Chapter 43: The Immune System Flashcards
Innate vs. adaptive immunity
Innate immunity is common to all animals and is present from birth
Adaptive immunity is found only among vertebrates and develops after exposure to pathogens
Components of the innate immune system
Barrier defenses
Cellular innate defenses
Local inflammatory response
Antimicrobial peptides and proteins
Cellular innate defenses
Phagocytic cells dedicated to detecting, devouring, and destroying pathogens that include:
- Neutrophils
- Macrophages
- Dendritic cells
- Eosinophils
- Natural killer cells
- Mast cells
Many cellular involve the lymphatic system
Toll-like receptor
Found expressed on the surface of phagoctic cells or on the inner surface of vesicles formed by endocytosis
Binds to fragments of molecules characteristic of a set of pathogens to signal phagocytosis such as:
- Double-stranded RNA characteristic of certain viruses
- Lipoplysaccharides commonly found on the surface of baterium
Neutrophils
Phagocytic cells of the innate immune system that circulate in the blood and are attracted by signals from infected tissues
Macrophages
LARGER phagocytic cells of the innate immune system that stimulate adaptive immunity by presenting antigens that they engulf
Some migrate throughout the body while others are found in specific organs or tissues such as the spleen
Dendritic cells
Phagocytic cells of the innate immune system that stimulate adaptive immunity by presenting antigens that they engulf
Mainly populate tussues such as the skin that are in contact with the environment
Eosinophils
Phagocytic cells of the innate immune system that are defend against multicellular pathogens such as parasitic worms by discharging destructive enzymes
Often found beneath the epithelium
Natural killer cells
Phagocytic cells of the innate immune system that circulate through the body and detect abnormal surface proteins on some virus-infected and cancerous cells
Do NOT enfulf stricken cells but instead release chemicals that lead to cell death which inhibit the spread of virally infected or cancerous cells
Lymphatic system structures
Consists of lymphatic vessels and structures that trap foreign substances such as the lymph nodes and lymphoid organs:
- Adenoids
- Tonsils
- Thymus
- Spleen
- Peyer’s patches- in small intestines
- Appendix
Antimicrobial peptides and proteins
Function in innate defense by attacking pathogens or impeding their reproduction
- Interferons
- Complement system
Interferons
Proteins secreted by virus-infected cells that induce nearby uninfected cells to produce substances that inhibit viral replication
Limit cell-to-cell spread of viruses in the body
Control viral infections such as colds and influenza
Complement system
Consists of roughly 30 proteins in blood plasma that circulate in the inactive state and are activated by substances on the surface of many pathogens
Activation by antibodies results in a cascade of biochemical reactions that form pores in the membranes of target cells which lead to lysis of the invading cells
Local inflammatory response
- Begins when activated macrophages discharge cytokines that recruit neutrophils to the site of injury
- Mast cells release signaling molecule histamine that triggers nearby blood cessels to dilate and become more permeable
- Activated complement proteins promote further histamine release attracting more phagocytic cells
- Enhanced blood flow to the site helps deliver antimicrobial peptides that result in an accumulation of pus
- Pus and excess fluid are eventually taken up in lymph and transported to lymph nodes where pathogens are phagocytized by macrophages
- Dendridic cells are usually located outside of the lymphatic system but migrate to the lymph nodes after interacting with pathogens
Systemic inflammatory response
Cells in injured or infected tissue often secrete molecules that stimulate the release of additional neutrophils from the bone marrow
Fever can be induced in response to substances released by activated macrophages that cause the body’s thermostat to reset to a higher temperature