Lymphoid Organs

Red pulp

Acidophilic, soft, dark, red masses in H&E part of spleen where majority of RBC's are

Splenic pulp

Another term for the parenchyma of the spleen

Ampulla of Thoma

Another term for the terminal branch of penicillar artery

Medullary cords

Arrangement of the medulla of lymph nodes; anastomosing cords; medullary sinuses would branch and anastomose and would fragment the parenchyma into strands or cords

White pulp

Basophilic, dark-staining in H&E part of spleen where majority of lymphocytes are

Subcapsular/ Primary/ Germinal sinus

Beneath the capsule; the space between the capsule & nodule

Splenic artery => (enter hilum and follow trabecula) trabecular artery =>reaches 2mm diameter (leaves trabecula) => enters white pulp => acquires PALS => artery surrounded by CT and becomes Central artery => diameter is 25 micra => enters red pulp => branch repeatedly => forms penicillar artery (penicillus of Ruysch) which has at least 5 branches

Blood vessels in the spleen

Venous sinuses

Blood-filled spaces of the red pulp

Thymus

Broad, flat bilobed mass of lymphoid tissue found just beneath the upper part of the sternum

Reticular CT Dense irregular fibrous CT

CT of stroma of lymphoid organs (2)

Dense fibrous CT

CT of the capsule of the thymus

Germinal center (of Flemming)

Cells are actively dividing therefore nodes produce lymphocytes; arranged diffusely

Bilroth's cord or Splenic cord

Cells in the red pulp are arranged in cords with spaces in between

Parenchyma

Cellular part of lymphoid organs

Germinal center (of Flemming)

Central pale-staining part of the cortex of lymph nodes; medium and large lymphocytes

Medulla

Central part of the parenchyma of lymph nodes; forms cellular cords; no lymphatic nodules

Lymphoid Organs

Collection of lymphoid tissue in fixed location & with definite structural characteristics

Tonsils

Collection of lymphoid tissues in the mucous membrane of the upper part of the respiratory & digestive parts

Lymphoid CT

Component CT of parenchyma; responsible for the production of lymphocytes

Lymphocyte

Component cell of parenchyma of lymphoid organs

Cortex Medulla

Components of the parenchyma of the lymph node (2)

White pulp Red pulp

Components of the parenchyma of the spleen (2)

Cortex Medulla

Components of the parenchyma of the thymus (2)

Capsule Trabeculae Septa Reticular network

Components of the stroma of lymphoid organs (4)

Capsule Trabeculae Network of reticular fiber & cells

Components of the stroma of the lymph node (3)

Capsule Trabeculae Network of reticular fibers & cells

Components of the stroma of the spleen (3)

Capsule Septa Trabeculae

Components of the stroma of the thymus (3)

Reticular fibers B and T lymphocytes Macrophages

Composition of the splenic cord (3)

Hilum

Concavity or slight indentation of the lymph node where the entering BV emerge and exit

Cortex

Darker, peripheral part of the parenchyma of the thymus

Monocytes Plasma cell Macrophage

Differentiated B-lymphocytes of the parenchyma of lymphoid organs (3)

Afferent lymphatic vessels => subcapsular => cortical => medullary => efferent lymphatic vessels

Direction of the filtration of lymph

Trabeculae

Divide the parenchyma into smaller components called splenic lobule

Incomplete basal lamina

Due to this cell can enter into the venous sinuses of the spleen

Stave cells

Elongated endothelium that lines the sinusoids

Trabeculae

Extensions of the septa of the thymus which end at the cortico-medullary junction

Lymph

Extracellular fluid from the blood

Capsule of the spleen

Fibro-muscular; contains smooth muscle fibers

Stroma

Framework/lattice/scaffolding of lymphoid organs

Filtration of lymph Production of lymphocytes Immune defense

Functions of the lymph node (3)

-Filtration of blood -Blood reservoir -Iron storage -Production of lymphocytes -Immunologic defense

Functions of the spleen (5)

Medullary sinus

In the medulla; the space between medullary cords or between the trabeculae & medullary cords

Lymph node

It is an aggregation of lymphoid tissue in the course of lymphatic vessels; secondary lymphoid organ

Thymus

It is seeded with stem cells coming from the yolk sac and it is a site where T-lymphocytes mature; first organ seeded with lymphocytes from the bone marrow

Spleen

Largest lymphoid organ (about the size of a person's fist)

Left hypochondriac region

Location of the spleen

Between sternum and heart; anterior mediastinum

Location of the thymus

Pulp arteriole

Longest segment of the penicillar artery (2/3)

Plasma proteins Bacteria Cells

Lymph components (3)

Lymph node Spleen Thymus

Lymphoid organs as an organ (3)

Tonsils Peyer's Patch Confluent nodules of appendix

Lymphoid organs as part of an organ (3)

Splenic artery

Main blood supply of the spleen which become smaller venous sinuses

Lymphoid Organs

May be considered as an organ in themselves or part of an organ

Hassal's corpuscle or thymic corpuscle

Nest of epithelioid (epithelial-like) cells containing keratohyaline granules arranged concentrically in the thymus; unknown significance

Lymphatic nodules

Nodular arrangement of the cortex of lymph nodes

Axilla Inguinal area Abdominal area Cervical area (great vessels of the neck) Mesentery Prevertebral region

Occurences of the lymph nodes (6)

Endoderm

Origin of the thymus

Medulla

Pale, central part of the parenchyma of the thymus

Corona

Peripheral dark-staining part of the cortex of lymph nodes; small lymphocytes (big nucleus and scanty cytoplasm)

Cortex

Peripheral part of the parenchyma of the lymph node

Plasma cell

Present in the parenchyma of lymphoid organs and produces antibodies

Filtration of lymph

Primary function of lymph nodes

Filtration of blood

Primary function of the spleen

Thymus

Primary lymphoid organ

Dendritic cells (macrophages of lymph nodes) => processes antigens (mostly CHON/CHO) to stimlulate immune system => competent lymphocytes

Process of immune defense in the lymph nodes

Parenchyma

Represents functional component of the lymphoid organs because of lymphocyte

Lymph node

Rounded or kidney-shaped organ with an outer convex surface and inner concave surface

Immune defense

Secondary function of lymph nodes

Spleen and mouth

Secondary lymphoid organs

Sheathed artery

Segment of the penicillar artery with wall thickened with reticular cells and fibers and macrophages

Pulp arteriole Sheathed artery Terminal branch

Segments of penicillar artery (3)

Trabeculae or septa

Strands of CT that develop from the capsule, dividing the organs into smaller components or lobules

Splenic lobule

Structural & functional unit of the spleen

Reticular CT

Supporting CT of lymph nodes

Reticular network

Supports the component cells in the lymphoid organ (parenchymal cells)

Mucosa associated lymphoid tissues (MALT)

System of lymphoid tissues that lines body organs and cavities

F; arterioles-capillaries

T/F Each penicillar artery would divide into 2-3 arterioles and would acquire the sheath of Schweigger-Seidel

T

T/F In the lymph node, afferent vessels enter the convex side and efferent vessels exit from the concave side

F; CT-endothelium

T/F Lymphatic sinuses are lined with CT

F; present-absent

T/F Lymphatic sinuses are present in the spleen

F; not all-all

T/F Not all vessels in lymph nodes contain valves to ensure one-way flow of lymph: afferent (towards the node), efferent (away for the node)

T

T/F Sheathed capillaries would continue as simple capillaries and would terminate in the venous sinuses

F; elastic-fibrous

T/F The capsule of lymph nodes are made up of dense elastic CT and is thickened at the hilum

T

T/F The spleen has a hilus but doesn't have afferent lymph vessels

T

T/F Within lobules of the thymus, there are no networks or reticular tissue. Instead, reticular cells are present which will be connected by their processes. The reticular cells will form a reticulum which will support the cellular compound (parenchyma) (shorter and smaller than septa)

T

T/F The thymus has no afferent lymph vessels or lymphatic sinuses

Subcapsular/ Primary/ Germinal Cortical/ Secondary Medullary

The 3 lymphatic sinuses

Parenchyma of the thymus

The lymphocytes are diffusely arranged and will not form nodules only the inner lighter medulla and darker peripheral cortex of the Thymic lobules

When RBC is destroyed, iron is removed and stored in spleen

The reason for the function of the spleen as iron storage

Due to the suspended lymphocytes (stem cells)

The reason why the thymus is the primary lymphoid organ

Lymphatic sinuses

The spaces between cords and lymphatic tissues in lymph nodes where the lymph will pass through

Sheathed artery + sheath of Schweiger-Seidel

These make up the splenic ellipsoid

CT Capsule

This encloses all the lymphoid organs

Peri-arterial lymphoid sheath (PALS)

This is present in the white pulp since the lymphoid tissue in the white pulp are always associated with an artery; arranged diffusely/form nodules which may have a germinal center

Septa

This structure in the thymus divides the lobes to lobules (cortex & medulla); inward extensions of the capsule

Solid Organs Hollow Organs

Types of organs (2)

Discontinuous capillaries

What type of capillary are the venous sinuses?

Bone marrow

Where B-lymphocytes are honed in

Thymus

Where immunocompetent T-lymphocytes are honed in before being distributed to other lymphoid organs

Cortical/ Secondary sinus

Within the cortex; the space between the trabeculae & nodule