T5_Lymphatic System

Lymphatic System Overview

• Importance: The lymphatic system plays a crucial role in maintaining fluid balance, immune function, and digestive health.

Main Functions

5.1 Structure and Functions of the Vessels and Organs

• Lymphatic Vessels:

  • Types: Lymphatic capillaries, collecting lymphatic vessels, lymphatic trunks, and ducts.

  • Function: Return approximately 3 liters of lymph daily through a one-way system.

• Lymph:

  • Definition: A fluid that contains a mixture of water, proteins, and immune cells.

• Lymph Nodes:

  • Function: Cleanse lymph and act as sites for lymphocyte activation.

Structure of Lymphatic Vessels

5.2 Origin and Transport of Lymph

Lymphatic Capillaries

• Characteristics:

  • Highly permeable.

  • Have one-way minivalves.

  • Absorb fats directly from the digestive system (lacteals).

• Presence: Absent in bones and teeth.

Collecting Lymphatic Vessels

• Structure:

  • Thinner walls than veins, more internal valves, and more anastomoses.

  • Travel alongside superficial veins (skin) and deep arteries (deep lymphatic vessels).

Lymphatic Trunks and Ducts

• Right Lymphatic Duct:

  • Drains lymph from the right upper limb, right side of the head, and thorax.

  • Empties into the right internal jugular and subclavian veins.

• Thoracic Duct:

  • Drains lymph from the rest of the body.

  • Empties into the left internal jugular and subclavian veins.

Lymph Transport Mechanisms

• Propulsion:

  • Driven by the milking action of skeletal muscles.

  • Pressure changes during breathing.

  • Pulsations from nearby arteries.

  • Presence of valves prevents backflow.

  • Smooth muscle contractions in vessel walls.

Lymphoid Organs and Tissues

Types of Lymphoid Cells

• Adaptive Immune Cells: T cells and B cells (become plasma cells).

• Other Immune Cells: Macrophages, dendritic cells, and reticular cells.

Lymphoid Tissue Characteristics

• Function:

  • Site for lymphocyte homeostasis and proliferation.

  • Provides surveillance for pathogens.

• Types:

  • Diffuse Lymphoid Tissue: Loosely organized cells found in every organ.

  • Lymphoid Follicles: Tightly packed aggregates found in lymphoid organs or isolated.

Primary and Secondary Lymphoid Organs

• Primary Organs: Thymus and red bone marrow.

• Secondary Organs: Include lymph nodes, tonsils, spleen, Peyer's patches (in the small intestine), and the appendix.

Lymph Nodes

• Function: Serve as principal lymphoid organs that cleanse lymph and activate the immune system.

• Location: Clustered along lymphatic vessels, with significant clusters in areas such as the cervical, axillary, and inguinal regions.

Structure of Lymph Nodes

• Features:

  • Shape: Generally bean-shaped.

  • Composed of an external fibrous capsule, trabeculae, cortex, and medulla with lymph sinuses.

Circulation within Lymph Nodes

• Pathway: Lymph flows from afferent lymphatic vessels to the subcapsular sinus, through smaller sinuses to medullary sinuses, and exits via efferent vessels at the hilum.

Function Summary

• Primary Roles:

  • Filter lymph (macrophages destroy microorganisms and debris).

  • Activate lymphocytes against antigens.

Spleen Anatomy and Functions

Structure

• Components:

  • White Pulp: Contains lymphocytes around central arteries.

  • Red Pulp: Contains red blood cells and macrophages, involved in blood filtration.

Functions

• Roles:

  • Lymphocyte proliferation, immune response, and blood cleansing.

  • Stores iron, platelets, and monocytes.

  • Produces erythrocytes during fetal development.

Mucosa-Associated Lymphoid Tissue (MALT)

• Collections:

  • Tonsils, Peyer's patches, appendix, located in walls of mucous membranes (respiratory and gastrointestinal tracts).

• Function: Prevent pathogen infiltration and generate memory lymphocytes.

The Thymus

• Characteristics:

  • Lacks B cells, focuses on T cell maturation.

  • Isolated from antigens via the blood-thymus barrier.

Developmental Aspects

• Lifecycle:

  • Largest and most active during childhood, gradually atrophies post-puberty.