Lymphatic system

Chapter 24: The Lymphatic System

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  1. Overview of the Lymphatic SystemComponents of the lymphatic system include:

  • Tonsils

  • Cervical lymph nodes

  • Right lymphatic duct

  • Thymus

  • Axillary lymph nodes

  • Thoracic duct

  • Spleen

  • Cisterna chyli

  • Mucosa-associated lymphoid tissue (MALT) in small intestine

  • Inguinal lymph nodes

  • Red bone marrow

  • Lymphatic vessels

  1. Objectives

  • Structure and function of lymphatic tissue (lymph fluid, vessels, ducts, organs).

  • Structure and function of primary and secondary lymphatic organs.

  • Role of immune system cells and their relationship with lymphatic system.

  1. What is the Lymphatic System?An open system comprising cells and organs that destroy or neutralize pathogens.The system carries excess interstitial fluids to the bloodstream and filters pathogens from blood.Blood pressure causes fluid leakage from capillaries, leading to fluid accumulation.Lymphatic system drains excess fluid back into the bloodstream.

  2. Functions of the Lymphatic System

  • Return Excess Fluid: Approximately 10% of fluid that leaves capillaries becomes interstitial fluid; lymph capillaries collect excess fluid.

  • Fat Absorption: Absorbs fats and fat-soluble vitamins from the digestive system and transports them to venous circulation through lacteals in the small intestine.

  • Defense Mechanism: Lymph nodes and organs filter lymph to destroy microorganisms.

  1. Structure of the Lymphatic SystemLymphatic vessels start as open-ended capillaries, merge into larger vessels, and empty into the bloodstream via ducts.About 500-600 lymph nodes located near groin, armpits, neck, chest, and abdomen; they facilitate lymph movement with the help of body movements, skeletal muscle contractions, and breathing.One-way valves (semi-lunar) ensure lymph flows toward the heart.

  2. Relationship with Cardiovascular SystemLymphatic ducts (thoracic and right lymphatic) return lymph to the junction of jugular and subclavian veins.Efferent lymphatic vessels transport lymph away from lymph nodes; afferent vessels bring lymph to lymph nodes.Lymphatic system aids in filtering blood plasma, phagocytosis, and immune reactions.

  3. Major Structures of the Lymphatic System

  • Major Trunks and Ducts:

    • Thoracic duct drains a larger portion of the body than the right lymphatic duct.

    • Specialized lymphatic capillaries in the intestine (lacteals) carry lipids; lymph in these capillaries is called chyle.

  1. Major Lymphatic TrunksLymphatic vessels unite to form trunks, which include:

  • Jugular trunks: head and neck.

  • Subclavian trunks: upper limbs and breast.

  • Bronchomediastinal trunks: deep thoracic structures.

  • Intestinal trunk: most abdominal structures.

  • Lumbar trunks: lower limbs, abdominopelvic wall, and pelvic organs.

  1. Lymphatic Organs

  • Lymph Nodes: Bean-shaped, less than 2.5 cm long; typically cluster in inguinal, axillary, and cervical areas.

  • Tonsils: Clusters of lymphatic tissue under mucous membranes (pharyngeal, lingual).

  • Spleen: Located in the upper left abdomen; filters blood, contains lymphocytes, acts as a blood reservoir.

  • Thymus: Located in the anterior mediastinum; processes and matures T-lymphocytes for immune defense.

  1. Types of Lymphoid Cells

  • Macrophages: Monocytes that engulf foreign substances and present antigens to other cells.

  • Dendritic Cells: Internalize antigens and present them to lymphocytes.

  • Lymphocytes: Most abundant lymphoid cells, developing from stem cells in bone marrow.

    • T-lymphocytes (T-cells): Target virally infected and cancer cells.

    • B-lymphocytes (B-cells): Produce antibodies against bacteria.

    • Natural Killer (NK) Cells: Destroy infected or diseased cells, such as cancer cells.

  1. Summary of Lymphoid Structures and FunctionsTable 24.2 highlights lymphoid structures/organs, their functions, and locations:

  • Lymphoid Nodules: Filter antigens; located throughout the body.

  • MALT: Attacks antigens in food, air, or urine; located in GI, respiratory, genital, and urinary tracts.

  • Tonsils: Protect against inhaled/ingested antigens; located in the pharynx.

  • Thymus: Site of T-lymphocyte maturation; located in superior mediastinum.

  • Lymph Nodes: Filter lymph and mount immune response; located throughout the body.

  • Spleen: Filters blood, recycles aged erythrocytes; located in left upper abdomen.