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Lymphatic System
The Lymphatic System is closely associated with the venus half of
the circulatory system because it contains a network of vessels that
assist in circulating body fluids.
The lymphatic system has several jobs:
1. transports excess fluid to the bloodstream
2. absorbs fats
3. helps defend the body against disease-causing agents
General Overview of Lymphatic System:
This is a one way system. The lymph capillaries spiderweb between tissue
cells, blood capillaries, and loose connective tissue. Lymph capillaries are
very similar to blood capillaries but are so permeable that one would think
that they had an open end like a straw. The capillaries have a minivalve
system that acts as a one way door. The flaps open when the pressure is
high. Proteins, large debris, bacteria, and viruses are prevented from
entering the blood capillaries but easily enter the lymph capillaries. The
problem is that bacteria and viruses can then use the lymphatic system to
spread throughout the body. This is where the lymph nodes come in. The
lymph must be filtered, cleansed, and examined by the cells of the immune
system. After lymph nodes the lymph goes to the vessels, ducts, and finally
the subclavian vein.
The 3 lymphatic pathways
1. Lymphatic capillaries – microscopic closed-ended tubes. Walls are very
similar to blood capillaries. LYMPH is the fluid inside a lymph capillary.
2. Lymphatic vessels very similar to veins but thinner, also have semilunar
valves that prevent backflow. Lead to specialized organs called lymph
nodes.
3. Lymphatic trunks and collecting ducts – trunks drain lymph from the
vessels and named for the regions they serve. Lumbar trunk – lower limbs,
lower abdominal wall , and pelvic organs; intestinal trunk – abdominal
viscera; intercostal and bronchomediastinal trunk – thorax; subclavian trunk
– upper limb; jugular trunk – portions of the neck and head. Trunks then
join the collection ducts. Two collecting ducts: thoracic duct – larger and
longer of the two ducts and the right lymphatic duct.
Lymphatic Pathway
Lymphatic capillary ► Lymphatic vessel ► Lymph Node► Lymphatic
Vessel ► Lymphatic Trunk ► Collecting duct ► Subclavian vein
Lymph
Lymph is simply tissue fluid(interstitial fluid) that has entered a lymphatic
capillary. Lymph formation prevents the accumulation of excess tissue
fluid, or edema.
Tissue fluid delivers the nutrients, oxygen, and hormones required by the
cells.
Tissue fluid collects and carries away some cellular waste products.
90 percent of the tissue fluid returns to the capillary bed. Here it again
becomes plasma and continues its journey throughout the body as part of the
venous circulation.
Lymph is the 10 percent of the tissue fluid that is left behind. Normally the
amount of lymph circulating in the body is one to two quarts and it makes up
one to three percent of the body weight [6].
The role of tissue fluid is to deliver the groceries to the cells. The role of
lymph is to take out the trash that is left behind and to dispose of it.
As lymph continues to circulate between the cells it collects waste products that were left
behind including dead blood cells, pathogens, and cancer cells. This clear fluid also
becomes protein-rich as it absorbs dissolved protein from between the cells.
Lymph has 2 main functions:
1. returns the smaller protein molecules and fluid to the bloodstream
2. transports foreign particles to the lymph nodes
How does lymph move without a pump???
The lymphatic system is a pumpless system. Lymph is transported by:
1. milking action of the skeletal muscles
2. pressure changes during breathing
3. smooth muscle contraction in the larger lymph vessels
Any interruption in lymph flow can result in edema.
Lymph Nodes
Lymph nodes (lymph glands) are located along the lymphatic pathways.
They contain large numbers of lymphocytes and macrophages, which fight
invading microorganisms.
Structure:
Lymph nodes are kidney/bean shaped, less than one inch long, and buried in
connective tissue that surrounds them. Lymphatic vessels leading to the
node (afferent vessels) and (efferent vessels) leading out of the node. The
inside of the lymph node is divided into lymph nodules. The nodules are the
structural units of the lymph nodes. Lymph sinuses are found in the lymph
nodules that provide a system of chambers for the lymph to flow.
Functions:
1. filter potentially harmful particles from lymph before returning it to the
bloodstream.
2. monitor body fluids (surveillance) provided by lymphocytes and
macrophages
A. Lymphocytes – lymph nodes along with red bone marrow are
centers for lymphocyte production. These cells attack the
invading viruses, bacteria, and other parasitic cells that come
into the node.
B. Macrophages – engulf and destroy foreign substances, damaged
cells, and cellular debris.
Lymphatic Organs
Tonsils
Masses of lymphoid tissue that help protect against invading bacteria (oral or
nasal) Tonsils are one of you first lines of defense.
3 types of tonsils
1. Palatine tonsils--located on each side of the throat.
2. Pharyngeal tonsils--also known as adenoids are near the posterior
openings of the nasal cavity
3. Lingual tonsils--near the base of the tongue
Thymus
A soft, bilobed structure anterior to the aortic arch. Is larger in children than
in adults. Mainly responsible for producing a hormone called thymosin that
helps with the maturation of T lymphocytes.
Spleen
The largest lymphatic organ. Located in the left portion of the abdominal
cavity, inferior to the diaphragm, and posterior and lateral to the stomach.
Macrophages that line the spleen help to filter blood (damaged RBC’s) and
cellular debris.
Some common problems of the lymphatic system include:
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Glandular fever - symptoms include tender lymph nodes
Hodgkin’s disease - a type of cancer of the lymphatic system
Oedema - swelling caused by too much fluid in the tissues
Tonsillitis - infection of the tonsils in the throat.