Human Anatomy
General Features of the Lymphatic System
Lymphatic system anatomy for MBBS: lymph capillaries, vessels, nodes, thoracic and right lymphatic ducts and lymphatic spread, mapped to NMC codes AN6.1 to AN6.3.
MedNext Academy | 3 min read
General Features of the Lymphatic System
Lymphatic system anatomy for MBBS: lymph capillaries, vessels, nodes, thoracic and right lymphatic ducts and lymphatic spread, mapped to NMC codes AN6.1 to AN6.3.
This chapter outlines the lymphatic system, which drains tissue fluid and underpins immune defence. It covers lymph capillaries, vessels and nodes, the two great lymph ducts, and the clinical importance of lymphatic spread of infection and cancer.
High-yield: General Features of the Lymphatic System
- The lymphatic system returns tissue fluid to the blood and is central to immunity.
- Lymphatic capillaries are blind-ended and more permeable than blood capillaries, so they take up large molecules and cells.
- Lymph flows from capillaries into collecting vessels, through lymph nodes, into trunks and finally into the venous system.
- The thoracic duct drains the lower half of the body and the left upper quadrant into the left venous angle.
- The right lymphatic duct drains the right side of the head, neck, thorax and right upper limb into the right venous angle.
- Lymph nodes have an afferent supply entering the convex surface and efferent vessels leaving at the hilum.
- Lymph nodes filter lymph, add lymphocytes and mount immune responses to trapped antigens.
- The cisterna chyli, at the lower end of the thoracic duct, receives intestinal and lumbar lymph trunks.
- The lymphatic system has no lymphatics in avascular tissues such as the cornea, cartilage and epidermis.
- Spread of carcinoma commonly follows lymphatic drainage to regional nodes, which guides cancer staging.
- Lymphangitis is inflammation of lymph vessels and lymphadenitis is inflammation of lymph nodes.
- Obstruction of lymphatics causes lymphoedema, a firm non-pitting swelling.
- The spleen, thymus and tonsils are lymphoid organs but have no afferent lymphatics of the nodal type.
- Lacteals are specialised lymphatic capillaries in intestinal villi that absorb dietary fat.
Major drainage routes
- **Thoracic duct:** Drains both lower limbs, abdomen, left thorax, left head, neck and left upper limb into the left venous angle.
- **Right lymphatic duct:** Drains the right head, neck, thorax and right upper limb into the right venous angle.
- **Cisterna chyli:** Dilated lower end of the thoracic duct receiving intestinal and lumbar trunks.
- **Lymph node:** Filters lymph; afferents enter the convex surface, efferents leave at the hilum.
NMC competencies in this chapter
- **AN6.1:** Composition and functions of the lymphatic system
- **AN6.2:** Structure of lymph capillaries, vessels, nodes and ducts
- **AN6.3:** Applied anatomy including lymphatic spread of disease
Frequently Asked Questions
What does the lymphatic system do?
It drains excess tissue fluid back into the bloodstream, absorbs dietary fat through intestinal lacteals, and filters lymph through nodes where immune responses are mounted.
What does the thoracic duct drain?
The thoracic duct drains lymph from both lower limbs, the abdomen, the left half of the thorax, and the left side of the head, neck and upper limb, emptying into the left venous angle.
Why is lymphatic drainage important in cancer?
Carcinomas often spread first along lymphatic vessels to regional lymph nodes. Knowing the drainage of an organ tells the clinician which nodes to examine and biopsy for staging.
Which tissues have no lymphatics?
Avascular tissues such as the cornea, cartilage, epidermis and the central nervous system parenchyma lack conventional lymphatic vessels.
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