1. The Lymphatic System and Immunity22
The Lymphatic System and Immunity

2. Functions of the Lymphatic System
Defense
Lymphocytes residing in the lymphatic tissues protect the body against microorganisms and foreign substances. Such as viruses, bacteria, parasites, and fungi.
Immune system – not an organ system, but a population of cells that inhabit all of our organs and defend the body from agents of disease
The body harbors about 10,000 times as many bacterial cells as human cells
some beneficial; some potentially disease causing
Fluid balance
Excess interstitial fluid enters lymphatic capillaries and becomes lymph; drains into the circulatory system.
Fat Absorption
absorbs fat and other substances from the intestines using specialized vessels called lacteals

3. Components of the Lymphatic System
Lymph is fluid drained from interstitial spaces in all tissues. It is essential for fluid balance.
Main source of lymphocytes is from lymph leaving lymph nodes
Consistency of lymph determined by location. ex: after heavy fat absorption-milky color
No lymph present in CNS (brain /spinal cord), cartilage, cornea, bone marrow, bone, or teeth
Lymphatic capillaries and vessels transport the lymph
Lymph  Lymphatic Capillaries  Lymphatic collecting vessels  Lymph nodes  6 lymphatic trunks  2 Lymphatic ducts  Drain into large veins of the body.
Lymphatic tissues composed of aggregates of lymphocytes and macrophages that populate many organs in the body
Lymphatic organs
defense cells are especially concentrated in these organs
separated from other organs by connective tissue capsules

4. Lymphatic CAPILLARY Structures
Similar to blood capillaries; penetrate most tissues of the body. Increased permeability is due to: larger diameters and thinner walls
Endothelial cells are loosely attached Edges overlap one another forming flap-like mini-valves
Larger gaps allow bacteria and cells to entrance lymphatic capillary
Increases in interstitial fluid pressure separates the flaps.
Flaps push inward - fluid enters
Flaps push outward –fluid remains in vessel
2) Filaments anchor endothelial cells to surrounding structures - prevents sac from collapsing
3) Lacteals - special lymphatic capillaries in small intestine -Transport lipids from digestive tract

5. Higher pressure outside in interstitial fluid pushes flap open
Lower pressure inside vessel

6. Lymphatic Vessels
Lymph capillaries merge to form lymphatic vessels similar to veins with tunica interna (endothelial and valves), media (elastic and smooth muscle), externa (very thin) travel alongside veins/ arteries - share common connective tissue sheath
 one way valves prevent backflow
Lymph moves through vessels by the “milking action” of the skeletal muscles and pressure changes created by the respiration similar to action of veins.
Lymph from upper regions of the body flows through the help of gravity.
Lymph flows at lower pressures and speed than venous blood vessels
exercise significantly increases lymphatic return
Vessels flow through lymph nodes: bean shaped clusters of B and T cells found along the length of the vessels; lymph fluid moves slowly thru nodes to increase filtration of microorganisms

7. Lymph Trunks Jugular Subclavian Bronchiomediastinal Intercostal
Intestinal
Lumbar
Lymph is drained from major portions of body into six (6) lymphatic trunks: As lymphatic vessels exit from lymph nodes, they merge to form the 6 lymph trunks
Each lymphatic trunk drains fluid from a certain area of the body.
e.g. jugular trunks drain from the head and neck, subclavian trunks drain from the upper arms and superficial thoracic wall.

9. Lymphatic trunks drain into two lymphatic ducts
Thoracic duct: Main collecting duct of the lymphatic system. Receives lymph from the left side of the head, neck, and chest, the left upper extremity, and the entire body below the ribs.

10. Immune Cells of Lymphatic System
Macrophages- large, phagocytic cells of the connective tissue
Formed from monocyte WBCs. Phagocytize tissue debris, dead neutrophils, bacteria, and other foreign matter
antigen presenting cells (APCs)-process foreign; display antigenic fragments alerting the immune system to the pathogens
Neutrophils, basophils, eosinophils (WBCs)
LYMPHOCYTES: (WBC)
Natural killer LYMPHOCYTE (NK) cells –non-specific-INNATE
large lymphocytes that attack and destroy bacteria, transplanted tissue, host cells infected with viruses or have turned cancerous
responsible for immune surveillance
T LYMPHOCYTES (T cells) specific - mature in thymus
B LYMPHOCYTES (B cells) specific - differentiation into plasma cells that produce antibodies; mature in bone marrow
Dendritic cells - APCs found in epidermis, mucous membranes, and lymphatic organs. Alert T cells to presences of pathogens
Antimicrobial proteins - destroy bacteria
Reticular cells- branched stationary cells contribute to the connective tissue framework of a lymphatic organ; act as APCs in the thymus

11. Tonsils
Large groups of NODULES in the mucosa of the pharynx. Protection against bacteria entering the body through the mouth or nasal cavities.
Pharyngeal tonsil (adenoids) single tonsil on wall of nasopharynx
Palatine tonsils on each side wall; most often infected
Lingual tonsil in the back of the tongue

12. Lymphatic ORGANS Areas where lymphatic tissue is concentrated
Separated from other organs by a connective tissue CAPSULE
Primary Lymphatic organs:
where IMMUNE cells (lymphocytes, macrophages) are produced and mature to the point where they can produce a normal immune response. (immunocompetent)
e.g. red bone marrow and thymus gland
Secondary Lymphatic organs:
are the sites where the MATURE lymphocytes RESIDE and carry out immune response.
e.g. spleen, lymph nodes

13. Thymus Gland Large organ in infants but atrophied as adult.
2 lobed organ located in mediastinum
Site of maturation of T cells

14. Thymus Gland
Surrounded by a connective tissue fibrous capsule with trabeculae divide the gland into several lobules
Each lobule has cortex and medulla
Cortex (numerous lymphocytes)
Medulla (fewer lymphocytes)
Reticular cells separate cortex from medulla and reinforce the blood-thymus barrier
barrier prevents immature T cells from coming into contact with foreign antigens in the blood; contact with antigens at this stage would destroy T cells

15. Lymph Nodes . Located along lymphatic vessels; most numerous
Concentrated near mammary glands, axilla, groin, thoracic cavity, throat
Filter lymph through a network of sinuses
Dense CT capsule surrounds outer structure and extends inwardly as trabeculae.
Outer cortex contains lymphatic nodules filled with T-lymphocytes and macrophages
Inner medulla lymphatic tissue called medullary cords consist of B-lymphocytes, macrophages, plasma cells, reticular cells
Lymph enters the nodes via the afferent lymphatic vessel and leaves via the efferent lymphatic vessel .

16. T- lymphocytes
B- Lymphocytes

17. Lymphatic System
Metastasis – when cancerous cells break free from the original, primary tumor, travel to other sites in the body, and establish new tumors. Characteristic of malignant tumors
PRIMARY SITE where cancer cells travel via blood or lymphatic system and establish new tumors where they lodge
tend to lodge in the first lymph node they encounter
SECONDARY TUMOR sites can be predicted by direction of lymphatic flow from primary site; prevention of metastasis by removing nodes “downstream” from originate site.
Lymphoma - cancer of lymph cells that usually originate in the lymph nodes. There are multiple systems used to classify lymphoma based on cell type, prognosis, etc.
Lymphedema Blockage of lymph drainage from a limb
Causes severe swelling; often a consequence of surgically removing the lymph nodes in the armpit (axilla) or groin, or their damage caused by radiotherapy.
Interferes with immune system function

18. Largest lymphatic organ. Similar to a large lymph node - blood filter.
Spleen
Largest lymphatic organ. Similar to a large lymph node - blood filter.
CT Capsule; trabeculae, divide spleen into compartments Each compartment filled with:
White pulp – lymphocytes and macrophages Monitors blood for pathogens
Red pulp is lymphatic tissue filled with RBCs. (76%-79%).
Old and deformed cells deposited, RBC “graveyard”
Metabolizes (breaks down) hemoglobin recycling iron components
Transfers excess plasma from blood to lymphatic system –controls blood volume. Fluid flows into spleen out into interstitial fluid. Acts as blood reserve in event of hemorrhagic shock
The spleen often damaged by trauma/injury. Rupture can lead to bleeding, shock, death. Removal (splenectomy) may be required to prevent excessive bleeding.

19. The hilum - depression for splenic blood vessels

20. Antibodies Antibodies class of proteins called Immunoglobulins (Igs ).
Four polypeptide chains: two heavy and two light. Each light is held to a heavy by a disulfide bond.
Each chain has two regions; a constant region (C) which is the same within a class of antibody and a variable region (V) which varies from one antibody to the other.
V region from each chain has the antigen binding site to recognize and specifically attach to a particular antigen.
Sites for complement-binding- constant area of heavy chain
Antibodies

21. Five Classes of Antibodies
Named for the structure of their C region
IgA – plasma, mucus, saliva, tears, milk, and intestinal secretions; attack pathogens before they gain access to internal tissues; mother’s milk provides IgA antibodies to infant after birth; prevents pathogen colonization
IgD - B cell transmembrane antigen receptor to increase B cell activation; also known to activate basophils and mast cells
IgE - transmembrane protein on basophils and mast cells
Binds to mast cells and stimulates release of histamine - inflammation and allergy
IgG - constitutes 80% of circulating antibodies
resistance against many viruses, bacteria, and bacterial toxins; crosses placenta to fetus, COMPLEMENT FIXATION; Anti-Rh antibodies produced by Rh-negative mothers
IgM – in plasma and lymph - first class of antibody secreted after an antigen is encountered; eliminates pathogens before there is sufficient IgG available; produces anti-A and anti-B antibodies responsible for the agglutination of RBC; COMPLEMENT FIXATION. 21