The Lymphatic System

Lymphatic System

Overview

• The lymphatic system consists of three main parts:

  • Vessels: Structures through which fluid moves.

  • Fluid (Lymph): The fluid that moves through the vessels.

  • Lymph Nodes: Structures that clean the fluid as it passes through.

Lymphatic Vessels

• Comparison to Cardiovascular System:

  • In the cardiovascular system, capillaries become venules, which become veins.

  • Arteries branch into arterioles, which branch into capillaries.

• Lymphatic Vessel Hierarchy:

  • Lymphatic Capillaries: Smallest vessels.

  • Collecting Lymphatic Vessels: Formed by merged lymphatic capillaries, similar to veins.

  • Lymphatic Trunks: Formed by merged collecting lymphatic vessels.

  • Ducts: Largest vessels, formed by merged trunks.

• Mnemonic: "Creepy bands, terrible drivers" (Capillaries, Vessels, Trunks, Ducts).

Lymphatic Capillaries

• Location:

  • Interspersed among blood capillaries.

• Function:

  • Collect fluid lost by blood capillaries.

  • Fluid may require multiple attempts to enter.

• Structure:

  • Endothelial cells overlap like shingles.

  • Filaments tie cells down, creating trapdoor effect.

  • Fluid can enter but cannot exit easily.

Lymph Formation

• Lymph:

  • Fluid that enters lymphatic capillaries.

  • Similar to plasma but with fewer large proteins.

  • Contains nutrients and waste.

• Return Mechanism:

  • Lymphatic system returns fluid to the bloodstream.

Lymphatic Collecting Vessels

• Similarity to Veins:

  • Same layers as blood veins but slightly thinner.

• Flow:

  • Collecting vessels merge into trunks, which lead into ducts.

Ducts and Return to Bloodstream

• Thoracic Duct:

  • Dumps into the subclavian vein on the left side of the body.

• Right Lymphatic Duct:

  • Dumps into the subclavian vein on the right side of the body.

• Overall:

  • Lymphatic system returns fluid to the blood supply via these ducts.

Lymph Movement

• Absence of a Pump:

  • Unlike the cardiovascular system, the lymphatic system lacks a central pump like the heart.

• Mechanism of Movement:

  • Similar to how veins return blood to the heart.

  • Skeletal Muscle Contraction: Muscles push on lymph vessels, aiding movement.

  • Breathing: Pressure changes in the chest draw lymph through vessels.

  • Valves: Prevent backflow in vessels.

  • Smooth Muscle: Vasoconstriction aids in movement.

Lymph Nodes

• Location:

  • Clustered along lymphatic vessels.

  • Found throughout the body, including cervical, axillary, iliac, and inguinal regions.

• Function:

  • Filter lymph.

• Structure:

  • Cortex.

  • Medulla.

  • Afferent Lymphatic Vessels: Bring fluid into the node.

  • Efferent Lymphatic Vessels: Fewer vessels leading out of the node, which increases pressure, slowing down the flow.

• Components:

  • Macrophages (Large Eaters): Remove debris and pathogens.

  • T Cells: Identify and target foreign invaders.

  • B Cells: Produce antibodies.

Lymph Node Function

• Filtration:

  • Removes foreign substances and pathogens.

• Immune Activation:

  • T and B cells detect antigens and initiate an immune response.

• Clinical Significance:

  • Cancer Detection: Spread to lymph nodes indicates metastasis.

  • Biopsy: Testing of nodes (e.g., axillary nodes in breast cancer) to determine if cancer has spread.

Mucosa-Associated Lymphatic Tissue (MALT)

• Definition:

  • Specialized areas of lymphatic tissue associated with mucosa in the body.

• Examples:

  • Tonsils: Located in the oral cavity, clean debris and antigens.

  • Peyer's Patches: Surround the digestive system, particularly in the small intestine.

  • Appendix: Outcropping off the cecum filled with lymphatic tissue.

Tonsils

• Types: Palatine, lingual, pharyngeal.

• Tonsilliths: Hardened bacteria, white blood cells, and pus that can form on tonsils. They may be swallowed or coughed out and typically have a foul smell.