8: Lymphatic vessels and lymphoid tissue. nur

Transcription

1 8: Lymphatic vessels and lymphoid tissue nur

2 Lymphatic vascular system Functions return to the blood extracellular fluid (Lymph) from connective tissue spaces. ensures the return of water, electrolytes and plasma proteins to the blood. i.e plays a key role in homeostasis of the volume of extracellular fluid. also returns lymphocytes from the lymph nodes to the blood transports immunoglobulins (antibodies) from the lymphnodes to the blood.

3 Lymph capillaries in most organs close to blood capillaries (an exception is the CNS, cartilage, bone, bone marrow, placenta, teeth and thymus) begin as small blind-ending tubes. Have numerous valves Similar in structure to blood capillaries but thinner lack a basal lamina lack erythrocytes P. Kyamanywa DOS-FACMED nur

4 Lymph vessels drain into lymph nodes (for filtration) ultimately drain into two large lymphatic ducts in the area at the base of the neck thoracic duct, right lymphatic duct) to return the lymph to the blood. P. Kyamanywa DOS-FACMED nur

5 Lymphatic tissues

6 characterized by an abundance of lymphocytes no lymphatic tissue in myeloid tissue involved with lymphocyte production and immune responses. constant recirculation of lymphocytes (especially T-lymphocytes) between the lymph and blood. When they encounter foreign molecules or cells they activate a series of immune responses to neutralize and destroy the invader.

7 TYPES OF LYMPHATIC TISSUE 3 basic types: Loose lymphatic tissue dominated by reticular cells and fibers forms a loose, spongy network through which lymph flow is slow and cells are temporarily trapped Dense lymphatic tissue dominated by large populations of closely aggregated lymphocytes Nodular lymphatic tissue (lymphatic nodules) found in all the lymphatic organs apart from the thymus.

8 Thymus site where T-lymphocytes develop Located in the anterior neck First lymphoid tissue in embryonic dev t from epithelial outgrowths of primitive pharynx Lobulated and encapsulated 2 zones: cortex and medulla density of lymphocytes

9 Low mag of the thymus Cortex (C) Medull a M (M) M C C

10 Dark nuclei = T-cells Larger nuclei = endothelial reticular cells Arrow = Hassell s Corpuscle High mag of the medulla of the thymus

11 Lymph Nodes

12 kidney-shaped structures situated along lymphatic vessels 2 key functions serve as in-line mechanical filters of lymph by macrophages Storage of B and T-lymphocytes Encapsulated capsule forms radial extensions: trabeculae - to form incomplete compartments lymph node is divided into two regions: An outer cortical region An inner medullary region

13 2 key functions of lypmhnodes Filtration of lymph by the macrophages Storage of B and T-lymphocytes P. Kyamanywa DOS-FACMED nur

14 Diagram of a lymph node

15 Low mag of a lymph node Cx = cortex w/ lymphatic nodules (F); M = medulla; C = CT capsule

16 A lymphatic nodule with germinal center (GC)

17 Non-encapsulated Lymphatic Nodules

18 temporary structures, which may appear and disappear in the same site lack a connective tissue capsule mainly composed of dense aggregates of small B-lymphocytes P. Kyamanywa DOS-FACMED nur

19 Structure cells at the center of the nodule are much larger, with more cytoplasm less-stained central area is known as the germinal center - develops according to the functional state of the nodule ring of small B-lymphocytes surrounding the germinal center is referred to as the corona or mantle zone P. Kyamanywa DOS-FACMED nur

20 Cell types of the germinal center include activated B-lymphocytes (B-immunoblasts) mitotic cells plasma cells dendritic reticular cells macrophages P. Kyamanywa DOS-FACMED nur

21 Peyers Patches = lymphatic nodules in the ileum

22 Low mag of a palatine or lingual tonsil

23 Palatine Tonsil w/ SS non-k (arrow) Pharyngeal Tonsil w/ Resp epith (arrow = nodule)

24 The Spleen

25 largest lymphatic organ of the circulatory system acts as a blood filter to defend against microorganisms that succeeded to penetrate the blood system aged erythrocytes are broken down and destroyed by macrophages site of formation of activated lymphocytes responds promptly to antigens carried in the blood. Infection can result in an enlarged spleen (splenomegaly) fetal spleen (months 4-6) is hematopoietic (producing granulocytes and erythrocytes)

26 Structure dense connective tissue capsule, with connective tissue trabeculae White pulp lymphatic tissue surrounding arteries and nodules Red pulp sponge composed of cords of cells (splenic cords) and splenic sinusoids (venous sinusoids)

27 Splenic cords (Billroth cords) are composed of : reticular cells and fibers fixed and wandering macrophages lymphocytes plasma cells blood cells (erythrocytes, granulocytes) and platelets P. Kyamanywa DOS-FACMED nur

28 Diagram of the Spleen

29 Low magnification of the Spleen CT Trabeculae White pulp (lymphatic nodules) CT Trabeculae Thick CT capsule Red Pulp

30 Red Pulp White pulp Lymphatic nodules CT Trabeculae

31 Splenic circulation Splenic artery enters at the hilum and divides into trabecular arteries Trabecular arteries completely surrounded by a sheath of T- lymphocytes (periarterial lymphatic sheath or PALS) Central arteries (or central arterioles) penetrate the lymphatic nodules, usually in the periphery Lead to sinusoids

32 Circulatory System in the Spleen

33 Red Pulp White Pulp White Pulp Red Pulp

34 High mag of the splenic red pulp

35 Break 1. In the next session: Gastro-intestinal system and Respiratory system 2. Review : lymphatic system nur