Introduction to the Lymphatic System

Introduction to the Lymphatic System

• The lymphatic system is made up of lymphatic vessels, lymphocytes, and lymphatic organs
• It protects against invading pathogens by producing immune responses
• The lymphatic capillaries, which form networks in most tissues, collect tissue fluid called lymph
• The lymphatic capillaries unite to form larger vessels that drain into veins

Lymphatic System Components

• Lymphatic Vessels: Body-wide network of thin-walled vessels with abundant lymphatic valves; walls made up of attenuated endothelium; drain into lymph nodes.
• Cells:
  • Lymphocytes: B Cells, T Cells, and natural killer cells
  • Antigen-presenting cells: Dendritic cells, Langerhans’ cells, and macrophages
• Lymphatic “Tissue”: Diffuse and nodular
• Lymphatic “Organs”: Lymph nodes, spleen, and thymus

Functions of the Lymphatic System

• Drains fluid into the bloodstream
• Filters lymph
• Filters blood
• Helps fight infection by:
  • Producing lymphocytes that create antibodies
  • Housing macrophages in lymph nodes that engulf and kill foreign particles

Lymphoid Tissue

• Primary Lymphoid Tissue/Organ: Where lymphocytes develop from lymphoid stem cells (e.g., thymus and bone marrow)
• Secondary Lymphoid Tissue/Organ: Where formed lymphocytes are most active (e.g., spleen and lymph nodes)

Lymphatic Organs

Lymph Nodes

• Small, bean-shaped structures along the path of lymph vessels that serve as filters for bacteria and other foreign substances
• Several lymph vessels enter (afferents) the node on its convex aspect and a single or a few lymph vessels leave (efferents) the node through its hilum with blood capillaries
• Structure:
  • Outer fibrous capsule with trabaculae extending inward
  • Subcapsular Sinus
  • Cortex: Contains lymphoid follicles with pale staining germinal centers (containing rapidly dividing B-lymphocytes) and a rim of inactive B-lymphocytes
  • Medulla: Lymphocytes arranged in branching cords along the sinuses (medullary cords); primarily composed of macrophages and plasma cells
• Function:
  • Filtration of lymph
  • Proliferation of lymphocytes, contributing to the immune system

Spleen

• Contains a significant amount of lymphatic tissue that filters blood, not lymph
• Structure:
  • Thick capsule that sends septa into the spleen
  • White Pulp: Aggregation of lymphocytes around the central artery, composed of T-lymphocytes and lymphatic nodules with germinal centers (Malpighian bodies) containing B-lymphocytes
  • Red Pulp: Major part of the spleen; contains lymphocytes arranged in branching and anastomosing cords along the sinusoids
• Function:
  • Removes old RBCs
  • Produces lymphocytes
  • Removes blood-borne antigens
  • In fetal life, also serves as a site of erythrocyte production

Thymus

• Primary lymphoid organ
• Grows up to puberty and regresses in adulthood
• Structure:
  • Capsule sends incomplete septa into the parenchyma, dividing it into lobules
  • Cortex: Contains densely packed small lymphocytes and macrophages for phagocytosis
  • Medulla: Contains sparsely arranged larger lymphocytes and epitheliocytes; degenerated epitheliocyte cell aggregations appear as concentric eosinophilic masses called Hassall's corpuscles

This quiz covers the essential components and functions of the lymphatic system. Learn about lymphatic vessels, lymphocytes, and organs like lymph nodes and the spleen. Test your knowledge on how the lymphatic system helps protect the body against pathogens.