1. The Lymphatic System 20

2. Lymphatic System: Overview
The lymphatic system is:
A network of lymphatic vessels and lymphoid tissues and organs scattered throughout the body
Includes the lymph vessels, lymph nodes, spleen, thymus, tonsils and appendix

3. Lymphatic System Functions:
Returns fluid and leaked plasma proteins back to the blood
Lymph – interstitial fluid/plasma once it has entered lymphatic vessels
Houses WBC that defend the body

4. Lymphatic System: Overview
Figure 20.2a

5. Lymphatic System: Overview
Figure 20.1a

6. the principal lymphoid organs of the body
Lymph Nodes
the principal lymphoid organs of the body
Monitor cell debris in the lymph
Their two basic functions are:
Filters out debris
monitor for antigens and mount an immune attack against them

7. Structure of a Lymph Node
Figure 20.4a, b

8. Afferent
lymphatic
vessels
Cortex:
• Lymphoid follicle
• Germinal center
• Subcapsular sinus
Efferent
lymphatic
vessels
Follicles
Trabecula
Subcapsular
sinus
Hilum
Medulla:
Capsule
• Medullary
cord
• Medullary
sinus
Medullary
cords
Medullary
sinuses
Trabeculae
(a)
Capsule
(b)

9. Largest lymphoid organ, Functions
Spleen
Largest lymphoid organ,
Functions
Site of lymphocyte rapid growth
White blood cells
Immune surveillance and response
Cleanses the blood

10. Tonsils (in
pharyngeal
region)
Thymus (in
thorax; most
active during
youth)
Spleen (curves
around left side
of stomach)
Peyer’s patches
(in intestine)
Appendix

11. Structure of the Spleen
Capsule
Trabecula
Splenic cords
Venous sinuses
Red pulp
White pulp
Hilum
Splenic artery
Central artery
Splenic vein
Arterioles and
capillaries
(a)
(b)
Splenic artery
Splenic vein
Diaphragm
Capsule
Spleen
Adrenal
gland
Left
kidney
White pulp
Splenic
artery
Red pulp
Pancreas
(c)
(d)

12. Additional Spleen Functions
Stores breakdown products of RBCs for later reuse
Spleen macrophages salvage and store iron for later use by bone marrow
Stores blood platelets

13. Thymus
organ that secretes hormones (thymosin) that cause T lymphocytes to mature
functions strictly in the maturing of T lymphocytes
does not directly fight antigens

14. Tonsils (in
pharyngeal
region)
Thymus (in
thorax; most
active during
youth)
Spleen (curves
around left side
of stomach)
Peyer’s patches
(in intestine)
Appendix

15. Thymic
(Hassall’s)
corpuscle
Medulla
Cortex

16. trap and destroy bacteria and particulate matter
Tonsils
Simplest lymphoid organs; form a ring of lymphatic tissue around the pharynx
trap and destroy bacteria and particulate matter

17. Tonsils (in
pharyngeal
region)
Thymus (in
thorax; most
active during
youth)
Spleen (curves
around left side
of stomach)
Peyer’s patches
(in intestine)
Appendix

18. Aggregates of Lymphoid Follicles
appendix:
Destroy bacteria, preventing them from breaching the intestinal wall
Generate “memory” lymphocytes for long-term immunity

19. Tonsils (in
pharyngeal
region)
Thymus (in
thorax; most
active during
youth)
Spleen (curves
around left side
of stomach)
Peyer’s patches
(in intestine)
Appendix