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MCB 2340 control of microorganisms notes, Best review Document, Rasmussen College
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iHuman body’s defensesIntroduction
Today, people are able to travel around the world easily, increasing our exposure to new people, new
foods, and new cultures. But as we spread out, so do diseases. Emerging and re-emerging diseases need
to be monitored and managed to prevent the pandemic spread of disease and potential death.
National and global agencies are in place to support these efforts of prevention, but reality predicts the
inevitability of a global outbreak. Ultimately, it is the role of the immune system to identify and fight
off any organism of the body that has the potential to cause harm or disease.
Physical and chemical barriers are our first line of defense, but active immunity comes from the innate
and specific immune defenses. A strong immune system can adapt and fight off many infections, but as
we age or overwork our bodies, we weaken our immune systems and are more vulnerable to diseases.
In order to help us and society, scientists seek to understand and develop new and more effective
treatments against diseases.
Overview of specific adaptive immunity
How does the host defend against the pathogen?
The host defenses are a multilevel network of innate, non-specific protections and specific immunities
referred to as the first, second, and third lines of defenses.
First line of defense-nonspecific barriers that block invasion at the portal of entry. Physical barriers
include the skin and mucous membranes of the respiratory and digestive tract.
*the skin is a thick, though layer that is highly impervious and waterproof
*the flushing action of sweat glands helps to remove microbes
*the mucous membranes provide limited barrier protection as they are moist and permeable
*the mucous coat on the free surface on some membranes impedes the entry and attachment of
bacteria
*blinking and tearing flushes the eye’s surface with tears and removes irritants
*the constant flow of saliva helps carry microbes to the harsh conditions in stomach
*vomiting and defecation also evacuates noxious substances or microbes from the body
*the respiratory tract has nasal hair that traps particles, mucus which exerts a flushing action, ciliated
epithelium that flushes irritants upward and out of the lungs, reflex sneezing and coughing
*the genitourinary tract has partial protection from the flow of urine and vaginal secretions
*resident microbiota provides microbial antagonism that can block pathogens from epithelial surfaces
and create an unfavorable environment for pathogens by competing for nutrients or by altering local
pH
,*the normal microbiota of the skin appears to control localized immune reactions, including T-cell
activity
First line of defense
First line of defense-nonspecific barriers that block invasion at the portal of entry. Physical barriers
include the skin and mucous membranes of the respiratory and digestive tract.
*the skin is a thick, tough layer that is highly impervious and waterproof
*the flushing action of sweat glands helps to remove microbes
*the mucous membranes provide limited barrier protection as they are moist and permeable.
*the mucous coat on the free surface on some membranes impedes the entry and attachment
of bacteria.
*blinking and tearing flushes the eye’s surface with tears and removes irritants
*the constant flow of salvia helps carry microbes to the harsh conditions in stomach
*vomiting and defecation also evacuates noxious substances or microbes from the body
*the respiratory tract has nasal hair that traps particles, mucus which exerts a flushing action,
ciliated epithelium that flushes irritants upward and out of the lungs, reflex sneezing and
coughing.
*the genitourinary tract has partial protection from the flow of urine and vaginal secretions
*resident microbiota provides microbial antagonism that can block pathogens from epithelial surfaces
and create an unfavorable environment for pathogens by competing for nutrients or by altering local pH
*the normal microbiota of the skin appears to control localized immune reactions, including T-cell
activity
Nonspecific chemical barriers include:
*sebum from sebaceous glands
*antimicrobial secretions in the eyes including lysozyme
*high lactic acid and electrolyte concentration in sweat
*skin’s acidic pH and fatty acid content
*low pH in the stomach
*digestive juices and bile
*semen has antimicrobial chemicals to inhibit bacteria
*vagina has protective acidic pH maintained by normal biota
Components of the immune system
, The body components that are involved with the immune functions include:
*the mononuclear phagocyte system
*the interstitial spaces between tissue cells
*the blood stream
*the lymphatic system
Second line of defense
Second line of defense-nonspecific internalized system of protective cells and fluids that includes
inflammation and phagocytosis.
*white blood cells called macrophages wait in the mononuclear phagocyte system which provides a
passageway within and between tissues and organs
*macrophage wait in the MPS so that they are in place to attack foreign invaders as they arrive in the
lungs, skin, liver, lymph nodes, spleen and bone marrow.
*phagocytosis, inflammation, fever, and antimicrobial proteins are mechanisms important in the second
line of defense.
*neutrophils, eosinophils, monocytes, phagocytes are the main nonspecific responders to a foreign
particle
*neutrophils-leukocytes found in the largest number in the bloodstream
*they primarily fight bacterial infections
*eosinophils-target parasitic infections
*eosinophils and basophils are involved in allergic reactions
*mast cells-function similarly to basophils but can be found in tissues outside the bloodstream
*natural killer (NK) cells-lymphocytes that recognize and kill abnormal or infected cells by releasing
proteins that trigger apoptosis
*monocytes-large, mononuclear leukocytes that circulate in the bloodstream
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