Download Chapter 7 Body Systems

Chapter 20
Lymphatic System
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Overview of the Lymphatic
System
• Importance of the
lymphatic system
– Two most important
functions— maintain fluid
balance in the internal
environment and promote
body’s immunity
– Lymph vessels act as
“drains” to collect excess
tissue fluid and return it to
the venous blood just
before it returns to the
heart
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Overview of the Lymphatic
System
– Lymphatic system
• specialized component of the
circulatory system
• made up of lymph, lymphatic vessels,
and isolated structures containing
lymphoid tissue: lymph nodes,
aggregated lymphoid nodules,
tonsils, thymus, spleen, and bone
marrow
– Transports tissue fluid, proteins,
fats, and other substances to the
general circulation
– Lymphatic vessels begin blindly
in the intercellular spaces of the
soft tissues- do not form a closed
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circuit
Lymph and Interstitial Fluid
• Lymph (lymphatic fluid)
– Clear, watery-appearing fluid found in the
lymphatic vessels
– Closely resembles blood plasma in
composition
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Lymph and Interstitial Fluid
• Interstitial fluid (IF)
– Complex, organized fluid that fills the spaces
between the cells
– Resembles blood plasma in composition
– Along with blood plasma, constitutes the
extracellular fluid
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Lymphatic Vessels
• Distribution of lymphatic vessels (lymphatics)
(Figures 20-2 and 20-3)
– Lymphatic capillaries
• microscopic blind-end vessels where lymphatic vessels originate
• wall consists of a single layer of flattened endothelial cells
• networks branch and reconnect freely
– Lymphatic capillaries merge to form larger lymphatics
– drains into subclavian vein
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Lymphatic Vessels
• Structure of lymphatic vessels
– Similar to veins except lymphatic vessels have thinner
walls, more valves, and contain lymph nodes
– Lymphatic capillary wall is formed by a single layer of
thin, flat endothelial cells
– As the diameter of lymphatic vessels increases from
capillary size, the walls become thicker and have three
•
Semilunar valves are present
layers
every few millimeters in large
lymphatics and even more
frequently in smaller lymphatics
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Lymphatic Vessels
• Functions of the lymphatic vessels
– Remove high weight substances
• If anything blocks lymphatic return, blood protein
concentration and blood osmotic pressure 
– Lacteals absorb fats and other nutrients from
the small intestine
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Circulation of Lymph
• Lymph system re-circulates about 3 liters/day!
• From lymphatic capillaries, lymph flows through
progressively larger lymphatic vessels &
eventually reenters blood at the subclavian veins
• Lymphatic pump
– Lymphokinesis
• the movement of lymph
• can be visualized
– Lymph moves through the
system in right direction of
lots of valves
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Lymph Nodes
• Structure of lymph nodes
– Oval structures
– Nodes are a biological
filter
– Once lymph enters a
node, it moves slowly
through sinuses to drain
into the efferent exit
vessel
– lined with specialized
cells capable of
phagocytosis
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Lymph Nodes
• Functions of lymph nodes
1. Defense functions
•
Filtration
–
–
•
•
Mechanical filtration— physically stops particles
Biological filtration— biological activity of cells destroys and
removes particles
Phagocytosis— cells remove microorganisms and other
injurious particles from lymph and phagocytose them
If overwhelmed, lymph nodes can become infected or damaged
–
If infection blocks nodes, fluid accumulates  swollen
2. Hematopoiesis— lymphoid tissue is site for final stages
of maturation of some lymphocytes and monocytes
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Lymphatic Drainage of the
Breast
• Clinically important because cancer cells and
infections can spread along lymphatic pathways
to lymph nodes and other organs of the body
• Lymph nodes associated with the breast
– >85% lymph from the breast enters lymph nodes of
axillary region
– Remainder enters lymph nodes along lateral edges of
sternum
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Tonsils
• Form a broken ring under the mucous membranes in the mouth and back
of the throat—the pharyngeal lymphoid ring (Figure 20-17)
– Palatine tonsils— each side of throat
– Pharyngeal tonsils— near posterior opening of nasal cavity (adenoids
when swollen)
– Lingual tonsils— near base of the tongue
• Protect against bacteria that may invade
tissues around the openings between the
nasal and oral cavities
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Thymus
• Location and appearance of the
thymus
– Primary organ of lymphatic system
– Single, unpaired organ located in
the mediastinum
– Thymus is pinkish gray in childhood
– with advancing age, becomes
yellowish as lymphoid tissue is
replaced by fat
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Thymus
• Function of the thymus
– Plays vital role in immunity mechanism
1. Source of blood cells before birth
2. Shortly after birth, thymus secretes thymosin
and other regulators, which enables
lymphocytes to develop into T cells
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Spleen
• Location of the
spleen— left
hypochondrium
• Structure of spleen
– Ovoid in shape
– White pulp— dense
masses of
developing
lymphocytes
– Red pulp
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Spleen
•
Functions of the spleen
1. Defense
 macrophages lining spleen remove microorganisms from
blood and phagocytose them
2. Hematopoiesis
 monocytes and lymphocytes complete their development in
the spleen
3. Red blood cell and platelet destruction
 macrophages remove worn-out RBCs and imperfect
platelets and destroy them
 salvage iron and globin from destroyed RBCs
4. Blood reservoir
 stores blood
 FYI- As response to hemorrhage, spleen can “self- 18
transfuse” about 200 mL of blood!
Cycle of Life: Lymphatic System
• Dramatic changes throughout life
• Organs with lymphocytes appear before birth and grow until
puberty
• Postpuberty
– Organs atrophy through late adulthood
• Shrink in size
• Become fatty or fibrous
– Spleen— develops early, remains intact
• Overall function maintained until late adulthood
– Later adulthood
• Deficiency permits risk of infection and cancer
• Hypersensitivity— likelihood of autoimmune conditions
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