Acute Inflammation: Outcomes and Terminology

Hello :) In this post we'll take a look at the terminology used to describe the classifications of acute inflammation. We'll also discuss the possible outcomes of this process. 
 
 Outcomes of Acute Inflammation

There are four possible outcomes of acute inflammation: complete resolution, healing via fibrosis, abscess formation, or the progression to chronic inflammation. The outcome depends on the severity of the tissue damage, the ability of the cells to regenerate as well as the characteristics of the damaging stimulus. 

A few events are involved in the resolution of acute inflammation. Firstly, normal vascular permeability it returned. Oedema fluid and proteins are then drained into the lymphatics and this may also be consumed by macrophages through pinocytosis. Dead neutrophils and necrotic debris are also phagocytosed and the macrophages are disposed of. Macrophages also release growth factors which initiate the process of repair.  

Types of Acute Inflammation

The classification of an acute inflammatory lesion depends on the anatomical site and nature of the exudate. The suffix "itis" is added to the end of the name of the organ to show that it is inflamed. For example, encephalitis, tonsillitis, meningitis, hepatitis etc. 

The major component of the exudate is then added to this base word. There are seven types of exudate that may be seen (the name of the exudate is in blue, examples are in red):

1. Serous: this is serous fluid with increased amounts of cells and proteins. It is straw coloured and clots upon exposure to air (due to increased amounts of clotting factors). It is the mildest form of exudate. It is commonly seen in serous cavities (eg abdomen, thorax, pericardium etc) and may also be seen in burns. 
2. Serofibrinous: this is similar to serous exudates but has strands and flecks of fibrin. It is associated with an increased inflammatory response. It may be seen in feline infectious peritonitis. 
3. Fibrinous: this results from more extensive vascular leakage and clotting. In severe cases, the fibrin deposits within or over organs appears as white-tan, sticky, flaky material which may adhere to the material. It looks like butter has been smeared over the tissues. These exudates act to localise the lesion and as a scaffold for cell migration and healing. However, the reaction may become severe enough to enhance the initial injury (eg. fibrin deposition in the pericardium can restrict movement of the heart. An example of fibrinous inflammation is fibrinous pneumonia caused by acute Mannheima haemolytica infection.
4. Mucoid or Catarrhal: the tissue response consists of the secretion or accumulation of a thick gelatinous fluid containing abundant mucous and mucins from a mucous membrane. It may be seen in mild forms of bronchitis and tracheitis.
5. Haemorrhagic: this contains increased numbers of erythrocytes and appears as varying shades of dull red, brown or black. It is seen where there is damage to blood vessels. Eg  colitis in horses. 
6. Suppurative or Purulent: This type of exudate contains large numbers of dead and dying neutrophils and necrotic tissue debris which is liquefied by the neutrophils. It is often referred to as 'pus' and is seen with bacterial infections. It appears as a thick, pasty-white (yellow/green/brown) exudate. 
7. Diphtheritic: this occurs on mucous membranes which become necrotic and interwoven. Within the necrotic tissue is a fibrinous exudate. It appears as a sticky, yellow-brown exudate which adheres to the underlying surface. It may be seen in herpes virus in chickens.    

 The classification of the inflammation can be made more specific by including the time frame (acute, sub-acute or chronic). Eg acute suppurative hepatitis.


That's it for this post! See you next time :)