1. Chapter 24 Lymphatic System

2. Function of Lymphatic System
Transport excess interstitial fluid, called lymph in lymphatic system
interstitial fluid is fluid around cells; extracellular fluid includes interstitial fluid and blood plasma
Maintain fluid homeostasis
Check lymph for foreign material
Initiate immune response

3. Structure of Lymphatic System
Fig. 24.2
Structure of Lymphatic System
(a) Capillary bed and lymphatic capillaries
Arteriole
Tissue cells
Lymphatic
capillaries
Interstitial fluid
Capillary bed
Venule
Lymph vessels absorb excess fluid around capillary beds
arterial end of capillary bed forces fluid into interstitial space around cells
venous end of capillary bed reabsorbs most but not all fluid
Lymph vessels transport lipids and lipid- soluble vitamins from gastrointestinal tract around body

4. Structure of Lymphatic System
Fig. 24.2
Interstitial fluid
Capillary bed
Venule
Structure of Lymphatic System
Anchoring filament
Lymphatic
capillaries
Lymph
Tissue cells
Opening
Arteriole
Interstitial fluid
Endothelium of
lymphatic capillary
(a) Capillary bed and lymphatic capillaries
(b) Lymphatic capillary
Lymphatic capillaries are closed-end vessels interspersed through capillary beds (except in red bone marrow and CNS)
Larger diameter than blood capillaries; similar structure
Held in place by anchoring filaments

5. Structure of Lymphatic System
Fig. 24.3
(b) Lymphatic vessel, cross section
(a) Lymphatic vessel, longitudinal section
Overlapping
endothelial cells
Structure of
Lymphatic System
Valve open
(lymph flows forward)
Lymph
Direction of
lymph flow
Valve closed
(backflow of lymph is prevented)
LM 100x
Valve
Lymphatic vessel
Lymphatic capillaries merge into lymphatic vessels
Vessels have valves (like veins); prevents pooling of lymph
Lymph from GI tract is white because of fats, called chyle
b: © The McGraw-Hill Companies, Inc./Photo by Dr. Alvin Telser

6. Structure of Lymphatic System
Fig. 24.1
Structure of Lymphatic System
Tonsils
Afferent lymphatic vessels bring lymph to lymph node for filtering
Efferent lymphatic vessels take filtered lymph from lymph nodes
Lymph may pass through several lymph nodes in a cluster
Cervical lymph nodes
Right lymphatic duct
Axillary lymph nodes
Thymus
Thoracic duct
Spleen
Cisterna chyli
Mucosa-associated
lymphatic tissue (MALT) (in small intestine)
Inguinal lymph
nodes
Red bone marrow
Lymph vessels

7. Lymphatic trunks Drain lymph from major body regions
Fig. 24.4
Right jugular trunk
Left internal jugular vein
Right subclavian trunk
Left subclavian vein
Right lymphatic duct
Lymphatic trunks
Right
bronchomediastinal
trunk
Left bronchomediastinal
trunk
Drain lymph from major body regions
Formed from merging vessels
Superior vena cava
Thoracic duct
Lymph nodes
Azygos vein
Hemiazygos vein
Parietal pleura (cut)
Diaphragm
Cisterna chyli
Inferior vena cava
Left lumbar trunk
Intestinal trunk
Right lumbar trunk
(a) Posterior thoracic wall, anterior view

8. Lymphatic trunk drainage
Right jugular trunk
Left internal jugular vein
Right subclavian trunk
Left subclavian vein
Right lymphatic duct
Right
bronchomediastinal
trunk
Left bronchomediastinal
trunk
Jugular trunk; head and neck
Subclavian trunk; upper limbs, breasts, superficial thoracic wall
Bronchomediastinal trunks; deep thoracic structures
Intestinal trunks; most abdominal structures
Lumbar trunks; lower limbs, abdominopelvic wall, pelvic organs
Superior vena cava
Thoracic duct
Lymph nodes
Azygos vein
Hemiazygos vein
Parietal pleura (cut)
Diaphragm
Cisterna chyli
Inferior vena cava
Left lumbar trunk
Intestinal trunk
Right lumbar trunk
(a) Posterior thoracic wall, anterior view
Fig. 24.4

9. Lymphatic ducts Larger than trunks
Right jugular trunk
Left internal jugular vein
Right subclavian trunk
Left subclavian vein
Right lymphatic duct
Right
bronchomediastinal
trunk
Left bronchomediastinal
trunk
Larger than trunks
Lymphatic trunks drain into lymphatic ducts
Lymphatic ducts drain lymph into venous circulation
Cisterna chyli located at base of thoracic duct
receives lymph from left and right intestinal and lumbar trunks
Superior vena cava
Thoracic duct
Lymph nodes
Azygos vein
Hemiazygos vein
Parietal pleura (cut)
Diaphragm
Cisterna chyli
Inferior vena cava
Left lumbar trunk
Intestinal trunk
Right lumbar trunk
Fig. 24.4
(a) Posterior thoracic wall, anterior view

10. Fig. 24.4
Lymphatic ducts
(b) Lymph drainage pattern
Area drained by
right lymphatic duct
Area drained
by thoracic duct
Right lymphatic duct drains into junction of right subclavian vein and right jugular vein
Thoracic duct drains into junction of left subclavian vein and left jugular vein
receives lymph from left side of head and neck, left arm, left thorax, everything inferior to diaphragm

11. © Andy Crumo, TDR, WHO/Science Source
Edema
Edema = swelling
Lymphedema = swelling caused by blockage of lymph system
Usually caused by obstruction
Surgical removal of lymph nodes
Spread of malignant tumors
Scarring from radiation therapy
Trauma or infection
Elephantiasis = extreme lymphedema
In Southeast Asia and Africa, may be caused by filarial worms infecting lymphatic system
Elephantiasis (lymphatic filariasis) of the lower limb.
© Andy Crumo, TDR, WHO/Science Source

12. “Elephant Man,” Joseph Merrick
Condition NOT from edema
Probably caused by neurofibromatosis type I or Proteus syndrome
both pathologies of unchecked tumor growth

13. Lymphatic Structures – Lymph Nodules
Clusters of lymphatic cells with some extracellular connective tissue
Not lymph nodes (nodes have a connective tissue capsule)
Germinal center creates new immune cells
Sometimes many nodules together form larger structures
MALT
tonsils

14. Simple columnar epithelium
Lymphatic Structures –
MALT
Fig (a) MALT in small intestine
Mucosa-associated lymphatic tissue
Located in mucosa of GI, respiratory, genital, urinary tracts
Detect antigens and start immune response
Very prominent in small intestine
Peyer patches are large groups of lymphatic nodules in small intestine
LM 140x
Simple columnar epithelium
of small intestine
MALT (Peyer patches)

15. © Dr. P. Marazzi/Science Source
Lymphatic Structures –
Tonsils
Lymph nodules
Protect pharynx from infection
Frequently inflamed and infected (acute tonsillitis)
Tonsils redden and enlarge
Chronic tonsillitis may require tonsillectomy
© Dr. P. Marazzi/Science Source
Tonsillitis.
LM 40x
Lymphatic nodules
(c) Histology of tonsil

16. Lymphatic Structures – Tonsils
Fig. 24.8
Lymphatic Structures –
Tonsils
Pharyngeal tonsil
Opening of auditory tube
Palate
Palatine tonsil
3 groups
pharyngeal tonsils (AKA adenoids) in posterior wall of nasopharynx
palatine tonsils in posterolateral region of oral cavity
lingual tonsils along posterior 1/3 of tongue
Lingual tonsil
(b) Tonsils

17. Lymphatic Organs – Thymus gland Large in infants and young
Fig (a) Child’s thorax, anterior view
Lymphatic Organs –
Thymus gland
Thyroid gland
Right
lung
Left lung
Thymus
Large in infants and young
Almost nonfunctional in adults
Site where immune cells mature
2 thymic lobes surrounded by connective tissue
Heart
Diaphragm

18. Lymphatic Organs – Thymus gland
Fig. 24.9
Lymphatic Organs –
Thymus gland
Trabecula
Capsule
Cortex
Lobule
trabeculae (AKA septa) are fibrous extensions of capsule around thymus
divide thymus into lobules; each lobule has
outer cortex; immature T-cells
inner medulla; mature T-cells
Medulla contains thymic corpuscles (aged, degenerated cells)
Medulla
LM 20x
(b) Child’s thymus
Lymphocytes
Thymic
corpuscle
Epithelial cells
LM 320x
(c) Thymic corpuscle

19. Lymphatic Organs – Lymph Nodes
Fig
Lymphatic Organs –
Lymph Nodes
Medullary sinus
Medulla
T-lymphocytes
Medullary cord
B-lymphocytes
Germinal center
Dendritic cells
Small, round or oval structures located on lymph vessels
usually in clusters
Surrounded by tough capsule
Internal projections of capsule called trabeculae
Pathway for blood vessels and nerves
Lymphatic nodule
Trabeculae
Afferent lymphatic
vessels
Capsule
Lymphatic nodule
Cortex
Germinal center
Cortical sinus
Hilum
Valve
Efferent lymphatic
vessel
Medullary cords
Medullary sinus
Trabecula
Macrophage
(a) Lymph node and its components
Lymphocytes
Medulla

20. Lymphatic Organs – Lymph Nodes Outer cortex Inner medulla
Fig
Lymphatic Organs –
Lymph Nodes
Medullary sinus
Medulla
T-lymphocytes
Medullary cord
B-lymphocytes
Germinal center
Dendritic cells
Outer cortex
lymphatic nodules
lymphatic sinuses called cortical sinuses
Inner medulla
supported by medullary cords
sinuses called medullary sinuses
Hilum = indented portion of node; origin of efferent vessels
Lymphatic nodule
Trabeculae
Afferent lymphatic
vessels
Capsule
Lymphatic nodule
Cortex
Germinal center
Cortical sinus
Hilum
Valve
Efferent lymphatic
vessel
Medullary cords
Medullary sinus
Trabecula
Macrophage
(a) Lymph node and its components
Lymphocytes
Medulla

21. Fig. 24.10 Trabecula Capsule Germinal center within lymphatic nodule
Lymphatic vessels
Lymphatic nodule
Medullary sinuses
Lymph node
Cortex
Medullary cords
Blood vessels
Medulla
Muscle
LM 20x
(b) Lymph node section
(c) Lymph node and lymphatic vessels

22. Lymphatic Organs – Lymph Nodes
Swelling of lymph nodes indicates immune response (infection)
immune cells replicating and fighting off infection
Swollen, tender lymph nodes in cervical region + sore throat = cold
Swollen, tender lymph nodes all over body + sore throat + fever = mononucleosis
Firm , swollen lymph node (not tender) may = metastatic cancer
Cancer cells from cancer elsewhere in body travel through lymph system, lodge in lymph node and proliferate

23. Lymphatic Organs – Lymph Nodes Lymphoma = cancer of lymph nodes
Page 737
Lymphatic Organs –
Lymph Nodes
LM 1000x
Reed-Sternberg cell, a
characteristic of Hodgkin
lymphoma.
Lymphoma = cancer of lymph nodes
Hodgkin lymphoma usually affects young adults, people >60
double-nucleated Reed-Sternberg cell
Non-Hodgkin lymphoma more common
some kinds very aggressive and usually fatal
some kinds very slow-growing and responsive to treatment

24. Lymphatic Organs – Spleen
Fig
Lymphatic Organs – Spleen
(a) Anterior view of spleen
Largest lymphatic organ
Located between stomach and diaphragm
Diaphragmatic surface convex and rounded
Anteromedial border concave
contains hilum, blood vessels and nerves enter and leave
Surrounded by capsule with trabeculae
branches of splenic artery in trabeculae called trabecular vessels
Diaphragmatic
surface
Diaphragm
Visceral surface
Hilum
Splenic artery
Splenic vein

25. Lymphatic Organs – Spleen
Fig
Lymphatic Organs – Spleen
Central artery
White pulp
Red pulp
Splenic sinusoids
Trabecula
No cortex or medulla
Cells around trabeculae divided into
white pulp
associated with arterial supply
central artery surrounded by lymphatic cells
red pulp
associated with venous supply
splenic cords store extra red blood cells; released when more needed by body, ex. during exercise
splenic sinusoids act like enlarged capillaries; immune cells in lumen destroy old red blood cells
Splenic cords
Capsule
(b) Red and white pulp of spleen
Trabeculae
Red pulp
Central artery
White pulp
Capsule
LM 40x
(c) Histology of spleen