8.3 Acute and chronic inflammation
2 min read•july 25, 2024
is your body's rapid response to injury or infection. It's like a quick-fire defense system, causing , heat, , and pain. Chemical messengers like histamine and kickstart the process, while and rally the troops.
, on the other hand, is a long-term battle. It can last for weeks, months, or even years. Unlike acute inflammation's quick , chronic inflammation persists, potentially causing ongoing damage. It's often triggered by persistent infections, toxic exposures, or autoimmune disorders.
Acute Inflammation
Characteristics of acute inflammation
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- Acute inflammation manifests as rapid, short-term response to injury or infection typically lasting hours to days
- Cardinal signs encompass redness, heat, swelling, pain, and loss of function indicating inflammatory process
- Vascular changes involve increasing blood flow to affected area and heightened vascular permeability allowing plasma proteins and leukocytes to enter tissues
- Leukocyte infiltration occurs through margination (white blood cells adhering to vessel walls), (leukocytes migrating through vessel walls into tissues), and (directed movement of leukocytes towards injury site)
Chemical mediators in inflammation
- Histamine released by mast cells and basophils triggers vasodilation and
- Prostaglandins derived from arachidonic acid promote vasodilation and pain sensitization (aspirin blocks)
- Cytokines like (IL-1) and (TNF-α) activate endothelial cells and promote leukocyte adhesion while (IL-6) stimulates acute phase protein production
- Complement proteins enhance phagocytosis and attract leukocytes, increases vascular permeability and causes pain, and acts as vasodilator and antimicrobial agent
Chronic Inflammation
Acute vs chronic inflammation
- Duration differs with acute lasting hours to days while chronic persists for weeks to months or years
- Cellular involvement shifts from predominantly in acute to , lymphocytes, and plasma cells in chronic
- Tissue damage in acute is minimal and often reversible whereas chronic leads to progressive damage potentially causing and organ dysfunction
- Resolution patterns vary with acute typically resolving completely while chronic remains an ongoing process with periods of exacerbation and remission
Causes of chronic inflammation
- Persistent infections (tuberculosis, hepatitis C) maintain prolonged immune activation
- Prolonged exposure to toxic agents (silica dust, asbestos) leads to ongoing tissue damage
- Autoimmune disorders (rheumatoid arthritis, systemic lupus erythematosus) result from immune system mistakenly targeting self-antigens
- Mechanisms involve persistent antigen presence stimulating ongoing immune response, dysregulation of immune system failing to resolve acute inflammation, and granuloma formation organizing macrophages in response to persistent antigens
- Consequences include tissue remodeling and fibrosis, forming new blood vessels, and potential for malignant transformation in some cases
Key Terms to Review (26)
Acute inflammation: Acute inflammation is a rapid and early immune response to tissue injury or infection, characterized by the classic signs of redness, heat, swelling, pain, and loss of function. This process is crucial for healing and involves the activation of various immune cells, vascular changes, and the release of inflammatory mediators that work together to eliminate pathogens and initiate tissue repair.
Angiogenesis: Angiogenesis is the process through which new blood vessels form from pre-existing ones, essential for supplying nutrients and oxygen to tissues. This process is crucial during wound healing and in response to inflammation, as it helps deliver immune cells to sites of injury or infection, promoting recovery and tissue repair. Additionally, uncontrolled angiogenesis can contribute to diseases such as cancer, where tumors exploit this process to grow and spread.
Autoimmune diseases: Autoimmune diseases are conditions where the immune system mistakenly attacks the body's own cells and tissues, treating them as foreign invaders. This misdirected immune response can lead to inflammation and damage in various organs, highlighting the complex interplay between immune regulation, self-tolerance, and disease pathogenesis.
Bradykinin: Bradykinin is a peptide that plays a key role in the inflammatory response, functioning as a potent vasodilator that increases vascular permeability and promotes pain. Its production is stimulated by tissue injury or infection, leading to enhanced blood flow and inflammation at the site of damage. This process is critical for recruiting immune cells to the area, facilitating healing, and initiating the body's defense mechanisms.
Chemotaxis: Chemotaxis is the movement of cells towards or away from a chemical stimulus, often used by immune cells to locate sites of infection or inflammation. This process is crucial for the functioning of the immune system, as it directs leukocytes to areas where they are needed most to fight off pathogens and initiate repair processes.
Chronic Inflammation: Chronic inflammation is a prolonged and persistent inflammatory response that can last for months or even years, resulting in tissue damage and a variety of diseases. Unlike acute inflammation, which is a short-term and protective response to injury or infection, chronic inflammation often arises from the body's failure to eliminate the initial cause of inflammation, leading to continuous tissue injury and remodeling. This process is closely linked to various immune system activities, including leukocyte trafficking and the role of the lymphatic system in managing immune responses.
Chronic inflammatory diseases: Chronic inflammatory diseases are long-term health conditions characterized by persistent inflammation that can result from a variety of causes, including autoimmune disorders, prolonged exposure to irritants, or infections. This ongoing inflammation can lead to tissue damage and contribute to various diseases, significantly impacting an individual's overall health and quality of life.
Complement proteins: Complement proteins are a group of proteins that play a crucial role in the immune system by helping to identify and eliminate pathogens. These proteins work together in a cascade of reactions known as the complement system, enhancing the body's ability to fight infections and trigger inflammatory responses. Their actions include opsonization of pathogens, formation of the membrane attack complex, and promotion of inflammation, linking them closely to both innate immunity and the inflammatory response.
Cytokines: Cytokines are small signaling proteins that are crucial for cell communication in the immune system. They play an essential role in mediating and regulating immunity, inflammation, and hematopoiesis, linking innate and adaptive immune responses.
Diapedesis: Diapedesis is the process by which leukocytes (white blood cells) move out of the bloodstream and into surrounding tissues, allowing them to reach sites of infection or injury. This movement is crucial for immune response and inflammation, enabling leukocytes to migrate to areas where they are needed to combat pathogens and facilitate tissue repair.
Fibrosis: Fibrosis is the formation of excess fibrous connective tissue in an organ or tissue as a reparative response to injury or inflammation. This process can lead to scarring and stiffening of tissues, affecting their normal function. Fibrosis can occur in various organs and is often a consequence of chronic inflammation, linking it directly to conditions such as chronic lung disease, liver cirrhosis, and heart disease.
Immune Tolerance: Immune tolerance is a state of unresponsiveness of the immune system to specific antigens, which allows the body to coexist with certain proteins, tissues, or microbes without mounting an immune response. This phenomenon is essential for preventing autoimmune diseases and for the acceptance of transplanted tissues. Immune tolerance plays a significant role in maintaining a balanced immune response, ensuring that the body does not attack its own cells while still being able to respond to pathogens.
Increased vascular permeability: Increased vascular permeability refers to the condition where blood vessel walls become more permeable, allowing fluids, proteins, and immune cells to move from the bloodstream into surrounding tissues. This process is a key feature of inflammation, enabling the body to respond to injury or infection by facilitating the movement of immune cells to affected areas, but it can also lead to edema and tissue damage if excessive.
Inflammatory resolution: Inflammatory resolution is the process through which the body effectively shuts down and resolves inflammation after it has served its protective purpose. This involves a series of complex biochemical events that lead to the removal of inflammatory cells and the restoration of tissue homeostasis. Proper inflammatory resolution is crucial to prevent chronic inflammation, which can lead to various diseases and complications.
Initiation: Initiation refers to the beginning phase of the inflammatory response, where various signaling pathways and immune cell activities are triggered in reaction to injury or infection. This phase is crucial as it sets off a cascade of events that facilitate the recruitment of immune cells and the production of inflammatory mediators, leading to either acute or chronic inflammation depending on the context and duration of the stimulus.
Interleukin-1: Interleukin-1 (IL-1) is a pro-inflammatory cytokine that plays a crucial role in the immune response and the regulation of inflammation. It is produced mainly by activated macrophages and is essential for mediating various inflammatory processes, making it a key player in both acute and chronic inflammation. IL-1 promotes the recruitment of immune cells to sites of infection or injury and contributes to systemic responses like fever and the acute phase reaction.
Interleukin-6: Interleukin-6 (IL-6) is a cytokine that plays a critical role in immune response, inflammation, and hematopoiesis. It is produced by various cells, including macrophages and T cells, and is involved in both acute and chronic inflammatory processes. This multifunctional cytokine can promote inflammation and has been linked to various diseases, making it an important player in the immune system's regulation.
Macrophages: Macrophages are large immune cells that play a crucial role in the body's defense mechanisms by engulfing and digesting cellular debris, pathogens, and foreign substances. They originate from monocytes in the blood and are pivotal in both the innate and adaptive immune responses, acting as key players in inflammation, antigen presentation, and tissue repair.
Neutrophils: Neutrophils are a type of white blood cell that plays a vital role in the innate immune response, acting as the first line of defense against invading pathogens. They are essential for responding quickly to infections, especially bacterial and fungal, and are characterized by their ability to migrate to sites of inflammation and infection through the bloodstream and tissues.
Nitric Oxide: Nitric oxide is a colorless gas that acts as a signaling molecule in the body, playing a vital role in various physiological and pathological processes. It is produced by endothelial cells and is critical in regulating blood flow, immune responses, and inflammation. In the context of inflammation, nitric oxide serves as a mediator that can promote both protective and harmful effects depending on the context of its production and the environment in which it acts.
Prostaglandins: Prostaglandins are lipid compounds that have hormone-like effects in various tissues throughout the body. They are derived from fatty acids and play a crucial role in mediating inflammation, regulating immune responses, and facilitating communication between cells. Their production is often triggered by injury or infection, linking them directly to the body's response mechanisms and influencing both acute and chronic inflammatory processes.
Redness: Redness, or erythema, refers to the abnormal reddening of the skin or mucous membranes due to increased blood flow to the area. This occurs as a result of inflammation, where blood vessels dilate and become more permeable, allowing immune cells and proteins to reach the affected tissue more effectively.
Resolution: Resolution refers to the process by which inflammation subsides and tissue repair occurs following an inflammatory response. This involves the clearance of inflammatory cells, restoration of normal tissue architecture, and re-establishment of homeostasis. Understanding resolution is critical because it highlights the balance between inflammatory processes and tissue healing, ensuring that inflammation does not lead to chronic conditions.
Swelling: Swelling is the increase in volume or size of a body part due to an accumulation of fluid in the tissues, commonly occurring during inflammation. This process is a crucial aspect of both acute and chronic inflammation, as it reflects the body's response to injury or infection, allowing immune cells and necessary proteins to reach the affected area more effectively.
Tumor necrosis factor-alpha: Tumor necrosis factor-alpha (TNF-α) is a pro-inflammatory cytokine produced primarily by activated macrophages, playing a critical role in the regulation of immune responses, inflammation, and apoptosis. TNF-α is involved in both acute and chronic inflammatory processes, acting as a signaling molecule that recruits immune cells to sites of infection or injury and promoting the inflammatory response. Its dysregulation is implicated in various autoimmune diseases and chronic inflammatory conditions.
Vasodilation: Vasodilation is the process by which blood vessels widen due to the relaxation of vascular smooth muscle, leading to increased blood flow. This mechanism plays a crucial role in various physiological responses, particularly during acute inflammation, where enhanced blood supply is necessary for delivering immune cells and nutrients to affected tissues. Vasodilation not only contributes to redness and heat associated with inflammation but also facilitates the subsequent healing processes.