Inflammation, Infection, and Cellular Adaptation

Neutrophils

  • Neutrophils are among the first responders transported to the site of injury during the inflammatory response.
  • Their count peaks approximately 24 hours after the initial injury.
  • Neutrophils are the primary cells involved in initiating phagocytosis, the process of engulfing and removing pathogens or debris.
  • Macrophages also contribute to phagocytosis but arrive later, typically around 3-7 days post-injury.
  • There are two main categories of macrophages:
    • M1 Macrophages: Participate in the inflammatory response and play a role in adaptive immunity.
    • M2 Macrophages: Primarily involved in tissue healing and repair processes.

Invasion Stage of Infection

  • The invasion stage is characterized by the rapid reproduction of a pathogenic microorganism.
  • This reproduction occurs at the initial tissue site and can spread to tissues farther away.
  • The invasion triggers inflammatory and immune responses in the body.

Cardinal Signs of Inflammation

  • Localized findings of inflammation are also known as cardinal or classic signs.
  • These include:
    • Redness (rubor)
    • Edema (swelling)
    • Pain (dolor)
    • Heat (calor) at the site of injury.
  • The vascular phase is immediately activated in response to tissue injury.
    • There is an initial, rapid vasoconstriction at the injury site to isolate the area.
    • Vasodilation follows quickly to transport blood, oxygen, and nutrients to the injured site.
    • The blood delivers immune system cells, particularly neutrophils, to combat infection and facilitate healing.

Fever

  • Fever is a systemic manifestation of inflammation, distinguishing it from localized signs.
  • Fever can be beneficial in certain cases, specifically when heat-sensitive microorganisms are involved, as elevated temperatures can inhibit their growth and replication.

Metaplasia

  • Metaplasia is a form of cellular adaptation that occurs in response to injury.
  • When cells are injured, their normal function is impaired.
  • Cellular adaptation is a process to maintain or restore cellular function under stress.
  • Metaplasia involves a potentially reversible change in a mature cell type to another that is better able to survive in the altered environment of the injured tissue.
  • Example of Metaplasia:
    • An example of metaplasia is observed in the airways of smokers.
    • The normal cells of the trachea and bronchi are ciliated columnar epithelial cells.
    • Chronic exposure to smoke irritates these cells.
    • Over time, the ciliated columnar epithelial cells are replaced by stratified squamous epithelial cells.
    • This cellular change is an adaptation to the chronic irritation caused by smoking.