The Lymphatic System

The Lymphatic System Biology 2122 Chapter 20

Functions of the Lymphatic System 1. Drain Excess ‘interstitial’ fluid • 2-3 L of fluid lost from the blood stream/day 2. Transport dietary lipids • From GI tract to the blood (lipids and lipid-soluble vitamins) 3. Immune Response • A. Cell-mediated response • T-cell response (cytotoxic cells destroy antigens) • B. Humoral – response • Antibody-mediated (B-Cells)

Basic Structure 1. Lymph Fluid • Interstitial fluid ------ lymph capillaries 2. Lymph Vessels • Capillaries, ducts, etc. 3. Lymph Tissue and Organs • Specialized reticular tissue • Large numbers of lymphocytes • Organs: Thymus gland; Tonsils; Spleen

Tissues to the Heart Lost lymph fluid - returned to the heart. 1. Capillaries • Endothelial Cells and mini-valves • Supported by collagen • One way pressure from the capillaries move lymph towards the capillaries • Very permeable 2. Capillaries form vessels • Skin follow veins; viscera follow path of arteries • Lymph flows into the nodes • No lymph vessels (cartilage, epidermis, cornea- all avacular); CNS and red bone marrow

Chyle and Lacteals Lipids absorption take place in the small intestine Lacteals • Small capillaries in the absorptive cells • Lipids transported from lacteals into the blood • Specialized lipid absorption Chyle • In small intestine lymph is white or creamy due to lipid presence (lymph is normally clear)

Flow and Structure Capillaries ----- Collecting vessels ---- Nodes --- Trunks ------ Lymph ducts (thoracic and right lymphatic) ----- Internal jugular and Subclavian vein ---- Heart

On the way to the heart 1. Trunks – lumbar, intestinal, bronchomediastinal, subclavian, jugular • A. lumbar • B. intestinal • C. bronchomediastinal • D. subclavian • E. Jugular 2. Thoracic (left lymphatic) duct • Cisterna chyli • Main duct for return of lymph to blood from left side of body • Drains into the L.internal jugular and L.subclavian vein

On the way to the heart 3. Right lymphatic duct • Receives lymph from right side of the body • Drains blood into venous blood at junction of R. internal jugular and R. subclavian veins

Flow of Lymph against Gravity Same problems as encountered by venous return Pumps • 1. Skeletal system pump • 2. Respiratory pump Organs and Tissues

Organs and Tissues 1. Primary Organs – stem cell division produces mature cells – immunocompetent • Red bone marrow • B – cells; pre-T cells • Thymus • Pre-T cells migrate to thymus to become immunocompetent 2. Secondary Organs • Site of immune system response • Nodes, spleen, nodules

Thymus • Bi-lobed- surrounded by CT and separated by capsule • Trabeculae -separates tissue into lobes • Lobe • Cortex -(T-cells and Dendritic cells, Epithelial cells and Macrophages) • Medulla – mature T-cells, dendritic cells and macrophoges • Thymic(Hassal’s corpusles)

Lymph Nodes Lymphatic Nodules • B-cells (primary lymphatic nodule) • Plasma and memory B cells in outer cortex (secondary lymphatic nodule) B-cell in primary nodule recognizes antigen and transforms into a secondary nodule • Germinal center • B-cells, follicular dendritic cells, macrophages Antigen presented by APC (B-cell; dendritic , etc.) B- cells develop into plasma and memory cells Inner cortex and medulla • Covered by Dense CT capsule

Spleen Covered by Dense CT capsule Visceral peritoneum – serous membrane Stroma • Trabeculae, reticular fibers and fibroblasts Parenchyma • 1. White pulp – lymphocytes and macrophages around central arteries (splenic artery branches) • 2. Red pulp – venous sinuses, cords of splenic tissue or splenic cords (RBCs, macrophages, lymphocytes, plasma cells, granulocytes

Nodules • No capsule • Found in mucous membranes (near lamina propria) in GI tract, urinary, reproductive, respiratory airways • “Mucosa-associated lymphatic tissue (MALT) • Can be small or larger tissue • Tonsils (5)-Pharyngeal area • Pharyngeal (adenoid- posterior nasopharynx) • Palatine (2)-posterior region of oral cavity (tonsillectomy) • Lingual (2)-base of tongue

The Lymphatic System