Lymphatic System

What is the Lymphatic System?

The lymphatic system is a one-way drainage system which transports a
colourless fluid called lymph, which consists of fluid, plasma proteins,
fats, cells and debris in the form of dead blood cells and bacteria, from
the tissues to the blood vascular system. It is also part of the body's
immune system, filtering the lymph as it passes through the lymph nodes,
killing bacteria by the action of blood cells called phagocytes and
producing another form of blood cell called lymphocytes. Nodes are usually
situated in groups, such as are found in the axilla (armpit) or inguinal
area (groin), and are often surgically removed in the treatment of cancer,
for example, at the same time as a mastectomy.

The lymphatic system is unlike the blood vascular system which is a true
circulatory system. Blood is pumped by the heart to all parts of the body
through the arteries to provide tissues with a constant supply of oxygen
and nutrients which are necessary for the body to work efficiently. The
transfer of oxygen, nutrients, fluid and protein from the blood to the
tissues takes place through the walls of the smallest blood vessels called
capillaries and is called capillary filtration. Approximately 90% of the
waste products and carbon dioxide pass from the tissues into the blood
stream in the same manner, that is, back through the capillary walls. This
complex exchange through the capillary walls takes place because of the
difference in the pressure of the blood and the pressure of the tissues at
the arterial and venous sections of the capillary circulation. The
de-oxygenated blood is then returned through the veins to the heart and
onto the lungs where it is re-oxygenated and pumped again around the
body.

It is imperative that the fluid and proteins are returned to the blood
circulation to maintain the normal body fluid balance and to enable the
waste products to be excreted from the body, but the remaining 10 % of
the fluid, large protein molecules and other particles in the tissues are
unable to pass back through the capillary walls and into veins due to the
pressure gradient. So, this mixture of fluid and large molecules is able to
pass from the blood into the tissues due to a relatively high blood
pressure in the capillaries but is unable to pass from the tissues back to
the blood due to a relatively low pressure in the tissues and the large size
of the protein molecules. This excess fluid and waste products are
returned to the blood system in the lymphatic system. The transportation
of lymph through the system takes place through a network of vessels.
The large particles and proteins pass, with tissue fluid, into the smallest
lymphatic vessels called capillaries which join to form larger vessels called
lymphatic collectors. On entering the lymphatic capillaries, the tissue
fluid is called lymph. The collectors possess one-way valves situated every
few millimetres along their course. These valves direct the flow of lymph
and prevent any back flow, the section of a collector between two valves
being called a lymphangion. Collectors join and become larger, eventually
forming the two largest lymphatic trunks in the body called the thoracic
duct and the right lymphatic duct. These empty their contents into the
blood system at the junction of two large veins on either side of the lower
neck immediately behind the collar bones. The excess fluid and waste
products are transported in the blood to the kidneys where they are
excreted in the urine.

Lymph drainage takes place through a superficial and a deep system and
there are connections between the two systems. The superficial lymphatic
vessels drain the skin and subcutaneous tissues and are situated
immediately below the skin. They may run independently or accompany
superficial veins. The deep lymphatic vessels drain the musculature,
internal organs and deep tissues. They always accompany deep veins with
which they are in close proximity. Lymph nodes do not have the ability to
regenerate, so those that are removed surgically in the treatment of
cancer are never replaced.

The body surface is divided into specific superficial lymphatic drainage
areas called territories, which drain lymph to specific lymph nodes. For
example, the trunk is divided into four territories, two upper and two
lower, the vertical dividing line being the mid-line of the body and the
horizontal dividing line being approximately at waist level. The dividing
line between any two territories is called a watershed. The upper
territories drain to their respective armpit nodes, right and left, and the
two lower territories drain to their respective groin nodes, right and left.

In addition, the two upper limbs and the two lower limbs are also divided
into territories, each limb being drained by the respective armpit or groin
nodes (See the charts to the right. These are available for sale from the
Publications page).

Lymph is pumped through the system in three ways:

1. Breathing raises and lowers the pressure within the abdomen and chest
with each inspiration and expiration. This causes a sucking effect in the
chest and a pumping effect in the abdomen which assist the lymphatic
flow in the deep lymphatic system including the two largest vessels in the
body, the thoracic duct and the right lymphatic duct. This is known as the
respiratory pump effect.

2. Contraction and relaxation of muscles during exercise create a
pumping effect on all tissues in the area by raising and lowering pressure,
including lymphatic and blood vessels. This is known as the muscle pump
effect.

3. Lymph is continually pumped from all parts of the body by the
rhythmical contraction of small sections of the lymph vessels, called
lymphangions, at a rate of 6-10 beats per minute when the body is at
rest. These contractions, and consequently the rate of the lymph flow
through the vessels, are increased by up to ten times, i.e. to 60 beats
per minute, in time of need, for example during exercise