Lymphoid Histology - Francis Boyl

Question 1

Describe the general histological structure of lymphoid tissue and organs

Answer 1

General structures:

Reticular CT. Large numbers of Lymphocytes (B&T-cells).
Antigen Presenting cells / Plasma cells
Plasma cells: more cytoplasm / RER.

Question 2

Describe histological structure of bone marrow / functions.

Answer 2

Trabeculae, Adipocytes, Sinusoids, Hemopoietic cords, Sinusoids

Structure: reticular CT, stroma*. (fibroblast cells)
Matrix: Collagen, proteoglycans

Function: Site of RBC/platelet formation, site of WBC formation.

Question 3

Thymus

structure
function

Answer 3

Structure: Find it in mediastinum, above heart. Begins to shrink at puberty. U will see: Cortex / Medulla *** contain thymocytes / thymic epithelial cells.

Cortex: 3 types of thymic epithelial cells (TECs): Squamous / Stellate / Squamous cortical.

darkly stained bc lots of lymphocytes.
function: primary site of T-cell maturation. T-cell development / maturation, elimination of pathogens.
additional funciton: central tolerance. selective removal of T cells.
positive selection of cortex: practice binding to MHC
negative selection of medulla: T-cells whose TCRs strongly bind to self antigens are removed.

Question 4

Spleen

Answer 4

Structure: Red pulp / white pulp.
also has outer capsule / capsule.

spleen function: filter blood. screens blood for foreign pathogens. This different from lymph node, bc that filters lymph.

Question 5

Lymph nodes

structure

function

Answer 5

structure: bean-shaped, encapsulated structure.
Has convex surface. Lymph comes in from afferent, leaves through efferent. Will see trabeculae capsule medulla cortex. Can form follicles.

Outer cortex: B cells
Paracortex: T cells. There is something called high endothelial venules here: entry point for 90% of circulating lymphocytes into lymph nodes.
Medulla: T and B cells, plasma cells.

function: filter lymph. facilitate antigen presentation / antigenic responses.

Question 6

MALT

Answer 6

line mucosa, or inner lining of respiratory / genitourinary tracts.
Major site of infection.
examples: tonsils / peyers patches / appendix
large irregular masses of lymphoid tissue.
Tonsils - 3 types: palatine / lingual / pharyngeal

Question 7

Thymus

Cortex / medulla
Lymphoid nodules
Lymphatic vessels
Unique features:

Answer 7

Cortex / medulla: Distinctly present
Lymphoid nodules: Absent
Lymphatic vessels: No afferents, few efferents in septa
Unique features: Hassall (thymic) corpuscles in medulla; epithelial-reticular cells in cortex and medulla.

Question 8

MALT

Cortex / medulla
Lymphoid nodules
Lymphatic vessels
Unique features:

Answer 8

Cortex / medulla: Absent
Lymphoid nodules: Present
Lymphatic vessels: No afferents; efferents
Unique features: Crypts lined by surface mucosa in tonsils; epithelial M cells in mucosa over peyers patches

Question 9

Lymph nodes

Cortex / medulla
Lymphoid nodules
Lymphatic vessels
Unique features:

Answer 9

Cortex / medulla: Present
Lymphoid nodules: Present in cortex only
Lymphatic vessels: Afferents at capsule, emptying into subcapsular sinus; efferent at hilum
Unique features: Thin paracortical region between cortex and medulla, with high endothelial venules (HEV); medullary cords and sinuses

Question 10

Spleen

Cortex / medulla
Lymphoid nodules
Lymphatic vessels
Unique features:

Answer 10

Cortex / medulla: Absent
Lymphoid nodules: Present in white pulp only
Lymphatic vessels: No afferents; efferents in trabeculae
Unique features: Minor white pulp component, with central arterioles; major red pulp component, with many sinusoids