Expansion
Returns interstitial fluid and protein, absorbs fat, and carries immune cells
Expansion
Functions
- Fluid balance: returns the 2 to 4 litres a day of filtered fluid not reabsorbed by capillaries
- Protein return: the only route by which escaped plasma protein returns to the blood. Without it, interstitial oncotic pressure would rise and oedema would be inevitable
- Fat absorption: lacteals carry chylomicrons from the gut
- Immune surveillance: lymph nodes filter lymph and are the site of antigen presentation
Flow is driven by intrinsic contraction of lymphatic smooth muscle, the skeletal muscle pump, respiration and arterial pulsation, with valves ensuring one-way flow.
Lymphoedema is protein-rich and characteristically non-pitting in established disease, with skin thickening.
- Primary: congenital, such as Milroy disease
- Secondary: surgery (especially axillary clearance), radiotherapy, malignant infiltration, and filariasis, the commonest cause worldwide
Because lymphatics also carry tumour cells, nodal status is central to cancer staging, and sentinel node biopsy exploits the orderly nature of lymphatic drainage.