3/24/25

Fever is an abnormal elevation in body temperature caused by agents like hydrogen, which induce fever.
Fever is essentially a resetting of the body's internal thermostat to a higher set point, aimed at:
Heating out pathogens.
Making the environment inhospitable for pathogens to replicate by limiting their access to nutrients.
Debate on Antipyretics:
Taking medications to reduce fever (antipyretics) can lower body temperature.
However, fevers serve an important purpose in fighting infections, so it may be beneficial to let a fever run its course for a limited time (e.g., one day).
Medical attention should be sought if a fever persists for an extended time to prevent issues with basic metabolic activities.

Inflammation is a localized response to tissue injury due to trauma or infection.
Purpose of Inflammation:
Limit the spread of infection/pathogen.
Isolate pathogens to prevent further injury and initiate destruction:
- Neutrophils: Key cells that destroy pathogens and debris.
- Macrophages: Help clean up damaged tissues and dead cells.
Four Cardinal Signs of Inflammation:
Redness
Swelling/edema
Heat
Pain
Some suggest adding loss of function as a fifth sign, particularly focusing on mobility in affected areas.

Begins with the release of chemical signals from injured tissue cells that activate endothelial cells of nearby capillaries.
Enhanced adhesion molecules on endothelial cells attract and modulate neutrophils so they adhere and migrate into the tissue (diapedesis).
Histamine Role: Released by mast cells, causes vasodilation and increases capillary permeability, allowing fluid and leukocytes to enter the damaged tissue.
Neutrophils follow chemotactic signals to the site of injury and perform phagocytosis, ingesting and destroying pathogens.

Immune system comprises several lines of defense:
First Line: Skin and mucous membranes (nonspecific defense)
Second Line: Inflammation and other nonspecific mechanisms
Third Line: Specific immune response (adaptive immunity) occurs if the pathogen surpasses the first two defenses.

Specificity and Memory: Key characteristics of specific immunity.
Specificity: Targets specific pathogens rather than attacking all (like first two lines of defense).
Memory: Remembers past pathogen exposures for quicker and more effective responses in future encounters.

Two main forms: Cellular (cell-mediated) and Humoral (antibody-mediated).
Cell-mediated Immunity:
- Involves T lymphocytes.
- Targets pathogens hiding inside cells (e.g., viruses) and involves activation of cytotoxic T cells to kill infected cells.
Humoral Immunity:
- Involves B lymphocytes producing antibodies to flag extracellular pathogens and toxins for destruction by other immune cells.

Cytotoxic T Cells: Directly kill infected cells.
Helper T Cells: Support the function of other immune cells, including B cells and cytotoxic T cells.
Regulatory T Cells: Help maintain balance in the immune response to prevent overactivity.
Memory T Cells: Sustain memory of previously encountered pathogens for enhanced future responses.

Antibodies are produced by B cells and have several classes:
IgA: Found in mucosal areas, breast milk; provides passive immunity to newborns.
IgG: Most abundant antibody in blood; provides long-term protection, crosses placenta.
IgM: First antibody produced in response to an infection; involved in primary immune response.
IgE: Related to allergic reactions.
IgD: Helps with B cell activation.

Active Immunity:
Natural: Body produces antibodies in response to real infections.
Artificial: Body produces antibodies following vaccination.
Passive Immunity:
Natural: Transfer of antibodies from mother to fetus (placenta) or through breast milk.
Artificial: Emergency administration of antibodies from another source (e.g., antivenom).