Chapter 20 The Lymphatic System Use the video clip: CH 20 - Lymph Node Anatomy for a review of lymph node structure G.R. Pitts, J.R. Schiller, and James F. Thompson, Ph.D.

The Lymphatic System Basic organization Functions Lymph fluid in lymph vessels Structures: organs with lymphatic tissue, red bone marrow, liver and spleen Functions return interstitial fluid and proteins to the blood transport dietary fats to adipose tissue protect against cancer & infection resistance - fight off disease nonspecific resistance - general protection against disease immunity - specific protection susceptibility - lack of resistance

Lymph Flow More fluid moves out of the blood capillaries by filtration than returns by reabsorption - Starling’s Law ≈ 3Ll day of lymph is generated Proteins escaped from the blood or secreted by tissues are transferred back to the blood by the lymphatics Lymph flow is facilitated by muscle pumps, the respiratory pump, valves, and smooth muscle (in the walls of the trunks & thoracic duct) Smaller vessels drain into larger vessels

Lymphatic Capillaries “Blind ended,” covered vessels between cells, larger than capillaries Not found in avascular tissues (CNS, cartilage) nor in the splenic pulp, and bone marrow

Lymphatic Capillaries Structure/Function regulates fluid flow Anchoring filaments - from lymphatic endothelium attach to surrounding tissues Endothelial cells overlap high hydrostatic fluid pressure separates cells, fluid into caps hydrostatic fluid pressure in cap prevents fluid movement out minivalve

Lymph Flow Follows Venous Circulation Lymph vessels have the same organization and routing as the vascular tree

Lymphatic Flow (cont.) Lymphatic vessels have no separate pump (heart) All lymph returns to the vena cava and to the right side of the heart

Lymphatic Flow (cont.) Lymph ducts Right lymphatic duct about ½ inch long drains lymph from upper right side of body (arm & head) Thoracic (left) duct main collecting duct of the lymphatic system 38-45 cm long drains 75% of body begins as a dilation known as the cisterna chyli located anterior to lumbar disk #2

Lymphatic Flow (cont.) Lymph returns to the venous drainage through right and left lymphatic ducts at the junction of the internal jugular and subclavian veins

Summary of Lymphatic Vessels Lymph Flow from smallest to largest: Capillaries  vessels  trunks  ducts Lymph vessels anastomose and supply and drain lymph nodes along their course

Two Main Types Of Lymphocytes B lymphocytes = B cells attack microbes, especially bacteria develop into plasma cells to produce antibodies (Ab) bind to antigen to form antibody-antigen (Ag-Ab) complexes complexes prevents Ag from interacting with other body cells or molecules memory B cells – dormant until future exposure to Ag T lymphocytes = T cells regulate many immune responses attack viruses, fungi, transplants, cancer, some bacteria 4 types of T cells cytotoxic (killer) T cells - destroy foreign invaders helper T cells - assist B cells and cytotoxic T cells suppressor T cells – help bring immune response to an end memory T cells - dormant until future exposure to Ag

Lymphocyte Development primary lymphatic organs - site of lymphocyte (B cell and T cell) production bone marrow - produces B cells, immature T cells T cells migrate to the thymus gland to mature or die if determined to be improper secondary lymphatic organs sites of activated immune responses lymphatic nodules (lymph follicles) lymph nodes, spleen, tonsils

Other Lymphoid Tissue Cells Macrophages & Dendritic cells Phagocytize foreign substances and cells Transport them to lymphatic tissues Process foreign things into individual antigens Present Ags to T & B lymphocyte to help activate them Reticular cells Similar to fibroblasts Produce reticular fibers (stroma) that provide the framing structure for other cells in lymphoid organs

Lymphatic Tissue - General Stroma of reticular connective tissue (except thymus) Parenchyma of macrophages, B and T lymphocytes, occasional other leukocytes May or may not have a connective tissue capsule

Lymphatic Organs – Thymus Gland Two lobes between the sternum and the heart Thymocytes produce hormones Atrophies with age (starting ~20) Structure/Function Outer cortex – immature T cells screened for functional capacity stimulated to proliferation stimulated to maturation Inner medulla defective T cells degenerate mature T cells move into blood

Lymphatic Organs – Lymph Nodes Anatomy oval, bean shaped small structures scattered throughout body along lymph vessels may be deep or superficial concentrated along the respiratory tree and GI tract, in the mammary glands, axillae, and groin filter lymph fluid to trap foreign organisms, cell debris, and tumor cells

Circulation in the Lymph Nodes Lymph enters via a number of afferent lymphatic vessels It then enters a large subcapsular sinus and travels into a number of smaller sinuses It meanders through these sinuses and exits the node at the hilus via efferent vessels The node acts as a “settling tank,” because there are fewer efferent vessels, lymph stagnates somewhat in the node This allows lymphocytes and macrophages time to carry out their protective functions Only lymph nodes filter lymph!

Cancer Metastasizes To Lymph Nodes Cancer cells from the tumor are first trapped in a lymph node

Lymphatic Organs - Spleen largest lymphoid organ in the body fibrous capsule with arteries, veins, and efferent lymph vessels located between stomach and diaphragm

Spleen Functions: White Pulp a site of immune surveillance and response macrophages phagocytize bacteria, worn-out RBC's, platelets hemoglobin is recycled and components transferred to liver macrophage antigen-presentation and lymphocyte activation and proliferation some B cells mature into plasma cells

Spleen Functions: Red Pulp Site of fetal erythrocyte production (normally ceases after birth) Stores ~ 1 L of blood which can be released during an emergency (hemorrhage)

Unencapsulated Lymphatic Tissue Diffuse lymphatic tissue Small scattered patchs In nearly every organ Lymphoid follicles (nodules) More organized, more cellular clusters small bronchus

Mucosa-Associated Lymphatic Tissue (MALT) found in the lamina propria of mucous membranes of the GI tract, respiratory tract, urinary tract, and reproductive tract Peyer’s patches in the intestines

Lymphatic Organs - Tonsils lymphoid tissue beneath the mucosae tonsilar crypts trap micro-organisms immune cells destroy the micro-organisms palantine tonsils – largest and most frequently infected

Lymphadenopathy Enlarged lymph nodes due to increased drainage from inflammatory lesions or infections. Associated with malignant and nonmalignant diseases. Lymphocyte leukemia with severe lymphadenopathy

Hodgkin’s Disease: one of the significant malignant lymphomas Cervical lymph nodes

Burkitt’s Lymphoma Commonly found in central Africa and New Guinea. Associated with Epstein-Barr virus which causes infectious mononucleiosis in North America and Europe. Rarer American type has extensive marrow replacement. Cancerous cell is a B lymphocyte.

End Chapter 20