - to support collagen
Proteoglycans - GAGs attached to a core protein
What determines the properties of a connective tissue?
The composition of the ECM
Name the 2 types of connective tissue?
Loose connective tissue
Dense irregular connective tissue
Which type of connective tissue contain numerous cells, has a lose fiber arrangement in a viscous matrix?
Give some examples
Loose connective tissue
Haematopoietic/lymphatic tissue
What type of connective tissue has a dense woven network of collagen and fibres in a viscous matrix?
Give some examples
Dense irregular connective tissue
Joint capsules
Tendons and ligaments
Define ‘wound’
Injury or trauma to tissues that results in a disruption of the function and structure of a tissue
Name the 4 stages of wound healing
Haemostasis
Inflammation
Proliferation
Remodelling
What happens during the haemostasis stage of wound healing?
How long does this stage last?
Wound closed by clotting (coagulation cascade)
Platelets and fibrin adhere to site
Formation of a thrombus
<24 hours
What 3 cell types are present in the inflammatory stage of wound healing?
What do they do?
How long does this stage last?
Platelets - control bleeding
Macrophages - prevent infection
Neutrophils - inflammation
0-4 days
What happens during the proliferative phase of wound healing?
How long does this stage last?
Angiogenesis
Epithelialisation
Contraction
Fibrous tissue formation
1-14 days
What happens during the remodelling phase of wound healing?
How long does this stage last?
Maturation of cells
Collagen remodelling and realignment
Day 21 - years
Name the 2 types of tissue repair
Regeneration
Scar formation
Define tissue repair
The restoration of the structure and function of a tissue
What 3 molecules are present in the regeneration of tissue?
Platelet-derived growth factor (PDGF)
Vascular endothelial growth factor (VEGF)
Transforming growth factor-beta (TGF-B)
TGF-B does what at a wound site?
How is it activated?
Lays down new collagen
-by converting fibroblasts into myofibroblasts
Activated by macrophages
Give a brief description of labile tissues with some examples
Continuously proliferating to replace dead/sloughed off cells
Skin, GI tract, salivary gland tissues
Give a brief description of stable tissues with some examples
Cells that normally exist in a non-dividing state, but can enter the cell cycle in response to injury
Normally not full regeneration, just compensatory growth
Parenchymal liver cells, kidney, pancreas
Give a brief description of permanent tissues with some examples
Non-dividing cells that lead to scar formation if damaged
Cardiac and skeletal tissue
What are growth factors?
Proteins that stimulate proliferation, migration, and differentiation of cells
Stimulate the entry of cells into the cell cycle
Which cells produce growth factors?
Macrophages
Lymphocytes
As part of the inflammatory process
What is the role of the ECM in regeneration?
Stores and presents growth factors
Acts as a scaffold for migrating cells to adhere to
What happens in scar formation?
Replacement of damaged parenchymal cells with connective tissue
Incomplete restoration of architecture and function
Where does scar formation occur?
Severe/chronic injuries that result in damage to parenchymal cells and connective tissue
Permanent non-dividing tissues
Which growth factor stimulates angiogenesis?
VEGF
How does angiogenesis occur?
Sprouting of new vessels from existing ones
Involves endothelial cell proliferation an migration
Describe the formation of granulation tissue
Migration and proliferation of fibroblasts to the site of injury
Deposition of ECM proteins produced by these cells
Derived from growth factors - TGF-B
What is involved in the degradation of collagens and other ECM components during the remodelling phase of wound healing?
Matrix metalloproteinases (MMPs)
Depending on the nature and size of the wound, the healing of skin wounds occurs by:
First intention (primary union)
Second intention (secondary union)
When does wound healing by first intention occur?
Healing of a clean, uninfected surgical incision
Epithelial regeneration is the principle mechanism of repair
Outline the 6 stages of wound healing
- Incisional space fills with fibrin-clotted blood
- Neutrophils migrate from the incision margin to the fibrin clot
- Epithelial cells migrate and proliferate along the dermis
- Neutrophils have been replaced macrophages. Angiogenesis in full swing. Granulation tissue begins to invade space
- Collagen accumulation, fibroblast proliferation
- Remodelling continues to increase wound tensile strength
When does wound healing occur by second intention?
Large wounds at sites of abscess formation, ulceration, infarction
Scar formation is followed by wound contraction - mediated by the action of myofibroblasts
Give some differences between second intention and first intention healing
Second intention:
A larger clot or scab
Intense inflammation
Larger defects that require more granulation tissue
Wound contraction
List the 6 stages of fracture healing
Haematoma
Granulation tissue
Callus formation
Woven bone
Lamellar bone
Remodelling
Describe the haematoma stage of fracture healing
Bleeding from ruptured vessels
Inflammatory reaction - phagocytes move to area
Describe the granulation tissue stage of fracture healing
Granulation tissue replaces the haematoma
Cell proliferation occurs in response to growth factors/cytokines
Describe the callus stage of fracture healing
Formation of callus (irregular swelling at bone ends)
Initially made from fibrocellular material and cartilage
Describe the woven bone stage of fracture healing
Osteoprogenitor cells proliferate and form woven bone
Describe the lamellar bone stage of fracture healing
Woven bone is replaced by mature lamellar bone
Describe the remodelling stage of fracture healing
Osteoclasts and osteoblasts remodel lamellar bone into a form related to function in response to stresses
Excessive callus is resorbed
What 6 local factors could affect tissue repair?
Infection
Mechanical factors
Foreign bodies
Size of wound
Location of wound
Type of wound
What 6 systemic factors could affect tissue repair?
Nutritional status
Metabolic status
Circulatory status
Hormones
Age
Collagen disorder
Name the 3 complications of tissue repair
Inadequate formation - dehiscence
Excessive formation - keloid scars (excessive collagen), proud flesh (excessive granulation tissue)
Formation of contracture - fibrosis of connective tissue that prevents normal mobility of the tissue. Myofibroblasts play a role. Severe burns
