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prepared by
Leslie Hendon
University of Alabama,
Birmingham
CHAPTER
21
Part 1
The Lymphatic
and Immune
Systems
Copyright © 2011 Pearson Education, Inc.
The Lymphatic System
•  Lymphatic vessels collect excess tissue
fluid and blood proteins from loose
connective tissue and return tissue fluid and
blood proteins to bloodstream
•  Carry fluid to great veins in the neck
•  Fluid flows only toward the heart
•  Once tissue fluid is within lymphatic vessels it
is termed lymph
The Lymphatic and Immune Systems
•  Lymphatic system
•  Main function is to return excess tissue fluid to
blood vascular system
•  Lymphatic vessels collect tissue fluid
•  Immune system
•  Protects our bodies from foreign organisms
•  Confers immunity to disease
•  Main components
•  Lymphocytes, lymphoid tissue, and
lymphoid organs
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Orders of Lymphatic Vessels
•  Lymph capillaries
•  Smallest lymph vessels
•  First to receive lymph
•  Lymphatic collecting vessels
•  Collect from lymph capillaries
•  Lymph nodes are scattered along collection
vessels
•  Lymph trunks
•  Collect lymph from collecting vessels
•  Lymph ducts
•  Empty into veins of the neck
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Copyright © 2011 Pearson Education, Inc.
Lymphatic Capillaries
Lymphatic Capillaries
•  Located near blood capillaries
•  Receive tissue fluid from CT
•  Lacteals—specialized lymphatic capillaries
•  Increased volume of tissue fluid
•  ‘Mini’ valve flaps open and allow fluid to
enter
•  Located in the villi of the small intestines
•  Receive digested fats
•  Fatty lymph—chyle
•  High permeability allows entrance of:
•  Tissue fluid and protein molecules
•  Bacteria, viruses, and cancer cells
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1
Distribution and Features of Lymphatic
Capillaries
Venous system
Lymphatic Collecting Vessels
Arterial system
•  Accompany blood vessels
•  Composed of the same three tunics as blood
vessels
•  Contain more valves than veins do
Heart
Lymphatic system
Lymph duct
Lymph trunk
Lymph node
Lymphatic
collecting
vessels, with
valves
Blood
capillaries
Lymphatic
capillary
(a) Structural relationship between a capillary
bed of the blood vascular system and
lymphatic capillaries
Tissue
fluid
Tissue cell
Blood
capillaries
Lymphatic
capillaries
•  Helps direct the flow of blood
•  Lymph propelled by
Filaments anchored
to connective tissue
•  Skeletal muscles bulging
•  Nearby arteries pulsing
•  Tunica media of the lymph vessels
Endothelial cell
Flaplike minivalve
Fibroblast in loose
connective tissue
(b) Lymphatic capillaries are blind-ended tubes in which
adjacent endothelial cells overlap each other,
forming flaplike minivalves.
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Lymph Nodes
•  Cleanse the lymph of pathogens
•  Human body contains around 500
•  Superficial lymph nodes located in
•  Cervical, axillary, and inguinal regions
•  Deep nodes are
•  Tracheobronchial, aortic, and iliac lymph
nodes
Figure 21.1
•  Lymph flow is unaided by heartbeat
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General Distribution of Lymphatic Collecting
Vessels and Regional Lymph Nodes
Regional
lymph
nodes
Internal
jugular vein
Entrance of
right lymphatic
duct into vein
Entrance of
thoracic duct
into vein
Thoracic
duct
Cisterna
chyli
Cervical
nodes
Axillary
nodes
Aorta
Inguinal
nodes
Lymphatic
collecting
vessels
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Microscopic Anatomy of a Lymph Node
Drained by the right
lymphatic duct
Drained by the
thoracic duct
Figure 21.2
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Microscopic Anatomy of a Lymph Node
Cortex
Afferent
lymphatic
vessels
•  Fibrous capsule—surrounds lymph nodes
•  Trabeculae—connective tissue strands
•  Lymph vessels
Lymphoid follicle
Germinal center
Subcapsular sinus
Efferent lymphatic
vessels
•  Afferent lymphatic vessels
•  Efferent lymphatic vessels
Hilum
Medulla
Medullary cord
Medullary sinus
Capsule
Trabeculae
(a) Longitudinal view of the internal structure
of a lymph node and associated lymphatics
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Copyright © 2011 Pearson Education, Inc.
Figure 21.3a
2
Microscopic Anatomy of a Lymph Node
Microscopic Anatomy of a Lymph Node
Macrophage
Follicles
Trabecula
Reticular cells
on reticular
fibers
Subcapsular
sinus
Lymphocytes
Capsule
Medullary
sinus
Reticular
fiber
Medullary
cords
Medullary
sinuses
(c) Reticular tissue within the medullary sinus (540X)
(b) Photomicrograph of part of a lymph node (14X)
Figure 21.3b
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Lymph Trunks
Figure 21.3c
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The Lymphatic Trunks
•  Lymphatic collecting vessels converge
•  Five major lymph trunks
•  Lumbar trunks
•  Receives lymph from lower limbs
•  Intestinal trunk
•  Receives chyle from digestive organs
•  Bronchomediastinal trunks
•  Collects lymph from thoracic viscera
•  Subclavian trunks
•  Receive lymph from upper limbs and thoracic wall
•  Jugular trunks
•  Drain lymph from the head and neck
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Right jugular trunk
Right lymphatic duct
Right subclavian
trunk
Right subclavian vein
Right bronchomediastinal trunk
Brachiocephalic veins
Superior vena cava
Internal jugular veins
Azygos vein
Esophagus
Trachea
Left jugular trunk
Left subclavian trunk
Left subclavian vein
Entrance of thoracic
duct into vein
Left bronchomediastinal trunk
Ribs
Thoracic duct
Cisterna chyli
Hemiazygos vein
Right lumbar trunk
Left lumbar trunk
Inferior vena cava
Intestinal trunk
(a) Major lymphatic trunks and ducts in relation to veins
and surrounding structures, anterior view
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The Lymphatic Trunks
Thoracic duct
Figure 21.4a
Lymph Ducts
Aorta
•  Cisterna chyli
Azygos vein
on vertebral
bodies
•  Located at the union of lumbar and intestinal trunks
•  Thoracic duct
•  Ascends along vertebral bodies
•  Empties into venous circulation
•  Junction of left internal jugular and left subclavian
veins
•  Drains three quarters of the body
•  Right lymphatic duct
•  Empties into right internal jugular and subclavian
veins
(b) Thoracic duct (colored green)
along the posterior thoracic wall
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Figure 21.4b
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3
The Immune System
Role of Lymphocytes
Recognizes specific foreign molecules
Destroys pathogens effectively
Key cells—lymphocytes
Also includes lymphoid tissue and lymphoid
organs
•  Lymphoid organs include:
•  Infectious organisms attacked by
inflammatory response
• 
• 
• 
• 
•  Lymph nodes, spleen, thymus, tonsils,
aggregated lymphoid nodules, and appendix
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•  Macrophages, then lymphocytes
•  Are effective fighters of infectious organisms
•  Each lymphocyte recognizes a specific foreign
molecule
•  Antigens are any molecules inducing a
response from a lymphocyte
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Lymphocytes
Lymphocytes
•  B lymphocytes and T lymphocytes are the
two main classes of lymphocytes
•  Cytotoxic T lymphocytes
•  B lymphocytes
•  Become plasma cells
•  Secrete antibodies
•  Mark cells for destruction by macrophages
•  Respond primarily to bacteria and bacterial
toxins
•  Attack foreign cells directly
•  Binds to antigen-bearing cells
•  Perforates cell membrane
•  Signals cell to undergo apoptosis
•  Destroy virus infected cells and some
cancer cells
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Copyright © 2011 Pearson Education, Inc.
Lymphocyte Function
Lymphocyte Activation
Target cell,
bearing antigen
T lymphocyte
Dead target cell
•  Lymphocytes originate in bone marrow
•  Some travel to the thymus gland
Antigen
1 T lymphocyte binds to
target cell, secretes proteins
that lyse the cell’s membrane,
and signals the cell to die.
(a) Action of cytotoxic T lymphocyte
B lymphocyte
Plasma cell
2 T lymphocyte detaches
from target cell.
Antibodies
Bacterium
3 Target
cell dies by
apoptosis.
Surface antigen
Macrophage
2 Antibodies bind to
antigens on bacteria,
marking the bacteria for
destruction.
(b) Differentiation and activity of B lymphocyte
1 B lymphocyte gives rise
to plasma cell, which
secretes antibodies.
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3 Antibody-coated
bacteria are avidly
phagocytized.
Figure 21.5
•  T lymphocytes
•  Some stay in bone marrow
•  B lymphocytes
•  Able to recognize a unique antigen
•  Gain immunocompetence
•  Travels through blood stream
•  Meets and binds to a specific antigen
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4
Lymphocyte Activation
Lymphocyte Activation
•  During activation
•  Both T and B lymphocytes produce clones of
•  Lymphocyte is presented its antigen by
•  A macrophage
•  Or a dendritic cell
•  Effector lymphocytes
•  Respond immediately, then die
•  Memory cells
•  Wait until the body encounters the antigen
again
•  Basis of acquired immunity
•  Prevent subsequent infections of the same
illness
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Copyright © 2011 Pearson Education, Inc.
Lymphocyte Activation
Immature
lymphocytes
Red bone
marrow
Thymus
Bone
marrow
Lymph
nodes, spleen, and other
lymphoid tissues
Lymphoid Tissue is...
1 Lymphocytes destined to become T cells
migrate (in blood) to the thymus and develop
immunocompetence there. B cells develop
immunocompetence in red bone marrow.
Red bone marrow: site of
lymphocyte origin
Primary lymphoid organs:
site of development of immunocompetence as B or T cells
Secondary lymphoid organs:
site of antigen encounter, and
activation to become effector
and memory B or T cells
2 Immunocompetent but still
naive lymphocytes leave the
thymus and bone marrow. They
“seed” the lymph nodes, spleen,
and other lymphoid tissues where
they encounter their antigen.
3 Antigen-activated immunocompetent lymphocytes
(effector cells and memory
cells) circulate continuously in
the bloodstream and lymph and
throughout the lymphoid
organs of the body.
Figure 21.6
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Lymphoid Tissue
•  The most important tissue of the immune
system
•  Two general locations: mucous membranes
of...
•  Digestive, urinary, respiratory, and
reproductive tracts
•  Mucosa-associated lymphoid tissue
(MALT)
•  Lymphoid organs (except thymus)
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Lymphoid Organs...
Intestine
Lymphoid
follicle
Muscle
layers
Lumen
•  Bone marrow
•  Thymus
Mucous
membrane
lining small
intestine
Lumen of
intestine
Germinal
center
Lymphoid tissue from mucosa of small
intestine (14×)
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•  Designed to gather and destroy infectious
microorganisms and to store lymphocytes
•  Primary lymphoid organs
Figure 21.7
•  Secondary lymphoid organs
•  Lymph nodes, spleen, tonsils
•  Aggregated lymphoid nodules
•  Appendix
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5
Lymphoid Organs
Thymus
...include:
•  Immature lymphocytes develop into T
lymphocytes
•  Secretes thymic hormones
•  Most active in childhood
•  Functional tissue atrophies with age
•  Composed of cortex and medulla
Tonsils (in pharyngeal
region)
Thymus (in thorax; most
active during youth)
•  Medulla contains Hassall’s corpuscles (thymic
corpusles)
Spleen (curves around
left side of stomach)
•  Differs from other lymphoid organs
Aggregated
lymphoid
nodule (in intestine)
•  Functions strictly in lymphocyte maturation
•  Arises from epithelial tissue
Appendix
Figure 21.8
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Thymus
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Lymph Nodes
•  Function
Cortex
Thymus
Medulla
Thymic
corpuscle
(a)Thymus located in the superior
mediastinum
•  Lymph percolates through lymph sinuses
•  Most antigenic challenges occur in lymph
nodes
•  Antigens destroyed and activate B and T
lymphocytes
(b) Micrograph of thymic tissue
showing part of a lobule
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Figure 21.9
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Spleen
Spleen
•  Largest lymphoid organ
•  Two main blood-cleansing functions
•  White pulp
•  Removal of blood-borne antigens
•  Removal and destruction of old or defective blood
cells
Site of hematopoiesis in the fetus
Destruction of antigens
Site of B cell maturation into plasma cells
Phagocytosis of bacteria and worn-out RBCs,
WBCs and platelets
•  Storage of platelets
• 
• 
• 
• 
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•  Thick sleeves of lymphoid tissue
•  Blood-borne antigens are destroyed as they activate
the immune response
•  Provides the immune function of the spleen
•  Red pulp
•  Surrounds white pulp
•  Composed of
•  Venous sinuses
•  Splenic cords
•  Responsible for disposing of worn out RBCs
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Spleen
Spleen
Capsule
Trabecula
Splenic cords
Venous sinuses
Arterioles
and
capillaries
Red pulp
Splenic artery
Splenic vein
Hilum
(a) Diagram of the spleen,
anterior view
Adrenal
gland
Central artery
Pancreas
Splenic vein
Figure 21.10a, b
Tonsils
White pulp
Left
kidney
White pulp
Splenic artery
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Spleen
Splenic
artery
(b) Diagram of spleen histology
Capsule
Diaphragm
Red pulp
(c) Photograph of the spleen in its normal
position in the abdominal cavity,
anterior view
(d) Photomicrograph of spleen tissue (7×).
The white pulp, a lymphoid tissue with many
lymphocytes, is surrounded by red pulp
containing abundant erythrocytes.
Figure 21.10c, d
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Palatine Tonsil
Pharyngeal tonsil
•  Simplest lymphoid organs
•  Four groups of tonsils
Palatine tonsil
Lingual tonsil
•  Palatine, lingual, pharyngeal, and tubal tonsils
(just behind the openings of the auditory tubes into the pharynx)
•  Arranged in a ring to gather and remove
pathogens
•  Underlying lamina propria consists of MALT
Tonsil
(Mucosa-associated lymphoid tissue)
Tonsillar crypt
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Aggregated Lymphoid Nodules and Appendix
Germinal centers in
lymphoid follicles
Figure 21.11
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Aggregated Lymphoid Nodule
•  abundant MALT in walls of intestines
• 
•  Fights invading bacteria
•  Generates a wide variety of memory lymphocytes
•  Aggregated lymphoid nodules (Peyer’s patches)
•  Located in the distal part of the small intestine
•  Appendix—tubular offshoot of the cecum
Aggregated
lymphoid nodules
(Peyer’s patch)
Smooth muscle in
the intestinal wall
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Figure 21.12
7
Disorders of the Lymphatic and Immune
Systems
Disorders of the Lymphatic and Immune
Systems
•  Chylothorax
•  Hodgkin’s disease
•  Leakage of fatty lymph into the thorax
•  Lymphangitis
•  Inflammation of a lymph vessel
•  Mononucleosis
•  Malignancy of lymph nodes
•  Non-Hodgkin’s lymphoma
•  Uncontrolled multiplication and metastasis of
undifferentiated lymphocytes
•  Viral disease caused by Epstein-Barr virus
•  Attacks B lymphocytes
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The Lymphatic and Immune Systems
Throughout Life
•  Lymphatic vessels and lymph nodes
•  Develop from lymphatic sacs
•  Thymus originates as an outgrowth of the
endoderm
•  Spleen, lymph nodes, and MALT
•  Arise from mesodermal mesenchyme
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