1. Chapter 20 The Lymphatic System
Use the video clip: CH 20 - Lymph Node Anatomy
for a review of lymph node structure
G.R. Pitts, J.R. Schiller, and James F. Thompson, Ph.D.

2. The Lymphatic System Basic organization Functions
Lymph fluid in lymph vessels
Structures: organs with lymphatic tissue, red bone marrow, liver and spleen
Functions
return interstitial fluid and proteins to the blood
transport dietary fats to adipose tissue
protect against cancer & infection
resistance - fight off disease
nonspecific resistance - general protection against disease
immunity - specific protection
susceptibility - lack of resistance

3. Lymph Flow
More fluid moves out of the blood capillaries by filtration than returns by reabsorption - Starling’s Law
≈ 3Ll day of lymph is generated
Proteins escaped from the blood or secreted by tissues are transferred back to the blood by the lymphatics
Lymph flow is facilitated by muscle pumps, the respiratory pump, valves, and smooth muscle (in the walls of the trunks & thoracic duct)
Smaller vessels drain into larger vessels

4. Lymphatic Capillaries
“Blind ended,” covered vessels between cells, larger than capillaries
Not found in avascular tissues (CNS, cartilage) nor in the splenic pulp, and bone marrow

5. Lymphatic Capillaries
Structure/Function regulates fluid flow
Anchoring filaments - from lymphatic endothelium attach to surrounding tissues
Endothelial cells overlap
high hydrostatic fluid pressure separates cells, fluid into caps
hydrostatic fluid pressure in cap prevents fluid movement out
minivalve

6. Lymph Flow Follows Venous Circulation
Lymph vessels have the same organization and routing as the vascular tree

7. Lymphatic Flow (cont.) Lymphatic vessels have no separate pump (heart)
All lymph returns to the vena cava and to the right side of the heart

8. Lymphatic Flow (cont.) Lymph ducts Right lymphatic duct
about ½ inch long
drains lymph from upper right side of body (arm & head)
Thoracic (left) duct
main collecting duct of the lymphatic system
38-45 cm long
drains 75% of body
begins as a dilation known as the cisterna chyli located anterior to lumbar disk #2

9. Lymphatic Flow (cont.)
Lymph returns to the venous drainage through right and left lymphatic ducts at the junction of the internal jugular and subclavian veins

10. Summary of Lymphatic Vessels
Lymph Flow from smallest to largest:
Capillaries  vessels  trunks  ducts
Lymph vessels anastomose and supply and drain lymph nodes along their course

11. Two Main Types Of Lymphocytes
B lymphocytes = B cells
attack microbes, especially bacteria
develop into plasma cells to produce antibodies (Ab)
bind to antigen to form antibody-antigen (Ag-Ab) complexes
complexes prevents Ag from interacting with other body cells or molecules
memory B cells – dormant until future exposure to Ag
T lymphocytes = T cells
regulate many immune responses
attack viruses, fungi, transplants, cancer, some bacteria
4 types of T cells
cytotoxic (killer) T cells - destroy foreign invaders
helper T cells - assist B cells and cytotoxic T cells
suppressor T cells – help bring immune response to an end
memory T cells - dormant until future exposure to Ag

12. Lymphocyte Development
primary lymphatic organs - site of lymphocyte (B cell and T cell) production
bone marrow - produces B cells, immature T cells
T cells migrate to the thymus gland to mature or die if determined to be improper
secondary lymphatic organs
sites of activated immune responses
lymphatic nodules (lymph follicles)
lymph nodes, spleen, tonsils

13. Other Lymphoid Tissue Cells
Macrophages & Dendritic cells
Phagocytize foreign substances and cells
Transport them to lymphatic tissues
Process foreign things into individual antigens
Present Ags to T & B lymphocyte to help activate them
Reticular cells
Similar to fibroblasts
Produce reticular fibers (stroma) that provide the framing structure for other cells in lymphoid organs

14. Lymphatic Tissue - General
Stroma of reticular connective tissue (except thymus)
Parenchyma of macrophages, B and T lymphocytes, occasional other leukocytes
May or may not have a connective tissue capsule

15. Lymphatic Organs – Thymus Gland
Two lobes between the sternum and the heart
Thymocytes produce hormones
Atrophies with age (starting ~20)
Structure/Function
Outer cortex – immature T cells
screened for functional capacity
stimulated to proliferation
stimulated to maturation
Inner medulla
defective T cells degenerate
mature T cells move into blood

16. Lymphatic Organs – Lymph Nodes
Anatomy
oval, bean shaped small structures scattered throughout body along lymph vessels
may be deep or superficial
concentrated along the respiratory tree and GI tract, in the mammary glands, axillae, and groin
filter lymph fluid to trap foreign organisms, cell debris, and tumor cells

17. Circulation in the Lymph Nodes
Lymph enters via a number of afferent lymphatic vessels
It then enters a large subcapsular sinus and travels into a number of smaller sinuses
It meanders through these sinuses and exits the node at the hilus via efferent vessels
The node acts as a “settling tank,” because there are fewer efferent vessels, lymph stagnates somewhat in the node
This allows lymphocytes and macrophages time to carry out their protective functions
Only lymph nodes filter lymph!

18. Cancer Metastasizes To Lymph Nodes
Cancer cells from the tumor are first trapped in a lymph node

19. Lymphatic Organs - Spleen
largest lymphoid organ in the body
fibrous capsule with arteries, veins, and efferent lymph vessels
located between stomach and diaphragm

20. Spleen Functions: White Pulp
a site of immune surveillance and response
macrophages phagocytize bacteria, worn-out RBC's, platelets
hemoglobin is recycled and components transferred to liver
macrophage antigen-presentation and lymphocyte activation and proliferation
some B cells mature into plasma cells

21. Spleen Functions: Red Pulp
Site of fetal erythrocyte production (normally ceases after birth)
Stores ~ 1 L of blood which can be released during an emergency (hemorrhage)

22. Unencapsulated Lymphatic Tissue
Diffuse lymphatic tissue
Small scattered patchs
In nearly every organ
Lymphoid follicles (nodules)
More organized, more cellular clusters
small
bronchus

23. Mucosa-Associated Lymphatic Tissue (MALT)
found in the lamina propria of mucous membranes of the GI tract, respiratory tract, urinary tract, and reproductive tract
Peyer’s patches
in the intestines

24. Lymphatic Organs - Tonsils
lymphoid tissue beneath the mucosae
tonsilar crypts trap micro-organisms
immune cells destroy the micro-organisms
palantine tonsils – largest and most frequently infected

25. Lymphadenopathy
Enlarged lymph nodes due to increased drainage from inflammatory lesions or infections.
Associated with malignant and nonmalignant diseases.
Lymphocyte leukemia with severe lymphadenopathy

26. Hodgkin’s Disease: one of the significant malignant lymphomas
Cervical
lymph nodes

27. Burkitt’s Lymphoma Commonly found in central Africa and New Guinea.
Associated with Epstein-Barr virus which causes infectious mononucleiosis in North America and Europe.
Rarer American type has extensive marrow replacement.
Cancerous cell is a B lymphocyte.

28. End Chapter 20