Chapter 8 Lymphoid organs

General organization of lymphoid organ: largely consist of lymphoid tissue Reticular tissue: stellate-shaped with processes to form network Diffuse lymphoid tissue Lymphoid nodules Cells: Lymphocyte (chiefly) Plasma cell antigen presenting cell other cells

a. Diffuse lymphoid tissue: no clear boundary mainly consists of T-lymphocyte postcapillary venules: -high endothelial venules, lining of tall cuboidal cells -opening for lymphocyte enter lymphoid tissue from blood Lymphoid nodule Diffuse LT

b. Lymphoid nodule: spherical or ovoid have clear boundaries mainly composed of B-lymphocyte germinal center: lighter-stained central zone, these cells produce antibody-synthesizing plasma cells

Cells of lymphatic tissue

1) Lymphocyte: a. T-lymphocytes: cytotoxic T cell: Tc C- kill the tumor cell, virus infective cell and foreign cell helper T cell: Th C- stimulate the B-lymphocyte differentiate into plasma cell suppressor T cell: Ts C – regulate the function of B-lymphocyte and T-lymphocyte b. B-lymphocytes: become into plasma cell c. NK cell: attack virus infective cell and tumor cell without previous stimulation

3) Antigen presenting cell: a. dendritic cell b.macrophage 2) Plasma cell 3) Antigen presenting cell: a. dendritic cell b.macrophage Antigen processing is a necessary preliminary step for activation of T cell.

4) other cells: granulated cell mast cell blood platelet blood-bone stem cell Function: i.      immunologic defense ii.     immune surveillance iii.    immune homeostasis

Lymphatic organs: central lymphatic organs: produce the lymphocyte antigen-independent proliferation contain: thymus---T-lymphocyte bone marrow---B-lymphocyte peripheral lymphatic organs: receive the lymphocyte and perform the immune response antigen-dependent proliferation contain: lymph node spleen tonsils

The immune system: Immune response: consists of the lymphatic organs, lymphocytes of the blood and lymph, and collections of different types of lymphocytes dispersed throughout the connective tissue. is essential to the body’s immunological defense against bacteria, viruses and other foreign bodies. Immune response: Cellular immunity: involving mainly T-lymphocytes Humoral immunity: involving mainly B-lymphocytes Mast cells, macrophages and other white blood cells are also involved in the immune response.

thymus A flattened, bi-lobed structure lying in the superior mediastinum In the new-born child it is at its greatest size relative to body size Thymus continue to grow until puberty when it is replaced by fibrofatty tissue

Structure: Capsule ( C.T.) interlobular septa (trabecula) Endothelial reticular cell (ERC) Lymphocyte: thymocyte Macrophage: secrete IL-1 Cortex: ERC Lymphocyte: few Macrophage: secrete IL-1 Thymic corpuscles Medulla:

Thymus

Cortex medulla

The cortex of thymus A very active site of lymphocyte production More than 90% of the thymocyte degenerate in this area, only less than 10% of thymocyte will mature and leave the thymus as T-lymphocytes through the postcapillary venules. Endothelial reticular cell (ERC)

The medulla of thymus Hassall’s ( thymic) corpuscles a characteristic feature of the thymus their significance is as yet unknown

Hassall’s ( thymic) corpuscles spherical or ovoid body, 20-150um in diameter, composed of concentrically-arranged epithelial reticular cells, the central cells often show degeneration

Blood-thymus barrier: provide a stable environment for lymphocytes developing in the cortex---prevents circular antigens from reaching the thymic cortex where T cells are being formed Consists of : endothelial cell of continuous capillary very thick basement membrane perivascular space with macrophage in it basement membrane of ERC ERC or their processes with desmosome

Thymus function: the thymic epithelial reticular cells can secrete thymic hormones (thymosin, thymolin, thymopoietin) induce the stem cell to differentiate into T-lymphocyte

Adult thymus has high infiltration of adipose tissue (A)

Older adult thymus has large amounts of adipose tissue

Lymph node A mass of lymphatic tissue enclosed in a capsule of connective tissue Widely scattered along the course of lymph vessels Concentrated in area in neck, axilla (arm pits), and groin.

---capsule: CT, trabeculae or septa Structure ---capsule: CT, trabeculae or septa ---cortex: outer densely-stained part ---medulla: inner paler-stained part hilum

Structure: capsule trabecula cortex several afferent lymph vessels, lymphoid nodule (B-LC) internodule zone out cortex: (superficial cortex) inner cortex: diffuse lymphoid tissue (T-LC) (paracortical zone) subcapsular sinus: peritrabecular sinus macrophage cortical lymphatic sinuses

capsule outer cortex inner cortex

SS: subcapsular sinus T: trabecular

Capsule Subcapsular sinuses Trabeculae

Afferent lymph vessels GC

Postcapillary venules in inner cortex

Medulla ---medullary cord: LT cord: B-lymphocyte, plasma cell, macrophage, mast cell ---medullary sinus: similar to cortical sinus and connect with them more macrophage

capsule outer cortex inner cortex

Passage of lymph in lymph node Afferent lymph vessels Subcapsular sinus Cortical sinuses Medullary sinuses Efferent lymph vessels

Lymph enters afferent lymph vessels passes through subcapsular sinuses and down through trabecular sinuses around trabeculae.

Efferent lymph vessels in hilum

Recirculation of lymphocytes: Lymphoid tissue Efferent lymphatic vessel Postcapillary venules Blood circulation

Functions of lymph node Filter the lymph Place to perform the immune response Involve in the recirculation of lymphocyte

Spleen located in the passages of blood capsule white pulp structure red pulp marginal zone structure parenchyma

Structure: capsule: D.C.T. containing smooth muscle----trabecular; capsule is covered by mesothelium The splenic artery branch into trabecular arteries

White pulp: gray-white spots periarterial lymphatic sheath: - diffuse lymphoid tissue : T-lymphocyte, macrophage - central artery splenic corpuscle: -lymphoid nodules: B-lymphocyte, macrophage

Marginal zone: between White pulp and Red pulp splenic corpuscle Marginal zone: between White pulp and Red pulp T-, B-lymphocyte, macrophage, less erythrocyte marginal sinus: central artery’s branch- channel for antigen and lymphocyte enter lymphoid tissue function: first capture, recognize antigen and induce immune reaction

Red pulp: splenic cord: Lymph tissue cord B-,T-lymphocyte, macrophage, erythrocytes function: filter blood splenic cord splenic sinus

splenic sinus: Blood sinus; 12-14um endothelial cell: rod-liked, gap Reticular fiber basal lamina: incomplete Abundant macrophage splenic sinus splenic cord endothelial cell

splenic A→trabecular A→central A branches → marginal sinuses → Blood supply of spleen Study by yourself splenic A→trabecular A→central A branches → marginal sinuses → penicillar arterioles (including: pulp arteriole→ sheathed capillary→ arterial capillary) → splenic sinus→ pulp venule→ trabecular vein→ splenic vein

Function: a. filter the blood b. immunological defence c. production of blood cells in fetus d. blood storage: 40 ml

Tonsil (Study by yourself) ---palatine tonsil ---pharyngeal tonsil ---lingual tonsil

structure Mucosa stratified squamous epithelium Capsule: C.T. form crypts lymphocyte infiltration lymphatic nodules diffuse lymphatic tissue Lamina propria Capsule: C.T.

Tonsil

Mononuclear phagocyte system (Study by yourself) monocyte young monocyte Bone marrow Blood CT: macrophage Liver: Kuffer cell Lung: dust cell Nerve tissue: microglia Osseous tissue: osteoclast Skin: Langerhans cell Tissues or organs

Function of MPS: phagocytosis participate in immune reaction secrete bioactive substances