1. Lymphatic System

2. Lymph & Lymphatic Vessels
Lymphatic system functions
Transport and house lymphocytes and other immune cells
Return excess fluid in body tissues to blood to maintain blood volume
Lymphatic system components
Lymph vessels, lymphatic issues and organs
Lymph is the fluid transported within lymph vessels

3. Lymph & Lymphatic Capillaries
Characteristics of lymph
Some fluid leaves blood capillaries and is not reabsorbed by them
This interstitial fluid moves into lymphatic capillaries where it is then called lymph
Components of lymph
Water, dissolved solutes, and small amount of protein
Sometimes cell debris, pathogens, or cancer cells

4. Lymphatic capillaries
Small, closed-ended vessels that absorb interstitial fluid
Interspersed around most blood capillaries
Absent in avascular tissues, red marrow, spleen, and CNS
Slightly larger than blood capillaries; no basement membrane
Walls are made of overlapping endothelial cells
Have flaps between cells through which fluid enters but can’t exit
Anchoring filaments hold endothelial cells to nearby structures

6. Movement of lymph into lymphatic capillaries
Hydrostatic pressure of interstitial fluid pushes it into capillary
Anchoring filaments linking endothelial cells to surrounding structures prevent vessel collapse
Pressure of lymph inside vessel forces intercellular openings (“flaps”) of capillary wall to close with lymph inside
Lymph moves through vessels of larger and larger size
Lymphatic capillaries, lymphatic vessels, lymphatic trunks, and lymphatic ducts
Ultimately, fluid is returned to blood circulation

7. Lymphatic Vessels, Trunks, and Ducts
Lymphatic vessels are fed by lymphatic capillaries
Located adjacent to arteries and veins
Have all three vessel tunics (intima, media, externa)
Have valves to prevent pooling and backflow of lymph
Lymphatic system lacks a pump; moves lymph using:
Skeletal muscles and respiratory pumps (as seen in veins)
Pulsatile movement of blood in nearby arteries
Rhythmic contraction of smooth muscle in larger lymph vessel walls
Some vessels connect to lymph nodes for lymph filtration

8. Lymphatic trunks are fed by lymphatic vessels
Jugular trunks drain lymph from head and neck
Subclavian trunks drain upper limbs, breasts, and superficial thoracic wall
Bronchomediastinal trunks drain deep thoracic structures
Intestinal trunks drain most abdominal structures
Lumbar trunks drain lower limbs, abdominopelvic wall, and pelvic organs

9. Lymphatic ducts are fed by lymphatic trunks
Largest lymphatic vessels
Bring lymph to venous blood circulation
There are two: right lymphatic duct and thoracic duct
Right lymphatic duct is near right clavicle
Drains upper right quadrant of body
Right side of head and neck, right upper limb, and right side of thorax
Delivers lymph to junction of right subclavian and right internal jugular veins
Thoracic duct is largest lymphatic vessel
Runs from diaphragm to junction of left subclavian and left jugular veins
Saclike cisterna chyli at its base
Receives lipid-rich chyle from GI tract
Drains lymph from left side of head and neck, left upper limb, left side of thorax, abdomen, and both lower limbs

11. Lymphedema
Accumulation of interstitial fluid due to interference with lymphatic drainage
Causes swelling and pain in affected area
May interfere with wound healing and contribute to infection
Most caused by blockage of lymph vessels
E.g., trauma or infection of lymph vessels or tumors
E.g., radiation therapy scarring or surgical removal of lymph nodes
Controlled with compression garments, exercise, massage
Extreme cases known as elephantiasis
Caused by infection with parasitic worms

12. Overview of Lymphatic Tissue and Organs
Primary lymphatic structures
Involved in formation and maturation of lymphocytes
Red bone marrow and thymus
Secondary lymphatic structures
Do not form lymphocytes, but house them and other immune cells
Sites of immune response initiation
Include lymph nodes, spleen, tonsils, and lymphatic nodules
Include MALT (mucosa-associated lymphatic tissue)

13. Primary Structures: Red Bone Marrow
Located between trabeculae of spongy bone
In flat bones of skull, ribs, and sternum, vertebrae, ossa coxae, heads of humerus and femur
Site of hemopoiesis: production of blood’s formed elements
Formed elements include T-lymphocytes and B- lymphocytes
T-lymphocytes migrate to thymus to complete maturation

14. Primary Structures: Thymus
The thymus is involved in T-lymphocyte maturation
Located in mediastinum
Larger in children than adults
Grows until puberty, then regresses; gradually replaced by adipose tissue
Consists of two thymic lobes, each surrounded by connective tissue capsule
Trabeculae of capsules subdivide lobes into lobules
Each lobule has outer cortex and inner medulla regions
Both regions are lymphoepithelial (contain lymphatic cells and epithelial tissue)
Cortex contains immature T-lymphocytes
Medulla contains mature T-lymphocytes

16. Secondary Lymphatic Structures
House lymphocytes and other immune cells within a reticular connective tissue matrix
Organized into lymphatic organs and aggregates of lymphatic nodules
Organs have a complete capsule of dense irregular connective tissue
Spleen and lymph nodes
Other lymphatic structures have an incomplete capsule or lack one
Tonsils, MALT, diffuse lymphatic nodules

17. Secondary Structures: Lymph Nodes
Lymph nodes filter lymph, remove unwanted substances
Small, oval, encapsulated structures
Located along deep and superficial pathways of lymph vessels
Occur in clusters receiving lymph from body regions
Cervical lymph nodes receive lymph from head, neck
Axillary lymph nodes receive lymph from breast, axilla, and upper limb
Inguinal lymph nodes in groin receive lymph from lower limb and pelvis

18. Lymph node components Afferent lymphatic vessels bring lymph to node
An efferent vessel drains a lymph node
Located at hilum (involuted portion of node)
Dense connective tissue capsule encloses node
Trabeculae of capsule subdivide node into compartments
Outer cortex, inner medulla

19. The cortex contains lymphatic nodules
Reticular fibers support a germinal center
Houses proliferating B-lymphocytes and some macrophages
Surrounding mantle zone contains T- lymphocytes, macrophages, and dendritic cells
Cortical sinuses are tiny open channels lined by macrophages

20. Lymph flow through nodes
Lymph enters through several afferent vessels
Creates pressure to push it through node to the single exit vessel
Lymph is monitored for presence of foreign material
Macrophages remove foreign debris from lymph
Lymphocytes may initiate immune response
Lymphocytes proliferate especially in germinal centers
Can cause enlarged nodes that can be palpated in neck and axilla
Lymph exits node through efferent vessel
May then pass to neighboring lymph node

22. Lymphoma Malignant neoplasm from lymphatic structures
Nontender, enlarged lymph node
Possible night sweats, fever, and weight loss
Hodgkin lymphoma
Affects young adults and people over 60
If caught early, cured by excision, radiation, and chemotherapy
Non-Hodgkin lymphoma
More common
Some kinds aggressive, others slow growing

23. Secondary Structures: Spleen
The spleen is the largest lymphatic organ
Located in left upper abdominal quadrant
Lateral to left kidney and posterolateral to stomach
Posterolateral aspect is convex and rounded
Anteromedial border is concave
Hilum: indentation where blood vessels and nerves enter
Splenic artery supplies blood; splenic vein drains it
Surrounded by connective tissue capsule
Trabeculae from capsule extend into spleen dividing red and white pulp

24. Tissues of the spleen White pulp Red pulp
Clusters of T- and B-lymphocytes and macrophages around central artery
Red pulp
Contains erythrocytes, platelets, macrophages, and B-lymphocytes
Splenic cords: cells and reticular connective tissue in red pulp
Splenic sinusoids: very permeable capillaries
Storage site for erythrocytes and platelets

25. Monitoring blood as it flows through the spleen
The spleen filters and monitors blood (not lymph)
White pulp monitors it for foreign materials and bacteria
Macrophages in sinusoids of red pulp remove particles
Phagocytize bacteria, debris, defective erythrocytes and platelets
Path of flow: splenic artery, central artery, sinusoids, venules, splenic vein
Summary of functions: eat foreign particles, clear defective erythrocytes and platelets, store erythrocytes and platelets
In first 5 months of fetal life, spleen makes blood cells
This function can be reactivated under certain conditions
E.g., some hematologic disorders

26. Secondary Structures: Tonsils
Immune surveillance of inhaled and ingested substances
Tonsillar crypts
Invaginations that trap material
Contain lymphatic nodules
Some with germinal centers

27. Secondary Structures: Nodules
Clusters of lymphatic cells with some extracellular matrix
Not completely surrounded by connective tissue capsule
Scattered nodules termed diffuse lymphatic tissue
Found in every body organ
Help defend against infection
In some areas, group together to form larger structures
E.g., MALT

28. Secondary Structures: MALT
Mucosa-associated lymphatic tissue
Located in gastrointestinal, respiratory, genital, and urinary tracts
Found in lamina propria of the mucosa
Help defend against foreign substances
Prominent in small intestines, especially ileum
Peyer patches: large collections of lymphatic nodules within the wall of the GI tract