5.4
Réponse Inflammatoire I : Vasculaire et Cellulaire
La réponse inflammatoire est la défense du corps contre l'infection, la blessure ou l'irritation causées par les bactéries, les traumatismes, les toxi…
La réponse inflammatoire est un mécanisme de défense de l’organisme contre les infections, les blessures ou les irritations.
Elle peut être aiguë, durant des jours ou des semaines, ou chronique, durant plusieurs mois à des années.
L’inflammation aide à identifier et à détruire les agents pathogènes et à éliminer les éléments tissulaires endommagés afin que le corps puisse guérir.
Cette réponse est observée aux niveaux vasculaire et cellulaire. Les deux sont des composants cruciaux du processus inflammatoire aigu.
Au stade vasculaire, les petits vaisseaux sanguins près du site de la blessure se contractent d’abord pour éviter la perte de sang.
Les artérioles et les veinules qui fournissent du sang à cette zone se dilatent, ce qui augmente le flux sanguin et provoque des rougeurs et de la chaleur locales.
De plus, la libération de médiateurs cellulaires, tels que l’histamine, la bradykinine et les prostaglandines, dans la zone blessée augmente la perméabilité vasculaire aux fluides riches en protéines et en cellules immunitaires, ce qui provoque un gonflement, une douleur et une perte de fonction.
Au cours de la phase cellulaire, les globules blancs, ou WBC, traversent les vaisseaux sanguins et se précipitent vers le site de la lésion, provoquant une augmentation du nombre global de globules blancs.
Les globules blancs, comme les neutrophiles et les monocytes, engloutissent les agents pathogènes et ingèrent des débris cellulaires et des corps étrangers. À la suite de la phagocytose pathogène, des pyrogènes sont libérés, provoquant de la fièvre.
View the full transcript and gain access to JoVE Core videos
Q1: What is the inflammatory response and why does the body trigger it?
The inflammatory response is a defense mechanism against infection, injury, or irritation from bacteria, trauma, toxins, or heat. It helps locate and destroy pathogens while removing damaged tissue elements to promote healing. This response occurs at both vascular and cellular levels, with fluid, blood products, and nutrients migrating to the injured area, resulting in redness, heat, swelling, pain, and loss of function.
Q2: What happens to blood vessels during the vascular stage of inflammation?
During the vascular stage, small blood vessels near the injury site initially constrict to prevent blood loss. The arterioles and venules then dilate, increasing blood flow and causing local redness and heat. Cell mediators like histamine and bradykinin are released, increasing vascular permeability and allowing protein-rich fluids to flow into the area, causing swelling and pain.
Q3: How do white blood cells respond during the cellular stage of inflammation?
During the cellular stage, white blood cells, including neutrophils and monocytes, pass through blood vessels and rush to the injury site, increasing overall WBC count. These cells engulf pathogens through phagocytosis and ingest cell debris and foreign material. This phagocytic activity releases pyrogens from bacterial cells, which trigger fever as part of the systemic inflammatory response.
Q4: What role do cell mediators play in the inflammatory response?
Cell mediators such as histamine, bradykinin, and prostaglandins are released in the injured area during inflammation. These mediators increase vascular permeability, allowing protein- and immune-cell-rich fluids to escape blood vessels and enter surrounding tissue. This fluid accumulation causes the characteristic swelling, pain, and temporary loss of function associated with acute inflammation.
Q5: How long can inflammation last and what are the different types?
Inflammation can be acute, lasting days or weeks, or chronic, lasting several months to years. Acute inflammation is the initial response to injury or infection, characterized by vascular and cellular changes. Chronic inflammation represents a prolonged response when the body cannot fully resolve the initial insult, potentially leading to tissue damage and systemic complications.
Q6: What systemic signs indicate that inflammation is occurring throughout the body?
Systemic inflammation produces signs beyond the local injury site, including fever, increased white blood cell count, malaise, anorexia, nausea, and vomiting. Lymph node enlargement may also occur as lymphoid tissues respond to infection. In severe cases, organ failure can develop, indicating that the inflammatory response has become widespread and potentially harmful.
Q7: Why does fever develop as part of the inflammatory response?
Fever develops when white blood cells engulf pathogens through phagocytosis during the cellular stage of inflammation. This phagocytic activity releases pyrogens from bacterial cells, which are fever-inducing substances. Pyrogens circulate through the bloodstream and act on the body's temperature-regulating center, raising the set point and causing fever as part of the systemic inflammatory defense.