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

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