nonspecific host defense mechanisms
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Nonspecific Host Defense Mechanisms. Host Defense Mechanisms. Ways in which the body protects itself from pathogens There are 3 lines of defense. The first two lines of defense are nonspecific. The body’s way of destroying all foreign substances that enter including pathogens - PowerPoint PPT PresentationTRANSCRIPT
Nonspecific Host Defense Mechanisms
Host Defense Mechanisms
Ways in which the body protects itself from pathogens
There are 3 lines of defense.The first two lines of defense are nonspecific.
The body’s way of destroying all foreign substances that enter including pathogens
The third line of defense is specific. Antibodies are produced in response to an
antigen.
First Line of DefenseSkin
Serves as a physical barrier to pathogensFew microbes can penetrate intact skin
Mucous MembranesAlthough they are only one cell layer thick,
they are a physical barrier to pathogens.Goblet cells produce mucus that entrap
pathogens and prevent them from causing infection.
www.nlm.nih.gov
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What are some chemical and cellular examples for
the first line of defense?
•Regarding the skin?•Mucous membrane cells?•Digestive tract?
First Line of DefenseMicrobial Antagonism
When the presence of the normal flora prevents colonization of pathogens
This may happen because of: Competition for colonization sites Competition for nutrients Production of substances that kill other bacteria
Second Line of DefenseIf pathogens get passed the first line of
defense, they are usually destroyed by the second line of defense.
These involve chemical and cellular reactions by the body, which result in:FeverProduction of interferonsActivation of the complement systemInflammationChemotaxisPhagocytosis
TransferrinA protein that is made in the liver and has a
high affinity for iron.Its role in the body is to store and deliver iron
to host cells. During an infection, its production is greatly
increased in the body.Binds to the iron present so that other
microbes cannot use this essential nutrient
Fever Increase in normal body temperature (above
100°F)Pyrogens stimulate the production of a fever.
May originate from outside (i.e. pathogens) or inside the body (i.e. Interleukin 1 – IL-1)
Helps body in following ways:Stimulates white blood cells (leukocytes) to go
and destroy invadersReduces free plasma ironInduces the production of IL-1 that results in
the activation of leukocytes in the immune response
www.mcmua.com
Interferons Small, antiviral proteins produced by virus-
infected cellsAttach to other host cells to prevent further
viral replication“interfere” with viral replicationLimits spread of disease so that other
responses may help fight pathogens
The Complement SystemInvolves about 30 proteins found in normal
blood plasma that interact together in response to the presence of a foreign substance
Results in a complex stepwise reaction called the complement cascade
Which results in:Attraction of phagocytes to sites where they
are neededActivation of leukocytesLysis of bacteria and other foreign cellsIncreased phagocytosis
Acute-Phase ProteinsProteins found in blood plasma that greatly
increase in response to infection, inflammation, and tissue injury
Help to prevent infection and promote tissue repair
Example : C-reactive proteinWhich is used as a marker for inflammation
CytokinesChemical mediators that are released from
many different types of cells in the human body.
Help cells to communicate with each otherAid in communication within the immune
system and between the immune system and other systems
If another type of cell has the right receptors, it can recognize the presence of cytokines.
Inflammation Occurs as a result of an injury, irritation,
microbial invasion, or bacterial toxin4 signs of inflammation:
Redness, heat, swelling, painResults in a cascade of events that work to:
Localize an infectionPrevent the spread of microbial invadersNeutralize any toxins being produced at the
siteAid in the repair of damaged tissue
Inflammation Vasodilation (increase in the diameter of
capillaries), which increases blood flow to the siteResults in redness and heat
Increased permeability of capillaries, allowing the escape of plasma and plasma proteinsCauses edema (swelling)
Exit of leukocytes from the capillaries and their accumulation at the site of injuryInjury or infection attracts chemotactic agents
which in turn attract leukocytes
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Phagocytosis The process by which phagocytes surround
and engulf foreign materialPhagocytes – phagocytic white blood cells
www.nytimes.com
Cellular Elements of the Blood
Erythrocytes (red blood cells)Thrombocytes (platelets)Leukocytes (white blood cells)
Granulocytes Basophils Eosinophils - Phagocytic Neutrophils - Phagocytic
Monocytes/Macrophages - PhagocyticLymphocytes
B cells T cells Natural killer cells
www.nytimes.com
4 Steps in Phagocytosis 1. Chemotaxis
Phagocytes are attracted by chemotactic agents to the site where they are needed.
2. AttachmentPhagocyte attaches to an object.
3. IngestionPseudopodia surround the object, and it is taken
into the cell.4. Digestion
The object is broken down and dissolved by digestive enzymes and other mechanisms.
Phagocytosis
www.biolcell.org
The End