THE LYMPHATIC SYSTEM

1. THE LYMPHATIC SYSTEM

2. What exactly is this System? • Which organs are involved? • What is the function of the Lymphatic System? • How does it work?

4. Jobs of Lymphatic System: Lymphatic System which consists of vessels and organs plays two vital roles in our lives: • The vessels essentially maintain interstitial fluid levels by carrying excess fluids as well as any plasma proteins, back into the CVS. • The organs, house critical immune cells such as lymphocytes which carryout our body defense against infection and disease as well as offer ACQUIRED IMMUNITY .

5. Lymphatic Characteristics • Lymph – excess tissue fluid carried by lymphatic vessels ( general definition) • Properties of lymphatic vessels • One way system toward the heart • No pump • Lymph moves toward the heart by • Milking action of skeletal muscle • Rhythmic contraction of smooth muscle in vessel walls

6. Composition of Lymph • Lymph is usually a clear, colorless fluid, similar to blood plasma but low in protein • Its composition varies from place to place; after a meal, for example, lymph draining from the small intestine, takes on a milky appearance, due to lipid content. • Lymph may contain macrophages, viruses, bacteria, cellular debris and even traveling cancer cells.

7. Edema is the excess accumulation of fluids in tissue spaces. This can slow down normal exchange of nutrients and metabolites. Filtration of the extracellular fluid exceeds drainage. Anything that causes increased capillary pressure, such as decreased plasma protein, increased capillary permeability or lymphatic blockage, can result in swelling and congestion of the extravascular compartment. EDEMA

9. Lymphatic Vessels • Lymph Capillaries • Walls overlap to form flap-like minivalves • Fluid leaks into lymph capillaries • Capillaries are anchored to connective tissue by filaments • Higher pressure on the inside closes minivalves

10. What Type of Vessels Make up the Lymphatic System? • The vessels are called lymphatics. • They are thin-walled and are analogous to veins. • Small lymphatics are similar to capillaries only more porous; Larger vessels are called collecting vessels: both have valves. • 2 large Ducts: Right LYMPHATIC DUCT and THORACIC DUCT (BOTH EMPTY INTO THE RT AND LT SUBCLAVIAN VEINS) • Lymph flows only TO THE HEART (ONE WAY). • This is a low-pressure, pumpless system. Lymph moves via skeletal muscles and pressure changes in thorax during breathing only.

12. Lymph Carries … • Harmful materials that enter lymph vessels • Bacteria • Viruses • Cancer cells • Cell debris

13. Lymph Nodes • Then Lymph Nodes take the germ-filled lymph and • Filter lymph before it is returned to the blood • Defense cells within lymph nodes • Macrophages – engulf and destroy foreign substances • Lymphocytes – provide immune response to antigens

14. Where are these lymph nodes?

17. The Lymphatic System • Consists of two semi-independent parts • Lymphatic vessels • Lymphoid tissues and organs • Lymphatic system functions • Transport fluids back to the blood • Play essential roles in body defense and resistance to disease

18. Lymphatic Organs: • A Lymph Node- Important lymphocytes of the immune response are matured here. • Spleen: DESTROYS RBCs and Resevoir of Blood; IT IS THE LARGEST Lymph organ and it filter blood of bacteria and antigen-filled cells. • Thymus Gland-produces hormone, thymosin, functions in programing lymphocytes T and B cells; T-cells matured here ( become immunocompetent) • Tonsils-Traps bacteria and other microbes in throat. • Peyer’s Patch-capture and destroy bacteria in intestine, thereby preventing them from penetrating the intestinal wall.

19. Lymph Node Structure • Most are kidney-shaped, less than 1 inch long • Cortex • Outer part • Contains follicles – collections of lymphocytes • Medulla • Inner part • Contains phagocytic macrophages

20. Fluid enters afferent vessels Exists efferent vessels Germinal center of follicle – These enlarge during time of plasma cell production (B Cells) Medulla- Phagocytes are located here Anatomy of a Lymph Node

21. SPLEEN • Filters blood of bacteria, viruses and other debris • Destroys worn out blood cells. It then returns (or recycles) some of the breakdown products of RBCs to the liver ..for example Fe, so that more RBCs can be made .The unusable portion of worn-out blood is excreted in bile. • Another function: Stores platelets and acts as a blood reservoir. • Lymphocytes are produced; RBCs also made in fetus only.

22. Body’s Defense System:

23. Physical and Chemical • Skin - largest organ of the body • Skin Flora • Sweat and Sebum • Mucous membranes on inside: • in gut • in lungs • Tear ducts

25. Immune System • Inflammatory response • Immune response

26. Leukocytes White blood cells, also called leukocytes, are continuously made in the bone marrow White Blood Cells. There are a variety of leukocytes and they are all derived from hematopoietic stemcells. Leukocytes specific for immunity are called lymphocytes

28. Your Immune System Levels of Immunity: • First Line of Defense PHYSICALBARRIERS The Skin, Mucus Membranes and Cilia • Inflammation Innate Responses Phagocytes plus other WBCs • Adaptive Immune Response  Cells with “memory” of past infections are released to defend invaders.

29. White blood cells - from bone marrow • Three groups of white blood cells are important • Macrophages: "big eaters" - phagocytic cells • Two types of Lymphocytes • 2. T cells • 3. B cells

30. Innate and Acquired Immune Responses

31. Breaking the Barriers: Portals of Entry • Skin • Mucus membranes line your gastrointestinal tract, genitourinary tract, respiratory tract and your eyes. • Microbes can gain entrance past these portals of entrance when you: breath,touch your eyes(if your fingers are contaminated), touch yourgenitals, or ingest microbes. Of course if you get a splinter or cut in skin, microbes then gain entrance.

33. Inflammatory Response • When cells are injured they release inflammatory chemicals called histamines and Kinins • Causes blood vessels to dilate and capillaries to become leaky. • Activates pain receptors. • Attracts phagocytes and lymphocytes (neutrophiles) to area. • Inflammatory response does 3 things: 1. Prevents spread of damaging agents to nearby tissue 2. Disposes of pathogens and 3. Sets the stage for healing.

35. Inflammatory Response • Tissue invaded locally • Release of histamines • Dilate blood vessels • Swelling • Fluid from capillaries • Increased heat • Redness • Macrophages move in • ……..INFLAMMATION!

36. Containment and Destruction of Pathogens • Fibrinogen now in tissue clots, trapping pathogens • Heparin prevents clotting at site of injury • pathogens are in a fluid pocket surrounded by clot • Chemotaxis • leukocytes are attracted to chemotactic chemicals • Neutrophils are quickest to respond • phagocytosis • respiratory burst • secrete cytokines for recruitment of macrophages and neutrophils • macrophages and T cells secrete colony-stimulating factor to stimulate leukopoiesis ( to produce more WBC from Stems)

37. Tissue Repair • Blood platelets and endothelial cells in injured area secrete a cytokine, PDGF, that stimulates fibroblasts to multiply and synthesize collagen • Facilitated by hyperemia that provides materials needed and heat that increases metabolism • Fibrin clot may provide a scaffold for repair • Pain limits use of body part allowing for repair

38. Lymphocytes Found At Site of Infection (Innate Response) • Macrophages- are large phagocytic cells that act as scavengers devouring pathogens and worn-out cells. • Neutrophils-the first cells at the site of inflammation. They destroy invaders by the use of digestive enzymes.( These are also phagocytes) • Dendritic Cells-eat pathogens and activate other immune cells. Dendritic cells take pieces of “chewed”pathogens and “present” them. • Natural Killer Cells-kill virus-infected cells and cancerous cells.

40. What’s The Difference between the Innate and Acquired? • Acquired Immunity is 1. antigen specific 2. Systemic 3. Has Memory (recognizes previous encountered pathogens)

41. Local Infection- The pathogen has caused an infection of tissues at surface of skin or mucous membranes. • Systemic infection- From the skin or mucous membranes the pathogen enters either the bloodstream or lymphatic system…hence the name systemic

42. Where Are T Cells And B Cell Made?

43. During a systemic infection the acquired immune response will: • Recognize specific antigens • Make specific ..antibodies and killer T Cell • Then have memory of thess antibodies and T cells for ….a future encounter.

44. Where Do We Get the names T and B? T stands for Thymus-dependent B stands for Bursa of Fabricius in which they were first discovered.

46. Where Do Lymphocytes Originate? • All Lymphocytes originate in the RED BONE MARROW called hematoblasts in a process called hematopeiosis. • Whether or not it becomes a B cell or a T cell depends on WHERE it become IMMUNOCOMPETENT (Capable of responding to a specific antigen) • Certain lymphocytes migrate to Thymus (these will become T cells as they undergo a maturation process under the direction of the hormone Thymosin.

47. What About B Cell Immunocompetence? • B Cells actually mature and gain their immunocompetence in the BONE MARROW. ( we do not know much about their cues) • In the Lymph nodes the B- cells transform into plasma cells which produce antibodies.

49. MEMORY • Some B and T cells have what is called “memory”. Memory Cells have the ability to divide on short notice to produce more of all of the T and B cells. This is the basis of acquired immunity. After the initial response, some of Bs and Ts which were amplified in response to antigen ARE RESERVED and circulate in lymphatic system..for years or even life. If same antigen enters body again immune response will take place RAPIDLY and without full-blown illness.

50. What is an APC? • Antigen Presenting Cell (APC) • Antigen-something,usually a protein or bacteria that is recognized by the body as foreign. • APC can be dendritic cells or macrophages; they ingest pathogens and place pieces of them ( antigens) on their cell membranes so that they can trigger a response from helper T cells.