Unit 8B - Impact of lymphatic disorder and associated treatments
Aim
Understand the impact of the disorder on the physiology of the lymphatic system and the associated corrective
treatment.
Introduction of The Lymphatic System
The human Lymphatic system comprises primarily three different functions. The first function is returning
“excess” interstitial fluid (Interstitial fluid is the body fluid between blood vessels and cells, containing nutrients
from capillaries by diffusion and holding waste products discharged out by cells due to metabolism) to the
blood, From all the fluid that leaves the capillary, about 90% is returned back, meaning the other 10% does not
return becomes part of the interstitial fluid that encompasses the tissue cells. Tiny protein molecules may often
“leak” through the capillary wall further increasing the osmotic pressure of the said fluid[1]. This further hinders
the return of the fluid into the capillaries, fluid tends to gather within the tissue spaces. Subsequently, blood
volume and blood pressure decrease significantly and the volume of the tissue fluid increases, which results in
extreme swelling. Lymph capillaries will pick up on the overabundance of interstitial fluid and proteins,
returning the, to the venous blood. So once the fluid finally enters the lymph capillaries, it is named the Lymph.
The second function within the human lymphatic system is the absorption of fats/ fat-soluble vitamins from the
digestive system snd the successive transport of these materials to the venous circulation. The mucosa (A
mucous membrane or mucosa is a membrane that lines various cavities in the body and covers the surface of
internal organs. It consists of one or more layers of epithelial cells overlying a layer of loose connective tissue)
that ropes the small intestine is engulfed with finger-like projections called villi which absorb nutrients from the
food you eat and then shuttle those nutrients into your bloodstream so they can travel where they're needed.
There are blood capillaries and special lymph capillaries, named lacteals (the lymphatic vessels of the small
intestine which absorb digested fats), blood capillaries are known to absorb the most nutrients, however, these
fats and fat-soluble vitamins are being absorbed by the lacteals[2]. That lymph in the lacteals has a white colour
to them due to their high-fat content, called chyle.
The third area, most well known of the function of the
lymphatic system is the defence against overpowering
microorganisms as well as diseases, playing a huge role in
the bodies immune system, as the primary site for cells
linking with the adaptive immune system includes B-cells
and T-cells. Lymph nodes and lymphatic organs filter out the
lymph to move foreign particles, these organs also have
lymphocytes that destroy organisms that try invading. The
cells within the lymphatic system behave in a manner to the
antigens found or by cells directly and even by other
“dendritic cells”, which act as messengers between the
innate and the adaptive immune systems. When an antigen
is identified, an immunological response begins which
involves the activations as well as enlistment for more cells
(production of antibodies and cytokines)[3].
Lymph
The Lymph is a fluid that runs through the lymphatic system, a system that is composed of lymph channels
and intervening lymph nodes which there function being to return fluid to the central circulation from the
tissues. The interstitial fluid streams into the lymph capillaries, this fluid is then transported along a larger
lymphatic vessel through the lymph nodes, which then substances are removed by tissues lymphocytes and
circulating lymphocytes are added to the fluid, in turn, then emptying into the right/left subclavian vein, where it
then mixes with central venous blood. Because the lymph is derived from the interstitial fluid, its composition is
constantly changing as blood and neighbouring cells exchange materials within the interstitial fluid. Blood
supplies nutrients and vital metabolites to the cells of a tissue and collects the waste products that are
,produced, this requires the exchange of respective constituents between blood and tissue cells[4]. The
exchanges do not happen directly however enters the intermediary which is the interstitial fluid, occupying the
spaces found between the cells. When the blood and neighbouring cells regularly take and give substances
from the fluid. Water and other types of solutes can pass between the fluid and blood through diffusion via the
gaps between the capillary walls which are named intercellular clefts; meaning that they are a dynamic
equilibrium with one another[5].
When circulating the lymphatic system, tubular vessels travel the lymph back to the blood, which overall
replaces the volume lost during the formation of interstitial fluid, these channels are called the lymphatic
channels or lymphatics[6]. Compared to the cardiovascular system, the lymphatic system is not shut. There are
amphibian and reptilian species that have lymph hearts that are essentially central pumps, which are usually
found in pairs, however humans and some other mammals do not have a lymph heart. Even though they have
low pressure, their movement occurs due to peristalsis which is a thrust of the lymph due to alternate
contractions and relaxation of the muscle tissue, values and compressing during contraction of adjacent
skeletal muscle and arterial pulsation. Lymph that goes through the lymph vessels from the interstitial area
does not flow backwards due to the presence of valves. If there is excessive hydrostatic pressure that
accumulates in the lymphatic vessels, some fluid may leak back into those areas which then contributes to the
formation of edema[7].
Lymphatic Vessel
Unlike blood vessels, Lymphatic vessels only carry fluid away from tissues. The smallest types of lymphatic
vessels are the lymph capillaries, which start in the tissue spaces as “blind-ended” sacs. These capillaries are
located in all regions of the body apart from the bone marrow, the central nervous system and tissues like the
epidermis, which lack blood vessels[8]. The wall of the lymph capillary is made up of endothelium which simply
squamous cells overlap to form a one-way valve, this is a perfect arrangement as it permits fluid to enter the
capillary but also prevents the lymph from leaving the vessel itself[9].
The structure of these vessels is based on blood vessels,
which has an inner lining to it of a single flattened
epithelial cell, composed of a certain type of epithelial
called endothelium (the name for these cells are
endothelial cells)[10]. This layer acts to mechanically
transport fluid from the basement membrane (for tissue
support and acts as a platform) that rests are suspended,
so it leaks with ease. The layer after that is where the
smooth muscle is located and arranged in a circular
fashion around the endothelium, that its contractions or
relaxing periods alter the calibre of the lumen[11]. The outer layer, which is called the adventitia, that consists of
fibrous tissue. Its structure is seen only in larger lymphatics, whereas smaller lymphatics have a few layers
Lymph capillaries lack the muscle layer and outer adventitia, as they move forward, they are joined with other
capillaries and continually grow larger, to then take on the adventitia, then the smooth muscle. Conducting
system of the lymphatic consists of two types, the initial lymphatics that specialize in the collection of the lymph
from the fluid, and the larger lymph vessels that set the lymph ahead. Compared to the cardiovascular system,
the lymphatic system is not closed and does not have a central pump[12]. Its movement occurs even in low
pressure.
The lymph capillaries empty into larger collecting lymphatics. These are contractile lymphatics transport lymph
using a mix of smooth muscle walls, which contract to aid in transporting lymph, additionally valves to prevent
the lymph from flowing backwards. The collecting lymph vessel gathers lymph from more and more lymph
capillaries along its length, it becomes larger and eventually becomes an afferent lymph vessel as it enters a
lymph node. The lymph filters through the lymph node tissue and leaves via an efferent lymph vessel. The
efferent lymph vessel may drain directly into one of the lymph ducts or may empty into another lymph node as
its afferent lymph vessel[13]. Both the lymph ducts return the lymph to the bloodstream by emptying it into the
subclavian veins. The Lymph vessels consist of functional units known as lymphangiomas which are segments
, separated by semilunar valves. These segments propel or resist the flow of lymph by the contraction of the
encircling smooth muscle depending upon the ratio of its length to its radius[14].
Lymph Node (Glands)
A lymph node (gland) is a bean-shaped organ in the lymphatic system and also the adaptive immune system.
There is a large number of lymph nodes that are linked throughout the body by the lymphatic vessels. They
are important sites of lymphocytes that include B and T cells. Lymph nodes are critical for the proper function
of the immune system, filtering out any foreign particles including cancer cells, but it does not have a
detoxification function. In the lymphatic system, a lymph node is known as the secondary lymphoid organ. A
lymph node is sealed in a fibrous capsule and is made up of an outer cortex and an inner medulla[15]. Lymph
nodes become inflamed or enlarged in various diseases, which may range from trivial throat infections to
life-threatening cancers. The condition of lymph nodes is very important in cancer staging, which decides the
treatment to be used and determines the prognosis. Lymphadenopathy refers to glands that are enlarged or
swollen. When inflamed or enlarged, lymph nodes can be firm or tender[16].
These glands are found in various areas so the body,
more so concentrated near the trunk or divided into
groups. Overall there are 450 nodes within an adult
body. Some nodes can be felt when enlarged, for
example, the axillary lymph nodes that are located
under the arm, the head and neck have the cervical
lymph nodes and the inguinal lymph nodes are found
near the groin crease. Most of the lymph nodes lie
within the trunk which is adjacent to many other
important organ structures within the body like the
tracheobronchial lymph nodes (found in the trachea
and main bronchi) and the paraaortic lymph nodes[17].
The draining process of the lymph nodes ranges from
person to person; even asymmetrical on each side of
the body. In the central nervous system, there are no
nodes located, this separates the body by the blood-brain barrier[18].
The main function of these nodes is to filter and identify infection to then fight it off. In order for this to happen,
nodes contain lymphocytes which is a white blood cell, that includes B cells and T cells. They will circulate
throughout the bloodstream, to then enter and reside in the nodes. B cells will produce antibodies, meaning
they have a target, which would be an antigen, that then binds to it; this stimulates an immune response. Each
one of the B cells is different types of antibodies, so this process is driven in the lymph nodes. It enters the
bloodstream as naive cells produced in the bone marrow. Once entered, they will enter the lymphoid follicle,
where they will then multiply and divide, producing antibodies of different types. If these cells are stimulated,
they will go on to make more antibodies to help fight any future infections the body may get, if not stimulated it
will go through apoptosis and die[19].
Thymus Gland
This gland is one of the specialized primary lymphoid organs of the immune system. Within this gland, the
thymus, its T-cells mature. These cells are critical to the adaptive immune system, where the body adapts
specifically to foreign invaders[20]. The thymus is located in the upper front part of the chest, in the anterior
superior mediastinum which is behind the sternum, and in front of the heart. It is made up of two lobes, each
consisting of a central medulla and an outer cortex, surrounded by a capsule. The thymus is made up of
immature T cells that are called thymocytes, as well as lining cells called epithelial cells which help the
thymocytes develop. T cells that successfully develop react appropriately with Major histocompatibility complex
immune receptors of the body and not against proteins of the body[21]. The thymus is largest and most active
during the neonatal and pre-adolescent periods. Once a human hits early teens, the thymus begins to
decrease in size and activity and the tissue of the thymus is gradually replaced by fatty tissue. Nonetheless,
