Download LYMPHATIC SYSTEM AND IMMUNITY The Lymphatic System

LYMPHATIC SYSTEM AND IMMUNITY
The Lymphatic System
Consists of: Lymphatic vessels, Lymphatic tissues, Lymph (fluid), bone marrow
Functions of the Lymphatic System are:
- returns tissue fluid to the venous system
- immunity (lymphocytes)
- transports absorbed fats from intestine to blood
Components
Lymph Capillaries
- close ended
- in villi of GI called lacteals
- have porous junctions that allow:
- interstitial fluid, proteins, microorganisms, and absorbed fat to pass through
- fluid once inside lymphatic capillaries is called lymph
- capillaries empty into lymphatics which empty into ducts after passing through
nodes
Two Main Ducts
1. The Thoracic duct empties into the left subclavian vein and drains lymph from:
- the left side of the head, neck and chest
- the left arm
- the entire body below the ribs
2. The Right Lymphatic duct empties into the right subclavian vein and drains lymph
from:
- the upper right side of the head an neck
- the right arm
- the right side of the thorax, lung, and heart
- part of the liver
Lymphatic Tissue
Lymphatic nodules
- usually solitary
- found in the lamina propria of the G.I., Respiratory airways, Urinary tract, and
reproductive tracts
- some are in large aggregates like:
- pharyngeal tonsils
- Peyer's patches
Lymph Nodes
- capsulated with extensions called trabeculae
- composed of a:
1. Cortex with lymphocytes arranged in follicles including:
- T cells, Macrophages, Follicular Dendritic Cells (activate T cells)
- B cells
2. Medulla which contains:
- macrophages
- plasma cells (that secrete antibodies)
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- lymph flow through the node is one way. Afferent lymphatic vessels > sinuses>
efferent lymphatic vessels
- nodes filter the lymph and trap antigens which are destroyed by immune cells
Tonsils - are multiple aggregates of large lymphatic nodules
- there are three types
1. Pharyngeal tonsils (adenoids) - found in the nasal pharynx
2. Palatine tonsils - found on the soft palate
3. Lingual tonsils - found on the base of the tongue
- all function in protection against antigens passing through the oral and nasal cavity.
Spleen a large gland with two kinds of tissue
1. White pulp - lymph tissue with lymphocytes.
2. Red Pulp - venous sinuses that contain splenic cords with macrophages, plasma
cells, and granulocytes
- functions:
1. Immunity - through B cells
2. Phagocytosis of old red blood cells and platelets via fixed macrophages
3. Stores and releases blood when needed.
Thymus gland
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- found in the mediastinum (the space between the lungs) in children only
- capsulated
- confers immunity on T cells.
- secretes hormones that stimulate the immune system
NONSPECIFIC IMMUNITY
- provides a general response against a broad range of pathogens
Skin and Mucous Membranes
Mechanical Factors
Epidermis of the skin - creates a physical barrier to the passage of microbes
Mucous Membranes (including mucous and hair) - traps and filters microbes
attempting to enter the body through a natural opening (nose, mouth, etc.)
Cilia together with mucous traps microbes and dust particles in the respiratory
tract
Lacrimal apparatus, Saliva, and urine wash away microbes from the surface of
the eyes, mouth and urethra.
Defecation and vomiting removes microbes from the G.I. tract
Chemical Factors
Acid pH of the skin inhibits microbe growth
Unsaturated fatty acids in sebum have antimicrobial substances
Lysozyme - an antimicrobial substance found in tears, saliva, nasal secretions,
and tissue fluids
Hyaluronic acid in connective tissues prevents the spread of noxious agents
in localized infections
Gastric juice with its low pH destroys bacteria and most toxins
Antimicrobial substances
Interferons protect uninfected cells from viral infections
Complement proteins that can lyse microbes, promote phagocytosis, and
increase inflammation
Natural Killer Cells kill a wide variety of microbes and tumor cells
Phagocytes ingest microbes, toxins etc. Examples: neutrophils, eosinophils, and
monocytes (macrophages)
Inflammation confines and destroys microbes and aids in tissue repair
Fever makes interferon work faster, inhibits microbe growth, and speeds up
the bodies physiological responses to aid in repair
Specific Immunity the bodies defense against specific pathogens such as:
- Bacteria - viruses - foreign tissues
- this specific resistance is called IMMUNITY
- substances that the immune system recognizes as foreign are called
antigens
- two properties make immunity different from nonspecific defenses:
1. Specificity for one antigen and only one antigen
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2. Memory for that same antigen should it reappear
- carried out by two types of lymphocytes that develop from stem cells in the
bone marrow: T cells and B cells
- there are two types of immune responses:
1. Cell-mediated (cellular) immunity - T cells
2. Antibody-mediated (humoral) immunity - B cells
Antigens
- any chemical substance that the immune system can recognize as foreign
- must have two important qualities:
1. Immunogenicity - or the ability to provoke and immune response
2. Reactivity - the ability to react with antibodies and form an
antigen/antibody complex
- antigens that have immunogenicity and reactivity are said to be complete
antigens
- some antigens have reactivity but not immunogenicity and are referred to as
haptens
- haptens can provoke an immune response if they attach themselves to a
larger carrier molecule (ex: the pneumonia bacterium attaches to penicillin)
- antigens have regions on their cell membranes that trigger immune responses.
These regions are called antigenic determinant (epitopes)
- most antigens have multiple determinant sites
- the immune system can recognize over a billion antigen determinants.
Cytokines
- are a class of protein hormones that function as colony stimulating factors to
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increase the production of white blood cells in the bone marrow.
Antibodies
- B cells when presented with an antigen differentiate and divide by mitosis to
produce Memory cells and plasma cells
- plasma cells secrete antibodies that are specific for the antigen presented to the B
cell.
- antibodies are Y shaped globulin proteins with two antigen binding sites (bivalent)
- five classes of immunoglobins are recognized in humans:
IgG, IgA, IgM, IgD, and IgE
Cell-Mediated Immunity
- T cells recognize a particular antigen
- the T cell then undergoes proliferation and differentiation to become
effector cells that carry out the immune response that results in
elimination of the antigen
How T Cells recognize antigens
- the cell membrane of T Cells have T cell receptors that bind with specific antigens
- when this occurs it is known as the first signal
- T cells also need costimulators (like interleukin) to achieve activation
- once activated or sensitized it Proliferates (divides) and differentiates
to form clone cells that carry out different immune response. These clone cells
include:
Helper T cells - secrete cytokines which carry out a variety of immune responses
(see exhibit 22.2 on page 703)
Cytotoxic T cells - lyse antigens and inject lymphotoxin substances
Delayed hypersensitivity T cells - release cytokines and active monocytes
Suppressor T cells - may down regulate other T cells
Memory T cells - are stored in lymphatic tissue - can remember the original
invading antigen and respond to it more quickly upon second exposure
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Antibody Mediated (Humoral) Immunity
- B cells can respond to specific antigens
- in the presence of antigens B cells become activated when an antigen binds
to antigen receptors on the cells surface
- B cells enlarge and divide to produce plasma cells or memory cells
- plasma cells produce antibodies designed to specifically bond with the antigen
that activated the B cell
- the antibodies bind with the specific antigen and form antigen/antibody complexes
which are immediately phagocytized by phagocytic cells
- memory cells are stored in lymphatic tissues to await the return of the same antigen
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Immunological Memory
- the immune response is much faster the second time it is exposed to the same antigen
- the first exposure or primary response takes the immune system several days to
produce high levels of antibodies
- when the same antigen returns (could be decades) later the secondary response
occurs which results in the rapid production of antibodies that have a higher
affinity for the antigen than the first response. This results in the immediate
destruction of the antigen
Self-Regulation
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- your own T cells must be able to recognize your own body cells so they do
not attack yourself. this is called self-regulation
- T cells must not react to peptide fragments from your own body cells - this
is known as immunological tolerance
- B Cells also have these same capabilities
- loss of immunological tolerance leads to autoimmune disorders
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