Lymphoid organs

Question 1

Primary lymphoid organs

Answer 1

Where WBCs are produced and mature Bone Marrow Thymus Bursa of Fabricius in Birds Ileal Peyer’s patches near ileocaecal junction (B cells) in ruminants, pigs, horses, dogs and humans

Question 2

Secondary Lymphoid Organs

Answer 2

Where WBCs reside and ecnounter antigen Lymph nodes Spleen tonsils Mucosa-associated lymphoid tissues (MALT) Haemal nodes (ruminants) Caecal tonsils (birds)

Question 3

Function of lymphatic tissue

Answer 3

Capture fluid lost from blood Control infection Lymphatic transport

Question 4

Lymphatic nodules (follicles)

Answer 4

-secondary lymphatic organs and loose connective tissue of the body -densly packed spherical aggregation of lymphocytes; predominantly B cells

Question 5

Where is red marrow

Answer 5

In flat bones -skull, ribs, sternum, pelvis, vertebrae, heads of long bones

Question 6

Where is yellow marrow

Answer 6

Found in the shaft of long bones -As the animal ages, adipose tissue replaces the marrow in the long bones.

Question 7

Structures of the bone marrow stroma

Answer 7

Collagen fibres Reticular fibres - reticular cells, fibroblasts, fat cells, osteogenic cells Stromal elements impact on cell differentiation in the bone marrow

Question 8

Function of the thymus

Answer 8

differentiation of T lymphocytes Development of immunological tolerance

Question 9

Structure of the thymus

Answer 9

Question 10

General structure of the lymph node

Answer 10

Question 11

Thymic epithelial cells role in immunity

Answer 11

They are antigen presenting cells and are present in positive selection of the thymocytes

Question 12

Primary B cell follicles contain

Answer 12

Mature maive B cells

Question 13

Secondary B cell follicles contain

Answer 13

Outer mantle of non proliferating B cells

Inner pale germinal centre containing proliferating and maturing B cells, antigen-presenting follicular dendritic cells and helper T cells

Question 14

3 Lymph Node regions

Answer 14

Cortex: B cells

Paracortex: T cell rich

Medulla: Blood vessles, sinuses and medullary chords with plasma cells, macrophages and B cells

Question 15

Entry of lymphocytes into lymph nodes

Answer 15

• 10% from afferent lymph with dendritic cells and macrophages
• 90% from the blood

Question 16

Species differentiation of porcine lymph nodes

Answer 16

• ‘Inside out’ architecture
• Lymphoid follicles are in the middle of the organ, diffuse lymphoid tissue in the outer zone.
• Afferent lymphatics enter at the hilus
• Effernt lymphatics leave at the node surface
• lymphocytes leave via the blood rather than the lymph

Question 17

Functions of the spleen

Answer 17

• Clearing particulate and other antigens
• clearing microorganisms
• Clearing aged red cells and remnants of DNA and ribosomes from reticulocytes
• B cell response to bacterial antigens
• Reservoir of RBC and platelets

Question 18

Spleen white pulp

Answer 18

Periarteriolar lymphoid sheaths (PALS)

Primary and secondary follicles

marginal zome and mantle or corona

Question 19

Red pulp of spleen

Answer 19

-Filter and trap damaged erythrocytes and associated debri

Question 20

Animals that hace closed splenic circulation

Answer 20

Cats and dogs

Question 21

Defensive spleen

Answer 21

Human, primates, mice, rats, rabbits

Limited contractile ability

Extensive periarteriolar lymphoid sheaths, numerous lymphoid follicles

Question 22

Storage Spleen

Answer 22

Dogs, cats, horses, ruminants and pigs

Capsule and trabeculae have well developed smooth muscle - reservoir for blood

-smaller PALS and fewer lymphoid follicles

Question 23

Gut-associated lymphoid tissue (GALT)

Answer 23

• Ileal and jejunal Peyers patches in the intestinal wall
• Diffuse lymphoid tissue outside of organised lymphatic structures
• tonsils
• appendix in humans

Question 24

Mucosa-associated lymphoid tissue (MALT)

contain what cells

Answer 24

• B cell follicles
• plasma cells in diffuse lymphoid tissue
• tonsillar surface is smooth in dogs and cats; horses and ruminants have invaginations and crypts which increase surface area
• No afferent lymph; efferent lymph in tonsillar capsule