• Clinical science

Lymphatic system


Primary lymphatic organs

The primary lymphatic organs are the bone marrow and thymus. They are the site at which lymphocytes form and mature. Both B lymphocytes and T lymphocytes arise from hematopoietic stem cells in the bone marrow. While B lymphocytes remain within the bone marrow during the process of maturation. T lymphocytes migrate to the thymus to mature and differentiate.

Bone marrow

Bone marrow: B cell maturation – Thymus: T cell maturation


Thymus: third pharyngeal pouch

DiGeorge syndrome is caused by an abnormal development of the 3rd and 4th pharyngeal pouches which prevents the formation of thymus and parathyroid glands. As a result, patients with DiGeorge syndrome have an increased susceptibility to viral as well as fungal infections, and hypocalcemia.

Secondary lymphatic organs

The secondary lymphatic organs are the spleen, lymph nodes, and mucosa-associated lymphatic tissue,e.g., the Peyer patches and tonsils. It is in the secondary lymphatic organs that antigen presentation occurs. They are also the site of differentiation of mature, naive lymphocytes into effector cells.


For more information see spleen.

Lymph nodes

  • Function
  • Location
    • Throughout the body in close proximity to organs and large vessels
  • Structure
    • Bean-shaped organ surrounded by fibrous capsule with trabeculae
    • Numerous afferent lymphatic vessels enter through the capsule.
    • The trabecular sinus leads lymph from the subcapsular sinus to the medullary sinus.
    • The hilus allows blood vessels and efferent lymphatic vessel to enter or leave the lymph node
    • The entering artery and vein branch into a large capillary network, which forms the post-capillary high endothelial venules.
  • Histology
  • Clinical significance

Mucosa-associated lymphoid tissues (MALT)

MALT include the tonsils, Peyer patches, and solitary lymphoid follicles of the mucosa. The structure of MALT resembles that of other secondary lymphatic organs but it is also composed of a specialized reticular epithelium (follicle-associated epithelium) with a humoral defense mechanism . The follicle-associated epithelium of the gut-associated lymphatic tissue (GALT) contains M cells, which allow transcytosis of antigens into the lamina propria.

Peyer patches

  • Function
    • Immune system activation in response to ingested pathogens
      • M cells transport antigens from the intestinal lumen to antigen-presenting cells (e.g., macrophages) → B cells within the germinal center detect antigens and differentiate to plasma cells that secrete IgAIgA acquires a secretory component and becomes secretory IgA → secretory IgA is transported across the intestinal epithelium and secreted on the luminal surface of the gut
  • Location: ileum (lamina propria and submucosa)
  • Structure
    • Similar to other secondary lymphatic organs
    • No surrounding capsule
  • Histology
    • Aggregates of lymphoid follicles: contain numerous lymphocytes and dendritic cells
    • Follicle-associated epithelium : site of specialized M cells


  • Function: Waldeyer tonsillar ring (first line of defense against inhaled or ingested pathogens)
  • Structure: similar to other secondary lymphatic organs
  • Location and histology:
Pharyngeal tonsils (adenoids)

Palatine tonsils

Lingual tonsils Tubal tonsils
  • Roof and posterior wall of the nasopharynx
  • Tonsillar fossa on both sides of the oropharynx
  • Base of the tongue
  • Lateral wall of the nasopharynx

Lymphatic drainage

The thoracic duct is a lymphatic structure that originates in the abdomen and travels through the thorax to drain in the venous system. It carries both emulsified fat and lymph, which together are referred to as chyle. Injury to the lymphatic channels, particularly the thoracic duct, causes chylothorax.

Lymph node clusters

Lymph node cluster Location

Lymphatic basin (Afferent lymphatics)

Efferent lymphatic drainage

Conditions associated with lymphadenopathy

Cervical lymph nodes Deep cervical lymph nodes
  • Head and neck

Supraclavicular lymph nodes

  • Supraclavicular fossa, closer to the sternal end of the clavicle
  • Right supraclavicular nodes
  • Left supraclavicular nodes (Virchow nodes)
    • Left thorax
    • Left upper extremity,
    • Abdomen
    • Pelvis
Thoracic lymph nodes Mediastinal lymph nodes
Hilar lymph nodes
Abdominal lymph nodes

Pre-aortic lymph nodes

Celiac lymph nodes
  • Around the celiac arterial trunk
  • Cisterna chyli (dilated sac at the lower end of the thoracic duct)
Superior mesenteric lymph nodes
  • From distal duodenum to the splenic flexure of the colon
Inferior mesenteric lymph nodes
  • From the descending colon till the upper rectum
Para-aortic lymph nodes
  • Lateral aspect of the aorta, around the renal vein
  • Gonads (testes or ovaries)
  • Kidneys
  • Lymph from the common iliac nodes
Pelvic lymph nodes Internal iliac lymph nodes
  • Around the internal iliac arteries
External iliac lymph nodes
  • Around the external iliac arteries
Common iliac lymph nodes
  • Around the common iliac vessels
Lower extremity lymph nodes Superficial inguinal lymph nodes
  • Superficial fascia of the thigh in the region of the femoral triangle

  • Arranged in the shape of “T”

    • The upper horizontal group lie along the inguinal ligament

    • The lower vertical group lie along the terminal part of the long saphenous vein

Deep inguinal lymph nodes
Popliteal lymph nodes
  • Popliteal fossa
  • Lateral surface of the foot, heel, and posterior surface of the calf
  • Deep parts of the leg, running along the anterior and posterior tibial vessels, and the knee joint.
  • Infections or melanoma of the lower extremity
Upper extremity lymph nodes Axillary lymph nodes
  • Deep fascia of the axilla
    • Anterior group (pectoral)
    • Posterior group (subscapular)
    • Lateral group (humeral)
    • Central group (lies in axillary fat)
    • Apical group (behind the pectoralis minor)
  • Anterior group: mammary and pectoral regions
  • Posterior group: upper back and posterior neck
  • Lateral group: upper limb
  • Central group: lymph from the anterior, posterior, and lateral groups
  • Apical group
    • Lymph from the central group
    • Upper outer quadrant of the breast
  • Infections of the upper extremity
  • Malignancy of the breast
  • Melanoma of the upper extremity

Epitrochlear lymph nodes

(supratrochlear lymph nodes)

  • Forearm and hand

  • Infections of the hand and forearm

  • Kaplan. USMLE Step 1 Anatomy Lecture Notes 2016. Kaplan Publishing; 2015.
  • Murphy K, Weaver C. Janeway's Immunobiology. Garland Science; 2016.
  • Le T, Bhushan V,‎ Sochat M, Chavda Y, Zureick A. First Aid for the USMLE Step 1 2018. New York, NY: McGraw-Hill Medical; 2017.
last updated 03/29/2019
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