Download Overview of the Lymphatic System

Chapter 20 – Lymphatic
System
Dr. Kim Wilson
Overview of the Lymphatic System
• Component of the
circulatory system
• Functions:
• Maintains fluid
balance in the
internal
environment and
immunity
• Collects
absorbed fat from
the intestines and
transport it to the
systemic veins
Components of the Lymphatic System
•
•
•
•
Lymph (lymphatic fluid)
• Clear, watery, moving fluid derived from blood and tissue fluid
• Closely resembles blood plasma in composition but has a lower
percentage of protein; isotonic
Lymphatic vessels (lymphatics)
• Return lymph to the blood
• Contain lymphocytes and other defensive cells
Isolated structures containing lymphoid tissue: lymph nodes,
aggregated lymphoid nodules, tonsils, thymus, spleen, and bone marrow
(Figure 20-2)
Interstitial fluid
• Complex, organized fluid that fills the spaces between the cells and is
part of the extracellular matrix
• Resembles blood plasma in composition with a lower percentage of
protein
• Along with blood plasma, constitutes the extracellular fluid
The Lymphatic System and Fluid Balance
• Lymph transports tissue fluid,
proteins, fats, and other
substances to the general
circulation
• Fluid from plasma moves into
interstitial spaces (some fluid
accumulates)
• As fluid builds up it is drained by
the lymphatic vessels
• Lymphatic vessels begin blindly
in the intercellular spaces of the
soft tissues; do not form a closed
circuit
• Lymph vessels act as drains to
collect excess tissue fluid and
return it to the venous blood just
before it returns to the heart
LYMPHATIC VESSELS
(LYMPHATICS)
•
DISTRIBUTION and DRAINAGE
• Start as microscopic lymphatic
capillaries, consisting of a single
layer of flattened endothelial cells
• Lymphatic capillaries merge to form
larger lymphatics and eventually
form the main lymphatic trunks,
the right lymphatic ducts, and the
thoracic duct
• Lymph from upper right quadrant 
empties into right lymphatic duct 
right subclavian vein
• Lymph from rest of the body
empties into the thoracic duct 
drains into left subclavian vein
• Thoracic duct originates from a
dilated structure known as the
cisterna chyli (chyle cistern) in
lumbar region of intestinal tract
Lymphatic Drainage in the Head and Neck
Structure of Lymphatic Vessels
• Don’t form a closed ring like blood
vessels
• Similar to veins except for these
exceptions:
• Have thinner walls
• Have more valves
• Contain lymph nodes
• Functions of the lymphatic vessels
• Remove high-molecular-weight
substances and particulate matter
from interstitial spaces
• Lacteals (lymphocytes in the villi
of the small intestines) absorb fats
and other nutrients from the small
intestine
Circulation of Lymph
• From lymphatic capillaries, lymph
flows through progressively larger
lymphatic vessels to reenter blood at
the junction of the internal jugular
and subclavian veins (Figure 20-5)
• The lymphatic pump
• Lymphokinesis: the movement
(flow) of lymph; can be
visualized in a lymphangiogram
(Figure 20-6)
• Lymphokinetic actions: activities
that result in a central flow of
lymph
LYMPH NODES
• STRUCTURE
• Oval, bean-shaped
• Part of lymphatic vessels (lymph
filters through each node)
• House lymphocytes and
monocytes
• Trabeculae extend from the
covering capsule toward the
center of the node
LYMPH NODES (cont.)
• FUNCTION
• Nodes are a type of biological
filter
• Once lymph enters a node, it
moves slowly through sinuses
to drain into the efferent exit
vessel (Figure 20-10)
• LOCATION
• Most lymph nodes occur in groups
• Groups with greatest clinical
importance are
• preauricular lymph nodes
• submental and submaxillary
groups
• superficial cervical
• superficial cubital, axillary, iliac
• inguinal lymph nodes
Functions of Lymph Nodes
1. Defense
• How? Two mechanisms:
• Filtration
• Mechanical filtration: physically stopping particles from
progressing further in the body
• Biological filtration: biologic activity of cells destroys and
removes particles
• Phagocytosis
• Reticuloendothelial cells remove microorganisms and
other injurious particles from lymph and phagocytose
them (biological filtration)
• If overwhelmed, lymph nodes can become infected or
damaged
2. Hematopoiesis
• Final site for maturation of some lymphocytes and monocytes
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: located on each side of the throat
• Pharyngeal tonsils: located near the posterior opening of the nasal cavity
• Lingual tonsils: located near the base of the tongue
• Tubal tonsils: located near the openings of the auditory (eustachian) tubes
FUNCTION: Protect against bacteria that may invade tissues around the openings
between the nasal and oral cavities; bacteria are trapped in tonsillar crypts and put
in close contact with immune system cells
THYMUS
•
•
STRUCTURE
• Pyramid-shaped lobes are
subdivided into small lobules
• Each lobule is composed of a
dense cellular cortex and an
inner, less-dense medulla
LOCATION/APPEARANCE (Figure
20-18)
• Primary central organ of
lymphatic system
• Single, unpaired organ located in
the mediastinum, extending
upward to the lower edge of the
thyroid and inferiorly as far as the
fourth costal cartilage
• Thymus is pinkish gray in
childhood; with advancing age,
becomes yellowish as lymphoid
tissue is replaced by fat
THYMUS (cont.)
• FUNCTIONS
• Plays vital role in immunity
mechanism
• Source of lymphocytes
before birth
• Shortly after birth, secretes
thymosin and other
regulators, which enables
lymphocytes to develop
into T cells (Figure 20-19)
SPLEEN
•
•
LOCATION
• Left hypochondrium, directly below the diaphragm, above the left kidney and
descending colon and behind the fundus of the stomach
STRUCTURE
• Ovoid in shape
• Surrounded by fibrous capsule with inward extensions that divide the organ
into compartments
• White pulp: dense masses of developing lymphocytes
• Red pulp: near outer regions, composed of a network of fine reticular fibers
submerged in blood that comes from nearby arterioles; composed of cords
of white blood cells and related cells surrounded by sinusoids
Functions of the Spleen
• DEFENSE
• Filtration and phagocytosis: monocytes live in the
lining of blood vessels in the spleen  carry out
phagocytosis as blood passes through
• HEMATOPOIESIS
• Formation of blood cells (lymphocytes, monocytes,
and platelets)
• RBC AND PLATELET DESTRUCTION
• By monocytes in blood vessels
• BLOOD RESERVOIR
• Stores large amounts of blood (350 ml)
• In emergency, can squeeze blood into general
circulation
The Lymphatic Cycle Through Life
• 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
Summary of Main Points
• Lymphatic system drains away excess water from large
areas
• Lymph is conducted through lymphatic vessels to nodes,
where contaminants are removed
• Lymphatic system benefits the whole body by
maintaining fluid balance and freedom from disease