Anatomy 2 Ch 21 Lymphatic System
Overview of the Lymphatic System
The lymphatic system is crucially linked to the immune system, primarily focusing on:
The spleen
Lymph nodes
Lymphatic vessels
Bone marrow
Importance of leukocytes (white blood cells) in immune responses.
Cell Composition of the Human Body
The human body is made up of approximately 30 trillion cells.
Composed of over 200 different cell types.
Majority of cells classified into four major tissue types.
Interestingly, bacterial cells in the body may outnumber human cells:
Home to a substantial amount of commensal flora (healthy bacteria) that play a vital role in health.
Commensal Flora
Commensal bacteria are beneficial and assist in:
Nutrient absorption, particularly vitamins.
Maintaining a balanced microflora.
Pathogenic bacteria may arise due to imbalances or infections, especially after antibiotic use, disrupting the healthy flora.
Immune System Overview
The immune system's primary components include:
Innate immune system: First line of defense against pathogens.
Adaptive immune system: Responds to specific pathogens using memory.
Leukocytes are critical in both innate and adaptive immunity.
Lymphatic System Functions
The lymphatic system is a one-way circulatory system:
Similar to the venous system but unique in its function to collect lymph fluid.
Lymphatic capillaries gather excess interstitial fluid (15% of plasma) not recaptured by venules:
Considerable daily loss of fluid (2-4 liters) if not recaptured.
Process of Recapturing Lymph Fluid
Lymphatic vessels work to reclaim this interstitial fluid, now called lymph, and return it to the circulatory system:
Lymph fluid passes through lymph nodes, which filter and cleanse lymph fluid.
Clusters of immune cells (lymphocytes) in lymph nodes can be activated against pathogens or foreign cells.
Differences Between Fluid Types
Three terms for fluid based on location and composition:
Plasma: Fluid component of blood before it is filtered.
Interstitial Fluid: Fluid between cells after filtration
Lymph: Fluid that has entered the lymphatic system and contains less protein than plasma and interstitial fluid.
Anatomy of Lymphatic Capillaries
Composed of
Endothelial cells that overlap (like shingles) for easy fluid entry.
No basal lamina, making them highly porous.
Anchoring filaments made of fibrillin help maintain structural integrity of the capillaries.
Integrins are transmembrane proteins that connect cells to the extracellular matrix.
Mechanisms of Lymph Flow
Lymph does not have a pump; instead, it relies on:
Skeletal muscle pump: Movement of skeletal muscles aids in lymph flow.
Respiratory pump: Pressure changes during breathing facilitate lymph movement.
Pulsation of adjacent arteries also assists in moving lymph towards the heart.
Lymphatic Vessels and Their Structures
Lymphatic vessels initially start from capillaries to larger collecting vessels, then to lymphatic trunks, and finally collecting ducts:
The system resembles the vascular system in layering (tunica interna, media, externa).
Valves present in larger vessels prevent backflow of lymph, ensuring it moves toward the heart.
Lymphatic Trunks and Ducts
Six paired lymphatic trunks collect lymph:
Jugular, subclavian, bronchomediastinal, intercostal, lumbar trunks—along with an intestinal trunk.
Lymph drains into two main ducts:
Right lymphatic duct: Drains lymph from the right side of the head, neck, and upper limb.
Thoracic duct: Drains lymph from the lower body and the left side, leading to the left subclavian vein.
Dietary Lipids and Lymph
Dietary lipids absorbed from the intestines enter the lymphatic system through lacteals and eventually reach the bloodstream via the thoracic duct:
This process avoids the hepatic portal system, which normally processes nutrients absorbed from the gut.
Functional Summary
The lymphatic system plays a critical role in fluid recovery, immune system support, and nutrient absorption:
By filtering the lymph through lymph nodes, it contributes to immune surveillance and response to pathogens.