Lymph is fluid in lymphatic vessels which originates in interstital spaces.
Content
- Derived from ISF so similar compisition
- Mostly water
- Electrolytes in same composition as ISF
- Small amount of proteins, including clotting factors
- Hepatic lymph has higher protein (sinusoids very permeable)
- Lymphocytes and antigen-presenting cells
- Following meal, chylomicrons = chyle
Circulation
- Blind-ended lymphatic capillaries with permiable BM (everywhere except CNS, bone, cartilage)
- \(\to\) lymphatic vessels with one-way valves
- \(\to\) travel through lymph nodes
- \(\to\) converge into the right lymphatic duct (20%) and cysterna chyli which becomes thoracic duct (80%)
- These drain into the right and left subclavian respectively
- Drainage is enabled by breathing and muscle pumps
Function
- Fluid return: Starling forces at capillary result in 2ml/min of fluid escaping into interstitium, this is returned at same rate by lymph. If capillary leak > lymph drainage \(\to\) oedema.
- Protein return: protein which escapes vessels (typically sinusoids) is returned to circulation
- Lymph nodes filter and phagocytose bacteria. Lymphocytes proliferate in response to antigen presentation.
- Dietary fats + fat-soluble vitamins transported to circulation as chyle