The Lymphatic System and Lymphoid Tissue – Comprehensive Study Notes

Fluid balance

Reclaim excess interstitial fluid (ISF) and return it to blood circulation.

Protection / Immunity

House, mature, and mobilise leukocytes (lymphocytes, macrophages, etc.).

Fat absorption

Pick up dietary lipids in intestines via lacteals and shunt them to blood.

Lymph

The fluid component of the lymphatic system, clear and colourless, derived from blood plasma but with less protein.

Lacteals

A specialised type of lymphatic capillary in intestinal villi that absorbs emulsified fats.

Thoracic duct

The larger of the two terminal lymphatic ducts, draining the left head/neck, left thorax, left upper limb, abdomen, pelvis, and both lower limbs.

Right lymphatic duct & Thoracic duct

The two terminal lymphatic ducts that empty into the venous angles.

Lymph nodes

Bean-shaped, encapsulated structures located along lymphatic vessels that filter lymph and are sites of immune activation.

Spleen

The largest lymphoid organ, located in the LUQ, which filters blood, removes microbes and old RBCs, and is a site of fetal erythropoiesis.

Thymus

The bilobed gland in the mediastinum, most active in childhood, which is the site of T-lymphocyte maturation and selection.

MALT (Mucosa-Associated Lymphoid Tissue)

A diffuse system of lymphoid tissue guarding mucosal surfaces where pathogens first contact the body (e.g., tonsils, Peyer patches, appendix).

Peyer patches

Aggregates of lymphoid follicles mainly in the distal ileum that monitor intestinal bacteria and generate memory lymphocytes.

Lymphadenopathy

General term for diseased or enlarged lymph nodes.

Lymphadenitis

Inflammation of lymph node(s), often painful and warm, typically secondary to a local infection.

Lymphangitis

Acute inflammation of lymphatic vessels, often streptococcal, presenting as a red 'streak' extending proximally from a wound.

Lymphedema

Chronic interstitial fluid accumulation due to lymphatic obstruction or insufficiency.

Splenomegaly

Enlargement of the spleen, often due to congestion, haemolysis, infection, leukaemia/lymphoma, or storage diseases.

Hodgkin Lymphoma (HL)

A malignancy of lymphocytes originating in lymphoid tissue, characterized by the presence of Reed–Sternberg cells and orderly contiguous spread.

Non-Hodgkin Lymphoma (NHL)

A heterogeneous group of lymphocyte malignancies that are more common than HL, often disseminated at diagnosis, and lack Reed–Sternberg cells.

Filter lymph; site of lymphocyte activation

The principal function of lymph nodes.

MALT

An acronym for Mucosa-Associated Lymphoid Tissue.

GALT

An acronym for Gut-Associated Lymphoid Tissue.

T-cells

The type of cells matured by the thymus.

Lymph

The fluid typically found in lymphatic capillaries after fluid entry.

Mass balance principle

The fluid balance principle stating that whatever exits capillaries must re-enter circulation (blood + lymph).

More permeable and blind-ended

How lymphatic capillaries differ from blood capillaries.

Mechanism of lymph propulsion that involves contraction compressing vessels (e.g., during exercise).