The Lymphatic System

1. 20 The Lymphatic System

2. Lymphatic System: Overview • Consists of two semi-independent parts: • A network of lymphatic vessels • Lymphoid tissues and organs scattered throughout the body • Lymphatic vessels return interstitial fluid (fluid in the tissues) and leaked plasma proteins back into the bloodstream • Once interstitial fluid has entered lymphatic vessels, it is called lymph

3. Lymphatic System: Overview Figure 20.2a

4. Lymphatic System: Overview Figure 20.1a

5. Lymphatic Vessels • One-way system, lymph flows toward the heart • Lymph vessels include: • Microscopic, permeable, blind-ended capillaries • Lymphatic collecting vessels • Trunks and ducts

6. Lymphatic Capillaries • Similar to blood capillaries, with modifications: • Very permeable • Loosely joined endothelial minivalves • Withstand interstitial pressure and remain open • The minivalves function as one-way gates that: • Allow interstitial fluid to enter lymph capillaries • Prevent lymph from escaping out of the capillaries

7. Lymphatic Capillaries Figure 20.1b

8. Lymphatic Capillaries • During inflammation, lymph capillaries can absorb: • Cell debris • Pathogens • Cancer cells • Lacteals – specialized lymph capillaries present in lining of the small intestines • Absorb digested fat and deliver chyle(fatty lymph) to the bloodstream

9. Lymphatic Collecting Vessels • Have the same three tunics as veins • Have thinner walls, with more internal valves • Anastomose(branch off) more frequently • Collecting vessels in the skin travel with superficial veins • Deep vessels travel with arteries

10. Lymphatic Trunks • Lymphatic trunks are formed by the union of the largest collecting ducts • Lymph is delivered into one of two large trunks • Right lymphatic duct – drains the right upper arm and the right side of the head and thorax • Thoracic duct – arises from the cisternachyli and drains the rest of the body

11. Lymphatic Trunks Figure 20.2b

12. Return of Lymph to Heart Figure 20.2a

13. Lymph Transport • The lymphatic system lacks a pumping organ • Vessels operate under low pressure • Uses the same methods as veins to propel lymph: • Pulsations of nearby arteries • Contractions of smooth muscle in the vessel walls • Contractions of skeletal muscle

14. Major Tissue Type: Reticular Connective Tissue • Network of reticular fibers. Weblike. • Loosely bound together to support lymphocytes and macrophages

15. Lymphoid Cells • Lymphocytes are the main cells involved in the immune response • Two main varieties: • T cells • B cells • Both are produced in the red bone marrow – so it is classified as a primary lymphatic organ. • B cells mature in the red bone marrow. • T cells must travel to the thymus gland to mature; thus the name “T”

16. Lymphocytes • T cells • Manage the immune response • Directly attack and destroy virus - infected cells and tumor cells • B cells • Produce antibodies which circulate in the blood and attack foreign substances (antigens)

17. Macrophages • Macrophages – big “eaters” • When monocytes leave the blood stream and enter tissues they transform into macrophages and “eat up” viruses, bacteria, especially in chronic infections like T.B.

18. EDEMA • Swelling caused by abnormal amount of interstitial (between cells) fluid. • Common in lower extremities when right side of the heart is damaged. • Common in lungs when left side of the heart is damaged.

19. Lymph Nodes • Principal lymphoid organs of the body • Embedded in connective tissue and clustered along lymphatic vessels • Aggregations of these nodes occur near the body surface in inguinal, axillary, and cervical regions of the body Figure 20.4a

20. Lymph Nodes • Two basic functions: • Filtration – macrophages destroy microorganisms and debris • ***Only part of the lymphatic system that filters lymph *** • Immune system activation – monitors for antigens and mounts an attack against them

21. Structure of a Lymph Node Bean shaped and surrounded by a fibrous capsule Figure 20.4a, b

22. Circulation in the Lymph Nodes • Lymph enters via afferent lymphatic vessels • It then enters a large sinus and travels into smaller sinuses • It meanders through these sinuses and exits the node at the hilus via efferent vessels • Because there are fewer efferent vessels, lymph flow slows down in the node • This allows lymphocytes and macrophages time to carry out protective functions

23. Lymphoid Organs Figure 20.5

24. Other Lymphoid Organs • The spleen, thymus gland, and tonsils • Peyer’s patches and bits of lymphatic tissue scattered in connective tissue • All are composed of reticular connective tissue • All help protect the body

25. Spleen • Largest lymphoid organ, located on the left side of the abdominal cavity beneath the diaphragm • It is served by the splenic artery and vein, which enter and exit at the hilus • Functions: • Site of lymphocyte proliferation (in WHITE pulp) • Immune surveillance and response • Cleanses the blood

26. Additional Spleen Functions • Breaks down and stores products of RBCs for later reuse (in RED pulp) • Spleen macrophages salvage and store iron for later use by bone marrow • Site of fetal erythrocyte production (normally ceases after birth) • Stores blood platelets • Does NOT filter lymph

27. Structure of the Spleen Highly vascular Figure 20.6a, b

28. Ruptured Spleen White/Red Pulp Areas

29. Thymus • A bilobedorgan located • in the inferior neck and extends into the mediastinum where it partially overlies the heart • Size of the thymus varies with age: • It increases in size and is most active during childhood • It stops growing during adolescence and then gradually atrophies • By this time, enough T lymphocytes have matured; vaccinations and antibodies formed from exposure to illnesses has occurred

30. Thymus • The thymus differs from other lymphoid organs in two important ways • Secretes hormones that cause T lymphocytes to mature, enabling them to recognize pathogens and initiate an immune response • It does not directly fight antigens • It is classified as a primary lymphatic organ.

31. Tonsils • Simplest lymphoid organs; form a ring of lymphatic tissue around the pharynx • Location: • Palatine tonsils – either side of the posterior end of the oral cavity • Lingual tonsils – lie at the base of the tongue • Pharyngeal tonsil – posterior wall of the nasopharynx (referred to as ADENOIDS if enlarged) • Tubal tonsils – surround the openings of the auditory tubes into the pharynx

32. Tonsils • Lymphoid tissue of tonsils contains follicles with germinal centers • Tonsil masses are not fully encapsulated • Epithelial tissue overlying tonsil masses invaginates (folds in on itself), forming blind-ended crypts • Crypts trap and destroy bacteria and particulate matter

33. INFECTED TONSILS - Tonsilitis

34. Aggregates of Lymphoid Follicles • Peyer’s patches – isolated clusters of lymphoid tissue, similar to tonsils • Found in the wall of the distal portion of the small intestine • Similar structures are found in the appendix • Peyer’s patches and the appendix: • Destroy bacteria that entered the body via the mouth or anus, preventing them from penetrating the intestinal wall • Generate “memory” lymphocytes for long-term immunity

35. MALT • MALT – mucosa-associated lymphatic tissue • Protects passages that open to the EXTERIOR • Peyer’s patches, tonsils, and the appendix (digestive tract – mouth and anus) • Lymphoid nodules in the walls of the bronchi (respiratory tract – mouth and nose and ears) • Mucosal lining of the reproductive and urinary system ( urethra and vagina)

36. Breast Cancer/Lymph Nodes Axillary lymph nodes

37. Lymph Node Biopsy • Standard treatment for breast cancer was removal of the breast(s) and the axillary lymph nodes. • Now it is sometimes possible to biopsy the sentinel nodes (those closest to the tumor). • Dye is injected near the tumor and then sentinel nodes are identified if they are stained with dye. • If cancer has not spread, surgery is less invasive. • Sentinel node biopsy is used with other tumors, not just breast.

38. Post Surgery Care • When multiple regional lymph nodes are removed, the patient may experience side effects such as lymphedema (swelling caused by excess fluid build-up), numbness (nerve damage), infection and difficulty moving the affected body area. • Patients must avoid pressure (lifting heavy objects, having blood pressure taken, etc.) in affected area. • Wear an elastic stocking to reduce swelling, especially when flying.