Cellular Responses to Inflammation and the Pathophysiology of Inflammation and Infection

Recruitment of White Blood Cells (WBCs): The cellular response is initiated when chemical mediators draw white blood cells to the site of tissue injury. Leukocytes are capable of squeezing through existing gaps in the capillary walls to exit the bloodstream and enter the inflamed tissue.
Leukocyte Classifications: The primary leukocytes involved in this response include:
- Neutrophils.
- Monocytes.
- Lymphocytes.
- Macrophages.
Chemotaxis: This is the process by which leukocytes move through the tissue toward the site of injury by following chemical gradients.
Phagocytosis: The culmination of the cellular response where phagocytes (specialized leukocytes) engulf and degrade bacteria and cellular debris.
Exudate Formation: The products resulting from phagocytosis, combined with plasma and other blood cells, form a substance known as exudate. This collection of fluid and cells contributes directly to the clinical manifestations of swelling and pain.

Cell-Derived Mediators: Chemicals released directly from cells to facilitate the inflammatory response include:
- Histamine.
- Serotonin.
- Prostaglandin.
Plasma-Derived Mediators: Chemicals originating from the blood plasma that assist in mediating inflammation include:
- Bradykinin.
- The clotting system.
- The complement system.

Determination of Treatment: The specific treatment for inflammation is dictated by several factors:
- The location of the inflammation within the body.
- The underlying cause (e.g., autoimmune response, direct physical injury, or infection).
Pharmacological Management: Medications used to manage inflammation include:
- Non-steroidal anti-inflammatory drugs (NSAIDs) (prevent prostaglandins from being synthesised)
- Aspirin
- Paracetamol
- Corticosteroids: These medications function by binding to glucocorticoid receptors to suppress the inflammatory response.
Non-Pharmacological Treatments: Often referred to as the RICE protocol and lifestyle interventions:
- Rest.
- Ice.
- Compression.
- Elevation.
- Adequate nutrition, specifically including anti-inflammatory foods.

Definition: Infection is characterized as the invasion and multiplication of microorganisms within body tissue.
Infectious Agents: Infections are caused by various pathogens and their metabolic byproducts, including:
- Bacteria.
- Viruses.
- Parasites.
- Fungi.
- Toxic products produced by these pathogens.
Modes of Transmission:
- Direct: Contact with infected blood and body fluids.
- Indirect: Through contaminated water, food, or surfaces (fomites).
- Vectors: Via intermediate organisms, such as mosquitoes.
Vulnerable Populations: Certain groups are at a higher risk of infection, including:
- The elderly.
- Individuals with chronic diseases.
- Patients on immunosuppressant therapy.
- Patients undergoing chemotherapy.
- Young children.

Physical Barriers: The first line of defense includes:
- Skin.
- Mucous membranes.
- Tears and earwax.
- Stomach acid.
- Urine and vaginal secretions.
- Antimicrobial factors present in saliva, tears, and prostatic fluids.
Respiratory Defenses: Specific mechanisms within the respiratory system include:
- Humidification.
- Filtration.
- The mucociliary lining.
Mechanical Clearing: The flushing actions of the urinary tract and the bowel help expel pathogens.

The Chain of Infection: For an infection to occur, a specific six-step chain must be established:
1. A causative agent.
2. A source for the agent.
3. A portal of exit from that source.
4. A means of transmission.
5. A portal of entry into the new host.
6. A susceptible person.
Post-Invasion Outcomes: Once microorganisms successfully invade the body, they must multiply. Following multiplication, three primary outcomes are possible:
1. The microorganisms continue to multiply and overwhelm the host's defenses.
2. A state of balance is reached, resulting in a chronic infection.
3. The body, either through its own means or with medical intervention, destroys and eliminates the invading microorganisms.

Virulence Factors: Specialized molecules or properties of disease-causing microorganisms that increase the severity of the disease they cause.
Evasion Tactics: Microorganisms have evolved various ways to bypass body defenses:
- Blocking physical or chemical defense mechanisms.
- Interfering with the production of antibodies and T cells.
- Using capsules: Protective outer layer coats that prevent white blood cells from ingesting the microorganism and causing lysis
Biofilms: Some bacteria produce a biofilm that allows them to attach to host cells and foreign materials, such as:
- Peripheral IVC (Intravenous Catheters).
- Suture material.
- Medical implants.
Biofilm Function: Biofilms protect microorganisms from being reached by the host immune response and from the effects of antibiotics.

Immune Identification: White blood cells and antibodies identify and eliminate pathogens that have successfully bypassed physical barriers.
Cellular Proliferation: The body increases the count of specific white blood cells, namely neutrophils and monocytes, to engulf and destroy invaders.
Killer T Cells: The immune system produces these specialized white blood cells to recognize and kill invading organisms directly.
Antibody Function: Antibodies attach to microorganisms to immobilize them, kill them outright, or assist neutrophils in targeting them.
Fever: An increase in body temperature is a protective response to both infection and injury.

Systemic (Whole Body) Symptoms: These indicate the infection has spread or is affecting the entire system:
- Fatigue.
- Loss of appetite and weight loss.
- Fevers, night sweats, and chills.
- Aches and pains.
- Tachycardia (elevated heart rate).
- Tachypnea (elevated respiratory rate).
Localized Symptoms: These are specific to the site of infection or entry:
- Skin rashes.
- Coughing.
- Runny nose.