1. Lymphatic System

2. Lymph Fluid
Once interstitial fluid in cardiovascular system leaves capillaries and enters lymph capillaries, fluid is called “lymph fluid”

3. Lymph Movement Lymphatic system lacks an organ that acts as a pump
Vessels are low-pressure conduits
Movement
Contraction of skeletal muscles against lymphatic vessels
Smooth muscle contraction
Valves in lymphatic vessels
Breathing
Obstruction of system leads to edema

4. Lymphoid Cells
Lymphocytes are the main cells involved in the immune response
The two main varieties are T cells and B cells

5. Lymphocytes T cells and B cells protect the body against antigens
Antigen – anything the body perceives as foreign
Bacteria and their toxins; viruses
Mismatched RBCs or cancer cells

6. Lymphocytes T cells B cells Manage the immune response
Attack and destroy foreign cells
B cells
Produce plasma cells, which secrete antibodies
Antibodies immobilize antigens

7. Other Lymphoid Cells
Macrophages – phagocytize foreign substances and help activate T cells
Dendritic cells – spiny-looking cells with functions similar to macrophages
Reticular cells – fibroblastlike cells that produce a stroma, or network, that supports other cell types in lymphoid organs

8. Part 2: Lymph Nodes and Organs of Lymphatic System
Tonsils
Spleen
Thymus

9. McGraw-Hill Image

10. Lymph Nodes Their two basic functions are:
Filtration – macrophages destroy microorganisms and debris
Immune system activation – monitor for antigens and mount an attack against them

11. Lymph Nodes Lymph nodes are the principal lymphoid organs of the body
Nodes are imbedded 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

12. Lymph Nodes Oval structures located along lymphatics
Enclosed by a fibrous capsule
Trabeculae extended inward from the capsule and divide the node into compartments
Nodes have two histologically distinct regions: a cortex and a medulla
Cortex = outer portion
Germinal centers produce lymphocytes
Medulla = inner portion
Medullary cords
Lymph enters nodes through afferent lymphatics, flows through sinuses, exits through efferent lymphatic

13. McGraw-Hill Image

14. McGraw-Hill Image

15. Lymph Node

16. McGraw-Hill Image

17. 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 and all help protect the body
Only lymph nodes filter lymph

18. Tonsils
Simplest lymphoid organs; form a ring of lymphatic tissue around the pharynx
Multiple groups of large lymphatic nodules
Locations –
Palatine tonsils: either side of the posterior end of the oral cavity
Pharyngeal tonsil: Posterior wall of nasopharynx
Lingual tonsils: Base of tongue
Tubal tonsils: Surround the openings of the auditory tubes into the pharynx

19. Tonsils

20. Tonsils
Lymphoid tissue of tonsils contains follicles with germinal centers
Tonsil masses are not fully encapsulated
Epithelial tissue overlying tonsil masses invaginates, forming blind-ended crypts
Crypts trap and destroy bacteria and particulate matter

21. Spleen Largest lymphatic organ Located between the stomach & diaphragm
Structure is similar to a node
Capsule present
But no afferent vessels or sinuses
Histology
Red pulp contains all the components of circulating blood
White pulp is similar to lymphatic nodules
Functions
Site of lymphocyte proliferation
Immune surveillance and response
Filters blood and stores blood

22. Additional Spleen Functions
Stores breakdown products of RBCs for later reuse
Spleen macrophages salvage and store iron for later use by bone marrow
Site of fetal erythrocyte production (normally ceases after birth)
Stores blood platelets

23. Structure of the Spleen
Surrounded by a fibrous capsule, it has trabeculae that extend inward and contains lymphocytes, macrophages…
Two distinct areas of the spleen are:
White pulp – area containing mostly lymphocytes suspended on reticular fibers and involved in immune functions
Red pulp – remaining splenic tissue concerned with disposing of worn-out RBCs and bloodborne pathogens

24. Spleen FG23_17B.JPG Title: The Spleen
Notes: (a) The shape of the spleen roughly conforms to the shapes of adjacent organs; transverse section. (b)Visceral surface of intact spleen; major anatomical landmarks. (c)Histological appearance of the spleen.
Keywords: spleen, transverse, abdominopelvic cavity, kidneys, pancreas, hilus, diaphragm, gastrosplenic ligament, stomach, liver, rib, white pulp, visceral surface, gastric area, splenic vein, splenic artery, renal area, histology, trabecular arteries, capsule, red pulp

25. Structure of the Spleen
Figure 20.6a-d

26. Thymus Gland
A bi-lobed organ that secrets hormones (thymosin and thymopoietin) that cause T lymphocytes to become immunocompetent (mature)
The capsule divides it into 2 lobes
Location – behind the sternum
Development
Infant – conspicuous
Puberty – maximum size
Maturity – decreases in size
Function
Differentiation and maturation of T cells

27. Internal Anatomy of Thymus
Thymic lobes contain an outer cortex and inner medulla
The cortex contains densely packed lymphocytes and scattered macrophages
The medulla contains fewer lymphocytes and thymic (Hassall’s) corpuscles

28. Thymus The thymus differs from other lymphoid organs in important ways
It functions strictly in T lymphocyte maturation
It does not directly fight antigens
T cell development: cells migrate from bone marrow and differentiate into T cells
The stroma of the thymus consists of star-shaped epithelial cells (not reticular fibers)
These star-shaped thymocytes secrete hormones that stimulate lymphocytes to become immunocompetent

29. Thymus Gland FG23_16A.JPG Title: The Thymus
Notes: (a)Location of thymus on gross dissection. (b)Anatomical landmarks on thymus. (c)Low-power light micrograph of thymus. (d)Higher magnification showing structure of Hassall's corpuscles.
Keywords: thymus, gross dissection, thyroid, trachea, lobe, septae, lobule, cortex, medulla, blood vessels, Hassall's corpuscles, epithelial cells, lymphocytes

30. 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, preventing them from breaching the intestinal wall
Generate “memory” lymphocytes for long-term immunity

31. MALT MALT – mucosa-associated lymphatic tissue is composed of:
Peyer’s patches, tonsils, and the appendix (digestive tract)
Lymphoid nodules in the walls of the bronchi (respiratory tract)
MALT protects the digestive and respiratory systems from foreign matter

32. Function of the Lymphatic System
Defense against harmful organisms and chemicals
2 types of defense
Nonspecific
Specific
Specific defense = immunity
Humoral immunity involves B cells that become plasma cells which produce antibodies that bind with specific antigens.
Cell-mediated immunity involves T cells that directly destroy foreign cells