BIO 203 Lecture Notes - Lecture 16: Mucous Membrane, Thermostat, Anatta
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25 Apr 2019
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The body’s defense system
● The body generally defends you against anything that it does not recognize as
being part of or belonging inside you
● Common targets of the defense system include
○ Pathogens
■ Disease-causing bacteria, viruses, prions, protozoans, fungi,
parasitic worms
○ Cancer cells
■ Once normal body cells whose genetic changes cause unregulated
cell division
Three lines of defense
● Physical and chemical surface barriers
○ Nonspecific
○ Keep foreign organisms or molecules out
● Internal cellular and chemical defenses
○ Nonspecific
○ Attack any foreign organisms or molecule that has gotten past the surface
barriers
● Immune response
○ Specific
○ Destroy specific targets and remember them
Physical barriers
● Skin
○ Nearly impenetrable
○ Waterproof
○ Resistant to most toxins and enzymes of invading organisms
● Mucous membranes
○ Line the respiratory and digestive tracts
○ Sticky mucus traps microbes
Chemical barriers
● Sweat and oil glands of the skin
○ Produce chemicals that slow or prevent the growth of bacteria
● The lining of the stomach
○ Produces hydrochloric acid and protein-digesting enzymes that destroy
pathogens
● Urine
○ Slows bacterial growth with acidity
○ Washes microbes from the urethra
● Saliva and tears
○ Contain lysozyme, an enzyme that kills bacteria
Second line of defense
● Defensive cells
● Defensive proteins
● Inflammation
● Fever
Defensive cells and natural killer cells
● Phagocytes (WBCs) that engulf pathogens
○ Neutrophils: arrive first
○ Macrophages: develop from monocytes that leave the circulatory system
○ Eosinophils: attack pathogens that are too large for phagocytosis, such as
parasitic worms
● Natural killer (NK) cells
○ Also a type of WBC
○ Search out abnormal cells, including cancer cells, and kill them
Interferons: slow viral reproduction
● Small proteins secreted by a cell infected by a virus
○ Attract macrophages and natural killer cells that destroy infected cells
○ Stimulate neighboring cells to make proteins that prevent the viruses from
replicating
Complement system: assists other defensive mechanisms
● Group of proteins that enhances both nonspecific and specific defense
mechanisms
● Destroy pathogens, enhance phagocytosis, stimulate inflammation
Inflammation
● Destroys invaders and helps repair and restore damaged tissue
● Four signs
○ Redness
○ Heat
○ Swelling
○ Pain
● Redness
○ Mas cells release histamine which causes blood vessels to dilate