Structural elements of the lymphatic system
The lymphatic system consists of several consecutive levels of vessel organization, each performing a specific task:
- Lymphatic capillaries (vasa lymphocapillaria). The smallest vessels with a wall consisting of a single layer of endothelium. Unlike blood capillaries, they are blindly ended at one end. By fusing, they form networks (retia lymphocapillaria) in all tissues and organs.
- Lymphatic vessels (vasa lymphatica). Formed by the convergence of capillaries. Their wall is thinner than that of blood vessels and includes three tunics: internal (tunica intima), middle muscular (tunica media), and external adventitial (tunica externa). An important feature of the vessels is the presence of paired semilunar valves (valvulae lymphaticae) ensuring the flow of lymph in only one direction, towards the heart.
- Lymph nodes (nodi lymphoidei). Lymph from capillaries is directed via vessels to the nodes, which act as biological filters.
Main lymphatic collectors
The main volume of lymph is collected into large collectors, which are then drained into the venous system.
- Thoracic duct (Ductus thoracicus). The largest lymphatic vessel. It drains lymph from the legs, pelvis, abdomen, as well as the left arm, left half of the chest, head, and neck. It begins in the abdominal cavity with a dilation — cisterna chyli (cisterna chyli), into which the intestinal and lumbar trunks empty. The duct ascends through the thoracic cavity (thoracic part) to the neck (cervical part), where it empties into the left venous angle.
- Right lymphatic duct (Ductus lymphaticus dexter). This is a short collector (about 1–1.5 cm). It collects lymph from the right upper half of the body: right arm, right part of the chest, head, and neck. The duct terminates by emptying into the right venous angle, which is formed by the union of the right internal jugular and right subclavian veins.
Lymphatic trunks
Lymphatic trunks (trunci lymphatici) are large regional vessels that form the main ducts.
Empty into the thoracic duct:
- Left and right lumbar trunks (truncus lumbalis sinister et dexter) — from the legs and pelvis.
- Intestinal trunks (trunci intestinales) — from the abdominal organs.
- Left jugular trunk (truncus jugularis sinister) — from the left half of the head and neck.
- Left subclavian trunk (truncus subclavius sinister) — from the left arm.
Empty into the right lymphatic duct:
- Right jugular trunk (truncus jugularis dexter) — from the right half of the head and neck.
- Right subclavian trunk (truncus subclavius dexter) — from the right upper extremity.
Note: the bronchomediastinal trunk may also approach the right lymphatic duct.
Main regional lymph nodes
Lymph nodes are grouped together depending on the drainage area:
- On the head and neck: occipital, mastoid, superficial and deep parotid, submandibular, and submental nodes. In the neck, lymph collects into lateral superficial and deep cervical nodes, including large palpable nodes (e.g., jugulodigastric and jugulo-omohyoid).
- On the upper extremity and chest: axillary nodes (the main collector from the arm and mammary gland), intercostal nodes, and paramammary nodes (the first stage of mammary gland drainage).
- On the lower extremity and in the pelvis: inguinal (superficial and deep) nodes, draining lymph from the legs and external genitalia, as well as external iliac nodes running along the vessels of the same name.
Briefly: answers to topical questions
Which lymphatic trunks empty into the thoracic duct?
The lumbar, intestinal, as well as the left jugular and subclavian trunks empty into the thoracic duct. The formation of the duct and subsequent lymph collection occur via the following large vessels:
- Left lumbar trunk (truncus lumbalis sinister) — collects lymph from the left lower extremity and pelvis.
- Right lumbar trunk (truncus lumbalis dexter) — collects lymph from the right lower extremity and pelvis.
- Intestinal trunks (trunci intestinales) — drain lymph from the abdominal organs.
- Left jugular trunk (truncus jugularis sinister) — from the left half of the head and neck.
- Left subclavian trunk (truncus subclavius sinister) — from the left upper extremity.
At the level of which vertebrae does the thoracic duct begin (where is the cisterna chyli located)?
The thoracic duct begins at the level from the 11th thoracic to the 2nd lumbar vertebra. Its initial dilation — the cisterna chyli (cisterna chyli) — is located on the anterior surface of the vertebral bodies from L2 to Th11 (predominantly at the level of the 1st–2nd lumbar vertebrae). The cistern is situated near the right crus of the lumbar part of the diaphragm and fuses with it.
Into which topographical parts is the thoracic duct anatomically divided?
Anatomically, the thoracic duct is divided into three topographical parts:
- Abdominal part (pars abdominalis) — located retroperitoneally above the cistern and passes through the aortic hiatus of the diaphragm.
- Thoracic part (pars thoracica) — passes through the thoracic cavity in the posterior mediastinum, ascending superiorly to the right of the aorta.
- Cervical part (pars cervicalis) — the terminal section at the neck level, which forms the arch of the thoracic duct and empties into the left venous angle.
Into which regional lymph nodes does lymph drainage from the mammary gland occur?
Lymph drainage from the mammary gland occurs into several groups of regional lymph nodes. The main drainage pathways:
- Axillary lymph nodes (nodi lymphatici axillares) — the main pathway, receiving about 75–80% of lymph (predominantly from the lateral quadrants).
- Parasternal lymph nodes (nodi lymphatici parasternales) — receive lymph from the medial quadrants.
- Supraclavicular lymph nodes — drain the superior regions of the gland.
- Infraclavicular lymph nodes (nodi lymphatici infraclaviculares) — receive lymph from the posterior region.
- Intercostal lymph nodes — from the posterior regions of the gland.
- Paramammary lymph nodes (nodi lymphoidei paramammarii) and interpectoral lymph nodes (nodi lymphoidei interpectorales).
Class and exam questions
What is the difference between lymphatic and blood capillaries?
Lymphatic capillaries are blindly ended at one end, whereas blood capillaries are part of a continuous closed bed between arteries and veins.
Which structure forms the origin of the thoracic duct?
The beginning of the thoracic duct is a dilation in the abdominal cavity — the cisterna chyli (cisterna chyli), formed by the convergence of the intestinal and lumbar trunks.
Where do the thoracic duct and the right lymphatic duct empty?
The thoracic duct empties into the left venous angle, and the right lymphatic duct into the right venous angle. These angles are formed by the union of the internal jugular and subclavian veins of the corresponding side.
What else to study on this topic
- Topography of the cisterna chyli
- Classification of cervical lymph nodes
- Lymph drainage pathways of the mammary gland
- Connection of the lymphatic system with the superior vena cava
- Structure of the valve apparatus of lymphatic vessels
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