1. The Lymphatic and Immune Systems
21 PART 1
The Lymphatic and Immune Systems

2. The Lymphatic and Immune Systems
Lymphatic system
Main function is to return excess tissue fluid to blood vascular system
Lymphatic vessels collect tissue fluid

3. The Lymphatic and Immune Systems
Protects our bodies from foreign organisms
Confers immunity to disease
Main components
Lymphocytes, lymphoid tissue, and lymphoid organs

4. Lymphatic vessels collect tissue fluid from loose connective tissue
The Lymphatic System
Lymphatic vessels collect tissue fluid from loose connective tissue
Carry fluid to great veins in the neck
Once tissue fluid is within lymphatic vessels it is termed lymph
Lymph flows only toward the heart

5. Functions of Lymphatic Vessels
Collect excess tissue fluid and blood proteins
Return tissue fluid and blood proteins to bloodstream

6. Orders of Lymphatic Vessels
Lymph capillaries
Smallest lymph vessels
First to receive lymph
Are highly permeable vessels
Collecting lymphatic vessels
Collect from lymph capillaries
Lymph nodes are scattered along collection vessels

7. Orders of Lymphatic Vessels
Lymph trunks
Collect lymph from collecting vessels
Lymph ducts
Empty into veins of the neck

8. Lymphatic Capillaries
Located near blood capillaries
Receive tissue fluid from CT
Increased volume of tissue fluid
Minivalve flaps open and allow fluid to enter
High permeability of lymphatic capillaries allows entrance of
Tissue fluid and protein molecules
Bacteria, viruses, and cancer cells

9. Lymphatic Capillaries
Lacteals
Are specialized lymphatic capillaries
Are located in the villi of the small intestines
Receive digested fats
Fatty lymph is termed chyle

10. Figure 21.1 Distribution and special features of lymphatic capillaries.
Venous system
Arterial system
Heart
Lymphatic system:
Lymph duct
Lymph trunk
Lymph node
Collecting lymphatic vessels, with valves
Lymphatic capillary
Blood capillaries
Filaments anchored to connective tissue
Endothelial cell
Flaplike minivalve
Tissue fluid
Tissue cell
Fibroblast in loose connective tissue
Blood capillaries
Lymphatic capillaries
Structural relationship between a capillary bed of the blood vascular system and lymphatic capillaries
Lymphatic capillaries are blind-ended tubes in which adjacent endothelial cells overlap each other, forming flaplike minivalves. 10

11. Collecting Lymphatic Vessels
Accompany blood vessels
Composed of the same three tunics as blood vessels
Contain more valves than veins do
Helps direct the flow of blood

12. Collecting Lymphatic Vessels
Flow of lymph is not aided by the heartbeat
Lymph is propelled by three weaker mechanisms
Bulging of skeletal muscles
Pulsing of nearby arteries
Tunica media of the lymph vessels

13. Cleanse the lymph of pathogens Human body contains around 500
Lymph Nodes
Cleanse the lymph of pathogens
Human body contains around 500
Superficial lymph nodes located in
Cervical region
Axillary region
Inguinal region

14. Lymph Nodes Deep lymph nodes are Tracheobronchial lymph nodes
Aortic lymph nodes
Iliac lymph nodes

15. Entrance of right lymphatic duct into vein Cervical nodes
Figure General distribution of collecting lymphatic vessels and regional lymph nodes.
Internal jugular vein
Regional lymph nodes
Entrance of right lymphatic duct into vein
Cervical nodes
Entrance of thoracic duct into vein
Axillary nodes
Thoracic duct
Cisterna chyli
Aorta
Inguinal nodes
Collecting lymphatic vessels
Drained by the right lymphatic duct
Drained by the thoracic duct 15

16. Microscopic Anatomy of a Lymph Node
Fibrous capsule
Surrounds lymph nodes
Trabeculae
Connective tissue strands extend inward to divide lymph node into segments

17. Microscopic Anatomy of a Lymph Node
Lymph enters convex aspect of a lymph node through
Afferent lymphatic vessels
Lymph exits a lymph node at the hilum through
Efferent lymphatic vessels

18. Figure 21.3a Structure of a lymph node.
Afferent lymphatic vessels
Cortex
Lymphoid follicle
Germinal center
Subcapsular sinus
Efferent lymphatic vessels
Hilum
Medulla
Medullary cord
Medullary sinus
Capsule
Trabeculae
Longitudinal view of the internal structure of a lymph node and associated lymphatics 18

19. Figure 21.3b Structure of a lymph node.
Lymphoid follicles
Trabecula
Subcapsular sinus
Capsule
Medullary cords
Medullary sinuses
Photomicrograph of part of a lymph node (72) 19

20. Figure 21.3c Structure of a lymph node.
Macrophage
Reticular cells on reticular fibers
Lymphocytes
Medullary sinus
Reticular fiber
Reticular tissue within the medullary sinus (690) 20

21. Collecting lymphatic vessels converge to form lymph trunks
Five major lymph trunks
Lumbar trunks
Receive lymph from lower limbs
Intestinal trunk
Receives chyle from digestive organs
Bronchomediastinal trunks
Collects lymph from thoracic viscera

22. Five major lymph trunks (continued)
Subclavian trunks
Receive lymph from upper limbs and thoracic wall
Jugular trunks
Drain lymph from the head and neck

23. Figure 21.4a The lymph trunks and ducts.
Internal jugular veins
Right jugular trunk
Esophagus
Right lymphatic duct
Trachea
Left jugular trunk
Right subclavian trunk
Left subclavian trunk
Right subclavian vein
Right broncho- mediastinal trunk
Brachiocephalic veins
Left subclavian vein
Superior vena cava
Entrance of thoracic duct into vein
Left broncho- mediastinal trunk
Azygos vein
Thoracic duct
Ribs
Cisterna chyli
Right lumbar trunk
Hemiazygos vein
Left lumbar trunk
Inferior vena cava
Intestinal trunk
Major lymphatic trunks and ducts in relation to veins and surrounding structures, anterior view 23

24. Figure 21.4b The lymph trunks and ducts.
Esophagus
Trachea
Aorta
Azygos vein
Vertebral body
Left broncho- mediastinal trunk
Sympathetic
trunk
Thoracic duct
Cisterna chyli
Crus of the diaphragm
Inferior vena cava
Thoracic duct along the posterior thoracic wall 24

25. Lymph Ducts Cisterna chyli Thoracic duct
Located at the union of lumbar and intestinal trunks
Thoracic duct
Ascends along vertebral bodies
Empties into venous circulation
Junction of left internal jugular and left subclavian veins
Drains three-quarters of the body

26. Lymph Ducts Right lymphatic duct
Empties into right internal jugular and subclavian veins

27. Recognizes specific foreign molecules Destroys pathogens effectively
The Immune System
Recognizes specific foreign molecules
Destroys pathogens effectively
Key cells of the immune system
Are termed lymphocytes

28. Includes lymphoid tissue and lymphoid organs Lymphoid organs
The Immune System
Includes lymphoid tissue and lymphoid organs
Lymphoid organs
Lymph nodes
Spleen
Thymus
Tonsils
Aggregated lymphoid nodules
Appendix

29. Infectious organisms trigger an inflammatory response
Lymphocytes
Infectious organisms trigger an inflammatory response
Organisms are attacked by
Macrophages, then lymphocytes

30. Lymphocytes effectively recognize a specific foreign molecule
Antigens are any molecules inducing a response from a lymphocyte

31. Cytotoxic T lymphocytes
B lymphocytes and T lymphocytes are the two main classes of lymphocytes
Cytotoxic T lymphocytes
Attack foreign cells directly
Bind to antigen-bearing cells
Perforate cell membrane
Signal cell to undergo apoptosis
Destroy virus-infected cells and some cancer cells

32. Lymphocytes B lymphocytes Become plasma cells
Plasma cells secrete antibodies
Mark cells for destruction by macrophages
Respond primarily to bacteria and bacterial toxins

33. Figure 21.5 Lymphocyte function.
Target cell, bearing antigen
Dead target cell
T lymphocyte
Antigen 1
T lymphocyte binds to target cell, secretes proteins that lyse the cell’s membrane, and signals the cell to die.
T lymphocyte detaches from target cell. 2 3
Target cell dies by apoptosis.
Action of cytotoxic T lymphocyte
B lymphocyte
Plasma cell
Antibodies
Bacterium
Surface antigen
Macrophage 1
B lymphocyte gives rise to plasma cell, which secretes antibodies.
Antibodies bind to antigens on bacteria, marking the bacteria for destruction. 2
Antibody-coated bacteria are avidly phagocytized. 3
Differentiation and activity of B lymphocyte 33

34. Lymphocyte Activation
Lymphocytes originate in bone marrow
Some travel to the thymus gland
T lymphocytes
Some stay in bone marrow
B lymphocytes

35. Lymphocyte Activation
Activated lymphocytes
Are able to recognize a unique antigen
Gain immunocompetence
Travel through bloodstream
Meet and bind to a specific antigen
Proliferate rapidly

36. Lymphocyte Activation
During activation
Lymphocyte is presented its antigen by
A macrophage or
A dendritic cell

37. Lymphocyte Activation
Both T and B lymphocytes produce clones of
Effector lymphocytes
Respond immediately, then die
Memory cells
Wait until the body encounters the antigen again
Basis of acquired immunity
Prevent subsequent infections of the same illness

38. Figure 21.6 Differentiation, activation, and recirculation of lymphocytes.
Primary lymphoid organs (red bone marrow and thymus)
Secondary lymphoid organs (lymph nodes, spleen, etc.)
Red bone marrow 1
Origin
• Both B and T lymphocyte precursors originate in red bone marrow.
Lymphocyte precursors 2
Maturation
• Lymphocyte precursors destined to become T cells migrate (in blood) to the thymus and mature there.
• B cells mature in the bone marrow.
Thymus
• During maturation, lymphocytes develop immunocompetence and self-tolerance.
Red bone marrow 3
Seeding secondary lymphoid organs and circulation
• Immunocompetent but still naïve lymphocytes leave the thymus and bone marrow.
• They “seed” the secondary lymphoid organs and circulate through blood and lymph.
Antigen 4
Antigen encounter and activation
Lymph node
• When a lymphocyte’s antigen receptors bind its antigen, that lymphocyte can be activated. 5
Proliferation and differentiation
• Activated lymphocytes proliferate (multiply) and then differentiate into effector cells and memory cells.
• Memory cells and effector T cells circulate continuously in the blood and lymph and throughout the secondary lymphoid organs. 38

39. Most important tissue of the immune system Two general locations
Lymphoid Tissue
Most important tissue of the immune system
Two general locations
Mucous membranes of
Digestive, urinary, respiratory, and reproductive tracts
Mucosa associated lymphoid tissue (MALT)
Lymphoid organs (except thymus)

40. Figure 21.7 Mucosa associated lymphoid tissue (MALT).
Intestine
Muscle layers
Lumen
Mucous membrane lining small intestine
Lymphoid follicle
Lumen of intestine
Germinal center
Mucosa of small intestine (7) 40

41. Primary lymphoid organs
Bone marrow
Thymus
Secondary lymphoid organs
Lymph nodes, spleen, tonsils
Aggregated lymphoid nodules
Appendix
Designed to gather and destroy infectious microorganisms and to store lymphocytes

42. Figure 21.8 Lymphoid organs.
Tonsils (in pharynx)
Thymus (in thorax; most active during youth)
Spleen (curves around left side of stomach)
Aggregated lymphoid nodules (in small intestine)
Appendix 42

43. Thymus
Site where immature lymphocytes develop into T lymphocytes
Secretes thymic hormones
Most active in childhood
Functional tissue atrophies with age

44. Composed of cortex and medulla
Thymus
Composed of cortex and medulla
Medulla contains thymic corpuscles
Differs from other lymphoid organs
Functions strictly in lymphocyte maturation
Arises from epithelial tissue

45. Thymus, located in the superior mediastinum
Figure The thymus.
Capsule
Cortex
Thymus
Medulla
Thymic corpuscle
Thymus, located in the superior mediastinum
Micrograph of thymic tissue 45

46. Lymph Nodes Function Lymph percolates through lymph sinuses
Most antigenic challenges occur in lymph nodes
Antigens destroyed and activate B and T lymphocytes

47. Largest lymphoid organ Two main blood-cleansing functions
Spleen
Largest lymphoid organ
Two main blood-cleansing functions
Removal of bloodborne antigens
Removal and destruction of old or defective blood cells
Site of hematopoiesis in the fetus

48. Spleen
Destruction of antigens
Site of B cell maturation into plasma cells
Phagocytosis of bacteria and worn-out RBCs, WBCs, and platelets
Storage of platelets

49. Spleen White pulp Thick sleeves of lymphoid tissue
Bloodborne antigens are destroyed as they activate the immune response
Provides the immune function of the spleen

50. Spleen Red pulp Surrounds white pulp Composed of Venous sinuses
Splenic cords
Responsible for disposing of worn-out RBCs

51. Figure 21.10a Structure of the spleen.
Splenic artery
Splenic vein
Hilum
Diagram of the spleen, anterior view 51

52. Figure 21.10b Structure of the spleen.
Capsule
Trabecula
Splenic cords
Splenic sinusoids
Arterioles and capillaries
Red pulp
White pulp
Central artery
Splenic artery
Splenic vein
Diagram of spleen histology 52

53. Figure 21.10c Structure of the spleen.
Diaphragm
Spleen
Adrenal gland
Left kidney
Splenic artery
Pancreas
Photograph of the spleen in its normal position in the abdominal cavity, anterior view 53

54. Figure 21.10d Structure of the spleen.
Capsule
White pulp
Red pulp
Photomicrograph of spleen tissue (30). The white pulp, a lymphoid tissue with many lymphocytes, is surrounded by red pulp containing abundant erythrocytes. 54

55. Simplest lymphoid organs Four groups of tonsils
Palatine, lingual, pharyngeal, and tubal tonsils
Arranged in a ring to gather and remove pathogens
Underlying lamina propria consists of MALT

56. Figure 21.11 Histology of the palatine tonsil.
Pharyngeal tonsil
Palatine tonsil
Lingual tonsil
Germinal centers in lymphoid follicles
Tonsillar crypt 56

57. Aggregated Lymphoid Nodules and Appendix
MALT—abundant in walls of intestines
Fight invading bacteria
Generate a wide variety of memory lymphocytes
Aggregated lymphoid nodules (Peyer’s patches)
Located in the distal part of the small intestine
Appendix—tubular offshoot of the cecum

58. Figure 21.12 Aggregated lymphoid nodules.
Aggregated lymphoid nodules (Peyer’s patch)
Smooth muscle in the intestinal wall 58