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Lymphatic System and Immunity (Lymphocytes Function (After digestion of…
Lymphatic System and Immunity
Intro:
Infection is caused by pathogens (pathogens are viruses and microorganisms that cause disease) The body is equipped with 2 types of defenses:
Innate- nonspecific resistance, 1st and 2nd lines of defense
Adaptive- specific resistance; 3rd and 4th line of defense
Innate Defenses:
First Line of Defense:
Physical Barriers
Hair- within the nose filters air containing microbes, dust, pollutants
Cilia- lines the upper respiratory tract; traps and propels inhaled debris to throat
Mucus Membrane- produce mucus which traps microbes
Urine- flushes microbes out of urethra
Skin- has a thick layer of dead cells in epidermis which provides a physical barriers
Defication and Vomiting- expel microorganisms
Chemical Barriers
Saliva- dilutes the number of microorganisms and washes the teeth and mouth
Acidity- on skin inhibit bacterial growth
Gastric Juice- in the stomach destroys bacteria and most toxins with acid
Sebum- unsaturated fatty acids; provides a protective film on skin and inhibits growth
Lysozyme- enzyme produced in tears, perspiration, and saliva can break down cell walls and thus acts as an antibiotic
Hyaluronic Acid- gelatinous substance that slows the spread of noxious agents
Second Line of Defense First Line of Cellular Defense
Phagocytosis- the process by which specialized cells engulf and ingest foreign particles in order to destroy them (2 types:)
Microphages: Neutrophils/Endophils
Macrophages: Monocytes (most active)
phagocytes remove and destroy foreign particles from tissue and body fluids
most active phagocytes in the blood are neutrophils and monocytes
phagocytic cells associated with the linings of blood vessels in bone marrow, liver, spleen, and lymph nodes constitute the reticuloendothelial tissue
monocytes give rise to macrophages (through diapedesis) that migrate to various body tissues
Immunological Surveillance
Natural Killer Cells
microbes, cancer cells, other abnormal cells
use perforins to rupture cell membranes
attack foreign material
enhance inflammation
special lymphocytes
Interferons
small antiviral proteins
released by activated lymphocytes, macrophages, and virus infected cells
Increase resistance to viral infected
slows the spread of the disease
Complement System
stimulate phagocytosis
destroy plasma membranes
attract phagocytes
promote inflammation
11 special complement proteins
Inflamation
Inflammation is a tissue response to damage, injury, or infection
blood vessels dilate, increasing capillary permeability
response includes localized tissue-redness, swelling, heat, and pain
chemicals released by damaged tissues attract various white blood cells to the site of injury
pus may form as WBC's, bacterial cells, and debris accumulate
A fibrous connective tissue sac may form around the injured tissue and thus prevent the spread of pathogens
Fever
other factors can also increase body temp, exposure to heat, UV light, acids, and bases
Increased body temp decreased blood iron levels, which increases phagocytic activity
infection causes lymphocytes to produce interleukin I, which increases body temperature
Types of Immunity
a person who receives a vaccine containing a dead or weakened pathogen; stimulation of the IR causes the person to develop induced acquired immunity
a person who receives an injection of gamma globulin that contains ready-made antibodies has induced acquired passive immunity; the patient does not have time to develop active immunity; immunity is only short term
a person who encounters a live pathogen, which stimulates a primary IR, and suffers symptoms of disease, develps naturally aquired active immunity
when antibodies pass through a placental membrane from a pregnant woman to her fetus, fetus develops naturally acquired passive immunity; short term immunity
Active Defenses of Immunity
Third Line of Defense
Adaptive Defenses of Immunity
Antigens
an antigen is a substance that causes the formation of an antibody and reacts specifically with that antibody
Before birth, body cells inventory the proteins and other large molecules present in the body ("self " proteins)
After the inventory, lymphocytes develop receptors that allow them to differentiate between foreign (non self) antigens and self antigens
when non self or foreign antigens enter human tissues, they combine with T cell and B cell surface receptors, and stimulate these cells to cause an immune response
Lymphocyte Origins
About half of these undifferentiated lymphocytes reach the thymus where they are processed into T cells
some undifferentiated lymphocytes are probably processed in the bone marrow and become B cells
lymphocytes originate in red bone marrow and are released into the blood before they become differentiated
Both T cells (70%-80% of circulating lymphocytes) and B (20%-30%) cells are transported through the blood to the lymphatic organs (lymph nodes, spleen, and thymus) where they reside and act in immune responses against foreign antigens
Lymphocytes Function
After digestion of the antigen, a self protein attaches a copy of the foreign antigen to the cell membrane of the macrophage
a gene of the major histocompatibility complex (MHC) codes for this self protein
a macrophage is typically the first cell to respond to an antigen, it then alerts lymphocytes to the invader
lymphocyte now recognizes and binds to the antigen presenting cell
Antigen presenting cells begin the immune response (macrophage, dendritic cells, and B cells)
T cells and B cells are activated and begin a chain of reactions that ultimately destroy/neutralize the invading antigen
T cells provide cell-mediated immunity (CMI)
T cells respond to antigens directly (cell by cell contact)
T cells secrete cytokines (lymphokines) to enhance other immune responses to antigens
colony stimulating factors- stimulate bone marrow to produce lymphocyte-
Interferons- block viral replication, stimulate macrophages to engulf viruses, stimulate B cells to produce antibodies, attack cancer cells.
Interleukins- control lymphocyte differentiation
Tumor necrosis Factor- stops tumor growth, etc.
Types of T Cells:
Helper T cells (CD4)- activatied when they encounter a displayed antigen for which it is specialized to react; once activated, they stimulate B cells to produce antibodies; CD4 stimulate antibody mediated immunity and secrete cytokines (CMI)
Memory T Cells- produced upon initial exposure to an antigen; allow for immediate response against subsequent exposure to the same antigen
Cytotoxic T Cells (CD8)- recognize foreign antigens on tumor cells and virus-infected cells
Stimulated Cytotoxic T Cells- proliferate into a large clone of cells that secrete perforin to destroy target cells
Natural Killer Cells- also use perforins to destroy tumor cells; both cytotoxic T cells and natural killer cells can lyse antigents
B Cells
interact with antigen-bearing agents indirectly by secreting antibodies
B Cell Activation
Once activated, B cell proliferates, enlarging into its clone
Activated B cells specialize into plasma cells that secrete antibodies
Antibodies react against the specific antigen-bearing agent that stimulated its production
B cell becomes activated when it binds to an activated T cell
A diverse population of B cells defends one against a large number of pathogens
Provide Antibody- mediated immunity:
Antibody Action- antibodies attack directly, activate complement, and stimulate local tissue changes that hinder antigen-bearing agents
Direct attachment involves:
agglutination
precipitation
neutralization
Activation of Complement:
chemotaxis
inflammation
lysis
opsonization
Antibody Molecules:
two heavy chains
two light chains
each immunoglobulin molecule consists of four chains of amino acids linked together
variable regions at the ends of these chains are specialized to react with antigens
they constitute the gamma globulin fraction of plasma
comprise antigen-binding site
antibodies are proteins called immunoglobulins
5 Major Types of immunoglobulins
IgM
first antibodies to be secreted after initial exposure to an antigen
occurs in plasma
about 6% of circulating antibodies
produced in blood transfusions
activates complement
IgD
occurs on the surface of most B clls
involved in activation of B cells
less than 1% of antibodies
IgG
occurs in plasma and tissue fluids
defends against bacterial cells, viruses and toxins
most abundant circulating antibody (80% of total)
activated complement
only antibody to cross placenta
IgE
occurs in exocrine gland secretions
promotes inflammation and allergic reactions because they cause the release of histamine from mast cells (basophils)
less than 1% of antibodies
IgA
occurs in exocrine gland secretions (tears, saliva, breast milk, etc.)
defends against bacterial cells and viruses
13% of circulating antibodies
levels decrease during stress, lowering resistance to infection
types of allergies
blood transfusions
antigen/antibody complex/inflammation
immediate