Drainage of Excess Tissue Fluid into Lymph Ducts
The lymphatic system plays a crucial role in draining excess tissue fluid, also known as interstitial fluid, from tissues and returning it to blood circulation.
Lymphatic system
A network of vessels, tissues, and organs that work together to drain excess tissue fluid and return it to the blood, while also aiding immune function.
Tissue Fluid and the Lymphatic System
- Capillaries leak plasma, forming tissue fluid, which delivers oxygen and nutrients to cells.
- Most tissue fluid is reabsorbed, but about 3 liters per day remains in tissues.
- Without removal, this excess fluid would cause swelling (oedema).
- The lymphatic system drains excess fluid via lymph ducts, returning it to the blood.
Lymphatic Vessels: Structure for Efficient Drainage
Thin Walls & Gaps for Easy Entry
- Lymphatic vessels have thin, permeable walls made of endothelial cells.
- Gaps between cells act as one-way flaps, allowing fluid in but not out.
- Blind-ended structure ensures fluid moves into the vessel and doesn’t escape.
The permeability of lymphatic vessels, due to their thin walls and gaps, makes them highly effective at collecting excess tissue fluid and preventing swelling.
Valves: Keeping Lymph Moving in One Direction
Lymph
Lymph is a clear, watery fluid that moves through the lymphatic system and carries nutrients, white blood cells, and other substances throughout the body.
- Low pressure in lymphatic vessels means fluid could flow backward.
- Valves prevent backflow, they open in one direction and close if fluid moves the wrong way.
- Skeletal muscles assist, as they contract, they push lymph forward, just like veins.
- Picture squeezing a tube of toothpaste.
- The pressure you apply pushes the toothpaste forward, but it doesn’t flow back because of the tube’s design.
- Similarly, valves in lymphatic vessels prevent backflow, keeping lymph moving toward the heart.
- Don’t confuse lymphatic valves with heart valves.
- While both prevent backflow, lymphatic valves are smaller and distributed throughout the lymphatic vessels, not confined to specific junctions.
Returning Lymph to Blood Circulation
- Lymph must rejoin the bloodstream.
- This happens via two major lymphatic ducts:
- Thoracic Duct – Largest lymph vessel, drains most of the body into the left subclavian vein.
- Right Lymphatic Duct – Drains lymph from right head, neck, chest, and arm into the right subclavian vein.
- Once in the subclavian veins, lymph mixes with blood and re-enters circulation.
Returning lymph to the bloodstream not only maintains fluid balance but also ensures the circulation of immune cells and filtered pathogens throughout the body.
Why Is This Important?
- Prevents Oedema – Removes excess fluid to avoid swelling.
- Boosts Immune Defense – Transports immune cells to lymph nodes to filter pathogens.
- Helps Nutrient Transport – Absorbs fats from digestion via lacteals in the small intestine.
- What is the role of valves in the lymphatic system?
- How do the thin walls of lymph ducts facilitate their function?
