Lymphatic vessels and lymphoid organs
The lymphatic system includes vessels, lymph nodes and organs involved in immune surveillance. Practice locating its structures and understanding basic lymphatic drainage.
212 explained questions · practice, exam and sprint · freeInterstitial fluid and proteins require a route back to the circulation. Fluid becomes lymph after entering blind-ended lymphatic capillaries through overlapping endothelial cells. Larger vessels contain valves favoring one-way flow. Skeletal movement, respiration and vessel-wall activity assist propulsion; there is no central pump equivalent to the heart. Drainage may pass through lymph node chains before reaching trunks and ducts.
The right lymphatic duct usually drains the right side of the head and neck, right upper limb and right thorax. The thoracic duct receives most remaining territories, including both lower limbs and the abdomen. Their terminations relate to the corresponding internal jugular–subclavian venous junctions. Right does not mean the entire right half of the body. A cisterna chyli may form an initial thoracic duct dilation, but its morphology varies.
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Afferent vessels bring lymph into a node and efferent vessels leave at its hilum. Cortex, paracortex and medulla organize immune-cell interactions. The spleen lies in the left upper abdomen and receives blood through its own vasculature. White pulp supports immune responses; red pulp filters blood and helps remove aging red cells. A question about a filtering lymphoid organ must distinguish lymph from blood.
Bone marrow and thymus are primary lymphoid organs associated with lymphocyte development or maturation. T cells undergo selection in the thymus. Nodes, spleen and mucosal lymphoid tissues support responses as secondary organs or tissues. Tonsils guard aerodigestive entrances. Intestinal lacteals transport absorbed lipids packaged in chylomicrons; lipid-rich lymph is called chyle. Lymphatic functions combine fluid balance, transport and immunity, but the lymphatic and immune systems are not identical.
| Structure or concept | Distinguishing feature |
|---|---|
| Lymph node | Receives and filters lymph; afferent and efferent vessels. |
| Spleen | Filters blood and supports immune responses. |
| Thymus | T-cell maturation and selection. |
| Lacteal | Lymphatic capillary within an intestinal villus. |
Try answering before opening the explanation. Each example develops a point from the guide.
Answer: Spleen
The spleen lies mainly in the left upper abdomen near stomach and diaphragm. Its circulation supports blood filtration, while its lymphoid regions participate in immune responses.
Why the other options do not fit: Thymus is principally mediastinal and thyroid is cervical. The appendix usually relates to the cecum in the lower right abdomen, not the described upper-left organ.
Answer: Lymph node
Lymph nodes receive lymph through afferent vessels and release it through efferent vessels. Their compartments support antigen–immune cell interactions. They filter lymph, whereas spleen filters blood.
Why the other options do not fit: Thymus supports T-cell maturation and selection; spinal cord is central nervous tissue. Neither spleen nor thymus replaces a lymph node along a lymphatic vessel chain.
Answer: Thoracic duct
The thoracic duct drains most body territories, including both lower limbs and abdomen, and usually ends at the left venous junction. The right duct receives a smaller right-upper territory.
Why the other options do not fit: The right duct does not drain the entire right half. Cystic and common hepatic ducts convey bile and belong to the biliary tree rather than lymphatic drainage.
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