Download Chapter 22: Lymphatic System

Chapter 22 The Lymphatic System
BIO 211 Lab
Instructor Dr. Gollwitzer
1
• Today in class we will discuss:
– Functions of the lymphatic system
– Identify the major components of the lymphoid
system
– Describe the structure and distribution of lymphatic
vessels
– Trace lymph flow from peripheral tissues to the heart
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Functions of the Lymphatic System
• Produces, maintains, and distributes lymphocytes
(primary cells of the lymphatic system)
• Returns fluids and solutes from the peripheral
tissues to circulation and maintains volume
• Distributes nutrients, waste products and
hormones from tissues of origin to general
circulation
– e.g., lipids absorbed by GI tract cannot enter
capillaries; enter lymphatics (lacteals) to return
to circulation
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Figure 22-1
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Components/Organization
• Lymphocytes = primary cells
• Lymphoid tissues = CT dominated by lymphocytes
– Lymphoid nodule = densely packed lymphocytes in areolar tissue; no
fibrous capsule
• Lymphoid organs = connected to lymphatic vessels and have a
capsule
– Nodes – filter and purify lymph and provide early warning system
– Thymus – produces mature T cells
– Spleen – filters and purifies blood
• Network of lymphatic vessels (lymphatics) = distribution
system that begins in peripheral tissues and ends at veins
• Lymph = fluid connective tissue similar to plasma, but with no
plasma proteins
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Lymphocytes
• 20-30% of circulating WBCs
• Most of lymphocytes are not circulating in blood;
found in tissues and organs
• Respond to presence of
– Invading pathogens (bacteria, viruses…)
– Abnormal body cells (virus-infected cells or cancer cells)
– Foreign proteins (toxins released from bacteria)
• Attempt to eliminate these threats or make them
harmless by a combination of physical and chemical
attacks
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Types of WBCs
Figure 19–10
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Lymphocytes
• Produced by lymphopoiesis in
– Red bone marrow (initial site)
– Lymphoid tissues (e.g., tonsils)
– Lymphoid organs (e.g., thymus)
• Derived from hemocytoblasts, lymphoid stem
cells
• Stored in lymphoid tissues and organs and red
bone marrow
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Lymphopoiesis
Figure 22-6
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3 Main Types of Lymphocytes
• T cells
– Thymus-dependent
• B cells
– Bone-marrow derived
• NK cells
– Natural killer cells
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Types of Lymphocytes
• T cells – 80% of circulating lymphocytes
– Cytotoxic T cells
• Attack foreign cells or cells infected by viruses
• Often involves direct contact
• Primary cells involved in CMI (cell-mediated immunity)
– Helper T cells
• Stimulate responses of T and B cells
• B cells must be activated by helper T cells before they can produce
antibodies
– Suppressor T cells
• Inhibit T and B cell activites
• Modify the immune response
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Types of Lymphocytes
• B cells – 15% of circulating lymphocytes
– Differentiate into plasma cells  antibodies
– Antibody + target antigen  destruction of target
compound or organism
– Anti-body-mediated immunity or humoral (liquid)
immunity
• Natural killer (NK) cells - 5% of circulating
lymphocytes
– Police of peripheral tissues = immunological surveillance
– Directly attack
• Foreign cells
• Cells infected with viruses
• Cancer cells
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Lymphoid Tissues
• CT dominated by lymphocytes
• Form lymphoid/lymphatic nodules
– Densely packed lymphocytes in areolar tissue
– No capsule
– Have germinal center where lymphocytes are
dividing
– Found in CT deep to epithelia lining respiratory,
digestive, and urinary tracts
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Lymphoid Tissues
• Include
– Tonsils = 5 large nodules in wall of pharynx
• 1 pharyngeal tonsil (adenoids) – in posterior superior wall of
nasopharynx
• 2 palatine tonsils – at posterior margin of oral cavity, along boundary
with pharynx
• 2 lingual tonsils – under tongue
– Vermiform appendix
• Blind pouch that contains fused lymphoid nodules
• Originates near junction between small and large intestines
– MALT (mucosa-associated lymphoid tissues)
• Collection of lymphoid tissues linked with digestive system e.g.,
Peyer’s Patches = clusters of lymphoid nodules deep to lining of
intestines
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Figure 22-7b
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Figure 22-7a
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Lymphoid Organs
• Tissue + capsule
• Distinguishing characteristic
– Fibrous CT capsule separates organs from
surrounding tissues
• Include
– Lymph nodes
– Thymus
– Spleen
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Lymph Nodes
• Filter/purify lymph
• Small (ca 1 in. max), kidney bean-shaped organs
• Anatomy
– Capsule - tough, fibrous CT that separates organ from
surrounding tissues
– Trabeculae - bundles of collagen fibers that extend
from the capsule and form partitions/walls
– Hilus - shallow indentation where vessels and nerves
enter/leave
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Lymph Nodes
• Anatomy (continued)
– Cortex - outer (B cells) and deep (T cells)
• Germinal centers = central zones in the cortex of a lymphoid nodule that
contain dividing lymphocytes
– Medulla - core; contains B cells and plasma cells organized into
medullary cords
– Sinuses - open passageways with incomplete walls
– Other cells: dendritic dells = “parenchymal” cells that bind
antigens; involved in initiation of immune response
– Lymph node vessels
• Afferent vessels - carry lymph to node from peripheral tissues
• Efferent vessel - carries lymph away from node toward venous
circulation at hilus
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Cortical sinus
Fig. 22-8, part 2, 9th edition
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Figure. 22-7, part 1, 7th edition
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Lymph Flow through Lymph
Node
• Occurs through network of sinuses
• From afferent lymphatics, enters subcapsular
sinus that contains a meshwork of
– Branching reticular fibers
– Macrophages
– Dendritic cells = antigen-presenting cells; involved
in initiation of immune response
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Lymph Flow through Lymph
Node
• To cortex
– Outer cortex contains B cells with germinal centers (like
lymphoid nodules)
– Deep cortex dominated by T cells; lymphocytes leave
blood stream and enter lymph nodes here
• To medulla/medullary sinus
– Core of lymph node
– Contains B cells and plasma cells organized into medullary
cords
• Exits via efferent lymphatic at hilus
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Lymph Nodes
• Aggregations of lymph nodes (“lymph glands” a
misnomer)
• Located where peripheral lymphatics connect with trunk
– Axillary
– Inguinal
– Cervical
• “Swollen glands”
– Indicate inflammation or infection in peripheral tissues
– Painful enlargement due to increase in number of lymphocytes
and phagocytes in response to minor, localized infection
– Nonpainful, chronic or excessive enlargement =
lymphadenopathy
• May occur in response to bacterial or viral infections, endocrine
disorders, cancer
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Functions of Lymph Nodes
• Filter and purify lymph before entering venous circulation
• Fixed macrophages in walls of sinuses engulf debris and
pathogens
• Remove 99% of antigens
– Some processed by macrophages and presented to nearby
lymphocytes
– Others bind to dendritic cells where they can stimulate
lymphocyte activity= antigen presentation = first step in
immune response
• Provide an early warning system
– Infection or abnormality in peripheral tissue  abnormal
antigens into interstitial fluid  lymph  lymph nodes 
stimulate macrophages and lymphocytes
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Thymus
•
•
•
•
Produces mature T cells
Location in mediastinum, posterior to sternum
Appearance is pink with a grainy consistency
Changes over lifespan
– Largest size (relative to body weight) in first 2 years of
life
– Maximum size just before puberty
– After puberty, begins to involute (get smaller)
– Continues to decrease in size and becomes fibrous;
may be cause of decreased immunity in older
population
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Figure 22-9 The Thymus
Thyroid gland
Trachea
Left
lobe
Right
lobe
THYMUS
Left
lobe
Right lobe
Right
lung
Septa
Left
lung
Lobule
Heart
Diaphragm
Anatomical
landmarks on
the thymus.
The appearance and position of the thymus in
relation to other organs in the chest.
Medulla
Septa
Cortex
Lymphocytes
Lobule
Thymic
corpuscle
Reticular
cells
Lobule
A thymic corpuscle
LM  550
Higher magnification reveals the unusual
structure of thymic corpuscles. The small
cells are lymphocytes in various stages of
development.
The thymus gland
LM  50
Fibrous septa divide the tissue of the thymus into lobules
resembling interconnected lymphoid nodules.
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Thymus
• Anatomy
– Has a capsule
– 2 connected lobes
– Septae (plural)
• Fibrous partitions; divide lobes into lobules
– Lobules
• Cortex - densely packed cells, including
– Dividing lymphocytes, arranged in clusters surrounded by…
– Reticular epithelial cells
» Maintain blood-thymus barrier
» Secrete thymic hormones (thymosins) that stimulate stem cell
divisions and T cell differentiation into mature T cells
» Mature T cells then migrate to medulla
• Medulla - no barrier so cells can now enter blood
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Spleen
• Filters/purifies blood
• Largest collection of lymphoid tissue
• Functions
– Removes abnormal blood cells and other blood
components by phagocytosis
– Stores iron from recycled RBCs
– Initiates immune responses by B cells and T
cells in response to antigens in circulating
blood
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Spleen
• Anatomy
– Soft consistency; reflects shape of organs that
surround it (stomach, left kidney, diaphragm)
– Fibrous capsule
– Hilus (groove, blood & lymphatic vessels enter/exit)
– Red pulp - large sinusoids containing many RBCs
plus macrophages and lymphocytes
– White pulp - dense lymphocytes  white
appearance; resembles lymphoid nodules; can
respond to any antigen in blood
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Spleen
• Impact to left side in automobile accidents,
contact sports…spleen can tear easily 
internal bleeding and circulatory shock
– Due to fragility, difficult to repair surgically
– Usually remove entire organ (splenectomy)
– Person survives without difficulty but at risk for
bacterial infections
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Figure 22-10, 7th edition
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Lymphatic Vessels
• From peripheral tissues to venous system
• Lymphatic capillaries
– “Terminal” lymphatics; misnomer because mark
beginning of lymphatic vessels
– Branches in peripheral tissues
– Different from regular capillaries
•
•
•
•
•
Originate as blind pockets
Larger in diameter
Thinner walls
In cross-section- have flattened/irregular outline
Lined by endothelium, with incomplete/absent
basement membrane
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Lymphatic Vessels
• Lymphatic capillaries (continued)
– Endothelial cells not tightly bound, but overlap
• Acts as 1-way valve, propels lymph in one direction
• Permits entry of large solutes, e.g., proteins, bacteria,
viruses, cell debris, but prevents their return to
intercellular spaces
– Present in almost every tissue and organ (except
cornea, bone marrow, CNS)
– Lacteals
• Special lymphatic capillaries in small intestine
• Transport lipids from digestive tract
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Figure 22-2
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Lymphatic Vessels
• Small lymphatic vessels
– Lead toward trunk (via larger lymphatics)
– Similar to veins
• Same vessel walls
• Minimal pressures
• Have valves
– Prevent backflow
• Often in close association with blood vessels
– Differ in relative size (smaller), general appearance
(e.g. color), and branching pattern
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Figure 22-3a, b
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Lymphatic Vessels
• Larger lymphatic vessels (2 kinds)
– Superficial lymphatics
• Found underlying membranes throughout body
(e.g., skin; mucus, serous)
– Deep lymphatics
• Largest vessels
• Accompany deeper arteries and veins
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Lymphatic Vessels
• Larger lymphatics converge to form large
lymphatic trunks (R&L)
– Jugular trunks
• Drain head, neck
– Subclavian trunks
• Drain upper limbs
– Bronchomediastinal trunks
• Drain thoracic tissues/organs
– Lumbar trunks
• Drain back, lower limbs
– Intestinal trunk
• Drain abdominopelvic area
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Figure 22-4b The Relationship between the Lymphatic Ducts and the Venous System
Brachiocephalic veins
Left internal jugular vein
Left jugular trunk
Right internal jugular vein
Thoracic duct
Right jugular trunk
Left subclavian trunk
Right lymphatic duct
Left bronchomediastinal
trunk
Right subclavian trunk
Right subclavian vein
Left subclavian
vein
Right bronchomediastinal
trunk
Superior
vena cava (cut)
First rib
(cut)
Azygos vein
Highest
intercostal
vein
Rib (cut)
Thoracic
duct
Thoracic
lymph nodes
Hemiazygos
vein
Parietal
pleura (cut)
Diaphragm
Cisterna chyli
Inferior vena cava (cut)
Right lumbar trunk
Intestinal trunk
Left lumbar trunk
The thoracic duct empties into the left subclavian vein. The right
lymphatic duct drains into the right subclavian vein.
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Lymphatic Vessels
• Lymphatic trunks empty into two large
collecting vessels
– Thoracic duct
• Collects lymph from tissues
– From L side of upper body (above diaphragm)
– Inferior to the diaphragm
– R lymphatic duct
• Collects lymph from tissues
– From R side of upper body (above diaphragm)
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Figure 22-4a, 7th edition
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Lymphatic Vessels
• Thoracic duct
– Base = expanded chamber = cisterna chyli
– Receives lymph from
• Inferior abdomen, pelvis, and lower limbs
– via R and L lumbar trunks and intestinal trunks
• Collects lymph from L bronchomediastinal trunk, L
subclavian trunk, and L jugular trunk
• Empties into L subclavian vein
• Right lymphatic duct
• Formed by merging of R jugular, R subclavian, and R
bronchomediastinal trunks
• Empties into R subclavian vein
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Lymph
• Fluid in lymphatic vessels
• Formed from blood plasma forced out of capillary by
hydrostatic pressure into interstitial spaces ( interstitial fluid)
• Interstitial fluid accumulates and increases pressure
• Lymphatics pick up excess so edema doesn’t occur
• As lymph returns to CVS, cells of immune system (e.g.
lymphocytes, macrophages in lymphoid tissues/organs)
monitor its composition and respond to signs of injury or
infection
• Cells
– 99% lymphocytes (T and B cells)
– Remaining 1% are primarily phagocytes = microphages (eosinophils,
neutrophils) and macrophages (monocytes)
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Lymphedema
• Blockage of lymph drainage from a limb
(e.g., following removal of lymph nodes)
– Causes severe swelling
– Interferes with immune system function
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