2. Lymphoid Tissue & Lymph Nodes Flashcards

Flashcards relating to lymphoid tissue, lymph nodes and other areas covered in the lecture notes.

Lymphoid Tissue

Connective tissue containing large numbers of lymphocytes (B Cells, T Cells, Natural Killer Cells) & monocyte lineages (macrophages, dendritic cells). May be diffuse (no discreet organisation) beneath epithelia of gastrointestinal, urogenital and respiratory tracts and provides a second line of defence.

Lymph nodes in birds

Birds lack lymph nodes and have a lot of lymphoid tissue (nodules).

Lymphoid Nodules

Dense, spherical aggregations of lymphocytes found in deep connective tissue of the gastrointestinal, urogenital & respiratory tracts where lymphocytes in centre undergo division.

Crypts

Blind-ending invaginations that collect particulate matter, which is then phagocytosed & passed to lymphoid tissue.

Peyer’s Patches

Beneath the epithelium of the distal ileum (the last part of the small intestine). Specialised M cells in the Peyer’s patches sample antigens directly from the intestinal lumen and transport them to APC.

Mucosa-associated lymphoid tissue (MALT)

Collective term for diffuse lymphatic tissue such as that within the digestive system, tonsils, nodules, and Peyer’s patches.

Lymph Nodes

An organ that all lymph flows through en route to the venous system. They vary in size depending on species and whether they are responding to foreign material.

Parenchyma

The functional tissue of an organ

Lymph node structure: Capsule

Outer fibrous layer of the lymph node.

Sinuses

Connective tissue network within lymph nodes containing reticular fibers, blood vessels, and macrophages for lymph passage. Can be referred to as sub capsular, cortical or medullary depending on their location. Lymph is filtered through the lymph node via the sinuses where macrophages phagocytose antigens for presentation to T cells in the cortex.

Cortex, Paracortex & Medulla

Region within lymph nodes containing parenchyma of lymphocytes, macrophages, and epithelial cells with a very organised structure.

Subcapsular Sinus

Site where lymph enters the lymph node via afferent lymphatic vessels, branching into the subcapsular sinus.

Cortex

Organised into follicles (nodules).

Primary Follicle

Area of tightly packed B lymphocytes within the outer cortex of a lymph node. Darkly stained.

Secondary Follicle

Area of a lymph node follicle undergoing response to antigen stimulation. Lightly stained germinal centre. They contain proliferating B lymphocytes and macrophages.

Corona (Marginal Zone)

Region of the lymph node that contains non-dividing B cells, helper T cells.

Interfollicular cortical tissue

Contains T cells

Paracortex

Deep cortex of the lymph node where T lymphocytes and macrophages are concentrated and T cells may modulate activity of B lymphocytes. T and B cells enter node at paracortex via specialised venules (most don’t come in via the afferent lymph).

High Endothelial Venules (HEV)

Specialized venules in the paracortex lined with cuboidal epithelium (not squamous) that allow lymphocytes (B and T cells) to enter from the blood. No tight junctions.

Medulla

Inner region of the lymph node consisting of medullary cords and medullary sinuses. The medullary cords contain plasma cells that secrete antibodies, as well as B lymphocytes, macrophages.

Hilus

The entry and exit point of the node and it contains efferent lymphatic vessels, afferent & efferent blood vessels and adipose tissue

Afferent Lymph

Lymph that carries debris, particulate matter, antigens, microbes, and very few lymphocytes into a lymph node.

Efferent Lymph

Lymph that carries very little debris & matter but is rich in lymphocytes, plasma cells, and antibodies exiting a lymph node.

Inverted Structure

Where follicles are located centrally and medullary cords are peripheral (seen in the pig).

Infection & inflammation

Cause swelling of regional node/s.

Lymphoma

Often causes swelling of all nodes.

Lymph Centres

Nodes that drain a specific area of the body. There’s lots of lymph centres in the mesentery.

Which lymph centres (nodes) are palpable?

(Sub)mandibular, superficial cervical, superficial inguinal, popliteal (and axillary in the cat)

(Sub)mandibular

Located at the angle of the jaw and drains the muzzle and tongue.

Superficial cervical

Located in front of the shoulder and drains the superficial neck and forelimb.

Superficial Inguinal Centre

Located on the inside of the hind limb and associated with mammary glands or scrotum.

Popliteal Centre

Located on the caudal stifle (popliteal fossa), draining distal limb.