Structures of Body Defenses

1. Structures of Body Defenses • Organization of the Lymphatic System • Lymph • A fluid similar to plasma but does not have plasma proteins • Lymphatic vessels (lymphatics) • Carry lymph from peripheral tissues to the venous system • Lymphoid tissues and lymphoid organs • Lymphocytes, phagocytes, and other immune system cells

2. Structures of Body Defenses • Function of the Lymphatic System • To produce, maintain, and distribute lymphocytes • Lymphocyte Production • Lymphocytes are produced • In lymphoid tissues (e.g., tonsils) • Lymphoid organs (e.g., spleen, thymus) • In red bone marrow • Lymphocyte distribution • Detects problems • Travels into site of injury or infection

3. Structures of Body Defenses • Lymphocyte Circulation • From blood to interstitial fluid through capillaries • Returns to venous blood through lymphatic vessels • The Circulation of Fluids • From blood plasma to lymph and back to the venous system • Transports hormones, nutrients, and waste products

4. Structures of Body Defenses • Lymphatic Vessels • Are vessels that carry lymph • Lymphatic system begins with smallest vessels • Lymphatic capillaries (terminal lymphatics)

5. Structures of Body Defenses • Lymphatic Capillaries • Differ from blood capillaries in four ways • Start as pockets rather than tubes • Have larger diameters • Have thinner walls • Flat or irregular outline in sectional view

6. Figure 22-2a Lymphatic Capillaries Smoothmuscle Endothelialcells Lymphaticcapillary Arteriole Venule Interstitialfluid Lymphflow Blood capillaries Loose connective tissue The interwoven network formed by blood capillariesand lymphatic capillaries.

7. Figure 22-2b Lymphatic Capillaries Lymphocyte Incompletebasementmembrane Lymphflow To largerlymphatics Looseconnectivetissue Interstitial fluid Lymphaticcapillary Interstitial fluid Bloodcapillary A sectional view indicating the movement of fluidfrom the plasma, through the tissues as interstitialfluid, and into the lymphatic system as lymph.

8. Structures of Body Defenses • Lymphatic Capillaries • Endothelial cells loosely bound together with overlap • Overlap acts as one-way valve • Allows fluids, solutes, viruses, and bacteria to enter • Prevents return to intercellular space

9. Structures of Body Defenses • Lymph Flow • From lymphatic capillaries to larger lymphatic vessels containing one-way valves • Lymphatic vessels travel with veins • Lacteals • Are special lymphatic capillaries in small intestine • Transport lipids from digestive tract

10. Figure 22-3a Lymphatic Vessels and Valves Artery Vein Artery Vein Lymphaticvessel Lymphaticvessel Towardvenoussystem Lymphaticvalve From lymphaticcapillaries

11. Figure 22-3b Lymphatic Vessels and Valves Lymphaticvalve Lymphaticvessel Like valves in veins, eachlymphatic valve consists ofa pair of flaps that permitmovement of fluid in onlyone direction. Lymphatic vessel and valve LM  63

12. Figure 22-4 The Relationship between the Lymphatic Ducts and the Venous System Brachiocephalic veins Left internal jugular vein Left jugular trunk Right internal jugular vein Thoracic duct Right jugular trunk Left subclavian trunk Right lymphatic duct Left bronchomediastinaltrunk Right subclavian trunk Right subclavian vein Left subclavianvein Right bronchomediastinal trunk Superiorvena cava (cut) First rib(cut) Azygos vein Highestintercostalvein Rib (cut) Thoracicduct Drainageof rightlymphaticduct Drainageof thoracicduct Thoraciclymph nodes Hemiazygosvein Parietalpleura (cut) Diaphragm Cisterna chyli Inferior vena cava (cut) Intestinal trunk Right lumbar trunk Left lumbar trunk

13. Structures of Body Defenses • Lymphoid Tissues • Connective tissues dominated by lymphocytes • Lymphoid Nodules • Areolar tissue with densely packed lymphocytes • Germinal center contains dividing lymphocytes

14. Figure 22-7a Lymphoid Nodules (Part 1 of 2) Intestinal lumen Aggregatedlymphoid nodule Underlyingconnective tissue Aggregated lymphoid nodules in large intestine LM  40 Aggregated lymphoid nodules in section

15. Figure 22-7a Lymphoid Nodules (Part 2 of 2) Intestinal lumen Mucousmembrane Germinal center Aggregatedlymphoid nodule Underlyingconnective tissue Aggregated lymphoid nodules in section

16. Figure 22-7b Lymphoid Nodules Pharyngealepithelium Pharyngeal tonsil Germinal centerswithin nodules Palate Palatine tonsil Lingual tonsil Pharyngeal tonsil LM  20 The positions of the tonsils and a tonsil in section. Notice the pale germinal centers, where lymphocyte cell divisions occur.

17. Structures of Body Defenses • Distribution of Lymphoid Nodules • Lymph nodes • Spleen • Respiratory tract (tonsils) • Along digestive, urinary, and reproductive tracts

18. Structures of Body Defenses • Mucosa-Associated Lymphoid Tissue (MALT) • Lymphoid tissues associated with the digestive system • Aggregated Lymphoid Nodules • Clustered deep to intestinal epithelial lining • Appendix (Vermiform Appendix) • Contains a mass of fused lymphoid nodules

19. Structures of Body Defenses • The Five Tonsils • In wall of pharynx • Left and right palatine tonsils • Pharyngeal tonsil (adenoid) • Two lingual tonsils

20. Structures of Body Defenses • Lymph Nodes • Trabeculae • Bundles of collagen fibers • Extend from capsule into interior of lymph node • Hilum • A shallow indentation where blood vessels and nerves reach the lymph node

21. Structures of Body Defenses • Lymph Nodes • Afferent lymphatics • Carry lymph • From peripheral tissues to lymph node • Efferent lymphatics • Leave lymph node at hilum • Carry lymph to venous circulation

22. Figure 22-8 The Structure of a Lymph Node (Part 1 of 2) Lymphnodes Lymphvessel Lymph nodeartery and vein Efferentvessel Hilum Lymph nodes Trabeculae Medullary sinus Medulla Cortex Outer cortex (B cells) Subcapsularspace Deep cortex(T cells) Afferentvessel Medullary cord(B cells andplasma cells) Capsule

23. Structures of Body Defenses • Lymph Node Function • A filter • Purifies lymph before return to venous circulation • Removes: • Debris • Pathogens • 99% of antigens

24. Structures of Body Defenses • Lymphatic Functions • Lymphoid tissues and lymph nodes • Distributed to monitor peripheral infections • Respond before infections reach vital organs of trunk • Lymph nodes of gut, trachea, lungs, and thoracic duct • Protect against pathogens in digestive and respiratory systems

25. 22-2 Structures of Body Defenses • Lymph Nodes (Glands) • Large lymph nodes at groin and base of neck • Swell in response to inflammation • Lymphadenopathy • Chronic or excessive enlargement of lymph nodes • May indicate infections, endocrine disorders, or cancer

26. 22-2 Structures of Body Defenses • The Thymus • Located in mediastinum • Atrophies after puberty • Diminishing effectiveness of immune system • Divisions of the Thymus • Thymus is divided into two thymic lobes • Septa divide lobes into smaller lobules

27. Figure 22-9a The Thymus Thyroid gland Trachea THYMUS Right lobe Leftlobe Leftlung Rightlung Heart Diaphragm The appearance and position of the thymus inrelation to other organs in the chest.

28. Figure 22-9b The Thymus Leftlobe Rightlobe Septa Lobule Anatomicallandmarks onthe thymus.

29. Figure 22-9c The Thymus Medulla Septa Cortex Lobule Lobule The thymus gland LM  50 Fibrous septa divide the tissue of the thymus into lobulesresembling interconnected lymphoid nodules.

30. 22-2 Structures of Body Defenses • Three Functions of the Spleen • Removal of abnormal blood cells and other blood components by phagocytosis • Storage of iron recycled from red blood cells • Initiation of immune responses by B cells and T cells • In response to antigens in circulating blood

31. Figure 22-10b The Spleen SUPERIOR Gastricarea Hilum Splenic vein Splenic artery Renalarea Splenic lymphaticvessel INFERIOR A posterior view of the surface of an intactspleen, showing major anatomical landmarks.

32. Figure 22-10c The Spleen White pulp ofsplenic nodule Capsule Red pulp Trabecularartery Central artery insplenic nodule The spleen LM  50 The histological appearance of the spleen. White pulp isdominated by lymphocytes; it appears purple becausethe nuclei of lymphocytes stain very darkly. Red pulpcontains a large number of red blood cells.