Lesson # 8

1. Lesson # 8 Chapter 22 The Lymphatic System-1 Objectives: 1- To describe the general functions of the lymphatic system. 2- To list the major lymphatic vessels. 3- To list the major classes of lymphocytes and the functions of each.

2. Functions of the Lymphatic System 1- Production, Maintenance, and Distribution of Lymphocytes that provide defense against infections. 2- Collection and Returning of Interstitial Fluid from Tissues to the Circulatory System. 3- Distribution of Nutrients, Waste, and Hormones from Tissues to the Circulatory System.

3. 1- Lymphocyte Production, Maintenance, and Distribution Immature lymphocytes are produced in the bone marrow. B lymphocytes mature the bone marrow and T lymphocytes mature in the thymus Lymphoid organs and tissues After maturation, most of the lymphocytes move into lymph nodes, the spleen and other lymphoid tissues

4. 2- Collection and Returning of Interstitial Fluid from Tissues to the Circulatory System. • Fluid continually filters from the blood capillaries into the tissue spaces. But the blood capillaries reabsorb only 85%. 15% (2 – 4 L/day) of the water and about half of the plasma proteins are not absorbed by capillaries. • One function of the lymphatic system is to reabsorb this excess and to return it to the blood. 7 mm Hg 85% 15% 13 mm Hg

5. 3- Distribution of Nutrients, Waste, and Hormones from Tissues to the Circulatory System • Special lymphatic vessels called lacteals in small intestine absorb dietary lipids that are not absorbed by the blood capillaries Lacteal

6. The Lymphatic System Lymphatic Vessels Diffuse Lymphoid Tissues Encapsulated Lymphoid Organs Lymph It is the recovered fluid. Lymph is usually a clear colorless fluid, similar to blood plasma but low in protein. - Lymphatic capillaries Aggregates of lymphocytes in the connective tissue of mucous membrane and various organs. They have well –defined anatomical sites and at least partial connective tissue capsules. - Lymphatic collecting vessels Mucosa-associated lymphatic tissue (MALT) - Lymphatic trunks 1- Lymph nodes - Collecting duct 1- Peyer patches in the distal portion of the small intestine. 2- Thymus 3- Spleen 2- Vermiform appendix 3- Tonsils (palatine tonsils and pharyngeal tonsils or adenoids). 4- Red Bone Marrow

7. Lymphoid Organs Lymphoid Tissues Lymphatic Vessels

8. Lymphatic Vessels The Lymphatic Capillariesconverge to form Small Lymphatic Vessels. Lymphatic system Cardiovascular system Subclavian veins The small lymphatic vessels travel alongside veins and arteries, and at irregular intervals they empty into lymph nodes. In the lymph nodes, bacteria are phagocytized and immune cells monitor the fluid for foreign antigens. Pulmonary circuit Collecting ducts (2) Lymphatic trunks (6) Lymphatic node The SmallLymphatic Vesselsconverge to form Major Lymph-Collecting Vessels (trunks and ducts) Superior vena cava Trunks: Small Lymphatic Vessels 1- Jugular trunks, 2- Subclavian trunks, 3- Bronchomediastinal trunks, 4- Intestinal trunk, and 5- Lumbar trunks Lymphatic capillaries Blood flow The names indicates their locations and part of the body they drain. The Lymphatic Trunks converge to form Collecting Ducts: 1- Right lymphatic duct Systemic circuit 2- Thoracic duct

9. 1- They originate like pockets rather than forming continuous tubes. 2- They have larger diameters. 3- They have thinner walls. 4- They have a flattened or irregular outline in sectional view. 1- Lymphatic Capillaries

10. The region of overlap of endothelial cells acts as a one-way valve, permitting the entry of fluid and solutes (even those as large proteins), as well as viruses, bacteria, and cell debris, but preventing their return to the interstitial space.

11. Special lymphatic vessels called lacteals in small intestine absorb dietary lipids that are not absorbed by the blood capillaries.

12. From the lymphatic capillaries, lymph flows into larger lymphatic vessels (small lymphatic vessels). 2- Small Lymphatic Vessels • Small lymphatic vesselsare often associated to blood vessels. • They carry lymph from lymphatic capillaries to lymphatic trunks. • The larger small lymphatic vessels have valves to prevent back flow of lymph, especially in the limbs.

13. Right Lumbar Trunk Thoracic Duct Cisterna Chyli Intestinal Lumbar Trunk Left Lumbar Trunk 3- Major Lymph-collecting Vessels: Lymphatic Trunks and Lymphatic Ducts Small lymphatic Vessels Lymphatic Ducts Lymphatic Trunks Lymphatic Capillaries Inferior Trunks Thoracic duct Cisterna Chyli Right lumbar trunk Left lumbar trunk Intestinal trunk Inferior vena cava

14. Superior Trunks Right Lymphatic Duct Right Jugular Trunk Right Subclavian Trunk Right Bronchomediastinal Trunk Left Jugular Trunk LEFT RIGHT Right Jugular Trunk Left Subclavian Trunk Thoracic Duct Right Subclavian Trunk Left Subclavian veint Right Lymphatic Duct Right subclavian vein Superior vena cava Right Bronchome-diastinal Trunk Left Bronchome-diastinal Trunk

15. Inferior Trunks

16. Right side of the tissues superior to the diaphragm Right Lymphatic Duct Tissues inferior to the diaphragm and from left side of the upper body Thoracic Duct Right Lymphatic Duct Thoracic Duct

17. Lymphocytes Red bone marrow 1- T lymphocytes (T cells) 80% 2- B lymphocytes (B cells) 10% - 15% T stem cell 3- Natural Killer Cells (NK cells) 5% - 10% Thymus 1- T lymphocytes (T cells) 80% T cells are born in the red bone marrow. They are released into the blood as still undifferentiated stem cells. T lymphocyte The thymus is the “school” where they mature into fully functional T lymphocytes. • They make up 80% of circulating lymphocytes. Three Main Types of T Cells: • 1- Cytotoxic T cells • They attack foreign cells and cells infected by viruses. They are responsible of cell-mediated immunity. • Helper T cells: • They stimulate function of T cells and B cells. • 2- Regulatory T cells • They control the sensitivity of immune response • Suppressor T cells: • Inhibit function of T cells and B cells. • 3- Memory T cells • They respond to a previously encountered antigen.

18. 2- B lymphocytes (B cells) 10-15% B cells are also born in the red bone marrow, but they remain there until they differentiate in functional B lymphocytes. B stem cell When stimulated, B cells can differentiate into plasma cells, which are responsible of the production of antibodies (humoral immunity). (humoral immunity) ANTIBODIES 3 -Natural killer (NK) cells 5-10% Plasma Cell • They are large lymphocytes that attack and destroy bacteria, transplanted tissue, and host cells infected with viruses or that have turned cancerous. • They are responsible for immune surveillance. B lymphocyte

19. Classes of Lymphocytes subdivided into B Cells T Cells NK Cells B cells make up1015% of circulatinglymphocytes. Approximately 80% ofcirculating lymphocytes areclassified as T cells. NK cells makeup the remaining510% ofcirculatinglymphocytes. can differentiate into Memory T Cells CytotoxicT Cells Helper T Cells SuppressorT Cells Plasma Cells Helper T cellsstimulate theactivation andfunction ofboth T cellsand B cells. Cytotoxic T cellsattack foreign cellsor body cellsinfected by viruses. Suppressor Tcells inhibitthe activationand functionof both T cells and B cells. Memory T cellsare a subset ofT cells thatrespond to a previouslyencountered antigen. When stimulated,B cells candifferentiate intoplasma cells, whichproduce and secreteantibodies.