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UNIT B Chapter 10: Circulatory System and Lymphatic System The Lymphatic System Consists of lymphatic vessels and the lymphoid organs. The lymphatic system has three main functions: 1. Return excess tissue fluid to circulation 2. Absorb fats from the digestive tract 3. Defend the body against disease TO PREVIOUS SLIDE Section 10.6 UNIT B Chapter 10: Circulatory System and Lymphatic System Section 10.6 Figure 10.21 Lymphatic system. Lymphatic vessels drain excess fluid from the tissues and return it to the circulatory system. Lymphatic vessels, like circulatory veins, have valves to prevent backward flow. TO PREVIOUS SLIDE UNIT B Chapter 10: Circulatory System and Lymphatic System Lymphatic Vessels Lymphatic vessels form a oneway system that begins with the lymphatic capillaries. Lymphatic capillaries (tiny, closed-ended vessels) absorb excess tissue fluid called lymph. • Tissue fluid contains water, solutes (nutrients, electrolytes, oxygen), and cellular products (hormones, enzymes, wastes) TO PREVIOUS SLIDE Section 10.6 Compare Lymphatic Capillaries to Blood Capillaries Lymphatic Capillaries • have valves, • are slightly larger in diameter, • have closed ends (unlike the loop structure of blood capillaries). • Unique structure permits interstitial fluid to flow in but not out. • The ends of the endothelial cells that make up the wall of a lymphatic capillary overlap. UNIT B Chapter 10: Circulatory System and Lymphatic System Movement of Lymph in Lymphatic Vessels • dependent on skeletal muscle contraction • One-way valves in the vessels prevent lymph from flowing backward TO PREVIOUS SLIDE Section 10.6 UNIT B Chapter 10: Circulatory System and Lymphatic System Movement of Lymph in Lymphatic Vessels The lymphatic capillaries join to form lymphatic vessels that merge before entering one of two ducts: • Thoracic duct: returns lymph collected from the left side of the body into the left subclavian vein • Right lymphatic duct: returns lymph collected from the right side of the body into the right subclavian vein TO PREVIOUS SLIDE Section 10.6 UNIT B Chapter 10: Circulatory System and Lymphatic System Section 10.6 Edema Edema is localized swelling caused by the accumulation of tissue fluid that has not been collected by the lymphatic system. • Occurs if too much tissue fluid is made and/or if not enough is drained away • Can lead to tissue damage and death TO PREVIOUS SLIDE UNIT B Chapter 10: Circulatory System and Lymphatic System Section 10.6 Lymphoid Organs Lymphoid organs contain large numbers of lymphocytes (white blood cells involved in adaptive immunity). There are two types of lymphoid organs: • Primary lymphoid organs: red bone marrow and thymus, where lymphocytes develop and mature • Secondary lymphoid organs: lymph nodes and spleen, where lymphocytes become activated TO PREVIOUS SLIDE UNIT B TO PREVIOUS SLIDE Chapter 10: Circulatory System and Lymphatic System Section 10.6 Figure 10.22 The lymphoid organs. The thymus (a) and red bone marrow (b) are the primary lymphoid organs. Blood cells, including lymphocytes, are produced in red bone marrow. B cells mature in the bone marrow. T cells mature in the thymus. The lymph nodes (c) and the spleen (d) are secondary lymphoid organs. Lymph is cleansed in the nodes, and blood is cleansed in the spleen. UNIT B Chapter 10: Circulatory System and Lymphatic System Primary Lymphoid Organs Red bone marrow • Contains a network of connective tissue fibres, along with stem cells that can divide and produce blood cells • Lymphocytes begin development in the • bone marrow o B lymphocytes (B cells) begin in bone marrow and then migrate to secondary lymphoid organs to mature o T lymphocytes (T cells) in bone marrow and then migrate to the thymus, where they mature and differentiate TO PREVIOUS SLIDE Section 10.6 UNIT B Chapter 10: Circulatory System and Lymphatic System Primary Lymphoid Organs Thymus • lobules, filled with T cells and supporting cells • Lobules are lined with epithelial cells that secrete hormones called thymosins, which are involved in the differentiation of T cells • T cells that react to the body’s own cells undergo apoptosis (programmed cell death) • T cells that leave the thymus can react to foreign molecules TO PREVIOUS SLIDE Section 10.6 UNIT B Chapter 10: Circulatory System and Lymphatic System Secondary Lymphoid Organs Spleen • Cleanses blood • Thin capsule surrounding white (filters debris and bacteria) and red pulp ( macrophages filter worn out RBC) • May be surgically removed due to trauma or disease, however the body becomes more susceptible to certain types of infections TO PREVIOUS SLIDE Section 10.6 UNIT B Chapter 10: Circulatory System and Lymphatic System Secondary Lymphoid Organs Lymph nodes • Cleanse lymph • Occur along lymphatic vessels • Connective tissue divides nodes into nodules, each of which contain B cells, T cells, and a sinus • As lymph passes through the sinuses, macrophages engulf pathogens. • Cancer cells can enter the lymph nodes and lymphatic vessels and move through to other regions of the body, where they produce secondary tumours (metastasis) TO PREVIOUS SLIDE Section 10.6