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IMMUNE SYSTEM: BIOS 255 Anatomy And Physiology III With Lab
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- Chamberlain College Of Nursng
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The lymphatic system consists of lymphatic fluid, lymphatic vessels, lymphatic tissue, and lymphaticorgans located throughout the tissues of the body. It functions to drain excess interstitial fluid from
the tissues, to initiate an immune response against disease by producing and transporting
lymphocytes, and to transport dietary lipids absorbed by the gastrointestinal tract into the blood.
COMPONENTS OF THE LYMPHATIC SYSTEM
Lymph
Lymph is a clear fluid similar in composition to blood plasma.
Lymphatic vessels
Lymphatic vessels are thin vessels that accompany arteries and veins throughout the body and transport
lymph.
Lymphatic tissue
Lymphatic tissue is a specialized form of reticular connective tissue that is composed of masses of
lymphocytes. These either occur alone as lymph nodules or are organized into various lymphatic organs.
Lymphatic organs
Lymphatic organs include the lymph nodes, which filter the fluid that flows through the lymphatic vessels,
the spleen, thymus, and red bone marrow.
FUNCTIONS OF THE LYMPHATIC SYSTEM
Fluid balance
The tissues of the body are supplied by minute blood capillaries that bring oxygen-rich blood and remove
carbon dioxide-rich blood. Fluid similar to blood plasma, called interstitial fluid, leaches from these
vessels into the surrounding tissue. Around 20 liters of fluid leaves the arterial capillaries every day, but
only 17 liters of fluid returns to the venous capillaries. Lymphatic vessels function to drain this excess fluid
from the tissues as lymph and return interstitial fluid to the blood.
Immunity
The lymphatic system is regarded as the center of the immune system. It includes white blood cells,
known as lymphocytes, which play a large part in immunity. Immunity refers to the body's ability to
defend itself against disease and infection and may be innate or adaptive (acquired).
We are born with innate immunity and it is non-specific, i.e., all foreign matter is attacked equally. It
forms the first and second line of defense and includes the skin, antimicrobial substances, and the body's
ability to provoke fever or inflammation.
,Adaptive immunity describes the body's ability to recognize and respond to specific foreign substances
and involves lymphocytes known as B-cells and T-cells. Adaptive immunity not only responds to specific
substances, but also remembers them so that it can respond more efficiently should they be encountered
again.
Transport
Some lipids are too large to pass through the capillary walls of the small intestine and therefore cannot be
absorbed. The lymphatic capillaries within the small intestine, known as lacteals, can absorb these large
lipid molecules and transport them into the venous circulation via the thoracic duct. Lymph containing
these lipids becomes a creamy white color and is referred to as chyle.
Lymphatic capillaries extend throughout the tissues of the body among blood capillary beds. Interstitial fluid,
similar in composition to blood plasma, leaches from the blood capillaries into the surrounding tissue, bathing the
cells and supplying each one with nutrients, oxygen, and water while also removing waste, carbon dioxide, and
water. Around 20 liters of fluid leave the capillaries every day, but only 17 liters return to the venous capillaries.
Few large proteins leave the blood capillaries as they are too large to pass through the capillary walls. Those
which do leave cannot return to the blood capillaries by diffusion as the concentration gradients are too high so
instead, they move into the lymph capillaries and are transported back to the venous circulation.
Lymphatic vessels function to drain this excess fluid from the tissues as lymph and return it into the blood
circulation. The capillaries have a unique structure which allows fluid to flow into the lymphatic capillaries and
into the larger lymphatic veins, but not out.
Lymphatic capillaries are formed by:
Lymphatic vessel cell
Overlapping cells forming the thin walls of the capillaries.
Capillary pore
, When the pressure of fluid outside the capillary is greater than that inside, the overlapping endothelial cells open,
forming a capillary pore, through which interstitial fluid flows into the vessel. If however, pressure is greater inside
the capillary, the cells remain tightly shut.
Anchor filaments
Anchor filaments are groups of cells containing elastic fibers. They extend out from either side of the capillary pores
holding the capillary in place within the surrounding interstitial cells. When the tissue is especially swollen with
fluid, the anchoring filaments pull on the endothelial cells, opening the pores further thus allowing more fluid to
flow into the lymphatic capillary.
Did you know?
In the small intestine, lymphatic vessels known as lacteals transport fats which are too
large to be absorbed by the blood capillaries into the venous circulation. When the lymph
contains fat, it becomes milky and is known as chyle.
LYMPHATIC DRAINAGE
Lymphatic vessels unite to form lymphatic trunks which accompany blood vessels and eventually unite to form
two main ducts: the thoracic duct and right lymphatic duct, which drain the lymph into the left and
right subclavian veins, respectively.
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