In this video we will discuss the
lymphatic system of the human body. Lymphatic system, is a part of both
the circulatory and immune systems. Lymphatic system consists of 3 major
components. Namely, lymph, lymphatic vessels, and lymphoid organs. We will discuss each
components in detail in three separate videos. This video discusses the Lymphatic vessels. Lymphatic vessels carry lymph from
the interstitial spaces of tissues, to the blood stream. Mainly they carry
proteins and large particulate matter, which can't be absorbed directly into the
blood capillaries. So lymphatic vessels act as an accessory pathway to return proteins from
the interstitial tissue, to the blood stream. Lymphatic vessels consist of, lymphatic
capillaries, collecting lymphatic vessels, lymphatic trunks, and the lymphatic ducts. The lymphatic capillaries are formed in the
interstitial spaces, as blind ended sacs. They are made of single layer of endothelial
cells. These endothelial cells are arranged in an overlapping fashion. Such that, it acts
as a unidirectional flap valve. Fluid and its suspended particles, can enter the lymphatic
capillaries from the interstitial tissue. But once entered the lymphatic capillaries, the
fluid and its suspended particles cannot escape out, due to the overlapping arrangement of the
endothelial cells of the lymphatic capillaries. As any back flow will close the flap valve. There
are also special types of lymphatic capillaries in the small intestine. These specialised
lymphatic capillaries are called lacteals. These lacteals absorb nutrients from the small
intestine, and drain it into the blood stream. It should be noted that the collapse of the
capillaries is prevented, by anchoring filaments binding the endothelial cells to the surrounding
structural tissues, in the interstitial spaces. The lymphatic capillaries join
to form larger lymphatic vessels, that carry the lymph away from the
tissues and into the bloodstream. The lymphatic vessels are two
types, superficial and deep vessels. Superficial lymphatic vessels run along the
subcutaneous layer of the skin. It accompanies the vein. The deep lymphatic vessels carry lymph away
from the internal organs to the blood stream. It accompanies the artery. The superficial lymphatic
vessels drain into the deep lymphatic vessels. Both superficial and deep lymphatic
vessels go through lymph nodes. The lymphatic vessels draining into the
lymph nodes are called afferent vessels, and the vessels that carry lymph away from the
lymph node are called efferent lymphatic vessels. These efferent lymphatic vessels join to
form larger vessels called lymphatic trunks. There are four paired and one unpaired
lymphatic trunk. They are named according to the region of the body; they drain the lymph.
The four paired lymphatic trunks are, jugular, which drains head and neck regions. Subclavian
lymphatic trunk, which drain the upper limbs. Bronchomediastinal lymphatic
trunk, which drains the chest. Lumbar lymphatic trunk drains the abdomen, pelvis,
and lower limb regions. The one unpaired lymphatic trunk is called Intestinal trunk, it drains chyle,
that is lymph rich in fats, from the intestines. The lymphatic trunks merge together
to form the two lymphatic ducts. Namely, right lymphatic duct and the thoracic
duct. The right jugular, the right subclavian and the right Bronchomediastinal lymphatic
trunks join to form the right lymphatic duct. The right lymphatic duct, then
drains into venous system, at the junction of the right subclavian
vein, and the right internal jugular vein. The paired lumbar trunks join to form the cisterna
chyli. The intestinal trunk usually drains into the left lumbar trunk, or it may directly drain
into the cisterna chyli. The cisterna chyli superiorly continues as the thoracic duct. The
thoracic duct enters the thoracic cavity through the aortic hiatus and ascends, to the right of
the midline, between the aorta and azygos vein. At the level of T5 vertebra, it crosses the midline
to reach the left side of the vertebral column. Then it ascends to the thoracic inlet and reaches
the root of the neck. Where it arches forward and drains into the venous system, at the junction
of left subclavian vein and left jugular vein. The lymphatics from the lower six
intercostal spaces of both sides, joins to form descending thoracic lymphatic trunk.
Which in turn drains into the thoracic duct. Thoracic duct, also receives the left upper
intercostal lymph trunk, that drains the left upper 5 intercostal spaces. It should be noted
that, the right upper intercostal lymph trunk, that drains the right upper 5 intercostal
spaces drain in to the right lymphatic duct. Before the termination of the thoracic
duct. It receives, left jugular lymph trunk, left subclavian lymph trunk, and the
left bronchomediastinal lymph trunk. So, 75% of the lymph of the human body is drained
by the thoracic duct. Except the right side of the head, neck, thorax, and right upper limb. These
regions are drained by the right lymphatic duct. Like veins, the lymphatic vessels, trunks and
ducts, have valves to prevent backflow of lymph. But number of valves are more than the veins. The right lymphatic, and the thoracic
duct opening into the venous system, is guarded by bicuspid valves. This allows
only the lymph to enter the blood stream. And prevents the blood from
entering the lymphatic system. There is no pump in the lymphatic system
like the heart in the cardiovascular system. The pressure gradients to move lymph through the
vessels come from the skeletal muscle contraction, respiratory movement, and contraction of
smooth muscles of the lymphatic vessels. Almost all tissues of the body have lymph
channels that drain excess fluid directly from the interstitial spaces. But
they are absent in the epidermis, central nervous system, bone marrow,
teeth, and other avascular tissues. It was believed for decades that central nervous
system does not have a lymphatic system, but recent research has revealed that, central nervous
system also has a lymphatic drainage system. It is too complex to explain it, in
this video. I have given the link to the research paper in the description.
Interested people can have a look at it. So, we conclude the video here.
Hope the video was useful. We will discuss about the formation
of the lymph, in the next video.