Anatomy chapters
Applied lymphatic system
How lymph is collected and returned to the blood, the main lymph node groups and ducts, and why lymphatic drainage matters in cancer spread and swelling.
- Lymph vessels collect tissue fluid and return it to the veins at the root of the neck.
- The thoracic duct drains everything except the right upper quarter of the body.
- Cancers spread along lymph to regional nodes, so knowing drainage tells you where to feel.
On this page
Overview
The lymphatic system is a one-way drainage system. It collects excess tissue fluid, called lymph, and returns it to the blood.
It also carries absorbed fat from the gut and filters lymph through lymph nodes, where immune cells meet antigens.
Applied questions ask where a region drains, where the main ducts run and end, and what happens when lymph is blocked or carries cancer.
Parts of the lymphatic system
- Lymph capillaries: blind-ended, very leaky tubes in the tissues.
- Lymph vessels: have valves, like veins. They pass through one or more groups of nodes.
- Lymph nodes: bean-shaped filters along the vessels.
- Lymph trunks and ducts: large channels that empty into the veins in the neck.
- Lymphoid organs: thymus, spleen, tonsils and the lymphoid tissue of the gut (Peyer's patches).
Lymph capillaries in the villi of the small intestine are called lacteals. They absorb fat, which makes the lymph milky. This milky lymph is called chyle.
Lymph vessels are absent from the brain and spinal cord (classical teaching), the bone marrow, cartilage and the epidermis.
Lymph nodes
Afferent vessels enter the node around its edge. Lymph filters through it and leaves through efferent vessels at the hilum.
Each region drains first to a regional group of nodes, and then on to deeper groups.
| Region | First nodes |
|---|---|
| Upper limb and breast | Axillary nodes |
| Lower limb, skin below the umbilicus, lower anal canal, external genitalia (not testis) | Superficial inguinal nodes |
| Head and neck | Deep cervical nodes (often via smaller groups first) |
| Testis and ovary | Para-aortic (lumbar) nodes |
| Gut | Nodes along the arteries that supply it |
The testis drains to the para-aortic nodes near L1–L2, not to the inguinal nodes, because it descended from the posterior abdominal wall.
The scrotum drains to the superficial inguinal nodes, but the testis drains to the para-aortic nodes.
The thoracic duct
The thoracic duct is the largest lymph vessel.
- Begins: at the cisterna chyli, a sac in front of the bodies of L1 and L2, on the right of the aorta.
- Enters the thorax: through the aortic opening of the diaphragm (T12), between the aorta and the azygos vein.
- Course: ascends behind the oesophagus, crosses from right to left at about T5, and climbs to the neck on the left side of the oesophagus.
- Ends: by opening into the junction of the left subclavian and left internal jugular veins.
It drains the whole body below the diaphragm, plus the left side of the thorax, head, neck and the left upper limb.
The thoracic duct drains three quarters of the body. Only the right upper quarter drains to the right lymphatic duct.
The right lymphatic duct
A short duct formed by the right jugular, subclavian and bronchomediastinal trunks. It ends at the junction of the right subclavian and right internal jugular veins.
It drains the right upper limb, the right half of the chest and the right half of the head and neck.
Clinical relevance
Spread of cancer
How it happens: cancer cells break into lymph vessels and are carried to the first group of nodes.
What you see: hard, painless, enlarged regional nodes. Breast cancer spreads first to the axillary nodes; cancer of the lower anal canal spreads to the inguinal nodes.
Virchow's node (Troisier's sign)
How it happens: abdominal cancer, classically stomach cancer, spreads up the thoracic duct to the nodes near its end.
What you see: an enlarged left supraclavicular node.
Sentinel node
The sentinel node is the first node a tumour drains to. Surgeons find it with dye or a tracer and test it. If it is free of cancer, the rest of the nodes are often spared.
Lymphoedema
How it happens: lymph drainage is blocked, for example after axillary node clearance or radiotherapy, or by filarial worms (filariasis).
What you see: firm swelling of the limb that does not pit easily later on, with thickened skin.
Chylothorax
How it happens: injury to the thoracic duct, for example during chest or oesophageal surgery.
What you see: milky fluid (chyle) in the pleural cavity.
Lymphadenitis
How it happens: infection spreads to the regional nodes.
What you see: tender, enlarged nodes. A septic toe or sole ulcer causes painful inguinal nodes.
Expect questions on the course and ending of the thoracic duct, the area drained by the right lymphatic duct, Virchow's node, and the drainage of the testis compared with the scrotum. Lymphoedema after breast surgery is a common applied angle.
Quick revision
- Thoracic duct: starts at the cisterna chyli (L1–L2), passes through the aortic opening, crosses right to left at T5.
- It ends at the junction of the left subclavian and left internal jugular veins.
- Right lymphatic duct: right head, neck, thorax and arm.
- Testis: para-aortic nodes. Scrotum: superficial inguinal nodes.
- Virchow's node: left supraclavicular, classic for stomach cancer.
- Lymphoedema: after node clearance, radiotherapy or filariasis.
Written by The House Job from standard anatomy references (Snell's Clinical Anatomy by Regions is the book named in the UHS PGET syllabus).
FAQ
Where does the thoracic duct begin and end?
It begins at the cisterna chyli in front of L1–L2 and ends at the junction of the left subclavian and left internal jugular veins.
What does the right lymphatic duct drain?
The right upper limb, the right half of the chest, and the right half of the head and neck.
Why is the left supraclavicular node enlarged in stomach cancer?
Cancer cells travel up the thoracic duct, which ends near these nodes.
Where does the testis drain?
To the para-aortic (lumbar) nodes, not to the inguinal nodes.