LYMPHATIC SYSTEM AND BODY DEFENSES

LYMPHATIC AND IMMUNE SYSTEM (COPY)

1. Describe the roles of the immune and lymphatic systems. 2. Explain why antibiotics are effective against bacteria but

not against viruses 3. Outline the role of skin and mucous membranes in defense

against pathogens. 4. Outline how phagocytic leucocytes ingest pathogens in the

blood and in body tissues. 5. Distinguish between antigens and antibodies. 6. Explain antibody production. 7. Describe the process of blood clotting. 8. Outline the principle of challenge and response, clonal

selection and memory cells as the basis of immunity. 9. Describe the production of monoclonal antibodies and their

use in diagnosis and in treatment. 10. Explain the principle of vaccination. 11. List the functions of the spleen and thymus.

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

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)

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

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

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.

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.

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.

LYMPH NODES

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

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

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

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

LYMPHOID ORGANS

WARM UP - IDENTIFY THE LYMPHATIC ORGAN AND FUNCTION(S)

Organ Function(s) Location

1. Explain the function of the Lymphatic System2. Explain the relationship between the lymphatic system and the

circulatory system.3. Explain the relationship between the Lymphatic System and the

Immune System.

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

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

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.

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

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

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

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

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)

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.

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

USE YOUR NOTES TO ANSWER THE FOLLOWING QUESTIONS

1. Outline the role of skin and mucous membranes in defense against pathogens.

2. Distinguish between antigens and antibodies.

3. Explain the principle of vaccination.4. List the functions of the spleen and thymus.5. Explain how the Lymphatic and Immune

system work together.

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

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.)

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

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

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

IMMUNITY DISORDERS

Allergy/hypersensitivity = overreaction to otherwise harmless antigen

Immunodeficiency = abnormalities in any immune element; example (AIDS)

Autoimmune disease = body’s self-tolerance breaks down, antibodies attack bodies own cells and tissues; example lupus