WEEK 2: The Pathology of Inflammatory response including wound healing and repair

Question 1

What is inflammation?

Answer 1

Inflammation is a complex local response of the living vascularized tissues to injury and mainly consists of responses of blood vessels and leukocytes.

Response of the vascularized tissues to an injurious stimulus is called inflammation.

Question 2

Inflammation may be divided into acute or chronic.
State the differences between acute and chronic inflammation.

Answer 2

ACUTE INFLAMMATION
*Rapid onset
*Short duration
*Predominant cells are neutrophils
*Is part of the response of the body tissues to physical and chemical damages, pathogen invasion, tissue necrosis, etc.

CHRONIC INFLAMMATION
*Slow onset
*Longer duration lasts for months or years.
*Lymphocytes and macrophages are predominant cells
*Is part of the response of the body tissues to prolonged irritation of chemicals; foreign particles – dust, surgical thread, etc.; infection by microorganisms that cannot be overcome for a long time by the body – tuberculosis, syphilis, brucellosis.

Question 3

Describe mechanisms in which the 5 cardinal signs of inflammation come about.

Answer 3

1.Redness: Increased blood flow and stasis
2.Heat; Increased blood flow
3.Swelling: Vascular permeability resulting in loss of proteins to the ECF
4.Pain: Chemical mediators such as prostaglandins and kinins
5.Loss of function: Due to pain

Question 4

Mention the various causes of acute inflammation.

Answer 4

1. Infections (bacterial, viral, fungal, and parasitic) and microbial toxins
2. Tissue necrosis:
   – Ischemia: e.g., myocardial infarction
   – Physical Agents
   -Mechanical trauma: e.g., blunt/penetrating/crush injuries
   -Thermal injury: e.g., burns or frostbite
   -Radiation
   -Electric shock
   - Sudden changes in atmospheric pressure
   – Chemical injury: e.g., strong acids and alkalis, insecticides, and herbicides
3. Foreign bodies: e.g., sutures, talc

4.Immune reactions:
– Hypersensitivity reactions
– Autoimmune diseases.

Question 4

Acute inflammation has two major components namely:

Answer 4

1. Reactions of blood vessels (vascular changes)
2. Reactions of leukocytes (cellular events)

Question 5

What is the purpose of Reactions of blood vessels (vascular changes).

Answer 5

Purpose: To deliver the circulating cells, fluids and plasma proteins from the circulation to sites of infection or tissue injury.

Question 6

State the 2 reactions of blood vessels in acute inflammation.

Answer 6

The reactions of blood vessels in acute inflammation consist of:
1.Changes in the vascular flow and caliber
2.Increased vascular permeability.

Question 7

Describe events that happen during changes in vascular flow and caliber.

Answer 7

1.Vasodilatation:
– Effect: Result is increased blood flow, local heat and redness.

– Chemical mediators involved:

Histamine, prostaglandins, platelet-activating factor, kinins and nitric oxide (NO).

2. Increased permeability of the microvasculature:

It leads to escape of protein-rich fluid from the circulation into the extravascular tissues.

– Chemical mediators involved: Histamine, leukotrienes, platelet-activating factor, kinins.

3. Slowing of blood flow:

It leads to the concentration of RBCs in small vessels and increased viscosity of the blood.

4. Stasis: It is responsible for localized redness.

5.Leukocyte events: Described later.

Question 8

During the changes in vascular permeability, exudation occurs.

Define exudation.
What is the effect of exudation?

Answer 8

Exudation: It is defined as the process of escape of fluid, proteins and circulating blood cells from the vessels into the interstitial tissue or body cavities.

Escape of a protein-rich fluid causes edema and is one of the cardinal signs of inflammation.

Question 9

Describe 5 ways in which vascular permeability can be achieved during acute inflammation response.

Answer 9

1. Contraction of endothelial cells:
   Contraction of endothelial cells lead to formation of endothelial gaps; this is the commonest mechanism of increased vascular permeability.

Increased vascular permeability and chemotaxis: Occurs predominantly in venules (except in lungs, where it occurs in capillaries)

2. Direct endothelial injury: e.g. burns, or infection by microbes.
3. Leukocyte-mediated vascular injury: The leukocyte (mainly neutrophils) which adheres to the endothelium during inflammation may themselves injure the endothelial cells.
4. Increased transcytosis: Process of transport of fluids and proteins through the channels called vesiculovacuolar organelle.
5. Leakage from new blood vessels:

During repair new blood vessels are formed (angiogenesis). These vessels are leaky till the endothelial cells mature.

Question 10

What is the purpose of LEUKOCYTIC/CELLULAR EVENTS.

Answer 10

This process delivers leukocytes capable of phagocytosis (neutrophils and macrophages) to the site of injury.

Question 12

LEUKOCYTIC/CELLULAR EVENTS occur in two ways. State them.

Answer 12

The events can be divided into:
1. Leukocyte recruitment
2. Leukocyte activation

Question 12

Normally, leukocytes move rapidly in the blood, and during inflammation, they slow down and escape to the site of injury/causative agent in the extravascular space.

What is leukocyte extravasation?

Answer 12

Leukocyte extravasation is the process of migration of leukocytes from the lumen of the vessel to the site of injury in the extravascular tissues.

Question 12

Leukocyte recruitment to sites of inflammation from the vessel lumen can be divided into the following steps:

1. In the lumen
2. Across lumen

3.Outside the lumen

Answer 12

Leukocyte recruitment to sites of inflammation from the vessel lumen can be divided into the following steps:

1.In the lumen:

Margination
*Movement of the leukocytes principally neutrophils towards the periphery of the blood vessel. Occurs due to increased vascular permeability. Vasodilatation and selectins have important role

Rolling
*Transient adhesion of leukocytes with the endothelial cells{ Mediated by selectins.

Adhesion
*Firm attachment of the leukocytes to the endothelial cells.
Mediated by heterodimeric leukocyte surface proteins called integrins.

2.Across lumen:
*Transmigration or Diapedesis
Migration across the endothelium and vessel wall

Occurs mainly in postcapillary venules.
Most important molecule: PECAM-1 (platelet endothelial cell adhesion molecule) or CD31.

After traversing the endothelium, leukocytes pierce basement membrane, probably by secreting collagenases, and enter extravascular tissue.

3.Outside the lumen:

Chemotaxis
*Migration in the tissues toward a chemotactic stimulus

*Unidirectional movement of the leukocytes towards site of injury along a chemical gradient.

*Bind to G-protein coupled receptors on the surface of leukocyte

*Causes actin polymerization and all movements.

Question 13

What is the Clinical Importance of Leukocyte Adhesion Molecules.

Answer 13

• Three main types of leukocyte adhesion deficiency (LAD) have been identified.
• All are transmitted as autosomal recessive disease.

Characterized by the inability of neutrophils to exit the circulation to sites of infection, leading to leukocytosis and increased susceptibility to infection.

Genetic deficiencies of leukocyte adhesion molecules cause recurrent bacterial infections.

Question 14

One way in which leukocytes activation takes place is by recognition of microbes, necrotic cells and foreign substances.

Name the cell surface receptors Leukocytes recognize microbes, necrotic cells and foreign substances by.

The most important of these receptors are:
* Toll-like receptors (TLRs):
* Inflammasome:

Describe their respective functions.

Answer 14

Develops in two sequential events:

1. Recognition of microbes, necrotic cells and foreign substances:

The most important of these receptors are:

• Toll-like receptors (TLRs): They can recognize extracellular and ingested microbes
• Inflammasome: multi-protein complex and can recognize products of dead cells (e.g., uric acid, microbial products).

Question 15

Another way Leukocyte activation can take place is through recognizing, internalizing, and digesting foreign material, microorganisms, or cellular debris by a process termed phagocytosis which consists of three steps.

State the 3 steps of phagocytosis.

Answer 15

Many leukocytes recognize, internalize, and digest foreign material, microorganisms, or cellular debris by a process termed PHAGOCYTOSIS.

It consists of three steps;
* Recognition and attachment
* Engulfment
* Killing or degradation of the ingested material.

Question 16

1.What is a phagolysosome?
2.What is a phagosome?
3. Describe the clinical Significance of Defects in Phagolysosome Function.

Answer 16

1. It is a cytoplasmic body formed by the fusion of a phagosome with a lysosome in a process that occurs during phagocytosis.
2. A vacuole in the cytoplasm of a cell, containing a phagocytosed particle enclosed within a part of the cell membrane.

Chédiak-Higashi syndrome: Autosomal recessive condition characterized by:

• Increased susceptibility to infections: Due to defective fusion of phagosomes and lysosomes in phagocytes.
• Leukocyte abnormalities include:
  – Neutropenia (decreased numbers of neutrophils)
  – Defective degranulation and delayed microbial killing.

Question 17

Killing and degradation of ingested microbial agents/particles occurs within neutrophils and macrophages.

What are the most important microbicidal agents?

Answer 17

Killing and degradation of ingested microbial agents/particles occurs within neutrophils and macrophages.

Most important microbicidal agents are:
1) reactive oxygen species and
2) lysosomal enzymes.

Question 18

1.Name the cell derived mediators of inflammation.
State their role.
Where are they derived from?

Answer 18

1.Vasoactive Amines: Histamine and Serotonin

ii. Vasoactive amines namely histamine and serotonin cause vasodilatation and increased vascular permeability.

Histamine and serotonin are preformed vasoactive cell-derived mediators.

iii. Source: Mast cells (richest source), blood basophils and platelets.

Platelets, some neurons and enterochromaffin cells in the gastrointestinal tract).

2.Arachidonic Acid (AA) metabolites
(Prostaglandins, Leukotrienes, and Lipoxins)

ii. Source: Derived from cell membrane phospholipids mainly by the enzyme phospholipase A2.

Can be enzymatically converted into prostaglandins and leukotrienes (both together called as eicosanoids).

Occurs along two major enzymatic pathways (next Fig.). These are.

*Cyclooxygenase pathway (produce prostaglandins)

*Lipoxygenase pathway (produces leukotrienes and lipoxins).

iii. Can mediate almost every step of inflammation.

3. Reactive Oxygen Species (ROS)

ii. ROS are chemically reactive oxygen-derived free radical.

Normally, they are rapidly inactivated.
But increased production can cause cell injury.

*Cell of origin: Leukocytes (neutrophils and macrophages).

Mechanism of production: Leukocytes during phagocytosis (after exposure to microbes, chemokines, and immune complexes) generate oxygen-derived free radicals.

4. Cytokines and Chemokines

i. These are polypeptides which function as mediators in immune responses and in inflammation (acute and chronic).

ii. Source: Cytokines are secreted by many types of cells (activated lymphocytes and macrophages, endothelial, epithelial, and connective tissue cells).

5. Nitic oxide
6. Platelet activating factor

Question 19

1. What are the 2 major cytokines involved in inflammation?
2. What is their source?

3.Name the stimuli for their production or release.

4.State their 3 major effects in inflammation.

5.Outline their systemic effects in inflammation.

Answer 19

1. Tumor Necrosis Factor and Interleukin-1
2. Source: Activated macrophages.
3. Stimuli: Endotoxin and other microbial products, immune complexes, physical injury, and many inflammatory stimuli.

Actions in inflammation (fig)
* Local effects:
– Endothelium: Endothelial activation and increased expression of endothelial adhesion molecules.

– Leukocytes: TNF increases the responses of neutrophils to other stimuli (e.g., bacterial endotoxin).

– During repair: Proliferation of fibroblasts and increased synthesis of collagen.

• Systemic effects:
  – Fever
  – Leukocytosis: A higher than normal level of white blood cells in the blood.
  – Systemic acute-phase reactions
  – Suppresses appetite: TNF contributes to cachexia seen in some chronic infections.

Question 20

1. What are chemokines?

2.Chemokines are classified four major groups namely____________.

3.Chemokines are responsible for chemotaxis of monocytes, eosinophils, basophils, and lymphocytes except ____________.

Answer 20

Chemotactic cytokines or chemokines are small proteins, which selectively attracts various leukocytes to the site of inflammation.

Classification: Chemokines are classified four major groups namely:
* C-X-C chemokines,
* C-C chemokines,
* C chemokines
* CX3C chemokines.

Action: Chemotaxis of monocytes, eosinophils, basophils, and lymphocytes except neutrophils.

They activate leukocyte and promote their recruitment to the sites of inflammation.

Question 21

State the plasma- proteins derived chemical mediators of inflammation.

Answer 21

1. Complement components.
   * C3a, C5a:

Are referred to as anaphylatoxins.
They cause smooth muscle contraction, vasodilation, histamine release from mast cells, and enhanced vascular permeability.

They also mediate chemotaxis, inflammation, and generation of cytotoxic oxygen radicals.

*C3b:

C3b is potent in opsonization: tagging pathogens, immune complexes (antigen-antibody), and apoptotic cells for phagocytosis.

Additionally, C3b plays a role in forming a C3 convertase when bound to Factor B (C3bBb complex), or a C5 convertase when bound to C4b and C2b (C4b2b3b complex) or when an additional C3b molecule binds to the C3bBb complex (C3bBb3b complex).

*C5b-9: MAC

2.Kinins
*Bradykinin: Vasodilation, lowers BP

Angiotensin-converting enzyme (ACE) is an enzyme that breaks down and inactivates bradykinin. BP drugs are ace inhibitors.

*Kallikrein: Same as bradykinin

3. Coagulation system

Question 22

What are the 4 main outcomes of acute inflammation?

Answer 22

1. Complete resolution – with total repair and destruction of the insult.

2.Fibrosis and scar formation (Organization) – occurs in cases of significant inflammation.
*Healing by connective tissue replacement.

3.Chronic inflammation – from a persisting insult

4.Formation of an abscess (suppuration)

• An abscess is a localized collection of pus surrounded by granulation tissue.

*Pus contains necrotic tissue with suspended dead and viable neutrophils and dead pathogens.

*It forms when the primary insult is a pyogenic bacterium and extensive tissue necrosis occurs.

Question 23

What is chronic inflammation mostly seen in?

What are the 3 main characteristics of chronic inflammation?

Answer 23

Seen in:

*Persistent infections
*Hypersensitivity diseases
*Prolonged exposure to exogenous or endogenous toxic agents­ e.g., silicosis, atherosclerosis

Characterized by:

*Infiltration with mononuclear cells ­macrophages, lymphocytes, and plasma cells

*Tissue destruction- hallmark of chronic inflammation

*Attempts at healing-via angiogenesis and fibrosis

Question 24

What are the main cells in Chronic Inflammation?
Where are they derived from?
Compare the half-life of macrophages and monocytes.

Answer 24

Main Cells in Chronic Inflammation: Macrophages

Macrophages are tissue cells derived from hematopoietic stem cells in the bone marrow and from progenitors in the embryonic yolk sac and fetal liver during early development.

Half-life of blood monocytes is about 1 day, whereas the life span of tissue macrophages is several months or years.

Question 25

State the 2 types of macrophages.

Answer 25

Two types of macrophages:
i. Activated macrophages
ii. Tissue macrophages: Tissue macrophages derived from projectors in embryonic yolk sac and fetal liver during each development.

Activated microphages are also called M1 macrophages or classically activated macrophages. They are stimulated by bacterial or viral infections and produce pro-inflammatory cytokines to fight the infection.

Tissue macrophages are also called M2 macrophages or alternatively activated macrophages. They are involved in wound healing, tissue repair, and anti-inflammatory responses.

Question 26

Tissue macrophages are named according to the organ they are found at.
1. Liver
2. Spleen
3. CNS
4. Synovium
5. Bone
6. Lung
7. Lymph nodes
8. Placenta
9.Kidney

Answer 26

1.Kupfer cells
2.Littoral cells
3.Microglia
4.Type A lining cells
5. Osteoclasts
6.Alveolar macrophages or dust cells
7.Sinus histiocytes
8.Hoff Bauer cells
9.Mesangial cells

Question 27

Lymphocytes are dominant population in the chronic inflammation seen in autoimmune and other hypersensitivity diseases.

1.State the role of lymphocytes.

Morphological pattern of lymphocytes macrophages is marked by granuloma formation.

2.What is granuloma?
Macrophages may get activated to form ___________.

3.Describe the process of granuloma formation.

Answer 27

Role of Lymphocytes

Dominant population in the chronic inflammation seen in autoimmune and other hypersensitivity diseases.
CD4+ T lymphocytes promote inflammation. via different cytokines

Activated B lymphocytes & antibody-producing plasma cells are also present.

MORPHOLOGICAL PATTERN

Characterized by formation of granuloma.

Granuloma is an aggregation of activated macrophages surrounded by mononuclear cells, principally lymphocytes.

Macrophages may get activated to form epithelioid cells (epithelium ­like cells).

Some of the cells may fuse together to form a bigger cell called a giant cell.

3. Injury»> inability to ingest the insult»> Failure of acute inflammatory response»>Persistence of the injurious agent»>Cell mediated response»>Recruiting of macrophages with epithelioid and giant cell formation»> Granuloma formation.

Question 28

Define the terms repair/ healing.

Under what circumstances is repair and healing used?

Answer 28

*Repair/healing refers to the incomplete restoration of tissue architecture and function after an injury.

*Repair is often used for parenchymal and connective tissues.
*Healing is used for surface epithelia.

Question 29

Repair of damaged tissues occurs by two types of reactions:
i. Regeneration
ii. Connective Tissue Deposition (Scar Formation)

Describe the 2 processes.

Answer 29

i. Regeneration

Proliferation of cells and tissues to replace lost structures. It results in complete restitution of lost or damaged tissue.

ii. Connective Tissue Deposition (Scar Formation)

Occurs by the laying down of connective (fibrous) tissue:
Fibrosis: extensive deposition of collagen
Organization: fibrosis develops in a tissue space occupied by an inflammatory exudate

Question 30

Outline steps in scar formation.

Answer 30

1.Injury
2. Inflammation
3. Angiogenesis
4. Formation of granulation tissue
5. Connective tissue deposition
6. Remodeling of connective tissue
7. Zinc dependent MMPS

Question 31

State the 3 phases of cutaneous wound healing.

Answer 31

1. Inflammation
2. Granulation tissue formation and re-epithelization
3. Wound contraction, ECM deposition and remodeling

Question 32

Three key cellular mechanisms are necessary for wound healing once hemostasis is achieved. Outline them.

Answer 32

Cellular migration
Extracellular matrix organization and remodeling
Cell proliferation

Question 33

Extracellular Matrix Sustains the Repair Process.

What is their function?

Three types of extracellular matrix contribute to the organization, physical properties and function of tissue. Outline the 3.

Answer 33

*Providing the key components of scar tissue and the stem cell niche.

Three types of extracellular matrix contribute to the organization, physical properties and function of tissue:
■ Basement membrane
■ Provisional matrix
■ Connective tissue (interstitial matrix or stroma)

Gradually, collagen is laid down by the fibroblasts to form the scar, which over time is modified by enzymes in the extracellular matrix through a process called remodeling.

This process involves the crosslinking of collagen fibers to strengthen the tissue and subsequent reshaping and partial resorption by metalloproteases.

Question 34

Repair can be impaired by numerous factors.
State 4 factors that may impair wound healing.

Answer 34

1. Mechanical factors such as excessive movement or pressure.
2. Infection which causes prolonged inflammation and tissue injury.
3. Diabetes, a disease in which retards healing by metabolic abnormality and vascular narrowing,
   leading to poor blood supply and favor new infections.

4.Compromised by supply.

Question 35

There are 2 types of wound healing. By first intention and by second intention.

Compare the 2.

Answer 35

BY FIRST INTENTION
*Clean and less damage to cells and tissue, uninfected surgical incision
* Less intense inflammatory reaction
* Limited granulation tissue is formed.

BY SECOND INTENTION
*Extensive loss of cell and infected
*More inflammatory response
*Much larger of granulation tissue formed
*Wound contraction is present

Question 36

State at least 3 complications in wound healing.

Answer 36

1.Deficient Scar Formation
*Wound Dehiscence: Wound dehiscence is a surgery complication where the incision, a cut made during a surgical procedure, reopens.

*Incisional Hernias: Hernias (protrusion of tissue) that are caused by incomplete surgical wound healing.

*Ulceration

2. Excessive Scar Formation in the Skin
   *Keloids and hypertrophic scars
3. Excessive Contraction