2012B11 Outline the important features of the lymphatic circulation.

· Lymph composition

· Anatomy

· Physiology

· Water

· Electrolytes

· Protein (almost from liver due to permeable sinusoids - total 20g/L, hepatic 50g/L)

· Fat (almost all from gut via cisterna chyli)

· Carbohydrate

· Immune cells (antigen-presenting cells including dendritic cells, macrophages)

· All coagulation factors (but low level of fibrinogen)

Lymphatics

· Located in all tissues except bone, cartilage, brain

· Three layers: intima, media, adventitia

· Anti-reflux valves

· Superficial lymphatics travel with veins

· Deep lymphatics travel with arteries

Ducts

· Right lymphatic duct: drains RUL, R H&N, R hemithorax

· Thoracic duct: drains everything else (N.B. Virchow’s node in supraclav fossa)

Lymph nodes

· Large groups in axilla, inguinal, cervical regions (for UL, LL, H&N respectively), abdomen

· Cisterna chyli: dilated sac at the lower end of the thoracic duct (for GIT)

Circulation

· Extrinsic pump: compression by skeletal muscle or arterial pulsation

· Intrinsic pump: smooth muscle

· Valves ensure unidirectional flow

· Production: 8-12L/day (↑if exercise, capillary leak e.g. sepsis, anaphylaxis)

· Reabsorption: 4-8L/day via LNs; 4L/day via ducts (↓ if lymphoedema, radiation, obstruction)

Role in health

· Return extravasated fluid and protein to circulation, minimise oedema

· Transport ingested fat to circulation (bypass liver -> prevent fatty liver)

· Transport antigen-presenting cells to lymph nodes

· Formation of concentrated urine: removal of protein-rich ISF from medulla, allows water to enter vasa recta, preserves osmotic gradient

Role in disease

· Lymphoedema

o Destruction e.g. surgery, radiation

o Obstruction e.g. tumour