Wound Healing Flashcards
1
Q
Define parenchyma
A
Parenchyma =
Organ specific cells related to the function
e.g. renal parenchyma = renal tubular epithelium
E.g. heart parenchyma = cardiac muscle cells
2
Q
Define stroma
A
Stroma = background tissue that provides structure, mechanical and nutritional support to the organ
3
Q
What are the 4 types of tissue and their functions?
A
- Epithelial –> characterised by close cell apposition, found at free surfaces.
- function of protection
- containment of body fluids
- absorption and secretion
- Connective tissue –> several types of cell and EC products
- mechanical reinforcement
- Immune surveillance
- diffusion of nutrients and waste
- Muscle
- gross movement by cellular contraction
- Nervous tissue:
- responsible for rapid long distance signalling
4
Q
Describe connective tissue:
Function
cell arrangement
make up
A
- Connective tissue function:
- mechanical reinforcement
- immune surviellance
- diffusion of nutrients and waste
- Cells not in close contact, embedded in ECM and can be vascularised (not in all cases e.g. cornea where collagen is arranged for transparency).
- Made up of:
- Fibrous components: Collagen and elastin
- GAG’s –> support collagen
- Proteoglycans –> GAG attached to core protein
5
Q
What are the two main types of connective tissue?
A
- Variation in the composition of ECM determines the properties of connective tissue
-
Two main types:
- Loose connective tissue
- Dense irregular connective tissue
Loose connective tissue:
- numerous cells
- loose fibre arrangement in viscous matrix
- e.g. haematopoetic and lymph connective tissue, found between many organs acts to both shock absorb, bind together and allow diffusion of nutrients
Dense irregular connective tissue:
- Dense woven network of collagen fibres in viscous matrix (more collagen than loose connective)
- Irregular means collagen arranged in random directions gives greater strength overall
- E.g. tendon/ joint capsule/ ligaments
*
6
Q
List the specialised forms of connective tissue
What are their definitive features?
A
- Loose connective tissue under the skin:
- formed of dermal cells, collagen, elastin and fibroblasts
- Adipose tissue:
- formed of adipocytes, specialised cells that store lipid within their cytoplasm
- adipose tissue found surrounding certain organs e.g. liver/ kidneys and for thermoregulation
- adipocytes sat on reticular fibre structure
- Reticular tissue:
- formed of reticulocytes that secrete a mesh supportive network on which other cells sit
- cartilage:
- formed of chondrocytes that occupy spaces called lacunae
- coil fibres and semi solid ECM
- Bone:
- dense, formed of osteoblasts, osteocytes,
- collagen fibres
- calcified ECM
- Blood:
- Formed of erythrocytes, leukocytes, thrombocytes –> proteins that are soluble for clotting
- ECM –> plasma
7
Q
Define wound
A
Wound = injury/ trauma to tissues that disrupts the function and structure of the tissue
8
Q
Define healing
A
Healing = process of returning to health. Restoration of structure and function of diseased tissues
9
Q
Describe the stages of wound healing
A
- Haemostasis –> 24 hrs
- wound closed by clotting/ coagulation cascade
- platelets/ fibrin adhere to site
- formation of a thrombus
- Inflammatory process –> 0-4 days
- platelets control bleeding
- macrophages to prevent infection
- neutrophils and inflammation
- Proliferative process –> 1-14 days
- angiogenesis
- epithelialisation
- contraction
- fibrous tissue formation
- Remodelling process –> day 21 (years)
- maturation phase
- collagen is remodelled and becomes realigned
- injured sites tend to be weaker than norm (80% tensile strength).
10
Q
Define tissue repair
What are the two types of tissue repair?
A
- Tissue repair = the restoration of structure and function of damaged tissue
- Two types:
- Regeneration -> complete restoration of tissue to normal state, with right cytokines and GF’s it will grow into idea cell type for that tissue
- Scar formation
11
Q
What is regeneration?
What growth factors are involved?
A
- Regeneration = new growth completely restores portions of damaged tissue to their normal state
- Driven by GF’s:
- PDGF’s
- VEGF
- TGF-B --> activated by macrophages, main role to close wound by laying down collagen. Coverts fibroblasts into myofibroblasts which lay down excess collagen
- ECM plays major function in regeneration
12
Q
What are three types of tissue that have different regenerative capacity?
A
- Labile tissues:
- continuously proliferating in order to replace the dead or sloughed off cells e.g. Skin/GI tract/ Salivary gland tissue
- Stable tissues:
- cells that normally exist in non dividing state
- may enter cell cycle in response to certain stimuli e.g. injury
- e.g. liver/ kidney/ pancreas
- Permanent tissue:
- non dividing cells leads to scar formation
- e.g. cardiac and skeletal
13
Q
What are Growth factors?
What do they stimulate?
where are they produced?
How do they act?
examples?
A
- Growth factors are proteins that stimulate:
- survival
- proliferation
- migration
- differentation
- Produced mainly by macrophages and lymphocytes at the site of injury as part of the inflammatory process
- other GF’s are produced by parenchymals cells or stromal cells in response to injury
- stimulates the entry of cells into the cell cycle
- GF’s produced transiently in response to external stimulus and act by binding cellular R’s
- examples: TGF=b, VEGF, EDGF, FGF
14
Q
What is the role of the ECM in wound healing?
A
- The ECM is the ever changing background for regeneration and wound healing
- Functions to:
- store and present growth factors
- act as a scaffold to which migrating cells can adhere
15
Q
Describe scar formation:
what is it?
when/ where does it occur?
A
- Scar formation = replacement of damaged parenchymal cells with connective tissue, incomplete restoration of architecture and function
- Occurs:
- severe and crhonic injuries that result in damage of parenchymal cells as well as connective tissue
- permanent non dividing tissues
- lymphocytes/ neutrophils/ macrophages activated in inflammatory process
- collagenous matrix laid down in irregular manner -> scar forms
21
Q
Describe the mechanism of skin healing by 1st intention/ primary union?
A
- Narrow incision space filled with fibrin clotted blood
- within 24 hrs neutrophils seen at incision margin and migrate towards fibrin clot –> acute inflammation
- within 24-48 hrs basal cells of epidermis from both sides start proliferating and migrating towards the incisional space. Wound is covered by layer of epithelium in 48 hours.
- Epidermal cells separate underlying viable dermis from overlying necrotic material forming scab.
- by day 3-7 neutrophils largely replaced by macrophages
- angiogenesis reaches its peak
- Fibroblasts also invade wound area by day 3, start froming new collagen fibrils
- granulation tissue progressively invades the incision space
- 2nd week –> continued collagen accumulation and fibroblast proliferation –> scar maturation
- remodelling of scar continues for months aiming to increase wound tensile strength
24
Q
How does second intention healing differ from first intention?
A
- 2nd intention occurs in larger wounds that can be infected
- involves a larger clot and scab formation
- inflammation is more intense as large tissue defects have a greater volume of necrotic debris, exudate and fibrin that must be removed
- Requires larger volume of granulation tissue to fill in the gaps - -> generally results in greater mass of scar tissue
- secondary healing involved contraction of wound
- -> w/in 6 wks large skin defects may be reduced to 5-10% of original size
26
Q
What are the stages of fracture healing?
A
- Haematoma
- Granulation tissue
- Callus formation
- Woven bone
- Lamellar bone
- Remodelling
Note there is some overlap in all these stages.
36
Q
Inadequate formation examples
A
- Dehiscence or rupture –> separation of layers of surgical wound
- Evisceration –> extrusion of viscera outside the body through a surgical incision
- Ulceration –> lesion through the skin or a mucous membrane resulting from loss of tissue usually with inflammation
37
Q
Examples of excessive complication of tissue repair
A
- Keloid formation –> accumulation of excess amount of collagen which gives rise to prominent raised scars
- Healing wound also can generate excessive granulation tissue which protrudes above the level of the surrounding skin and hinders re-epithelialisation “proud flesh”
