Transcript Chapter_020

Chapter 20
Lymphatic System
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 1
Overview of the Lymphatic System

Importance of the lymphatic system (Figure 20-1)

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

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
(Figure 20-2)

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 circuit
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 2
Lymph and Interstitial Fluid

Lymph (lymphatic fluid)

Clear, watery-appearing fluid found in the
lymphatic vessels

Closely resembles blood plasma in composition
but has a lower percentage of protein; isotonic

Elevated protein concentration in thoracic duct
lymph because of protein-rich lymph from the liver
and small intestine
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 3
Lymph and Interstitial Fluid

Interstitial fluid (IF)

Complex, organized fluid that fills the spaces
between the cells and is part of the ECM
(extracellular matrix)

Resembles blood plasma in composition with a
lower percentage of protein

Along with blood plasma, constitutes the
extracellular fluid
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 4
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 anastomose freely

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
and then into right subclavian vein

Lymph from rest of the body empties into the thoracic duct, which
then drains into left subclavian vein; thoracic duct originates as the
cisterna chyli (chyle cistern)
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 5
Lymphatic Vessels

Structure of lymphatic vessels (Figure 20-4)

Similar to veins except lymphatic vessels have thinner walls,
have 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 layers

Semilunar valves are present every few millimeters in large
lymphatics and even more frequently in smaller lymphatics
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 6
Lymphatic Vessels

Functions of the lymphatic vessels

Remove high–molecular weight substances and
even particulate matter from interstitial spaces

Lacteals absorb fats and other nutrients from the
small intestine
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 7
Circulation of Lymph

From lymphatic capillaries, lymph flows through progressively
larger lymphatic vessels to eventually reenter blood at the
junction of the internal jugular and subclavian veins (Figure 20-5).

Lymphatic pump

Lymphokinesis—the movement (flow) of lymph; can be visualized in a
lymphangiogram (Figure 20-6)

Lymph moves through the system in the right direction as a result of the
large number of valves

Breathing movements and skeletal muscle contractions (Figure 20-7)
establish a fluid pressure gradient, as they do with venous blood

Other factors, such as IF pressure, also drive lymphokinesis (Figure 20-8)

Lymphokinetic actions—activities that result in a central flow of lymph
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 8
Lymph Nodes

Structure of lymph nodes

Lymph nodes are oval structures enclosed by a fibrous
capsule (Figure 20-9)

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)

Trabeculae extend from the covering capsule toward the
center of the node

Cortical and medullary sinuses are lined with specialized
reticuloendothelial cells capable of phagocytosis
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 9
Lymph Nodes

Locations of lymph nodes

Most lymph nodes occur in groups

Location of groups with greatest clinical importance are
submental and submaxillary groups, and superficial
cervical, superficial cubital, axillary, iliac, and inguinal
lymph nodes (Figures 20-11 through 20-13)

Preauricular lymph nodes located in front of the ear
drain superficial tissues and skin on the lateral side of
the head and face
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 10
Lymph Nodes

Functions of lymph nodes—perform two distinct functions

Defense functions
• Filtration

Mechanical filtration—physically stops particles from progressing further in the body

Biological filtration—biological 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
(Figures 20-14 and 20-15)

Hematopoiesis—lymphoid tissue is site for final stages of
maturation of some lymphocytes and monocytes
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 11
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

Distribution of lymphatics in the breast (Figure 20-16)

Drained by two sets of lymphatic vessels
• Lymphatics that drain skin over breast with the exception of areola and nipple
• Lymphatics that drain substance of breast, as well as skin of areola and nipple

Superficial vessels converge to form a diffuse, cutaneous
lymphatic plexus

Subareolar plexus—located under areola surrounding nipple;
where communication between cutaneous plexus and large
lymphatics that drain the secretory tissue and ducts of the
breast occurs
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 12
Lymphatic Drainage of the Breast

Lymph nodes associated with the breast

More than 85% of lymph from the breast enters
lymph nodes of axillary region

Remainder of lymph enters lymph nodes along
lateral edges of sternum
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 13
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 throat

Pharyngeal tonsils—located near posterior opening of nasal cavity

Lingual tonsils—located near base of the tongue
Protect against bacteria that may invade tissues
around the openings between the nasal and oral
cavities
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 14
Thymus

Location and appearance of the thymus
(Figure 20-18)

Primary central organ of lymphatic system

Single, unpaired organ located in the mediastinum,
extending upward to lower edge of thyroid and
inferiorly as far as fourth costal cartilage

Thymus is pinkish gray in childhood; with advancing
age, becomes yellowish as lymphoid tissue is
replaced by fat
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 15
Thymus

Structure of the thymus

Pyramid-shaped lobes are subdivided into small
lobules

Each lobule is composed of a dense cellular
cortex and an inner, less dense, medulla

Medullary tissue can be identified by presence
of thymic corpuscles
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 16
Thymus

Function of the thymus

Plays vital role in immunity mechanism

Source of lymphocytes before birth

Shortly after birth, thymus secretes thymosin and
other regulators, which enables lymphocytes to
develop into T cells (Figure 20-19)
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 17
Spleen

Location of the spleen—in left hypochondrium, directly
below diaphragm, above left kidney and descending
colon, and behind fundus of stomach
(Figures 20-2 and 20-20)

Structure of spleen (Figure 20-21)

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, made up of a network of fine
reticular fibers submerged in blood that comes from nearby
arterioles
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 18
Spleen

Functions of the spleen

Defense—macrophages lining sinusoids of spleen remove
microorganisms from blood and phagocytose them

Hematopoiesis—monocytes and lymphocytes complete
their development in the spleen

Red blood cell and platelet destruction—macrophages
remove worn-out RBCs and imperfect platelets and destroy
them by phagocytosis; also salvage iron and globin from
destroyed RBCs

Blood reservoir—pulp of spleen and its sinuses store blood
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 19
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
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 20
The Big Picture: The Lymphatic
System and the Whole Body

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 promoting
freedom from disease
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 21