Lesson 2: Lymphatic System and Immunity

• Lymphatic System - a number of structures and organs containing lymphatic tissue red bone marrow
• Lymphatic System - A network of vessels that transports lymph from the tissues to the blood
• Primary Lymphatic Organs - sites where stem cells divide and become immunocompetent
• Primary Lymphatic Organs

  - Bone marrow and Thymus
• Secondary Lymphatic Organs - Sites where most immune response occur
• Secondary Lymphatic Organs

  - Lymph Nodes, Spleen, and Lymphatic Nodules
• Red Bone Marrow

  - immunocompetent B cells and pre t-Cells are produced

  - produces mature lymphocytes ( B-lymphocytes)
• Hematopoiesis - the process of producing blood cells in the bone marrow
• The B cell undergoes nearly all of its development in the red bone marrow, whereas the immature T cell, called a thymocyte, leaves the bone marrow and matures largely in the thymus gland.
• Thymus - bilobed organ located in the mediastinum between the sternum and the aorta
• Each thymic lobe consist of:

  - Outer Cortex

  - Central Medulla
• Lymph Nodes - “filters of the lymph”
• Trabeculae - capsular extension; provides support and routed for blood vessel
• Paracortex - inner cortex of the lymph nodes; consist mainly of T cells and dendritic cells
• B-cells - antibody-producing plasma cells that have migrated out into the medulla
• Route of Lymph Flow through lymph nodes:

  1. Afferent Lymphatic Vessel
  2. Subcapsular Sinus
  3. Trabecular Sinus
  4. Medullary Sinus
  5. Efferent Lymphatic Vessel
• Spleen - the largest single mass of lymphatic tissue in the body
• Spleen - “Filter of the Blood”
• Spleen - location of the immune reponses
• Splenic Cords - cords of splenic tissue
• Lymphatic Nodules - egg-shaped masses of lymphatic tissue that are not surrounded by a capsule
• Primary Functions of Lymphatic System:

  - Maintenance of Fluid balance in the internal environment

  - Transports dietary lipids

  - Carries out immune responses
• Lymphatic Nodules are also referred to as mucosa-associated lymphatic tissue
• White Blood Cells - also known as leukocytes, they are the most numerous type of blood cell.
• White blood cells - functions to fight infections
• WBC classified into: Granular, and Agranular
• Granulocyte (neutrophils, eosinophils, basophils)
• Agranulocyte (monocytes, lymphocytes)
• Normal WBC count: 4,000-11,000 per microliter of blood
• Neutrophils - trilobed, and makes up largest percentage of leukocytes
• Neutrophils releases enzyme called lysozymes that destroys certain bacteria and oxidants.
• Neutrophils - exhibit antibiotic activity against bacteria and fungi
• Monocytes - takes longer to reach the infected sites but arrive in large number
• Monocytes - clean up cellular debris and microbes via phagocytosis
• Eosinophils - deal with parasitic infections
• Eosinophils - control mechanisms associated with allergy
• Basophils - for short-term inflammatory response
• Histamine - A chemical released by mast cells that causes inflammation and vasodilation; for allergy & irritation
• Heparin - prevents blood from clotting too quickly
• Basophils - contains both histamine & heparin