3.1 Acute and Chronic Inflammation
3 min read•july 24, 2024
Inflammation is the body's protective response to injury or infection. It involves a complex interplay of immune cells, chemical mediators, and vascular changes that work together to eliminate threats and promote healing.
Understanding the inflammatory process is crucial for grasping how the body defends itself. From acute responses like sunburns to chronic conditions like arthritis, inflammation plays a key role in health and disease, affecting multiple body systems.
Inflammatory Response Characteristics
Acute vs chronic inflammation
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- Short-term response manifests rapidly within minutes to hours
- Lasts days to weeks resolving with healing or progressing to chronic state
- dominate cellular response engulfing pathogens and debris
- Characterized by rapid onset and (sunburn, minor cuts)
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- Long-term response develops slowly over days to years
- Persists for months to years causing ongoing tissue damage and repair
- and predominate mediating adaptive immunity
- Results in prolonged inflammation (rheumatoid arthritis, atherosclerosis)
Cardinal signs of inflammation
- Five cardinal signs
- redness due to increased blood flow
- heat from elevated metabolic activity and blood flow
- swelling caused by fluid accumulation in tissues
- pain from nerve ending stimulation by inflammatory mediators
- loss of function due to pain, swelling, and tissue damage
- Physiological explanations
- Redness and heat result from vasodilation increasing blood flow to affected area
- Swelling occurs as vascular permeability increases allowing fluid accumulation
- Pain arises when chemical mediators stimulate local nerve endings
- Loss of function stems from combined effects of pain, swelling, and tissue injury
Inflammatory Process Mechanisms
Immune cells in inflammation
- Key immune cells
- Neutrophils arrive first performing phagocytosis of pathogens and debris
- Macrophages engulf pathogens and present antigens to adaptive immune cells
- Lymphocytes coordinate adaptive immune responses (T cells, B cells)
- release and other mediators triggering early inflammatory response
- Chemical mediators
- Histamine causes vasodilation and increased vascular permeability
- promote vasodilation and sensitize pain receptors
- Leukotrienes guide chemotaxis and increase vascular permeability
- Cytokines facilitate cell signaling and regulate immune responses
- Complement proteins enhance opsonization and induce cell lysis
- Vascular changes
- Vasodilation increases blood flow to affected area
- Increased permeability allows fluid and protein exudation into tissues
- Cellular events
- Margination leukocytes adhere to vessel walls
- Diapedesis leukocytes migrate through vessel walls into tissues
- Chemotaxis directs leukocyte movement towards inflammatory stimuli
Systemic effects of inflammation
- Fever
- Pyrogens (IL-1, TNF-α) elevate body temperature
- Increases metabolic rate and oxygen consumption
- Acute phase response
- Liver produces acute phase proteins
- enhances opsonization and activates complement
- Fibrinogen increases blood viscosity and clotting risk
- Leukocytosis
- Elevated white blood cell count in circulation
- Fatigue and malaise
- Energy redirected to support
- Anorexia
- Decreased appetite from cytokine effects on hypothalamus
- Muscle protein catabolism
- Muscle breakdown provides energy and materials for acute phase proteins
- Neuroendocrine changes
- Increased cortisol production modulates inflammation
- Altered insulin sensitivity affects glucose metabolism
- Anemia of chronic disease
- Decreased red blood cell production and iron sequestration
- Cachexia
- Severe weight loss and muscle wasting in prolonged inflammation (cancer)
Key Terms to Review (23)
Acute Inflammation: Acute inflammation is the body's immediate and initial response to injury or infection, characterized by increased blood flow, vascular permeability, and the accumulation of immune cells at the site of damage. This process is essential for healing and serves as a protective mechanism against pathogens and tissue injury, often distinguishing it from chronic inflammation, which develops over a longer time frame and may lead to tissue damage.
Anti-inflammatory medications: Anti-inflammatory medications are drugs designed to reduce inflammation and alleviate pain caused by conditions such as arthritis, injuries, and various inflammatory diseases. By targeting the inflammatory response in the body, these medications help control symptoms associated with both acute and chronic inflammation, providing relief and improving the quality of life for those affected.
C-reactive protein: C-reactive protein (CRP) is a substance produced by the liver in response to inflammation, and it is often used as a marker to assess the presence and intensity of inflammatory conditions in the body. High levels of CRP are associated with acute and chronic inflammatory responses, including infections and autoimmune diseases, making it a significant indicator in clinical settings for monitoring disease activity and response to treatment.
Calor: Calor is a key term in inflammation that refers to the increase in temperature observed at the site of injury or infection. This rise in temperature is part of the body's inflammatory response, signifying increased blood flow and metabolic activity in the affected area. Calor contributes to the overall signs of inflammation, which also include redness, swelling, pain, and loss of function, working together to promote healing and combat pathogens.
Cellular Phase: The cellular phase refers to the stage of the inflammatory response characterized by the movement and activation of immune cells at the site of injury or infection. This phase involves various types of white blood cells, including neutrophils and macrophages, which play crucial roles in clearing pathogens, debris, and damaged tissue, ultimately aiding in the healing process. The cellular phase is critical in both acute and chronic inflammation as it helps determine the effectiveness of the immune response and influences the overall outcome of the inflammatory process.
Chronic Inflammation: Chronic inflammation is a prolonged inflammatory response that can last for months or years, characterized by the simultaneous destruction and healing of tissue. Unlike acute inflammation, which is a short-term response to injury or infection, chronic inflammation can arise from persistent infections, autoimmune diseases, or exposure to irritants, leading to tissue damage and various health issues over time. This ongoing process can significantly impact disease development, especially in conditions involving the nervous system and other systemic disorders.
Chronicity: Chronicity refers to the long-lasting nature of a disease or condition, often persisting for months or years. This concept is crucial in understanding how inflammation can transition from an acute phase, which is typically short-lived and aimed at resolving injury, to a chronic state where inflammation can lead to ongoing tissue damage and disease progression.
Corticosteroids: Corticosteroids are a class of steroid hormones produced in the adrenal cortex that play a crucial role in regulating various physiological processes, including metabolism, immune response, and inflammation. They are commonly used therapeutically to manage conditions such as allergies, asthma, autoimmune diseases, and inflammation-related disorders by mimicking the effects of hormones that are naturally produced by the body.
Cytokine Storm: A cytokine storm is an overreaction of the immune system, characterized by the excessive release of pro-inflammatory cytokines that can lead to severe tissue damage and systemic inflammation. This phenomenon often occurs in response to infections, autoimmune diseases, or certain therapies and can result in acute respiratory distress, multi-organ failure, and even death if not managed effectively. Understanding cytokine storms is crucial because they play a significant role in both acute and chronic inflammatory processes.
Dolor: Dolor refers to the sensation of pain, particularly in the context of inflammation. This term is crucial in understanding how the body responds to injury or infection, as pain is one of the hallmark signs of both acute and chronic inflammatory processes. Recognizing dolor helps in assessing the severity of inflammation and guiding appropriate treatment strategies.
Erythrocyte Sedimentation Rate: The erythrocyte sedimentation rate (ESR) is a blood test that measures the rate at which red blood cells settle at the bottom of a test tube over a specified period, usually one hour. A higher ESR can indicate inflammation, infection, or disease, making it an important marker for diagnosing various conditions, including those related to inflammation and joint disorders.
Functio laesa: Functio laesa refers to the impaired function of tissues or organs due to injury, inflammation, or disease processes. This term is particularly significant in understanding how acute and chronic inflammation can disrupt normal physiological functions, leading to symptoms such as pain, swelling, and loss of mobility. Inflammation plays a critical role in the body's healing process, but when it becomes chronic, it can exacerbate dysfunction and contribute to long-term damage.
Histamine: Histamine is a biologically active amine that plays a crucial role in the immune response and acts as a neurotransmitter in the body. It is primarily stored in mast cells and basophils and is released during allergic reactions, inflammation, and tissue injury. Histamine's effects include vasodilation, increased vascular permeability, and stimulation of gastric acid secretion, making it a key player in both acute inflammation and immune responses.
Immune Response: The immune response is the body's complex defense mechanism against foreign invaders, such as pathogens, and involves the recognition and elimination of these harmful agents. This process includes both innate and adaptive immunity, with acute and chronic inflammation playing crucial roles in the immediate and long-term response to infection. The immune response also involves various white blood cells and lymphoid tissues that work together to provide protection and maintain health.
Lymphocytes: Lymphocytes are a type of white blood cell that plays a crucial role in the immune system, specifically in recognizing and responding to pathogens such as viruses and bacteria. They are divided into two main categories: B cells, which produce antibodies, and T cells, which kill infected host cells or help activate other immune cells. Their functions are vital for both acute and chronic inflammation processes, where they help orchestrate the immune response and maintain homeostasis.
Macrophages: Macrophages are large immune cells that play a vital role in the body's defense against pathogens, tissue repair, and homeostasis. They originate from monocytes and are crucial for both innate and adaptive immunity, responding to infection and injury through processes like phagocytosis and the release of inflammatory cytokines. Their function connects them to both acute and chronic inflammation as well as the etiology and pathogenesis of various diseases.
Mast Cells: Mast cells are a type of white blood cell that play a crucial role in the immune response, particularly in inflammation and allergic reactions. They are found in connective tissues throughout the body and are loaded with granules containing histamine and other mediators that can promote inflammation, making them vital in both acute and chronic inflammatory processes. Their activation leads to the release of these mediators, which can cause blood vessel dilation, increased vascular permeability, and recruitment of other immune cells to the site of injury or infection.
Neutrophils: Neutrophils are a type of white blood cell and a crucial part of the immune system, primarily responsible for defending the body against infection and inflammation. They are the most abundant type of granulocyte and respond rapidly to sites of acute inflammation, making them key players in the body’s innate immune response. Their ability to quickly migrate to areas of tissue damage or infection helps to eliminate pathogens and initiate the healing process.
Prostaglandins: Prostaglandins are lipid compounds derived from fatty acids that have a wide range of physiological effects in the body, particularly in the inflammatory response and the reproductive system. They play critical roles in mediating inflammation, regulating immune responses, and influencing various reproductive processes such as ovulation and uterine contractions.
Resolution: Resolution refers to the process by which inflammation subsides and the affected tissue returns to its normal state following an injury or infection. This process is essential in both acute and chronic inflammation, as it helps to restore homeostasis and prevent further tissue damage. The resolution phase involves the removal of inflammatory cells, clearance of debris, and tissue repair, ultimately leading to healing and restoration of function.
Rubor: Rubor is a Latin term that refers to the redness of the skin or mucous membranes resulting from increased blood flow to an area, typically due to inflammation. This phenomenon is a hallmark sign of the inflammatory response, where blood vessels dilate and allow more blood to reach the affected tissues. Rubor, along with other signs such as calor (heat), dolor (pain), and tumor (swelling), helps to indicate the presence of an underlying pathological process.
Tumor: A tumor is an abnormal mass of tissue that arises when cells divide uncontrollably, which can be benign or malignant. Tumors result from various factors, including genetic mutations, environmental influences, and chronic inflammation, leading to an imbalance in normal cellular processes. They can affect surrounding tissues and organs, causing various symptoms depending on their size and location.
Vascular phase: The vascular phase is the initial response of blood vessels to injury, characterized by vasodilation and increased permeability. This phase plays a crucial role in acute inflammation as it allows for the delivery of immune cells and proteins to the site of injury or infection, setting the stage for further inflammatory responses.