lymphatic system and body defenses
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Lymphatic System and Body Defenses. Unit 11. Lymphatic System. Defense against disease Consists of two semi-independent parts: Network of lymphatic vessels Various lymphoid tissues and organs throughout body - PowerPoint PPT PresentationTRANSCRIPT
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LYMPHATIC SYSTEM AND BODY DEFENSESUnit 11
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LYMPHATIC SYSTEM Defense against disease Consists of two semi-independent parts:
Network of lymphatic vessels Various lymphoid tissues and organs throughout
body Lymphatic vessels transport fluids that have
escaped from the blood vascular system back to the blood.
Lymphoid organs house phagocytic cells and lymphocytes
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LYMPHATIC VESSELS Fluid is forced out of the blood in
the capillary beds, and most of it is reabsorbed at the venous ends.
About 3 L per day are left behind this becomes part of the interstitial fluid, and is now called lymph.
This fluid must return to the bloodstream in order to have enough volume for the cardiovascular system to function
If this does not happen, fluid starts to build up in the tissues, producing edema (swelling)
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LYMPHATIC VESSELS One way system vessels only flow towards the heart Low-pressure and pumpless system Lymph capillaries = microscopic, blind ended vessels
that spread out between tissues cells and blood capillaries in the loose connective tissues of the body.
Little valves at the end open when fluid pressure is higher in the interstitial space, but close up when the pressure is higher inside the lymphatic vessels prevents leaks
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LYMPHATIC VESSELS Large particles like proteins, cell debris,
bacteria, and viruses can’t enter blood capillaries, but they can enter lymphatic capillaries, especially in inflamed areas
Now the bacteria and viruses can travel throughout the body how do we solve that problem?
Lymph takes “detours” through lymph nodes gets cleaned of debris and “examined” by cells in the immune system
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LYMPHATIC VESSELS Lymph moves from lymph capillaries to successively
larger lymphatic vessels (lymphatic collecting vessels), similar to how blood moves from capillaries to venules to veins.
Lymph returns to venous system through one of two large ducts: Right lymphatic duct – drains lymph from right arm and right
side of head and thorax Thoracic duct – receives lymph from the rest of the body
Both ducts empty into subclavian veins Lymphatic vessels are thin walled and the larger ones
have valves to prevent backflow, like veins. Also helped by skeletal muscles “milking” the lymph along
and pressure change in the thorax during breathing.
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LYMPH NODES Help protect the body by removing foreign material
such as bacteria and tumor cells from the lymphatic stream as well as producing lymphocytes.
Lymph nodes = filters Large clusters can be found in the inguinal (hips),
axillary (armpits), and cervical (neck) regions of body.
Contain macrophages, which engulf and destroy bacteria, viruses, and other foreign substances found in lymph
Also contain lymphocytes, a type of WBC Active infection usually results in swollen glands due
to the trapping function of the nodes.
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LYMPH NODES Usually kidney-shaped, less than 1 inch long, and
“buried” in connective tissue that surrounds them. Each node is surrounded by a fibrous capsule Trabeculae = strands that extend into the capsule to
divide them into compartments Cortex = outer part of the node, contains collections
of lymphocytes called follicles Germinal centers = dark centers of follicles that
enlarge when B lymphocytes generate plasma cells Medulla = center of lymph node, contains phagocytic
macrophages Lymph enters through afferent lymphatic vessels,
moves through sinuses, and exits through efferent lymphatic vessels.
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LYMPH NODES
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SPLEEN Blood rich organ that filters blood Located on the left side of abdominal cavity,
curls around stomach Doesn’t filter lymph, it filters blood and cleans
out bacteria, viruses, and other debris Destroys worn out RBCs and returns their
breakdown products to the liver Stores platelets and acts as a blood reservoir
(like the liver) During hemorrhage, the spleen will contract
and empty its stored blood back into circulation to help keep levels normal
Forms all blood cells in a fetus, but only lymphocytes are made in adults
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THYMUS Lymphatic mass found low in throat overlying
the heart Produces hormones (thymosin and others)
that function in the programming of certain lymphocytes so that they can protect the body
Functions at peak levels only during youth
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TONSILS Small masses of lymphatic tissue that ring
the pharynx (throat) Trap and remove any bacteria or other
foreign pathogens entering the throat Sometimes they work too well get
congested with bacteria and become red, swollen, and sore = tonsillitis
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PEYER’S PATCHES Resemble tonsils, but found in wall of small
intestine Macrophages in ideal position to capture and
destroy bacteria lots of bacteria in intestine Help stop bacteria from penetrating intestinal
wall Peyer’s patches and tonsils are known as
mucosa-associated lymphatic tissue (MALT) MALT protects upper respiratory and digestive
tracts never-ending attacks of foreign matter
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LYMPHOID ORGANS
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BODY DEFENSES Two main systems:
Nonspecific – responds immediately to protect body from all foreign substances, reduces workload of specific defense system Intact skin and mucous membranes Inflammatory response
Specific – aka immune system, attacks particular foreign substances Lymphatic organs Blood vessels White blood cells
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SURFACE MEMBRANE BARRIERS First line of defense = skin and mucous
membranes Act as physical barriers Acid pH of skin inhibits bacterial growth Stomach mucosa makes hydrochloric acid
and protein-digesting enzymes, which helps kill pathogens
Saliva and tears contain lysozyme, an enzyme that destroys bacteria
Sticky mucus traps microorganisms in digestive and respiratory pathways
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CELLS AND CHEMICALS Second line of defense Phagocytes – engulfs a foreign particle and digests
it Natural killer (NK) cells – lyse and kill cancer cells
and virus-infected cells can react against any target. They attack the cell’s membrane and release chemicals that cause it to disintegrate
Fever – abnormally high body temperature, pyrogens are chemicals secreted by WBCs that raise body temperature, fevers can be very dangerous if they get too hot or last too long
Inflammatory response – triggered when body tissues are injured 4 cardinal signs = redness, heat, swelling, and pain.
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INFLAMMATORY RESPONSE Injured cells release histamine and kinins Cause blood vessels to dilate and capillaries
to become “leaky” increased blood flow Activate pain receptors Attract phagocytes and WBCs to area
chemotaxis = cells following chemical gradient
Swelling (edema) is the result causes more pain
The inflammatory response prevents the spread of damaging agents, disposes of cell debris and pathogens, and sets the stage for repair
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RECAP Lymphatic system defends against disease
Lymphatic vessels Various lymphatic tissues and organs Lymph
One way system towards the heart 1st line of defense = skin and mucus
membranes 2nd line of defense = cells, chemicals, and
inflammatory response
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IMMUNE SYSTEM Third line of defense Immune response – immune system’s
response to a threat; increases inflammatory response and provides protection against specific antigens
Recognizes foreign molecules (antigens) and actively works to destroy them
Can recognize previously encountered antigens and trigger immune responses
Immunology – study of immunity Some diseases that result from a
malfunctioning immune system: cancer, rheumatoid arthritis, AIDS
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THREE IMPORTANT ASPECTS OF IMMUNE RESPONSE: 1. Antigen specific – recognizes and acts
against particular pathogens or foreign substances
2. Systemic – Immunity is not restricted to the initial infection site
3. “Memory” – recognizes and mounts stronger attacks on previously encountered pathogens
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TWO KINDS OF IMMUNITY 1. Antibody-mediated immunity (humoral
immunity) = provided by antibodies present in body’s fluids.
2. Cell-mediated immunity = Lymphocytes themselves defend the body, either by directly lysing foreign cells or indirectly releasing chemicals that enhance inflammatory response
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ANTIGENS Any substance capable of exciting our
immune system and provoking an immune response.
Tend to be large Not normally present in our bodies Foreign intruders “non-self” Our own cells have self-antigens, which are
recognized by our body, but would trigger an immune response in someone else (organ transplant rejections)
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CELLS OF THE IMMUNE SYSTEM Lymphocytes
B lymphocytes (B cells) – produce antibodies and oversee antibody-mediated immunity
T lymphocytes (T cells) – do not produce antibodies and oversee cell-mediated immunity
Lymphocytes must be able to recognize body’s own cells so they won’t attack them
Lymphocytes get “trained” to recognize one distinct antigen to attack = immunocompetent
Since lymphocytes become immunocompetent before being exposed to antigens, we know it is our genes, not antigens, that determine what foreign substances we will be able to resist.
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CELLS OF THE IMMUNE SYSTEM Macrophages – “big eaters” Engulf foreign particles and present
fragments of these antigens on their own surfaces
Allow these particles to be recognized by immunocompetent T cells – antigen presenters
Macrophages secrete monokines, which activate T cells
Active T cells release chemicals that turn macrophages into killer macrophages
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ANTIBODY-MEDIATED RESPONSE Primary humoral response = Immature B cell
binds to antigen gets activated and undergoes clonal selection (mass produces an army of cells like itself)
Afterwards, most clones become plasma Some become long-lived memory cells and
can respond to the antigen when they encounter it later = secondary response
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TWO KINDS OF HUMORAL IMMUNITY Active immunity = B cells encounter antigens
and produce antibodies against them Naturally acquired = bacterial and viral
infections Artificially acquired = vaccinations
Passive immunity = Antibodies received from immune human or animal donor temporary protection that ends when “borrowed antibodies” naturally degrade in the body Naturally acquired = mother’s antibodies cross
over placenta to fetus Artificially acquired = After receiving immune
serum or gamma globulin (used for treating rabies, hepatitis, snake bites, botulism, tetanus, etc.)
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ANTIBODIES Also referred to as
immunoglobulins (Igs) Soluble proteins secreted
by activated B cells in response to an antigen capable of binding specifically to that antigen
Basic structure – four amino acid (polypeptide) chains linked by disulfide bonds
2 chains = Heavy chains, 2 chains = Light chains
Variable and constant regions
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ANTIBODIES Five major classes – IgM, IgA, IgD, IgG, IgE Remember – MADGE Slightly different biological roles Antibodies can function through:
Complement fixation = activated during nonspecific body defenses, antibodies attached to cellular targets cause the cell to lyse
Neutralization = antibodies bind to specific sites on bacteria or viruses, making them inactive
Agglutination = cross-linking between antibodies and antigens causes clumping
Precipitation = cross-linking makes clumps so big, they settle out of solution
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CELL-MEDIATED RESPONSE T cells are activated to form clones after binding with
“recognized” antigen Antigens must be “presented” by macrophages Different types of T cells:
Helper T cells = interact directly with B cells bound to antigens. They liberate lymphokines, chemicals that enhance the killing activity of macrophages, attract other leukocytes, or act as helper factors.
Cytotoxic (killer) T cells = directly attack and lyse infected and cancerous cells.
Delayed hypersensitivity T cells = release chemicals that enhance inflammation and promote a delayed allergic reaction
Suppressor T cells = terminate normal immune response by releasing suppressor chemicals
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IMMUNITY DISORDERS Allergy/hypersensitivity = overreaction to
otherwise harmless antigen Immunodeficiency = abnormalities in any
immune element (AIDS) Autoimmune disease = body’s self-tolerance
breaks down, antibodies attack bodies own cells and tissues
http://www.youtube.com/watch?v=l-2ilZA-_aw&feature=related