2. Kingdom of Saudi Arabia Ministry of Higher Education Majmaah University Faculty of Science in AlZulfi Presented by : Yazed Alharbi & Talaal Almutari Under supervision by Dr. Gomaa Abdelrahim Abdullalim Role of lymph node in immunity

3. A lymph node is a small ball or an oval-shaped organ of the immune system, distributed widely throughout the body including the armpit and stomach/gut and linked by lymphatic vessels.immune systemlymphatic vessels Lymph nodes are garrisons of B, T and other immune cells.garrisonsBTimmune cells Lymph nodes act as filters or traps for foreign particles and are important in the proper functioning of the immune system. They are packed tightly with the white blood cells called lymphocytes and macrophages.white blood cellslymphocytesmacrophages

4. Human lymph nodes are bean-shaped and range in size from a few millimeters to about 1–2 cm in their normal state. Lymphocytes, also known as white blood cells, are located within honeycomb structures of the lymph nodes.white blood cells Lymph nodes are enlarged when the body is infected, primarily because there is an elevated rate of trafficking of lymphocytes into the node from the blood, exceeding the rate of outflow from the node, and secondarily as a result of the activation and proliferation of antigen-specific T and B cells (clonal expansion).

6. Image for structure

7. 4.1- lymph nodes of the head and neck 4.2- lymph nodes of the thorax 3.3- lymph nodes of the arm 4.4- lower limbs

8. Structure The lymph node is surrounded by a fibrous capsule, and inside the lymph node the fibrous capsule extends to form trabeculae.capsuletrabeculae The substance of the lymph node is divided into the outer cortex and the inner medulla surrounded by the cortex all around except for at the hilum, where the medulla comes in direct contact with the surfacecortexmedulla

10. In the cortex, the subcapsular sinus drains to trabecular sinuses, and then the lymph flows into the medullary sinuses.subcapsular sinustrabecular sinusesmedullary sinuses The outer cortex consists mainly of the B cells arranged as follicles, which may develop a germinal center when challenged with an antigen, and the deeper cortex mainly consisting of the T cells.B cellsT cells There is a zone known as the subcortical zone where T-cells (or cells that are mainly red) mainly interact with dendritic cells, and where the reticular network is dense. The predominant site within the lymph nodes which contain T cells & accessory cells is also known as paracortex (reticular network).

11. There are two named structures in the medulla: The medullary cords are cords of lymphatic tissue, and include plasma cells, macrophages, and B cellsplasma cellsmacrophagesB cells The medullary sinuses (or sinusoids) are vessel-like spaces separating the medullary cords. The Lymph flows into the medullary sinuses from cortical sinuses, and into efferent lymphatic vessels. Medullary sinuses contain histiocytes (immobile macrophages) and reticular cells.medullary sinusesefferent lymphatic vesselshistiocytesreticular cells The Medulla contains large blood vessels, sinuses and medullary cords that contain plasma cells secreting antibody.

12. Thin reticular fibers, elastin and reticular fibers form a supporting meshwork called reticular network (RN) inside the node, within which the white blood cells (WBCs), the most prominent ones being lymphocytes, are tightly packed as follicles in the cortex. Elsewhere, there are only occasional WBCs.elastinreticular fiberswhite blood cells The RN provides not just the structural support, but also will provide surface for adhesion of the dendritic cells,macrophages and lymphocytes.dendritic cellsmacrophages

13. It allows for exchange of material with blood through the high endothelial venules and provides the growth and regulatory factors necessary for activation and maturation of immune cells.high endothelial venules The number and composition of follicles can change especially when challenged by an antigen, when they develop a germinal center.antigengerminal center A lymph sinus is a channel within the lymph node lined by the endothelial cells along with fibroblastic reticular cells and allows for smooth flow of lymph through them.lymph sinus

14. Thus, subcapsular sinus is a sinus immediately deep to the capsule, and its endothelium is continuous with that of the afferent lymph vessel. It is also continuous with similar sinuses flanking the trabeculae and within the cortex (cortical sinuses). The cortical sinuses and that flanking the trabeculae drain into the medullary sinuses, from where the lymph flows into the efferent lymph vessel.

15. LymphLymph circulates to the lymph node via afferent lymphatic vessels and drains into the node just beneath the capsule in a space called thesubcapsular sinus. The subcapsular sinus drains into trabecular sinuses and finally into medullary sinuses. The sinus space is criss-crossed by the pseudopods of macrophages, which act to trap foreign particles and filter the lymph. The medullary sinuses converge at the hilum and lymph then leaves the lymph node via the efferent lymphatic vessel towards either a more central lymph node or ultimately for drainage into a central venous subclavian blood vessel, most via the postcapillary venules, and cross its wall by the process of diapedesis.afferent lymphatic vesselssubcapsular sinuspseudopodsmacrophagesefferent lymphatic vesselvenous subclavian blood vesselvenulesdiapedesis 1- The B cells migrate to the nodular cortex and medulla. 2- The T cells migrate to the deep cortex ("paracortex").

16. Lymph nodes also have clinical significance. They become inflamed or enlarged in various conditions, which may range from trivial, such as a throat infection, to life-threatening such ascancers. In the latter, the condition of lymph nodes is so significant that it is used for cancer staging, which decides the treatment to be employed, and for determining the prognosis.throat infectioncancerscancer stagingprognosis Lymph node, showing (1) capsule, (2) subcapsular sinus, (3) germinal centers, (4) lymphoid nodule, (5 trabeculae.germinal centers