Lymphatic

System
Functions of the Lymphatic
System
• Fluid balance
• The lymphatic vessels transport
back to the blood fluids that have
escaped from the blood vascular
system
• Fat absorption
• The lymphatic system absorbs fats
and other substances from the
digestive tract
• Body defense
• The lymphatic system has
phagocytic cells and lymphocytes,
which play essential roles in body
defense and resistance to disease
Lymph
• Fluid that enters the
lymphatic vessels
• Originates from
extracellular fluid
• Contains products of
• Tissue metabolism
• Apoptotic cells
• Debris
• Immune cells
Lymphatic capillaries
• Permeable
• Blind-ended
• Found between the tissue cells
and blood capillaries
• Absorb the leaked fluid
• Transport the lymph to the
lymphatic collecting vessels and
lymph nodes
• Greater diameter (as wide as
100 μm) than blood capillaries
• Endothelial cells overlap each
other, forming minivalves
• Interstitial proteins cannot
enter the blood capillaries, but
they can enter lymphatic
capillaries
• The edges of the
endothelial cells form
flaplike mini-valves
• The valves act as one-
way swinging doors
• The flaps, anchored by
fine collagen fibers to
surrounding structures
• The flaps open when
the fluid pressure is
higher in the interstitial
space, allowing fluid to
enter the lymphatic
capillary
Lymphatics Vessels (Veins)
• Lymphatic collecting vessels
• Lymph is transported from lymph
capillaries through lymphatic
vessels(veins)
• Right lymphatic duct
• The right lymphatic duct drains
the lymph from the right arm and
the right side of the head and
thorax
• Thoracic duct
• The large thoracic duct receives
lymph from the rest of the body;
both ducts empty the lymph into
the subclavian vein on their own
side of the body.
Mucosa-Associated Lymphatic
Tissue (MALT)
• MALT acts as a sentinel to protect the
upper respiratory and digestive tracts
from the never-ending attacks of
foreign matter entering those cavities
• Peyer’s patches
• The tonsils
• Appendix
Peyer’s Patches
• Lymphoid follicles in the
mucus membrane in Wall
of small intestine
• Lymphoid follicles are
similar to lymph nodes
• Lymphoid follicles help
body fight infection
• The macrophages of
Peyer’s patches capture
and destroy bacteria
• The size, shape, and
overall distribution of
Peyer’s patches varies
from person to person
The tonsils
• Small masses of
lymphoid tissue
• Found around the
pharynx (the throat)
• Trap and remove any
bacteria or other
foreign pathogens
entering the throat
The Appendix
• The appendix sits in the lower
right abdomen
• The function of the appendix
is unknown.
• One theory is that the
appendix acts as a storehouse
for good bacteria, “rebooting”
the digestive system after
diarrheal illnesses
Other Lymphoid Organs
• Lymph nodes
• Spleen
• Thymus gland
Lymph nodes
• Help protect the
body
• Remove foreign
material such as
bacteria and tumor
cells
• Produce lymphocytes
that function in the
immune response.
Spleen
• Soft, blood-rich organ
• Located on the left side of the abdominal
cavity, just beneath the diaphragm
• Filters and cleanses the blood of bacteria,
viruses, and other debris
• Provides a site for
• Lymphocyte proliferation
• Immune surveillance
• Destroys worn-out red blood cells
Thymus Gland
• The thymus gland
functions at peak
levels only during
youth
• A lymphoid mass
found low in the throat
overlying the heart.
• Produces thymosin
and others, that
function in the
programming of
certain lymphocytes so
they can carry out
their protective roles
in the body
Lymphedema
• Lymph tissues, vessels or nodes are damaged
• Lymph cannot flow properly
• Lymph fluid will pool in areas causing swelling
•Macrophages. Within the lymph nodes are macrophages, which engulf and destroy bacteria, viruses, and
other foreign substances in the lymph before it is returned to the blood.
•Lymphocytes. Collections of lymphocytes (a type of white blood cell) are also strategically located in the
lymph nodes and respond to foreign substances in the lymphatic stream.
•Size and shape. Lymph nodes vary in size and shape, but most are kidney-shaped, less than 1
inch (approximately 2.5 cm) long, and “buried” in the connective tissue that surrounds them.
•Trabeculae. Each node is surrounded by a fibrous capsule from which strands called trabeculae extend
inward to divide the node into a number of compartments.
•Cortex. The outer part of the node, the cortex, contains collections of lymphocytes called follicles, many of
which have dark-staining centers called germinal centers.
•Plasma cells. These centers enlarge when specific lymphocytes (the B cells) are generating daughter cells
called plasma cells, which release antibodies.
•T cells. The rest of the cortical cells are lymphocytes “in transit”, the so-called T cells that circulate
continuously between the blood, lymph nodes and lymphatic stream, performing their surveillance role.
•Medulla. Phagocytic macrophages are located in the central medulla of the lymph node.
•Afferent lymphatic vessels. Lymph enters the convex side of a lymph node through the afferent lymphatic
vessels.
•Efferent lymphatic vessels. It then flows through a number of sinuses that cut through the lymph node and
finally exits from the node at its indented region, the hilum, via the efferent lymphatic vessels.