Classification and general features
The type of exudative inflammation is determined by the composition of the effusion. Four main types are distinguished:
- Serous.
- Fibrinous.
- Purulent.
- Putrid.
There are also variants that are not classified as independent types, as they represent admixtures to the main exudate. These include hemorrhagic inflammation (admixture of erythrocytes), catarrhal (admixture of mucus), and mixed (combination of different effusions).
The course of the process is most often acute; chronic forms are less common. In most cases, inflammation ends in restitutio ad integrum — complete restoration of the damaged tissue. Less commonly, scar tissue forms at the site of the focus.
Serous inflammation
This form produces a turbid fluid containing a moderate number of cells (lymphocytes, leukocytes, desquamated epithelium). Biochemically, the exudate is characterized by a protein content of up to 2.5% (albumin-to-globulin ratio from 0.55:1 to 2.7:1).
Causes of development:
- Viral infections (influenza, herpes, viral hepatitis, chickenpox) are the most frequent cause.
- Bacteria and allergens.
- Burns (thermal, chemical, radiation).
- Action of endo- and exotoxins causing plasmarrhagia.
Localization and manifestations: The process affects mucous, serous, and synovial membranes, the skin (blister formation), renal glomerular capsules, perisinusoidal spaces of the liver, and the stroma of parenchymatous organs. The main function of such effusion is to wash away toxins and microorganisms from surfaces.
Clinically, the process is accompanied by fever, moderate leukocytosis, and an elevated ESR. The danger of serous inflammation lies in fluid accumulation: in the meninges, it leads to brain compression; in the pleural cavity, to lung collapse (atelectasis); and impregnation of the interalveolar septa causes acute respiratory distress syndrome. The outcome is usually favorable, but transition to diffuse sclerosis is possible in parenchymatous organs.
Fibrinous inflammation
Characterized by the formation of a dense exudate with a high fibrin content. The mechanism is associated with tissue necrosis and platelet aggregation: under the action of tissue thromboplastin, fibrin precipitates, impregnating dead tissues and forming a light gray film. Microorganisms actively multiply under this film, releasing toxins.
Etiology includes exposure to viruses, allergens, toxins, and bacteria (e.g., Corynebacterium diphtheriae, Shigella, Mycobacterium tuberculosis, coccal flora).
Depending on the depth of necrosis and the type of epithelium, two forms are distinguished:
- Croupous inflammation (from Scottish croup — film). Develops on mucous or serous membranes covered by single-layer epithelium with a thin connective tissue base (trachea, bronchi, peritoneum, pleura). Necrosis is superficial, the film is thin and easily detached without forming ulcers. Example: croupous pneumonia.
- Diphtheritic inflammation (from Greek diphthera — leather/membrane). Occurs on stratified squamous non-keratinizing or transitional epithelium, as well as on single-layer epithelium with a loose, broad base (pharynx, esophagus, uterus, urinary bladder). Necrosis is deep; a thick film is tightly fused with tissues. When it separates, deep ulcers remain.
Outcomes: Cleansing of the focus occurs through autolysis — hydrolases of polymorphonuclear leukocytes (neutrophils) dissolve the fibrin. The croupous form usually ends in complete restitution. Diphtheritic inflammation heals via substitution (incomplete regeneration) with scar formation. If fibrin is not resorbed, it activates fibroblasts, and organization of the exudate takes place — replacement by connective tissue. On serous membranes, this leads to adhesions, fibrous plaques, and obliteration (overgrowth) of cavities.
Catarrhal inflammation (catarrh)
A specific variant that develops exclusively on mucous membranes. Its main feature is an admixture of mucus to any other type of exudate (serous, purulent, hemorrhagic).
Causes of catarrh include infections, allergic reactions (e.g., serous catarrh in allergic rhinitis), as well as chemical and thermal irritants. Example: purulent catarrh of the tracheal and bronchial mucosa.
Acute catarrh lasts 2–3 weeks and usually resolves without consequences. In a chronic course, irreversible changes develop in the mucous membrane: it may thin (atrophy) or, conversely, thicken (hypertrophy).
Briefly: answers to topical questions
Which cells and components make up purulent exudate?
Purulent exudate consists of a liquid part, solid elements, and cellular composition.
- Liquid part — includes albumins, globulins, complement components, and biologically active substances from blood plasma.
- Solid elements — contain a moderate amount of fibrin, tissue detritus from the inflammation focus, and microorganisms.
- Cellular composition — the predominant population is living and dead neutrophilic leukocytes (17–29%). Lymphocytes, macrophages, and often eosinophilic granulocytes are also present in the exudate.
In which infectious diseases is the development of hemorrhagic inflammation typical?
The development of hemorrhagic inflammation is typical for diseases accompanied by pronounced intoxication of the body. Such infections include:
- Influenza — severe forms of the disease.
- Plague — a particularly dangerous infection characterized by serous-hemorrhagic inflammation of lymph nodes and sepsis with hemorrhages.
- Anthrax — a particularly dangerous infection causing serous-hemorrhagic lymphadenitis, enteritis, or skin inflammation.
- Smallpox — a particularly dangerous infection characterized by the phenomenon of "black smallpox" due to the darkening of the exudate.
Which microorganisms cause putrid inflammation?
The cause of putrid inflammation is the addition of putrefactive microflora to a focus of purulent inflammation with pronounced tissue necrosis. Such microflora includes Proteus, clostridia, bacteroids, and fusobacteria. Upon breakdown of tissue protein, products of putrefactive decomposition are formed, including indole, skatole, hydrogen sulfide, and amines.
What is the complete pathogenesis of fibrinous exudate formation?
The pathogenesis of fibrinous exudate formation is based on the precipitation of fibrin in necrotic tissue. The process includes the following stages:
- The action of a damaging factor causes tissue necrosis and platelet aggregation in the focus.
- Tissue thromboplastin (thrombokinase) is released from necrotic cells.
- Vascular permeability increases, which ensures the exit of fibrinogen from blood plasma.
- Under the action of thrombokinase, fibrinogen is converted into fibrin.
- Fibrinous exudate impregnates dead tissue, resulting in the formation of a light-gray fibrinous film on the surface.
To avoid confusing the forms of fibrinous inflammation: Croupous — Circumferential / surface-level (superficial, the film is easily removed). Diphtheritic — Deep / base (deep lesion, the film is torn off together with the "base", leaving an ulcer).
Class and exam questions
Which cells are responsible for the resorption of fibrinous membranes?
Cleansing occurs via autolysis: hydrolases of polymorphonuclear leukocytes (neutrophils) break down the precipitated fibrin.
What will happen if the fibrinous exudate does not resolve?
The organization process is triggered. Fibrin activates fibroblasts, the exudate is replaced by connective tissue, which leads to the formation of scars, adhesions, or complete obliteration of cavities.
Can catarrhal inflammation occur in muscles or on the skin?
No, catarrh develops exclusively on mucous membranes, since its obligatory sign is the secretion of mucus.
What else to study on this topic
- Purulent inflammation: composition of exudate and clinical-morphological forms
- Putrefactive inflammation: etiology and pathogenesis features
- Hemorrhagic inflammation: causes of erythrocyte diapedesis into the exudate
- Mechanisms of plasmarrhagia in the formation of serous effusion
- Cellular composition of exudate depending on the type of pathogen
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