Chapter 20: Lymphatic System Flashcards
The Lymphatic System:
o Interstitial fluid quantity is partially based on the net result of hydrostatic (BHP, IFHP) and colloid osmotic pressures (BCOP, IFOP) at the blood capillaries.
o There is a net result of 3 liters / day fluid out of capillary beds and into interstitial spaces.
o The lymphatic system takes up this fluid + plasma proteins that have leaked leaked out and returns it to the circulatory system.
The 3 Parts of the Lymphatic System:
o 1) A network of lymphatic vessels (or lymphatics)
o 2) Lymph Fluid (reabsorbed interstitial fluid)
o 3) Lymph nodes (for body defense from pathogens)
Functions of the Lymphatic System:
o Fluid Recovery = Lymph system returns highly filtered (bacteria, viruses, cancer cells, debris) interstitial fluid and leaked plasma proteins back to the blood.
o Once interstitial fluid enters lymphatics, it is called lymph.
o Together with lymphoid organs and tissues, provide the structural basis of the immune system.
o Lipid Absorption (through lacteals). Lacteals found in the intestinal mucosa and absorbs fats = emulsifies fat, lymph fluid from this area called chyle (fatty lymph) goes to the blood.
Lymphatic Vessels:
o A one-way system where lymph flows toward the heart
o Lymphatic capillaries (smallest and drain into): lymphatic collecting vessels to lymphatic trunks to lymphatic ducts to right lymphatic duct to thoracic duct to SUBCLAVIAN VEINS.
Lymphatic Capillaries:
o Similar to blood capillaries, except
o Very permeable (take up cell debris, pathogens, and cancer cells).
o Endothelial cells overlap (like shingles on a roof) to form one-way minivalves, and are anchored by collagen filaments (anchoring filaments), preventing collapse of capillaries when IF increases.
o Anchoring filaments and allow endothelial mini-valves open when interstitial fluid pressure increases.
o When pressure inside lymphatic capillaries greater than interstitial fluid, the minivalves close.
o During inflammation, interstitial fluid increases which causes minivalves to open large enough to allow cell debris, pathogens, cancer cells.
Lymphatic Collecting Vessels:
o Similar to veins, except:
o Have thinner walls, with more internal valves have all three tunic layers = tunica intima, tunica media, tunica externa.
o Anastomose more frequently.
o Collecting vessels in the skin travel with superficial veins.
o Deep vessels travel with arteries.
o Nutrients are supplied from branching vasa vasorum (on the tunica externa).
Lymphatic Trunks:
o Formed by the union of the largest collecting vessels: o Paired lumbar. o Paired bronchomediastinal. o Paired subclavian. o Paired jugular trunks. o A single intestinal trunk.
Lymphatic Ducts:
o Lymph is delivered into one of two large ducts:
o Right lymphatic duct = drains the right upper arm and the right side of the head and thorax.
o Thoracic duct (left) arises from the cisterna chyli and drains the rest of the body.
o Each duct empties lymph into venous circulation at the junction of the internal jugular and subclavian veins on its own side of the body.
Lymph Transport:
o Lymph Fluid is propelled by:
o Pulsations of nearby arteries.
o Contractions of smooth muscle located in the walls of the lymphatics.
o Specialized valves prevent backflow.
o Skeletal muscle pump.
o Respiratory pump.
o Rapidly flowing blood of the subclavian veins.
Lymphoid Cells:
o Lymphocytes: are the main warriors of the immune system.
o Manufactured from hemocytoblasts in the bone marrow and migrate through blood to lymph tissue.
o T-lymphocytes are also manufactured in lymph nodes and spleen.
o There are two main varieties of lymphocytes:
o T cells (T lymphocytes) = 80%.
o B cells (B lymphocytes) = 15%.
Lymphocytes:
o T cells and B cells protect against antigens. They attack anything that the body perceives as foreign:
o Bacteria and their toxins; viruses.
o Mismatched RBCs or cancer cells.
o T cells: from hemocytoblast in bone marrow:
o Also made in lymph nodes and spleen.
o Manage, activate, and increases immune response.
o Travel to the thymus to become immunocompetent or naive lymphocytes (become “mature” when they encounter an antigen).
o Involved in intracellular immunity.
o Attack and destroy foreign cells.
o B cells: from hemocytoblast in bone marrow:
o Stay in the bone marrow to become immunocompetent or naive lymphocytes (“mature” when encounter antigens).
o Produce plasma cells, which secrete antibodies into blood (tag foreign antigens).
o Immunity throughout the entire body (humoral).
Other Lymphoid Cells:
o Macrophages: derived from monocytes and phagocytize foreign substances and help activate T cells (T Lymphocytes).
o Dendritic cells (Langerhans Cells) = APCs (antigen presenting cells) capture antigens and deliver them to lymph nodes and present them to lymphocytes.
o Reticular cells: Produce stroma or reticular fibers that supports cells in the lymphoid organs.
Lymphoid Tissue:
o Lymphoid tissue = reticular connective tissue (loose CT) that is dominated by lymphocytes from the blood capillaries.
o Houses and provides maturation and proliferation site for lymphocytes macrophages live on the reticular fiber network.
o Two main types of lymphoid tissue:
o Diffuse lymphatic tissue
o Lymphatic follicles (lymphatic nodules).
o Diffuse lymphatic tissue comprises scattered reticular tissue elements in every body organ except the thymus (turns to fat when adult but still produces T-lymphocytes). Larger collections in the lamina propria (= connective tissue just under endothelium) of mucous membranes and lymphoid organs.
o Lymphatic follicles (or nodules) are solid, spherical bodies of tightly packed reticular elements and immune cells (but not encapsulated).
o Germinal center for B cell (B lymphocyte) B cells mature, proliferate, and make plasma cells (antibodies) with the introduction of a specific antigen.
o Forms part of larger lymphoid organs.
Lymph Nodes:
o Principal lymphoid organs of the body.
o Lymph Nodes are embedded in connective tissue, in clusters along lymphatic vessels.
o Near the body surface in inguinal, axillary, and cervical regions of the body.
o Functions:
o Filter lymph: macrophages destroy microorganisms and debris before lymph returns to the blood vessels.
o Activate the Immune system: lymphocytes are activated and mount an attack against antigens.
Structure of a Lymph Node:
o Bean shaped
o External fibrous capsule
o Trabeculae from the fibrous capsule extend inward and divide the node into compartments
o Two histologically distinct regions:
o Cortex.
o Medulla.
o The outer cortex contains lymph follicles with germinal centers with dividing B cells.
o Dendritic cells (the grabbers) surround the lymph follicles.
o The deep cortex houses T cells. T cells circulate continuously among the blood, lymph nodes, and lymphatic vessels.
o Medullary cords: are extensions inward from the cortex and contain B cells, T cells, and plasma cells.
o Lymph sinuses: are large lymph capillaries throughout lymph nodes that contain macrophages. Subscapular sinus. Trabecular sinus. Medullary sinus (drains into efferent vessels).
