The Lymphatic System

1. The Lymphatic System LAB # 5 • 1- List the functions of Lymphatic System. • 2- Describe the exchange of blood plasma, extracellular fluid, and lymph. • 3-Describe the structure of a lymph node. • 4- Explain how the lymphatic system drains into the vascular system • 5- Describe the gross anatomy and basic histology of the spleen.

2. Functions of the Lymphatic System 1- Lymphocyte Production, Maintenance, and Distribution 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 in 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. 85% 7 mm Hg 85% 15% 13 mm Hg

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).

7. Lymphoid Organs Lymphoid Tissues Lymphatic Vessels

8. 1- Lymphatic Vessels

9. The lymphatic capillaries converge to form collecting vessels. Lymphatic system Cardiovascular system The collecting 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. Subclavian veins Pulmonary circuit Collecting ducts (2) Lymphatic trunks The collecting vessels converge to form lymphatic trunks. Superior vena cava The names indicates their locations and part of the body they drain Collecting vessels 1- Jugular trunks, 2- Subclavian trunks, 3- Bronchomediastinal trunks, 4- Intestinal trunk, and 5- Lumbar trunks Blood flow Lymphatic capillaries The lymphatic trunks converge to form collecting ducts. 1- Right lymphatic duct 2- Thoracic duct Systemic circuit

10. Right Lumbar Trunk Thoracic Duct Cisterna Chyli Intestinal Lumbar Trunk Left Lumbar Trunk 3- Lymphatic Trunks and Lymphatic Ducts Lymph Capillaries Collecting Vessels Lymphatic Trunks Lymphatic Ducts Inferior Trunks Thoracic duct Cisterna Chyli Right lumbar trunk Left lumbar trunk Intestinal trunk Inferior vena cava

11. Right Jugular Trunk Right Lymphatic Duct Right Subclavian Trunk Right Bronchomediastinal Trunk Left Jugular Trunk RIGHT LEFT 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 Superior Trunks

12. Inferior Trunks

13. 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

15. 2- Lymphoid Tissues and Lymph Nodes

16. Lymphoid Tissues Lymphoid tissues are areolar connective tissues with concentrations of lymphocytes. Germinal center When lymphocytes are densely packed they form lymphoid or lymphatic nodules or follicles. The lymphatic nodules or follicles have no fibrous capsule surrounding them. Lymphatic nodule or follicle It contains dividing lymphocytes.

17. MALT (Mucosa-Associated Lymphatic Tissue) It is the collection of lymphoid tissues that protect the epithelia of the respiratory, digestive, urinary, and reproductive systems. • Clusters of lymphoid nodules deep to the epithelial lining of the intestine are known as Peyer’s patches. • The appendix vermiform is other example of MALT. It walls contain a mass of fused lymphoid nodules.

19. Tonsils Pharyngeal tonsil or adenoid (single) Palatinetonsils (two) Lingual tonsils (two) They are large concentration of lymphoid nodules in the walls of the pharynx. Functions • They guard against ingested or inhaled pathogens.

21. Lymph nodes Lymphoid Organs Spleen Thymus Lymphatic organs have well-defined anatomical sites and have connective tissue capsule that separates the lymphatic tissue from neighboring tissues. - Lymph nodes - Thymus - Spleen Lymph nodes They are the smallest and most numerous lymphatic organs (about 450 in typical young adult). They range in diameter from 1 mm to 25 mm (about 1 inch)

22. Lymph nodes are wide-spread but specially concentrated in some locations. Axillary lymph nodes Cervical lymph nodes Lumbar lymph nodes Pelvic lymph nodes Inguinal lymph nodes

23. Lymph nodes are shaped like kidney beans. Lymphnodes Lymphvessel Lymph nodeartery and vein Efferentvessel Hilum Lymph nodes Trabeculae Medullary sinus Cortex Medulla Subcapsularspace Outer cortex (B cells) Deep cortex(T cells) Afferentvessel Medullary cord(B cells andplasma cells) Capsule Dense connective tissue

24. Lymph Node Functions: • 1- They filter and purify the lymph before return to venous circulation (they remove 99% of cell debris, bacteria, viruses, fungi). • 2- They provide an early warning system against infection in peripheral tissue, responding before infections reach vital organs of trunk. • 3- The first step in immune response takes place in the lymph nodes (extracted antigens are “presented” to lymphocytes).

25. The Thymus • The thymus is located in the mediastinum. • It atrophies after puberty. • The thymus is divided into two thymic lobes. Thymus • Septa divide lobes into smaller lobules. Leftlobe Rightlobe Septa Lobule

26. Septa Lobule Cortex • Mature • lymphocytes Medulla • Dividing lymphocytes Lobule The thymus gland LM  50

27. Medulla Septa Cortex Lymphocytes Lobule Reticularcells Lobule Thymiccorpuscle The thymus gland LM  50 A thymic corpuscle LM  550 T lymphocytes divide in the cortex and mature while they migrate to the medulla. • Mature T cells leave thymus by medullary blood vessels. • The thymus secretes thymic hormones that stimulate T cell differentiation.

29. The Spleen It is the body’s largest lymphatic organ. Parietal peritoneum Visceral peritoneum Spleen Stomach Diaphragm Rib Gastrosplenicligament Liver Pancreas Gastric area Aorta Diaphragmatic surface SPLEEN Hilum Renal area Kidneys

31. Histology of the Spleen White pulp isdominated by lymphocytes. White pulp ofsplenic nodule Capsule Red pulp contains a large number of red blood cells. Red pulp Trabecularartery Central artery insplenic nodule The spleen LM  50 Functions: 1- Removal of abnormal and worn out blood cells. • 2- Storage of iron recycled from red blood cells. • 3- Initiation of immune responses by B cells and T cells.