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Lecture 33 – Lymphatic System - Network of vessels and tissues carrying fluid lymph (from interstitial spaces) around the body - Carries out immune responses - System includes: o Lymphatic tissue  Reticular CT with lymphocytes: B cells and T cells (adaptive immunity, fighting new microbes or foreign invaders over time)  Found in many structures and organs (have capsule around the outside) o Red bone marrow  Where stem cells for blood cells (including lymphocytes) o Fluid-lymph  Intersititial fluid (blood plasma filtrate)  If accumulates: gets swelling o Lymphatic vessels: transport lymph around body Components of the Lymphatic System -

RED: primary lymphatic: stem cells dividing to create immune response of cells Thymus: turning lymphocytes into active form BLUE: secondary: immune response occurs, protects body against foreign invaders o Spleen o Lymph nodes: filters attached to vessels to lymphatic system, group in specific regions (back to blood supply) o Palatine tonsil: unlike lymph nodes and spleen, do not have capsule, just mass of lymphatic cells making lymph tissue o Small Intestine: mucosa layer have MALT regions, and found throughout the body, lymph tissue not capsule o Lymphatic vessels throughout the body, small veins, thinner walls, more valves, superficial in subcutaneous region, follow path way of superficial veins  Deep follow arteries o Lymph tissues in lower limbs merge together and pass through Cisterna Chyli start of thoracic duct, draining limbs from lower and abdominal region, how to move fat from small intestine (lacteal) to bloodstream, moves from thoracic duct into left subclavian vein o Right lymphatic duct: hypothetical duct, doesn’t really exist o Right lymph system connects to right subclavian vein

Functions of the Lymphatic System 1. Drains excess interstitial fluid (returns it to the blood): if it idd not drain, there would be a net loss in blood volume 2. Transport in dietary fats and lipid-soluble vitamins (ADEK) 3. Carry out immune responses – targets microbes and abnormal cells

Lymph vessels and capillaries Capillaries - Capillaries: between cells of many tissues, capillary beds - Larger and more permeable than blood capillaries - Endothelial cells organized to allow only ONE way flow of lymph, different from blood capillaries - Starting level of the system, needs to prevent stuff from coming back out - Merge to form vessels -

Image: typical capillary

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Tissues have embedded lymph bed Moves fluid out of capillary into interstitial cells Some fluid gets stuck in interstitial space  absorbed by lymph capillaries, becomes the lymph, since it originates from blood it is filtrate of the plasma Larger proteins from cells, dietary fats, absorbed in lymphatic capillaries due to high permeability Single capillary ZOOM: into capillary without backflow, endothelial cells are organized by overlapping with each other o Excess fluid in intersitial cells pushes the cells and makes an opening o Opening and closing is controlled by pressure on intersitial space or lymph vessels o If lymph vessels are full, pushes back on the cells and closes o Anchoring filament: tie the endothelium unto nearby tissues o 20 L/day are filtered, 3 L/day are drained into lymph vessels

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Vessels - Have thin walls and many valves (ONE WAY movement as it goes through the system Lymph Trunks and Ducts - From the lymphatic vessels, lymph passes through lymph nodes, and then into lymph trunks - Principal Trunks: o Lumbar: lower limbs, kidney, adrenal glands, pelvic, abdominal walls o Intestinal: intestinal system, spleen, liver o Bronchomediastinal: thoracic wall, lungs, heart o Subclavian: upper limbs o Jugular: head and neck region - Merge to form thorarcic duct or right lymphatix duct  most people do not have a right one, but it attaches directly to right subclavian vein -

Routes of Drainage Lumbar trunk, intestinal trunk, left lumbar trunk merge to form cisterna chyli

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Cisterna chyli start of thoracic duct, back to blood supply, adding it at left subclavian vein Before left subclavian: left jugular trunk and left subclavian trunk merge to form one single duct  with left internal jugular vein Thoracic duct  Drains majority of the body EXCEPT bronchomediastinal trunk, attached independently to left subclavian vein Right side: right bronchomediastinal trunk, subclavian trunk, jugular trunk majority of people the trunks join independently to right subclavian vein

Formation and Flow of Lymph Interstitial fluid  lymph capillaries  lymph vessels  lymph trunks  lymph ducts  subclavian veins -

Moves into lymphatic capillaries into lymph Afferent: leave capillary beds to lymph nodes Lymph nodes: filters for the lymph, remove substances through phagocytosis Efferent: away from lymph nodes Valves throughout, eventually form lymphatic ducts Empty lymph into subclavian veins at the junction

Movement of Lymph - Does not have pump to create pressure - Uses the same mechanisms to move blood in veins - External forces and pressures to move lymph in vessels 1. Skeletal Muscle Pump - Valves in the lumen of lymphatic vessels - Keep blood moving in one direction - At rest: both valves open - Muscle contraction pushes fluid, proximal valve opens distal valve closes - After contraction proximal valve closes, distal valve opens - Milks fluid from the vessel -

2. Respiratory Pump Alternate compression and decompression move lymph into thoracic vessels or ducts Before inhalation; fluid fills thoracic and abdominal vessels Inhalation expands thoracic cavity Compressing abdominal vessels, fluid is forced into thoracic vessels toward heart Exhalation, diaphragm moves upward decompressing abdominal vessels

Lymphatic organs and tissues - Primary: immune cells are immunocompetent (cells create immune response) o Red bone marrow (stem cells – form lymphocytes)  B cells, immunocompetent  Pre-T cell, immature form o Thymus—pre-T cells become immunocompetent T cells

Thymus - In mediastinum - Two lobes, each surrounded by capsule - Capsule wall go into center of thymus- trabeculae – divides each lobe in lobules - Each lobule has cortex and medulla region - Cortex pre-t cells begin to mature - Medulla mature T-cell, cells that die off are removed in cortex Secondary Lymphatix Organs and Tissues - Sites where most immune responses occur o Lymph nodes o Spleen o Lymphatic nodules (follicles)—masses of lymphatic cells grouped together without capsule  Mucosa associated lymphatic tissue (MALT): mucous membrane of GI, urinary, reproductive, respiratory o Tonsils- pharyngeal (adenoid, single mass, posterior of nasopharynx), palatine (two, posterior to oral cavity, removed tonisilis), lingual (base of tongue) o Appendix, and aggregated lymphatic follicles (peyer’s patches—ileum of small intestine) Lymph Nodes - Located along lymphatic vessels - 600 bean shaped nodes throughout body, typically occur in groups - Nodes in groin region, auxillary Structure - Bean shaped organ with capsule on outside - Stroma – supporting framework o Outer- capsule, dense CT  Trabeculeae divide nodes into compartments  Reticular fibres and fibroblasts - Parenchyma—functional component o Cortex (outer and inner)  Outer: aggregate of B cells – lymphatic nodules,  When grouped together, no invaders – primary  If microbe, B cells create immune response – secondary lymp nodule (in center: germinal center, cells around the center make the outer cortex)  Majority is secondary lymphatic nodules  Inner cortex o Medulla region  Medullary sinuses: spaces within the lymph node where lymph can move through  Lymph in medullary sinuses  exit through efferent (1 or 2 per lymph node)

Several afferent, but only one or two leave (have valves to prevent backflow) o Leave lymph node in the hilum 

Flow - Afferent lymph vessel  subcapsular sinus  trabecular sinus  medullary sinus  efferent lymphatic vessel -

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Passes by series of cell types, involved in creating immune response Germinal center in outer cortex: B cells, follicular dendritic cells, macrophages o Follicular collect antigens and bring them to B cells o B cells proliferate and turn into plasma cells (create antibodies) and memory B cells (remember the antigen for later) o Macrophages phagocytosis Cells around the germinal center: B cells moved into periphery Inner cortex: T cells and dendiritc cells – present antigens to T cell  cytotoxic T cells (attack and destroy antigen), helper T cells (help cytototic and B cells) Medullary: B cells, plasma cells, macrophages

B cells - Respond to antigen - Proliferate to form plasma cells  produce antibodies or memory B cells T cells - Cytotoxic T cells – attack antigens - Helper T cells – help cytotoxic cells and B cells Dendriticc cells - Form monocytes – present antigens to B and T cells Macrophages – phagocytosis Spleen - Lymphatic organ - Secondary - Largest mass of lymph tissue in the body - Between stomach, diaphragm, left kidney, left colic flexure of colon Structure - Stroma – similar to lymph node, surrounded by visceral peritoneum - Parenchyma o White pulp – lymph cells around central artery  B and T cells, macrophages  immune response o Red pulp – venous sinuses and splenic cords  Macrophages remove old RBC/platelets  general blood cell life cycle  Storage of platelets (1/3 storage of total supply)

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Different impressions: splenic artery and splenic vein inner portion is divided into trabeculae central arteries are surrounded by white pulp  immune response, same as lymph nodes veins are associated with red pulp  venous sinuses and splenic cords (spleen tissue)  macrophages get rid of dead cells, and store platelets...