Inflammation

Introduction 

 Inflammation

Inflammation is the physiological response to tissues damage or any injury and it is protective in nature. is a protective response by body to remove the injurious stimuli as well as to initiate the process of healing and tissue repair.

  • To eliminate the cause of the tissue damage. 
  • To repair injured and damaged tissue.
  • Inflammation is necessary for the survival of the host.
  • In the absence of inflammation the body would be unable to kill and eliminate infectious agents.
  • One of the innate defense mechanisms of the body. 

Defination 

  1. Inflammation is defined as complex series of events that occurs in vascularized living tissues in response to local injury or tissue damage.
  2. Inflammation is a local response of living tissue due to any agent which is fundamentally a protective response and ultimate goal is to get rid of initial cause cell injury

Causes of Inflammation

(A) Infectious (living) or Biological Cause

  • Bacteria
  • Virus
  • Mycoplasma
  • Fungi
  • Protozoa
  • Parasites

B. Non Infectious (Non living) Causes

1. Physical Agents

  • Heat
  • Cold
  • UV/Ionizing radiations
  • Trauma or Mechanical Injury

2. Chemical Agents

  • Acids
  • Alkalines
  • Organic poisons

3. Immunological Agents

  • Foreign body
  • Antigen-Antibody reaction (Auto immunity)

4. Psychological Agents

  •  Excitement

Types of Inflammation-

Inflammation is classified into 2 categories

  1. Acute inflammation
  2. Chronic inflammation

1. Acute inflammation- 

  • It is the initial reaction of tissue to an injury. Most common characters of acute inflammation are short duration, immediate onset etc.
  • Most common causes of acute inflammation are bacterial invasion, viral, parasitic infection, tissue injury due to trauma and other agents exposure.

The cells mainly involved in acute inflammation are-

  • Neutrophils (Primarily involved)
  • Eosinophils
  • Basophils
  • Monocytes

Possible result of acute inflammation may be 4 types-

1. Resolution- It means complete return of inflammed tissues to normal tissues. When tissue changes are mild and reversible, this result occurs. Some changes like vasodilation, increased vascular permeability, leucocytic infiltration are ceased that help in regeneration of damaged cells.

2. Complete repairing- When tissue damage is extensive then there is healing by fibrosis. In this condition there is no tissue regeneration.

3. Progressive to abscess formation- If inflammation is due to pyogenic bacterial infection then it will result in abscess formation.

4. Chronic inflammation- If causative agent persist for longer period then it may progress to chronic inflammation.

B. Chronic inflammation

  • It is an inflammation of delayed onset and prolonged duration, which can extend over a long period of time, (Many months or years). This type of inflammation may be due to prolonged exposure to toxic agents, persistent infections with some types of micro-organisms and autoimmunity. Acute inflammation may result in chronic inflammation.

The cells mainly involved in chronic inflammation are

  • Macrophages
  • Lymphocytes
  • Plasma cells
  • Mast cells
  • Eosinophils

Signs of inflammation-

  • Redness (Rubor)- Due to increased blood supply (vasodilation) to the area of inflammation
  • Swelling (Tumor)- Swelling appear due to escape of fluid into extra cellular space.
  • Heat (Calor)- Due to increase blood supply to the area.
  • Pain (Dolor)- Pain at the site of inflammation.
  • Loss of function (Function laesa)- Pain and swelling cause impairment in normal functions of affected organ.

Events in acute inflammation

  1. Vascular events
  2. Cellular events 

1. Vascular events in acute inflammation

A. Haemodynamic changes

 Persistent progressive vasodilation

  • Affects venules & capillaries
  • Increased  in blood volume lead to redness and warmth at site of inflammation.
  • Transudation of fluid in extracellular space
  • Swelling at local site of acute inflammation

B. Changes in vascular permeability

Increased Vascular  Permeability 

  •  In acute inflammation normally nonpermeable endothelial layer of microvasculature becomes leaky. 

2. Cellular events in acute inflammation

Cellular phase of inflammation consists of 2 process

A. Exudation of leukocytes

The changes leading to migration of leucocytes are-

  • Changes in the formed elements of blood
  • Rolling and adhesion
  • Emigration
  • Chemotaxis 

B. Phagocytosis 
Phagocytosis is defined as the process of engulfment of solid particulate material by the cells

Phagocytes (cell eating cells)

  • Microphages
  • Macrophages 

Steps in phagocytosis-

  • Recognition and attachment stage (opsonisation)
  • Engulfment stage
  • Secretion (degranulation) stage
  • Digestion or degradation stage

Chemicals of inflammation-

During tissue injury, several chemicals are released like-

  1. Prostaglandins
  2. Histamine
  3. Serotonin
  4. Bradykinin

The action of chemicals during inflammation

S.No Name of Chemicals           Action 
1.  Prostaglandins
  • Increase vascular permeability
  • Vasodilation or vasoconstriction.
2.  Histamine
  • Increase Vascular Permeability Vasodilation
  • Contraction of smooth muscles such as contraction of bronchi
3.  Serotonin
  • Increase Vascular Permeability
  • Constriction of blood vessels
4.  Bradykinin
  • Dilation of blood vemels.
  • Increase Vascular Permeability

 

Differences between Acute and Chronic inflammation

S.No. Feature Acute Inflammation Chronic inflammation
1.  Onset Fast- minutes to days, innate Immune response Slow- Months to years, Adaptive immune system
2.  Duration Hours to Days Months to years
3.  Cellular Infiltrate Mainly Neutrophis followed by macrophages Macrophases, plasma cells and lymphocytes
4.  Vascular changes Prominent (vasodilation, Increase permeability) Not prominent, angiogenesis
5.  Tissue Injury Self limited Progressive
6.  Fibrosis Usually mild Often severe
7.  Local and systemic signs Prominent Less

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