1. The Lymphatic System and Lymphoid Organs and Tissues20
The Lymphatic System and Lymphoid Organs and Tissues

2. Consists of three parts
Lymphatic System
Consists of three parts
A network of lymphatic vessels (lymphatics)
Lymph (fluid inside vessels)
Lymph nodes (cleanse the lymph)

3. Lymphatic System: Functions
Returns interstitial fluid and leaked plasma proteins back to the blood
Carry absorbed fat from intestine to the blood (through lacteals)
Once interstitial fluid enters lymphatics, it is called lymph
Together with lymphoid organs and tissues, provide the structural basis of the immune system

4. One-way system, lymph flows toward the heart
Lymphatic Vessels
One-way system, lymph flows toward the heart
Lymph vessels (lymphatics) include:
Lymphatic capillaries
Lymphatic collecting vessels
Lymphatic trunks and ducts

5. Figure 20.1
Lymphatic
system:
Lymph duct
Lymph trunk
Lymph node
capillary
Blood
capillaries
collecting vessels,
with valves
Heart
Arterial system
Venous system
Tissue
fluid
Tissue cell
(a) Structural relationship between a
capillary bed of the blood vascular
system and lymphatic capillaries.

6. Lymphatic Capillaries
Similar to blood capillaries, except
Very permeable (take up cell debris, pathogens, and cancer cells)
Endothelial cells overlap to form one-way minivalves, and are anchored by collagen filaments, preventing collapse of capillaries

7. Lymphatic Capillaries
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.

8. Lymphatic Capillaries
Absent from bones, teeth, bone marrow and the CNS
Lacteals: specialized lymph capillaries present in intestinal mucosa
Absorb digested fat and deliver fatty lymph (chyle) to the blood

9. Lymphatic Collecting Vessels
Similar to veins, except
Have thinner walls, with more internal valves
Anastomose more frequently
Superficial collecting vessels
in the skin, travel with superficial veins
Deep collecting vessels travel with arteries
Nutrients are supplied from branching vasa vasorum

10. Lymph is delivered into one of two large ducts
Lymphatic Ducts
Lymph is delivered into one of two large ducts
Right lymphatic duct drains the right upper arm and the right side of the head and thorax
Thoracic duct arises from the cisterna chyli and drains the rest of the body
Each empties lymph into venous circulation at the junction of the internal jugular and subclavian veins on its own side of the body

11. Cisterna Chyli Located anterior to L1, L2
Collects lymph from lower limbs and from the intestinal trunk that drains the digestive organs
In the intestines, specialized lymphatic capillaries called lacteals that transport absorbed fat from the small intestine to the blood stream
Fatty lymph is called chyle

12. lymphatic duct into vein
Regional
lymph nodes:
Internal jugular vein
Cervical nodes
Entrance of right
lymphatic duct into vein
Entrance of thoracic
duct into vein
Axillary nodes
Thoracic duct
Cisterna chyli
Aorta
Inguinal nodes
Lymphatic
collecting vessels
Drained by the right
lymphatic duct
Drained by the
thoracic duct
(a) General distribution of lymphatic collecting vessels
and regional lymph nodes.
Figure 20.2a

13. Internal jugular veins Esophagus Right lymphatic duct
Right jugular trunk
Internal jugular veins
Esophagus
Right lymphatic duct
Right subclavian trunk
Trachea
Left subclavian trunk
Right subclavian vein
Left jugular trunk
Right broncho-
mediastinal trunk
Left subclavian vein
Brachiocephalic veins
Entrance of thoracic
duct into vein
Superior vena cava
Left bronchomediastinal
trunk
Azygos vein
Ribs
Thoracic duct
Hemiazygos vein
Cisterna chyli
Right lumbar trunk
Left lumbar trunk
Inferior vena cava
Intestinal trunk
(b) Major lymphatic trunks and ducts in relation to veins and
surrounding structures. Anterior view of thoracic and abdominal wall.
Figure 20.2b

14. Lymph Transport Lymph is propelled by Pulsations of nearby arteries
Contractions of smooth muscle in the walls of the lymphatics
Skeletal muscle contraction
Breathing
Lymph movement is very slow and it depends on movement of adjacent tissues

15. Lymphoid Cells

16. Lymphoid Cells
Lymphocytes arise in red bone marrow and mature into 1 of 2 main varieties
T cells (T lymphocytes)
B cells (B lymphocytes)

17. T cells and B cells protect against antigens
Lymphocytes
T cells and B cells protect against antigens
Antigens are anything that the body perceives as foreign
These antigens will provoke an immune response
Bacteria and their toxins; viruses
Mismatched RBCs or cancer cells

18. Lymphocytes T cells B cells Manage the immune response
Attack and destroy foreign cells
B cells
Produce plasma cells, which secrete antibodies
Antibodies bind to antigens and mark cells for destruction

19. Other Lymphoid Cells
Macrophages phagocytize foreign substances and help activate T cells
Dendritic cells capture antigens and deliver them to lymph nodes
Reticular cells produce stroma that supports other cells in lymphoid organs (structural cells)

20. Macrophage Reticular cells on reticular fibers Lymphocytes
Medullary sinus
Reticular fiber
Figure 20.3

21. Types of Lymphoid Tissue
Diffuse lymphoid tissue
Lymphoid follicles (or nodes)

22. Diffuse Lymphoid Tissue
Loose arrangement of lymphoid cells and some reticular fibers
Found in virtually every body organ
Larger collections appear in mucous membrane areas, like the GI and respiratory tract

23. Principal lymphoid organs of the body
Lymph Nodes
Principal lymphoid organs of the body
Embedded in connective tissue, in clusters along lymphatic vessels
Near the body surface in inguinal, axillary, and cervical regions of the body
These are clinically important, as they are palpable on PE
Firm, somewhat rubbery non-fixed mass the size of a pea or larger

24. lymphatic duct into vein
Regional
lymph nodes:
Internal jugular vein
Cervical nodes
Entrance of right
lymphatic duct into vein
Entrance of thoracic
duct into vein
Axillary nodes
Thoracic duct
Cisterna chyli
Aorta
Inguinal nodes
Lymphatic
collecting vessels
Drained by the right
lymphatic duct
Drained by the
thoracic duct
(a) General distribution of lymphatic collecting vessels
and regional lymph nodes.
Figure 20.2a

25. Lymph Nodes
Functions
Filter lymph—macrophages destroy microorganisms and debris
Immune system—lymphocytes are activated and mount an attack against antigens

26. Structure of a Lymph Node
Surrounded by a dense, fibrous capsule, from which connective tissue strands called trabeculae extend inward dividing the node into compartments (follicles)
2 histologically distinct regions
Cortex
Superficial and deep
Medulla

27. Structure of a Lymph Node
Cortex
Superficial
Made up of follicles with germinal centers where B cells divide and proliferate
Deep
houses T cells
T cells circulate continuously between the blood, lymph nodes, and lymph, performing their surveillance role

28. Structure of a Lymph Node
Medulla
Medullary cords are thin inward extensions from the cortical lymphoid tissue and contain both types of lymphocytes
Lymph sinuses
Large lymph capillaries where macrophages reside and phagocytize foreign matter in the lymph as it flows by in the sinuses

29. Circulation in the Lymph Node
Lymph enters through many afferent vessels on convex side  large subcapsular sinus  smaller sinuses that cut through the cortex  medullary sinuses  exits node at hilum (indented region on concave side) with few efferent vessels

30. Circulation in the Lymph Node
Less efferent vessels, so the flow of lymph stagnates somewhat, allowing time for lymphocytes and macrophages to work
Lymph passes through several nodes before it is cleansed

31. (a) Longitudinal view of the internal structure of a lymph
Figure 20.4a
Afferent lymphatic
vessels
Efferent lymphatic
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

32. (b) Photomicrograph of part of a lymph node (72x)
Follicles
Trabecula
Subcapsular sinus
Capsule
Medullary cords
Medullary sinuses
(b) Photomicrograph of part of a lymph node (72x)
Figure 20.4b

33. Largest lymphoid organ, size of a fist
Spleen
Largest lymphoid organ, size of a fist
Located in the left side of the abdominal cavity, just beneath the diaphragm, lateral to the stomach
Blood supply
Splenic artery and vein that enter and exit the hilum (concave anterior surface)

36. (c) Photograph of the spleen in its normal position
Diaphragm
Spleen
Adrenal
gland
Left
kidney
Splenic
artery
Pancreas
(c) Photograph of the spleen in its normal position
in the abdominal cavity, anterior view.
Figure 20.6c

37. Spleen Function Functions
Site of lymphocyte proliferation and immune surveillance and response
Cleanses the blood of aged cells and platelets and debris

38. Spleen
Stores breakdown products of RBCs (e.g., iron) for later reuse
Releases other breakdown products to the blood for processing in the liver
Stores blood platelets and monocytes to be released when needed
Contains lymphocytes, macrophages, and huge numbers of erythrocytes

39. Histological Structure of the Spleen
Has a fibrous capsule and trabeculae
Two distinct areas
White pulp
Red pulp

40. Histological Structure of Spleen
White Pulp
Where immune function takes place
Composed mostly of lymphocytes suspended on reticular fibers
White pulp forms clusters around central arteries (small branches of the splenic artery) and form what appear to be islands in a sea of red pulp

41. Histological Structure of the Spleen
Red Pulp
Where worn out RBCs and bloodborne pathogens are destroyed
Contains lots of RBCs and macrophages that engulf the RBCs
Consists of splenic tissue that is not white pulp (the rest of the spleen)
Splenic sinuses (venous sinuses)
Splenic cords (reticular CT that separates splenic sinuses)

42. Thymus

43. Thymus
Size with age
In infants, it is found in the inferior neck and extends into the mediastinum, where it partially overlies the heart
Increases in size and is most active during childhood
Stops growing during adolescence and then gradually atrophies

44. Thymus
T lymphocyte precursors mature into T lymphocytes
Even though the gland atrophies, it continues to produce immunocompetent cells as we age, though at a declining rate

45. MALT

46. Mucosa-associated lymphoid tissue (MALT)
Lymphoid tissues present in all mucous membranes of the body
Function: filter and remove potential pathogens
Largest groupings are tonsils, Peyer’s patches in small intestine, and appendix
Also present in the mucosa of the respiratory tract (bronchi), genitourinary (GU) organs and the rest of the GI tract

47. Tonsils

48. Tonsils Simplest lymphoid organs
Form a ring of lymphatic tissue around the pharynx
Palatine tonsils
Located on either side at the posterior end of the oral cavity. Largest of the three types
Lingual tonsils
Located at the base of the tongue. Look lumpy.
Pharyngeal tonsil
Posterior wall of the nasopharynx
Aka adenoids

49. Tonsils
Function
Gather and remove pathogens entering the pharynx in food or inhaled air

50. Pharyngeal tonsil Palatine tonsil Lingual tonsil Tonsil
Tonsillar crypt
Germinal centers
in lymphoid follicles
Figure 20.8

51. Peyer’s Patches

52. Peyer’s Patches Peyer’s patches Clusters of lymphoid follicles
In the wall of the distal portion of the small intestine
Small intestine does most of the filtration and absorption of food, so it is important to have lymphoid tissue present to help filter out the pathogens/undesirable materials unwanted in the bloodstream
Destroy bacteria, preventing them from breaching the intestinal wall
Generate “memory” lymphocytes for long term immunity

53. Lymphoid nodules (follicles) of Peyer’s patch Smooth muscle in
the intestinal wall
Figure 20.9

54. Appendix

55. Appendix
Appendix
Tubular offshoot of the first part of the large intestine
Contains high concentration of lymphoid follicles
Destroy bacteria, preventing them from breaching the intestinal wall
Generate “memory” lymphocytes for long term immunity

57. REVIEW

58. collect excess fluid from interstitial spaces.
Lymphatic vessels:
collect excess fluid from interstitial spaces.
drain blood from lymph nodes.
are part of the venous system.
are built like arteries.
Answer: a. collect excess fluid from interstitial spaces.

59. Lymphatic capillaries owe their permeability to the presence of:
an open end that siphons fluid from the interstitial fluid.
minivalves in their walls.
tight junctions between adjacent cells.
proteins in the lymph fluid.
Answer: b. minivalves in their walls.

60. Surgery always results in tissue swelling.
Why would removal of lymph vessels from the right axillary region cause edema in the right arm?
Excess blood plasma builds up in regions where there are no lymph vessels.
Surgery always results in tissue swelling.
Blood is inefficiently circulated in areas where surgery has occurred.
Both b and c are true.
Answer: a. Excess blood plasma builds up in regions where there are no lymph vessels.

61. Blood capillaries, arteries, lymphatic vessels, subclavian vein
Which of the following represents a logical sequence of structures that contribute to the return of fluid into the blood via the lymphatic system?
Blood capillaries, arteries, lymphatic vessels, subclavian vein
Arteries, lymphatic vessels, blood capillaries, subclavian vein
Arteries, blood capillaries, lymphatic vessels, subclavian vein
Subclavian vein, arteries, blood capillaries, lymphatic vessels
Answer: c. Arteries, blood capillaries, lymphatic vessels, subclavian vein

62. The pumping of the heart
Which of the following contribute(s) to the flow of lymph through lymphatic vessels?
The pumping of the heart
The milking action of skeletal muscle contraction
Pressure changes in the thorax that result from breathing
Both b and c
Answer: d. Both b and c

63. Which of the following would the body perceive as an antigen?
Bacteria
Virus
Mismatched red blood cell
All of the above
Answer: d. All of the above

64. all of the above take place.
An advantage to having reticular connective tissue present in lymph nodes would be that:
the loose organization of reticular connective tissue provides niches for macrophages and lymphocytes.
lymph filters through the nodes and is exposed to lymphocytes and macrophages.
lymphocytes cycle to various areas of the body and back to lymph nodes.
all of the above take place.
Answer: d. all of the above take place.

65. The highest density of lymph nodes can be found ________.
in the arms and legs
in the brain
at the locations where lymphatic collecting vessels converge
in the intestines
Answer: c. at the locations where lymphatic collecting vessels converge

66. Lymph tends to stall inside lymph nodes. This is due to:
small-diameter spaces within the medulla.
the large volume of lymph entering the node.
fewer efferent lymphatic vessels than afferent lymphatic vessels.
fewer afferent lymphatic vessels than efferent lymphatic vessels.
Answer: c. fewer efferent lymphatic vessels than afferent lymphatic vessels.

67. _________ can enter lymph capillaries.
Bacteria
Large proteins
Interstitial fluid
All of the above
Answer: d. All of the above

68. The ______ is the largest lymphoid organ.
lymph node
Spleen
Thymus
tonsil
Answer: b. spleen

69. immunity; new red blood cell formation
Red pulp of the spleen is most concerned with _______, while white pulp is most concerned with _________.
immunity; new red blood cell formation
filtering lymph; T lymphocyte formation
blood filtering; immunity
urine formation; blood filtering
Answer: c. blood filtering; immunity

70. Which of the following lymphoid tissues removes defective red blood cells from the blood?
Lymph node
Thymus
Spleen
Peyer’s patches
Answer: c. Spleen

71. The thymus is important for:
T lymphocyte maturation.
removal of foreign antigens.
B lymphocyte maturation.
secretion of hormones that promote B lymphocyte immunocompetence.
Answer: a. T lymphocyte maturation.

72. Tonsils promote memory of pathogens by:
secreting antibodies into the blood.
trapping food particles to support bacterial growth.
trapping pathogens to develop immune cells with memory.
producing B lymphocytes.
Answer: c. trapping pathogens to develop immune cells with memory.