LYMPHATIC SYSTEM

Lymphatic System - functions Returns excess interstitial fluid (lymph) to blood (including lost plasma proteins) Transports dietary lipids from digestive system to blood Carries out Immune responses including: Production & Differentiation of Lymphocytes Formation of Antibodies Other specific responses against microbes or abnormal cells

Lymphatic System Components Lymph - fluid Lymphatic Vessels – transport lymph capillaries, vessels, trunks & ducts Lymphatic Organs and Tissues Primary: red bone marrow & thymus Secondary: lymph nodes, spleen, lymphatic nodules Primary lymphoid organs produce lymphocytes; secondary lymphoid organs house lymphocytes; stores, gathers & destroys infectious microorganisms within their tissues.

Lymph Fluid, similar to plasma Lost from blood capillaries Enters lymphatic system at lymph capillaries About 3 liters of interstitial fluid drain into lymph vessels daily Returned to bloodstream by series of lymph vessels

Lymph & Blood Capillaries Intertwine

Lymph Capillary

Lymph Vessels/Lymphatics Transport Lymph (one-way) to Blood (Subclavian Veins) Under low pressure Lymph flow assisted by: Muscular compression One-way valves to prevent backflow Respiratory pump Rhythmically contracting smooth muscle in walls of largest lymphatics

Lymphatic Ducts Two main channels drain lymph into veins: Thoracic Duct Begins as Cisterna Chyli - receives fatty lymph “chyle” from Digestive Organs Drains Lower Body + Upper Lt. Half into Lt. Subclavian Vein Right Lymphatic Duct Drains Upper Rt. Half into Rt. Subclavian Vein

Lymphatic Organs/Tissues - Primary Site of lymphocyte development (from stem cells) Red bone marrow Mature B cells Immature T cells Thymus T cells mature & differentiate Site of T-Cell maturation (immunocompetence); able to mount immune response

Thymus (Primary Lymphatic Organ) Mediastinum, between sternum & aorta Atrophies after puberty Populates secondary lymphatic organs & tissues with T-cells Specific regions are packed with rapidly dividing T-cells in process of gaining immunocompetence. Outer cells of secrete thymic hormones. Deeper region is the site of formation of Regulatory T Cells that slows /stops B & T cell activity once infection is over (may be involved in PREVENTING autoimmume diseases).

Lymphatic Organs/Tissues - Secondary Sites where most immune responses occur Lymph nodes Spleen Lymphatic Nodules M.A.L.T. Tonsils MALT – lymphatic nodules in mucosa including Peyer’s patches of small intestines.

Lymph Nodes Secondary Lymphatic Organs Located along lymph vessels Often in clusters, receiving lymph from specific regions Filter Lymph; lymph enters through afferent vessels, exits through efferent vessels Site of proliferation of B cells & T cells

Spleen Secondary Lymphatic Organ Blood filtered Macrophages phagocytize pathogens; lymphocytes perform immune functions Recycles RBCs & Stores Iron Stores blood & platelets Up to 1/3 of body’s platelets stored in spleen. In response to hemorrhaging, the spleen contracts, blood leaves the spleen & re-enters circulation. Also site of hemopoiesis in fetus.

Lymphatic Nodules Secondary Lymphatic Tissues Mucosa-associated lymphatic tissue (M.A.L.T.) Nodules in mucosa of G.I., urinary, reproductive tracts & respiratory airways Tonsils in pharynx (protect against inhaled/ingested foreign substances) Peyer’s patches (Lymph nodules) in small intestine M.A.L.T. = mucosa-associated lymphatic tissue

Immune System

Functions Antigens are substances capable of triggering an immune response. The Immune System: Patrols for antigens Recognizes, responds to, and eliminates foreign antigens Scavenges dead or dying cells

Three Immune Strategies Physical, chemical, & mechanical barriers to prevent entry Then to identify, and remove or neutralize invader: General (non-specific) Immune Defense Specific Immune Responses

Preventative Barriers Physical: Intact skin, mucous membranes, nasal hairs, sphincters to inhibit bacterial migration Chemical: Low pH of stomach, urine, vagina; sebum on skin; lysozyme in tears; prostatic secretions Mechanical: Cell turn over; trapping action of mucus; cilia; flushing action of tears, saliva, & urine; defecation

General Non-Specific Defenses Phagocytes – Neutrophils, Macrophages Natural Killer Cells – lymphocytes that lyse/kill abnormal cells (cancerous & virus-infected cells) Proteins – complement & interferon Inflammation – vasodilation & increased capillary permeability (redness, heat, swelling, pain) Fever Non-specific defenses do not depend on recognition of specific antigens. NK cells circulate in blood & lymph; use perforins to lyse abnormal cells. Complement binds to surface molecules on foreign cells. Interferon is secreted by virally-infected cells, attaches to nearby healthy cells & enables the healthy cells to resist being taken over by the virus. Inflammation includes redness & heat as a result of increased blood flow to the site (via histamine), more fluid leaks from capillaries resulting in swelling which activates pain receptors, pain tends to reduce use & facilitates healing. Inflammation prevents spread of pathogens & their agents, rids the body of debris & pathogens, facilitates healing. Fever stimulates spleen & liver to sequester iron & zinc, thereby reducing the reproductive capabilities of bacteria.

Specific Immune Responses Antigen-specific (relies on recognition of foreign antigens) Systemic (body-wide) Forms Memory (stronger future immune response) 2 types of Immune Response: Humoral (Antibody-Mediated) Cellular (Cell-Mediated)

Humoral Immunity B Cells (B-Lymphocytes) Mature in Bone Marrow Divide to form: Plasma Cells (Produce Antibodies) Memory B Cells Antibodies disable Bacteria & Viruses before they enter cells Mononucleosis: Epstein-Barr virus infects B cells, they enlarge & resemble monocytes (hence “mononucleosis”).

Cellular Immunity T Cells (T-lymphocytes) Mature in thymus Form memory T cells Directly attack Bacteria & Viruses Attack virus-infected cells & cancerous cells Influence B Cell Activity