1. Chapter 24 *Lecture Outline
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2. Chapter 24 Outline Functions of the Lymphatic System
Lymph and Lymph Vessels
Lymphatic Cells
Lymphatic Structures
Aging and the Lymphatic System
Development of the Lymphatic System

3. Functions Return interstitial fluid back to the bloodstream
Transport lipids and lipid-soluble vitamins into the bloodstream
3. Production and maturation of lymphocytes
Generate an immune response against
antigens in the interstitial fluid

4. Figure 24.1

5. Components of the Lymphatic System
Lymphatic capillaries
Lymphatic vessels
Lymphatic trunks
Lymphatic ducts
Lymphatic cells
Lymphatic nodules
Lymphatic organs

6. Lymph Lymph is comprised of: Interstitial fluid Solutes
Foreign materials

7. Lymphatic Capillaries
Lymphatic capillaries are closed-ended tubes that are found interspersed among most blood capillary beds.
They resemble blood capillaries but they have overlapping endothelial cells that act as one-way valves allowing interstitial fluid a one-way entrance into lymphatic capillaries.

8. Lymphatic Capillaries
Figure 24.2

9. Lymphatic Capillaries
The gastrointestinal tract contains specialized lymph capillaries called lacteals that collect not only interstitial fluid, but also lipids and lipid-soluble vitamins.
The lymph collected from the gastrointestinal system has a milky color due to the lipid absorption and is called chyle.

10. Lymphatic Vessels
Lymphatic capillaries merge to form lymphatic vessels.
They resemble venules, in that they have components of all three vascular tunics and possess valves similar to veins.
Afferent lymphatic vessels bring lymph to a lymph node.
Efferent lymphatic vessels transport filtered lymph away from the lymph node.

11. Lymphatic Vessels and Valves
Figure 24.3

12. Lymphatic Trunks
Left and right lymphatic trunks form from merging lymphatic vessels. Each trunk drains lymph from a specific region of the body, as follows:
Jugular trunks—head and neck
Subclavian trunks—upper limbs, breasts and
superficial thoracic wall
3. Bronchiomediastinal trunks—deep thoracic
structures
4. Intestinal trunks—most abdominal structures
Lumbar trunks—lower limbs, abdominopelvic
wall and pelvic organs

13. Lymphatic Trunks
Figure 24.4

14. Lymphatic Ducts
Lymphatic ducts are formed from the fusion of lymphatic trunks.
The right lymphatic duct is located deep to the right clavicle and returns lymph at the junction of the right subclavian and internal jugular veins.
The right lymphatic duct returns lymph from the right side of the head and neck, right upper limb and the right side of the thorax.

15. Lymphatic Ducts The thoracic duct is the largest lymphatic vessel.
It begins just inferior to the diaphragm as a rounded saclike structure called the cisterna chyli.
The thoracic duct collects lymph from most of the body (excluding the right lymphatic duct drainage).
The thoracic duct passes through the aortic opening of the diaphragm and returns lymph into the junction between the left subclavian and internal jugular veins.

16. Lymphatic Ducts
Figure 24.4

17. Thoracic Duct
Figure 24.4

18. Lymphatic Cells
There are several types of lymphatic cells that are located in the lymphatic and circulatory systems:
Macrophages=Monocytes (leukocytes)
Nurse cells=Epithelial at Thymus
Dendritic cells=Epithelial at L. Nodules
Lymphocytes=Most abundant

19. Types of Lymphocytes The body contains three types of lymphocytes:
T-lymphocytes (T-cells)
B-lymphocytes (B-cells)
Natural killer (NK cells)
All three cell types migrate through the lymphatic system and search for the presence of antigens.

20. T-Lymphocytes Make up about 70–85% of body lymphocytes
They express a plasma membrane coreceptor (CD) that can recognize a particular antigen
There are several types of T-lymphocytes; two main groups are:
helper T-lymphocytes
cytotoxic T-lymphocytes

21. Helper T-Lymphocytes
Primarily contain the CD4 coreceptor and are referred to as CD4+ cells or T4 cells
Many types of T4 cells, each one responds to a different antigen
T4 cells initiate and oversee the immune response in two ways:
present the antigen to other lymphocytes
secrete cytokines, which are hormones that activate other lymphatic cells

22. Cytotoxic T-Lymphocytes
Also called CD8+ cells or T8 cells, they contain the CD8 coreceptor
Come in direct contact with infected or foreign cells and kill them
Act only after activated by a helper T-lymphocyte that presents an antigen to it

23. Immune Response of T-Lymphocytes
Figure 24.5

24. B-Lymphocytes Make up about 15–30% of body lymphocytes
Contain antigen receptors to only one antigen and produce immunoglobulins or antibodies to that single antigen
B-lymphocytes become activated when presented with an antigen from a helper T-lymphocyte

25. B-Lymphocytes
Most of the activated B-lymphocytes become plasma cells that produce and secrete large amounts of antibodies.
Plasma cells may be either short-lived (less than a week) or long-lived (months or years).
The long-lived B-lymphocytes are called memory B-lymphocytes and confer years or lifetime immunity to certain antigens.

26. B-Lymphocytes and Their Role in the Immune Response
Figure 24.6

27. NK (Natural Killer) Cells
Also called large granular lymphocytes
Relatively small percentage of all lymphocytes
Tend to express the CD16 receptors
Unlike T-cells and B-cells that respond to one antigen, NK cells can kill a wide variety of infected cells and some cancerous cells

28. Types of Lymphocytes

29. Lymphopoiesis Lymphopoiesis is the process of lymphocyte development.
The final result of lymphopoiesis is that the lymphocyte becomes immunocompetent, meaning the cell can participate in the immune response.
All lymphocytes originate in the red bone marrow but their maturation sites differ.

30. Lymphopoiesis
Figure 24.7

31. Lymphatic Nodules
Oval clusters of lymphatic cells with some extracellular matrix but not surrounded by a connective tissue capsule
Center of nodule is called the germinal center; contains proliferating B-lymphocytes and macrophages
T-lymphocytes located outside the germinal center
Lymphatic nodules filter and attack antigens

32. MALT(Mucosa-Associated Lymphatic Tissue)
Lymphatic nodules located in the mucosa of the gastrointestinal, respiratory, genital, and urinary tracts
These nodules monitor and respond to antigens that may enter these tracts
MALT is very prominent in the ileum; these nodules are called Peyer patches

33. MALT in Small Intestine
Figure 24.8

34. Tonsils Located mainly in the pharynx
Large clusters of lymphatic cells and extracellular matrix that do not have a completed surrounding capsule
Outer edges are invaginated to form crypts, which allow for trapping of antigens to be presented to the lymphocytes

35. Tonsils
Figure 24.8

36. Tonsils There are three types of tonsils:
Pharyngeal tonsils (adenoids)—located in the posterosuperior wall of the nasopharynx
Palatine tonsils—located in the posterolateral wall of the oral cavity
Lingual tonsils—located along the posterior one-third of the tongue

37. Lymphatic Organs
Consists of lymphatic cells and extracellular matrix and is completely surrounded by a connective tissue capsule
The main lymphatic organs are:
thymus
lymph nodes
spleen

38. Thymus Bilobed organ located superficial to the heart
Consists of two fused thymic lobes, which are divided into lobules
Each lobule has an outer cortex and an inner medulla
Continues to grow until puberty and then begins to regress in size and function and, in adults, it becomes replaced mostly by adipose connective tissue

39. b,c: © The McGraw-Hill Companies, Inc./Photo by Dr. Alvin Telser
Thymus
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Trabecula
Thyroid gland
Right
lung
Left lung
Thymus
Capsule
Cortex
Lobule
Medulla
Heart
Diaphragm
LM 20x
(b) Child’s thymus
(a) Child’s thorax, anterior view
Lymphocytes
Thymic
corpuscle
Epithelial cells
LM 320x
(c) Thymic corpuscle
b,c: © The McGraw-Hill Companies, Inc./Photo by Dr. Alvin Telser
Figure 24.9

40. Function of Thymus Site of T-lymphocyte differentiation and maturation
Cortex contains immature T-lymphocytes
Medulla contains mature T-lymphocytes
In adulthood, T-lymphocytes can only be produced by cell division and not by the maturation of new cells in the thymus

41. Lymph Nodes
Small, round or oval structures located along the pathway of lymph vessels
Typically found in clusters ranging from 1–25 mm in diameter
The primary function of a lymph node is to filter antigens from the lymph and initiate an immune response

42. Lymph Nodes Most apparent lymph node clusters occur as:
axillary lymph nodes
inguinal lymph nodes
cervical lymph nodes

43. Major Lymph Node Aggregations
Figure 24.1

44. Structure of Lymph Nodes
Surrounded by a tough connective tissue capsule
Internal extensions of the capsule, trabeculae, project into the node
Lymphatic cells surround the trabeculae and lymphatic sinuses provide a pathway for lymph flow

45. Structure of Lymph Nodes
Lymph node is divided into outer cortex and inner medulla
Cortex consists of nodules and sinuses called cortical sinuses
The medulla contains medullary cords and medullary sinuses
Afferent vessels deliver lymph to the node
Lymph exits nodes via efferent vessels at an indentation of the node called the hilum

46. Structure of Lymph Node
Figure 24.10

47. Spleen There are several functions of the spleen:
Initiates an immune response when antigens are found in blood (white pulp function)
Serves as a reservoir for erythrocytes and platelets (red pulp function)
Phagocytizes old, defective erythrocytes and platelets (red pulp function)
Phagocytizes bacteria and other foreign materials

48. Spleen Largest lymphatic organ in body just lateral to left kidney
A splenic artery/vein enter/leave the spleen via a hilum or indentation on its medial surface
Spleen surrounded by a dense irregular connective tissue capsule, which sends extensions called trabeculae into the organ

49. Structure of Spleen
Figure 24.11

50. Spleen
Trabecular vessels (branches of splenic arteries and veins) extend within the trabeculae.
Cells around the trabeculae are subdivided into white pulp and red pulp.
Red pulp surrounds each cluster of white pulp.

51. Red and White Pulp of Spleen
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Central artery
White pulp
Red pulp
Splenic
sinusoids
Trabecula
Splenic cords
Capsule
(b) Red and white pulp of spleen
Trabeculae
Red pulp
Central artery
White pulp
Capsule
LM 40x
Figure 24.11
(c) Histology of spleen
c: © The McGraw-Hill Companies, Inc./Photo by Dr. Alvin Telser

52. Red and White Pulp of Spleen
The white pulp is associated with the arterial supply and consists of T- and B-lymphocytes and macrophages.
In the center of each cluster is a central artery.
The red pulp is associated with the venous supply.
Red pulp consists of splenic cords and splenic sinusoids that contain erythrocytes, platelets, macrophages, and some plasma cells.
Blood cells can easily enter and leave the blood stream in the spleen because of the discontinuous basal lamina of the capillaries in the splenic sinusoids.

53. Lymphatic Structures and Organs

54. Development of the Lymphatic System
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Jugular lymph sacs
Retroperitoneal lymph sac
Cisterna chyli
Posterior lymph sacs
(a) Week 6: Primary lymph sacs form
Developing
right lymphatic duct
Jugular lymph sac
Jugular
lymph sac
Superior vena cava
Superior vena cava
Developing
thoracic duct
Developing thoracic duct
Cisterna chyli
Cisterna chyli
Figure 24.12
Posterior
lymph sac
Posterior
lymph sac
(b) Week 9: Lymph vessels connect
to the lymph sacs
(c) Fetal period: Right lymphatic and thoracic ducts
form; lymph sacs will form lymph nodes

55. Development of the Thymus
Figure 24.13