Overview
This lecture covers the key structures and functions of the lymphatic system, emphasizing its role in fluid balance and immunity.
Major Lymphatic Structures
- The lymphatic system includes lymphatic capillaries, vessels, nodes, ducts, tonsils, spleen, thymus gland, and MALT (mucosa-associated lymphoid tissue).
- Lymph nodes are grouped in specific body regions (e.g., inguinal in the groin, axillary in the armpit, cervical in the neck).
- Lymphatic vessels are similar in structure to veins and transport lymph, a fluid derived from blood plasma.
- More lymphatic vessels exist in the body than veins, though less commonly noticed.
Lymphatic Circulation and Capillaries
- Lymphatic capillaries collect excess interstitial fluid (fluid surrounding cells) that does not return to the blood.
- This fluid, now called lymph, enters lymphatic vessels and is returned to the bloodstream before reaching the heart.
- Lymphatic vessels contain valves to prevent backflow, like veins.
Lymphatic Ducts and Drainage
- The thoracic duct drains lymph from below the diaphragm and the left side of the body into the left subclavian vein.
- The right lymphatic duct drains lymph from the right upper body into the right subclavian vein.
- The cisterna chyli is a large sac at the base of the thoracic duct collecting lymph from the lower body.
Lymph Nodes and Immunity
- Lymph nodes filter lymph and are sites where immune cells (B cells and T cells) are activated.
- B cells produce antibodies; T cells attack infected cells.
- Lymph nodes act as guard towers, housing immune cells until they respond to pathogens.
Tonsils and MALT
- Tonsils are lymphatic tissues located at the entrance of the respiratory and digestive tracts, exposed to inhaled or ingested pathogens.
- There are three pairs: palatine (commonly removed), pharyngeal (adenoids), and lingual tonsils.
- Tonsils trap pathogens and activate local immune responses, often swelling when inflamed.
Key Terms & Definitions
- Lymph — Fluid collected by lymphatic vessels from interstitial fluid.
- Lymphatic vessels — Tubes transporting lymph throughout the body.
- Lymph node — Small, bean-shaped organs filtering lymph and housing immune cells.
- Thoracic duct — Largest lymphatic duct, drains lymph from most of the body.
- Right lymphatic duct — Drains lymph from the right upper body.
- Cisterna chyli — Enlarged sac at the base of the thoracic duct collecting lower body lymph.
- Tonsils — Lymphatic tissues in the throat area involved in immune defense.
- MALT — Mucosa-associated lymphoid tissue, immune tissue in mucosal linings.
Action Items / Next Steps
- Review diagrams of lymphatic system structures and drainage pathways.
- Memorize key lymph node locations and functions.
- Be able to describe lymph flow from tissues back to the bloodstream.