1. The cardinal signs of inflammation are rubor (redness), calor (heat), tumor (swelling), dolor (pain), and loss of function. Seen here is skin with erythema, compared to the more normal skin at the far right.

2. Enlarged congested appendix with yellow to tan exudate and hyperemia, including the periappendiceal fat Diagnosis: acute appendicitis

3. Acute appendicitis: extensive neutrophilic infiltraton through the whole layers (transmural) with area of mucosal ulceration & exudate.

4. The mucosa shows ulceration and undermining by an extensive neutrophilic exudate. Neutrophils extend into and through the wall of the appendix in a case of acute appendicitis.

5. Acute inflammation is marked by an increase in inflammatory cells
Acute inflammation is marked by an increase in inflammatory cells. Here marked by an increase in segmented neutrophils (PMN's).

6. Seen here is vasodilation with exudation that has led to an outpouring of fluid with fibrin into the alveolar spaces, along with PMN's Diagnosis: acute inflammation in lung

7. Here PMN's that are marginated along the dilated venule wall (arrow) are squeezing through the basement membrane (the process of diapedesis) and spilling out into extravascular space. Diagnosis: acute inflammation

8. Seen here are mainly neutrophils, but there are also plasma cells, lymphocytes, and macrophages. Macrophages can phagocytoze other cells as well as cellular debris

9. Numerous neutrophils fill the alveoli in this case of acute bronchopneumonia in a patient with a high fever. Note the dilated capillaries in the alveolar walls from vasodilation with the acute inflammatory process.

10. The neutrophils are seen infiltrating the mucosa and submucosa of the gallbladder with vascular congestion and edema Diagnosis: acute cholecystitis

11. This example of edema with inflammation : there is marked laryngeal edema such that the airway is narrowed. This is life-threatening. Thus, fluid collections can be serious depending upon their location. Diagnosis: acute laryngitis

12. Here is an example of fluid collection into a body cavity, or an effusion. This is a right pleural effusion. Note the clear, pale yellow appearance of the fluid. This is a serous effusion with lung collapse.

13. The fibrin in this fluid can form a fibrinous exudate on the surfaces
The fibrin in this fluid can form a fibrinous exudate on the surfaces. Here, the pericardial cavity has been opened to reveal a fibrinous pericarditis with strands of stringy pale fibrin between visceral and parietal pericardium.

14. This yellow-green exudate on the surface of an inflamed, hyperemic (erythematous) bowel mucosa with purulent exudate on the surface Diagnosis: suppurative inflammation of colon

15. The abdominal cavity is opened at autopsy, here to reveal an extensive purulent peritonitis that resulted from rupture of the colon. A thick yellow exudate coats the peritoneal surfaces diagnosis: acute suppurative perritonitis

16. Extensive acute inflammation may lead to abscess formation, as seen here with rounded abscesses (the purulent material has drained out after sectioning to leave a cavity) in upper lobe and lower lobe.

17. Microscopically, the extensive neutrophilic exudate with fibrin, hemorrhage and necrotic debris of an acute abscessing pneumonia is seen here. Normal tissues are destroyed in the region of the abscess. the abscess is surrounded by an area of acute inflammation Diagnosis: acute abscess

18. One consequence of acute inflammation is ulceration
One consequence of acute inflammation is ulceration. This occurs on epithelial surfaces. Here the gastric mucosa has been lost, or ulcerated. A larger ulcer and several adjacent smaller ones with surrounding erythema

19. An esophageal acute ulcer is shown here in which the squamous mucosa has been lost. In the ulcer base are inflammatory cells and fibrin