Chapter 20 (Part I) - Lymphatic System

Chapter 20: The Lymphatic System

Overview

  • The Lymphatic System can be compared to the sewer system of the body.

    • Drains excess fluids and discards unwanted substances.

    • Serves as a navigation route for defense forces (immune cells) aside from the bloodstream.

  • Main components:

    • Lymphatic Vessels

    • Lymphatic Organs: Includes lymph nodes, spleen, and thymus.

    • Lymphatic Tissue: Includes tonsils, appendix, and Peyer’s patches.

Functions of the Lymphatic System

  • Regulation of Interstitial Fluid Volume

    • Interstitial fluid accumulates due to unequal hydrostatic and osmotic pressure leading to about 2-4 liters lost daily.

    • Lymphatic vessels collect excess interstitial fluid, which becomes lymph.

    • Lymph and interstitial fluid share a similar composition.

    • Lymphatic vessels transport excess fluid back to circulation, thereby preventing hypotonic blood.

  • Absorption of Dietary Fats

    • Fats from the small intestine, broken down during digestion, are unable to pass through capillaries.

    • They enter lymphatic vessels called lacteals and eventually get returned to the bloodstream.

  • Immune Functions

    • Lymphoid organs filter pathogens and house leukocytes for immune response.

    • Lymphatic vessels aid in mobilizing the immune system through pathways that complement the bloodstream.

    • Lymph nodes serve as sites where white blood cells (especially lymphocytes) reside before activation in response to infections.

Lymphatic Vessels

  • Structures are similar to blood vessels serving a network for lymph circulation.

    • Lymph is formed from excess interstitial fluid and has various components including water, proteins, fats, leukocytes, waste, and pathogens.

  • Composition of Lymph:

    • Made from water, proteins, fats, leukocytes, waste products, and damaged cells gathered from tissues.

  • Vessel Structure:

    • Lined by endothelium (simple squamous).

    • Walls allow flaps for larger fluid and cell entry, therefore functioning as a one-way system toward lymph nodes.

Direction of Lymph Flow

  • Afferent vs. Efferent Lymphatic Vessels:

    • Afferent: Carry lymph from tissues to lymph nodes.

    • Efferent: Carry lymph away from lymph nodes to major vein junctions returning lymph to the bloodstream.

Lymph Nodes

  • Function as checkpoint stations in the lymphatic system.

    • Key clusters found in axillae, neck, groin, and abdominal cavity.

    • Rich in lymphocytes (B-cells in cortex, T-cells in the middle, and macrophages in the medulla).

    • Serve as filtering points for pathogens and sources of lymphocyte activation.

Main Lymphatic Trunks and Ducts

  • Lymph-collecting vessels form larger trunks:

    • Nine Major Trunks include lumbar, jugular, and broncho-mediastinal trunks.

    • Two Primary Ducts: Thoracic Duct (drains left upper and lower body) and Right Lymphatic Duct (drains right upper body).

Lymphatic Vasculature

  • Movement of Lymph:

    • Circulation relies on the contraction of surrounding muscles and the pressure of nearby arteries, lacking direct pumping force.

    • Skeletal muscle movements aid lymph propulsion, underscoring the importance of physical activity in maintaining flow.

Normal vs. Obstructed Lymphatic Flow

  • Normal Flow: Ensures tissue hydration and nutrient delivery through lymphatic vessels.

  • Obstructed Flow: Results in conditions like lymphedema characterized by fluid retention in tissues.

Swollen Lymph Nodes

  • Commonly signify infection; lymphocyte proliferation causes node swelling indicating immune activation.

Lymphoid Tissues

  • Primarily composed of reticular tissue, lymphocytes (B-cells, T-cells), phagocytes, and reticular cells.

Mucosa-Associated Lymphatic Tissue (MALT)

  • Found in mucous membranes of the body, helping trap pathogens.

    • Key Locations include:

      • Gastrointestinal Tract: Peyer’s patches, tonsils, and appendix.

      • Genitourinary Tract: Limited presence in kidney and urethra areas.

      • Respiratory Passages.

    • Tonsils and Peyer's Patches are significant components of MALT and respond to oral and nasal pathogens through lymphocyte production.

The Spleen

  • Largest lymphoid organ located in abdominal cavity.

    • Functions in filtering blood, removing old erythrocytes, and pathogen filtering.

    • Contains:

      • Red Pulp: Destroys erythrocytes.

      • White Pulp: Contains leukocytes for pathogen clearance.

The Thymus

  • Located in the superior mediastinum, crucial for T-cell maturation.

    • Undergoes positive and negative selection processes ensuring proper immune function.

    • Maximal size around ages 12-14; reduces and replaces with fat over time, though it does not compromise overall immunity significantly.

Conclusion

  • The Lymphatic System plays essential roles in fluid regulation, fat absorption, and immune function, essential for general health.

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