The lymphatic system collects excess tissue fluid and returns it to the bloodstream. Its components include lymphatic vessels, lymph nodes, and lymph ducts. The immune system protects the body from foreign organisms using lymphocytes, lymphoid tissue, and lymphoid organs like the spleen, thymus, and lymph nodes. Lymphocytes recognize and destroy pathogens. When activated by antigens, they proliferate into memory and effector cells. Disorders can affect the lymphatic vessels or immune function.

1. The Lymphatic
and
Immune Systems
Chapter 20-21

2. Objectives
• Lymphatic System
– Lymphoid Organs
– Lymphoid Circulation
• Immune System
– Immune cells
– Immune cell function

3. The Lymphatic and Immune Systems
• Lymphatic system
– Main function is to return excess tissue fluid to blood
vascular system
– Lymphatic vessels collect tissue fluid
• Immune system
– Protects our bodies from foreign organisms
– Confers immunity to disease
– Main components
• Lymphocytes, lymphoid tissue, and lymphoid organs

4. The Lymphatic System
• Lymphatic vessels collect tissue fluid from loose
connective tissue
– Carry fluid to great veins in the neck
– Fluid flows only toward the heart
– Once tissue fluid is within lymphatic vessels it is termed
lymph
• Functions of lymphatic vessels – collect excess
tissue fluid and blood proteins
• Return tissue fluid and blood proteins to
bloodstream

5. Orders of Lymphatic Vessels
• Lymph capillaries – smallest
lymph vessels
– First to receive lymph
• Lymphatic collecting vessels –
collect from lymph capillaries
– Lymph nodes are scattered
along collection vessels
Lymphatic system
Lymph duct
Lymph trunk
Lymph node
Lymphatic
capillary
Blood
capillaries
Lymphatic
collecting
vessels, with
valves
(a) Structural relationship between a capillary
bed of the blood vascular system and
lymphatic capillaries
Heart
Arterial systemVenous system

6. Orders of Lymphatic Vessels
• Lymph nodes
– Scattered along collecting vessels
• Lymph trunks
– Collect lymph from collecting vessels
• Lymph ducts
– Empty into veins of the neck

7. 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 allows entrance of
– Tissue fluid and protein molecules
– Bacteria, viruses, and cancer cells

8. Lymphatic Capillaries
• Lacteals—specialized lymphatic capillaries
– Located in the villi of the small intestines
• Receive digested fats
• Fatty lymph—chyle

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

10. Lymphatic Collecting 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
• Lymph propelled by
– Skeletal muscles bulging
– Nearby arteries pulsing
– Tunica media of the lymph vessels
• Lymph flow is unaided by heartbeat

11. Lymph Nodes
• Cleanse the lymph of pathogens
• Human body contains around 500
• Superficial lymph nodes located in
– Cervical, axillary, and inguinal regions
• Deep nodes are
– Tracheobronchial, aortic, and iliac lymph nodes

12. General Distribution of Lymphatic Collecting Vessels and
Regional Lymph Nodes
Figure 21.2
Cervical
nodes
Entrance of
right lymphatic
duct into vein
Internal
jugular vein
Entrance of
thoracic duct
into vein
Thoracic
duct
Cisterna
chyli
Lymphatic
collecting
vessels
Axillary
nodes
Aorta
Inguinal
nodes
Regional
lymph
nodes
Drained by the right
lymphatic duct
Drained by the
thoracic duct

13. Microscopic Anatomy of a Lymph Node
• Fibrous capsule—surrounds lymph nodes
• Trabeculae—connective tissue strands
• Lymph vessels
– Afferent lymphatic vessels
– Efferent lymphatic vessels

14. Microscopic Anatomy of a Lymph Node
Figure 21.3a
Afferent
lymphatic
vessels
Efferent lymphatic
vessels
Capsule
Trabeculae
Hilum
Cortex
Lymphoid follicle
Germinal center
Subcapsular sinus
Medulla
Medullary cord
Medullary sinus
(a) Longitudinal view of the internal structure
of a lymph node and associated lymphatics

15. Microscopic Anatomy of a Lymph Node
Figure 21.3b
Follicles
Trabecula
Subcapsular
sinus
Capsule
Medullary
cords
Medullary
sinuses
(b) Photomicrograph of part of a lymph node (14X)

16. Microscopic Anatomy of a Lymph Node
Figure 21.3c
(c) Reticular tissue within the medullary sinus (540X)
Macrophage
Medullary
sinus
Reticular
fiber
Lymphocytes
Reticular cells
on reticular
fibers

17. Lymph Trunks
• Lymphatic collecting vessels converge
• Five major lymph trunks
– Lumbar trunks
• Receives lymph from lower limbs
– Intestinal trunk
• Receives chyle from digestive organs
– Bronchomediastinal trunks
• Collects lymph from thoracic viscera

18. Lymph Trunks
• Five major lymph trunks (continued)
– Subclavian trunks
• Receive lymph from upper limbs and thoracic wall
– Jugular trunks
• Drain lymph from the head and neck

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

20. The Lymphatic Trunks
Figure 21.4b
(b) Thoracic duct (colored green)
along the posterior thoracic wall
Azygos vein
on vertebral
bodies
Thoracic duct Aorta

21. Lymph Ducts
• Cisterna chyli
– 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

22. Right Lymphatic Duct
• Empties into right
internal jugular and
subclavian veins
Internal jugular veinsRight jugular trunk
Right lymphatic duct
Right subclavian
trunk
Right subclavian vein
Right broncho-
mediastinal trunk
Brachiocephalic veins
Superior vena cava
Azygos vein
Cisterna chyli
Right lumbar trunk

23. The Immune System
• Recognizes specific foreign molecules
• Destroys pathogens effectively
• Key cells—lymphocytes
• Also includes lymphoid tissue and lymphoid organs
• Lymphoid organs
– Lymph nodes, spleen, thymus, tonsils, aggregated
lymphoid nodules, and appendix

24. Lymphocytes
• Infectious organisms attacked by inflammatory
response
– Macrophages, then lymphocytes
• Are effective fighters of infectious organisms
– Each lymphocyte recognizes a specific foreign
molecule
• Antigens are any molecules inducing a response from a
lymphocyte

25. Lymphocytes
• B lymphocytes and T lymphocytes are the two main
classes of lymphocytes
• Cytotoxic T lymphocytes
– Attack foreign cells directly
• Binds to antigen-bearing cells
• Perforates cell membrane
• Signals cell to undergo apoptosis
• Destroy virus infected cells and some cancer cells

26. Lymphocytes
• B lymphocytes
– Become plasma cells
– Secrete antibodies
• Mark cells for destruction by macrophages
– Respond primarily to bacteria and bacterial toxins

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

28. Lymphocyte Activation
• Lymphocytes originate in bone marrow
• Some travel to the thymus gland
– T lymphocytes
• Some stay in bone marrow
– B lymphocytes
• Able to recognize a unique antigen
– Gain immunocompetence
• Travels through blood stream
– Meets and binds to a specific antigen

29. Lymphocyte Activation
• During activation
– Lymphocyte is presented its antigen by
• A macrophage
• Or a dendritic cell

30. 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

31. Lymphocyte Activation
Figure 21.6
Red bone
marrow
Bone
marrow
Immature
lymphocytes
Red bone marrow: site of
lymphocyte origin
Secondary lymphoid organs:
site of antigen encounter, and
activation to become effector
and memory B or T cells
Primary lymphoid organs:
site of development of immuno-
competence as B or T cells
Lymphocytes destined to become T cells
migrate (in blood) to the thymus and develop
immunocompetence there. B cells develop
immunocompetence in red bone marrow.
Immunocompetent but still
naive lymphocytes leave the
thymus and bone marrow. They
“seed” the lymph nodes, spleen,
and other lymphoid tissues where
they encounter their antigen.
Antigen-activated immuno-
competent lymphocytes
(effector cells and memory
cells) circulate continuously in
the bloodstream and lymph and
throughout the lymphoid
organs of the body.
1
2
3
Thymus
Lymph
nodes, spleen, and other
lymphoid tissues

32. 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)

33. Lymphoid Tissue
Figure 21.7
Lymphoid
follicle
Mucous
membrane
lining small
intestine
LumenMuscle
layers
Intestine
Germinal
center
Lumen of
intestine
Lymphoid tissue from mucosa of small
intestine (14)

34. Lymphoid Organs
• Primary lymphoid organs
– Bone marrow
– Thymus
• Secondary lymphoid organs
– Lymph nodes, spleen, tonsils
– Aggregated lymphoid nodules
– Appendix

35. Lymphoid Organs
• Designed to gather and destroy infectious microorganisms and to
store lymphocytes
Figure 21.8
Tonsils (in pharyngeal
region)
Thymus (in thorax; most
active during youth)
Spleen (curves around
left side of stomach)
Aggregated lymphoid
nodule (in intestine)
Appendix

36. Thymus
• Immature lymphocytes develop into T lymphocytes
• Secretes thymic hormones
• Most active in childhood
• Functional tissue atrophies with age
• Composed of cortex and medulla
– Medulla contains Hassall’s corpuscles (thymic corpuscles)
• Differs from other lymphoid organs
– Functions strictly in lymphocyte maturation
– Arises from epithelial tissue

37. Thymus
Figure 21.9
Cortex
Medulla
Thymic
corpuscle
(b) Micrograph of thymic tissue
showing part of a lobule
Thymus
(a)Thymus located in the superior
mediastinum

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

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

40. 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

41. Spleen
• White pulp
– Thick sleeves of lymphoid tissue
– Blood-borne antigens are destroyed as they activate the
immune response
– Provides the immune function of the spleen
• Red pulp
– Surrounds white pulp
– Composed of
• Venous sinuses
• Splenic cords
• Responsible for disposing of worn out RBCs

42. Spleen
Figure 21.10a, b
Splenic artery
Splenic vein
Hilum
(a) Diagram of the spleen,
anterior view
Arterioles
and
capillaries
Capsule
Trabecula
Venous sinuses
Red pulp
Splenic cords
White pulp
Central artery
Splenic artery
Splenic vein
(b) Diagram of spleen histology

43. Spleen
Figure 21.10c, d
(c) Photograph of the spleen in its normal
position in the abdominal cavity,
anterior view
Diaphragm
Spleen
Adrenal
gland
Splenic
artery
Pancreas
Left
kidney
(d) Photomicrograph of spleen tissue (7).
The white pulp, a lymphoid tissue with many
lymphocytes, is surrounded by red pulp
containing abundant erythrocytes.
Capsule
White pulp
Red pulp

44. Tonsils
• 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

45. Tonsil
Tonsillar crypt
Germinal centers in
lymphoid follicles
Pharyngeal tonsil
Palatine tonsil
Lingual tonsil
Palatine Tonsil
Figure 21.11

46. Aggregated Lymphoid Nodules & 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

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

48. Disorders of the Lymphatic
and Immune Systems
• Chylothorax
– Leakage of fatty lymph into the thorax
• Lymphangitis
– Inflammation of a lymph vessel
• Mononucleosis
– Viral disease caused by Epstein-Barr virus
– Attacks B lymphocytes

49. Disorders of the Lymphatic
and Immune Systems
• Hodgkin’s disease
– Malignancy of lymph nodes
• Non-Hodgkin’s lymphoma
– Uncontrolled multiplication and metastasis of
undifferentiated lymphocytes

50. The Lymphatic and
Immune Systems Throughout Life
• Lymphatic vessels and lymph nodes
– Develop from lymphatic sacs
• Thymus originates as an outgrowth of the endoderm
• Spleen, lymph nodes, and MALT
– Arise from mesodermal mesenchyme

51. Lymphatic System Video
• http://www.youtube.com/watch?v=BX8fBlme
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