21.1 Lymphatic System

21.1 Lymphatic System Chapter 21: Immune System General Function of the Immune System 1.Protect against foreign threat (RECOGNIZE) 2.Differentiate these foreign threats as non-self and engage (RESPOND) 3.Make second response a more effective response (REMEMBER) 21.1.1 The Lymphatic System Components and Functions COMPONENTS FUNCTIONS • Collection of organs, capillaries, vessels and tissues • Returns excess interstitial fluid to the venous system • Contains fluid (lymph) that circulates through vessels • Absorbs fats from the digestive tract and returns them to the venous system for processing by the liver • Contains lymph nodes and nodules • Produces and matures many immune cells 21.1.2 The Lymphatic System: Lymphatic Vessels • Vessels begin as fenestrated capillaries, composed of a single layer of endothelium attached to a basement membrane • Lymph is transported through progressively bigger vessels, through lymph nodes, until it reaches the vena cava • Larger lymphatic vessels contain one-way valves and smooth muscle 21.1.3 Lymphatic Tissues and Organs: The Thymus ANATOMY FEATURES • Flat, bi-lobed organ located in superior mediastinum above heart • Enlarges during childhood, then starts to atrophy as we enter our 20s • Each lobe is comprised of lobules held together by areolar connective tissue • Each lobe consists of a 21.1.4 Bone Marrow Is the Site of Leukopoiesis • Leukopoiesis begins in the bone marrow • Maturation may occur in the bone marrow, or continue in another organ, depending on the cell type 21.1.5 Lymphatic Tissues and Organs: Lymph Nodes LYMPH NODES: follicles consisting of lymphatic and non-lymphatic cells surrounded by a network of lymphatic capillaries • Each is supplied by afferent lymphatic vessels and drained by efferent lymphatic vessels • Outermost cortex: Blymphocytes, macrophages, dendritic cells • Paracortex: Tlymphocytes, dendritic cells 21.1.6 Lymphatic Tissues and Organs: The Spleen ANATOMY FEATURES • Filters blood, stores erythrocytes, removes defective erythrocytes/ platelets, recycles iron • Lies between 9th and 11th rib on left side of body • Contains red pulp and white pulp • Red pulp contains macrophages, erythrocytes, 21.1.7 Lymphocytes and Classification • Contain a single, large nucleus, a small amount of cytoplasm, and a wide range of proteins expressed on their surface • B lymphocytes: develop in bone marrow • T lymphocytes: begin development in bone marrow but complete it in thymus • Classified by surface proteins referred to as Cluster of Differentiation (CD) markers 21.1.8 Lymphocytes: T Cells and the T Cell Receptor The T cell receptor Cytotoxic T cells (TC) • Designed to destroy virus-infected and tumor cells • Releases perforin, granzymes and granulysin Memory T cells (TM) •• Expresses CD8 on its surface Carry the memory of antigen exposure after the antigen has left the body Regulatory T cells (TR) • Maintain immunological tolerance • Block T cell-mediated immune responses at the end of the response window Other T cell types • Natural killer T cells, mucosal-associated invariant T cells, gamma delta T cells 21.1.9 Lymphocytes: B Cells Memory B cells • Carry the memory of previous exposure to antigen • Generated after exposure to antigen by cytokine signaling Plasma B cells • Long-lived, non-proliferating antibody-secreting cells • Arise after exposure to antigen Other B cell types • Plasmablasts • Follicular B cells • Marginal zone B cells • Regulatory B cells 21.1.10 Positive and Negative Selection of Lymphocytes Positive selection: ensures lymphocytes are able to respond to antigen Negative selection: removes lymphocytes that bind strongly to self antigens 21.1.11 Outcomes of Negative Selection of Lymphocytes Receptor editing: change the lymphocyte receptor so it no longer recognizes self antigens Anergy: change the lymphocyte so it is no longer capable of an immune response Apoptosis: clonal deletion and cell death Ignorance: continue