The Lymphatic System
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Last updated 30 March 2006
The Lymphatic System
This page of notes is based purely on Dr. Ashwell's Lecture Summaries.
Click here to go to the lymphatics system notes
- The lymphatic system consists of:
- Lymphatic vessels (or lymphatics);
- Lymphoid tissue, which consists of circulating
lymphocytes as well as aggregates of lymphocytes
and their associated cells.
The Functions of the Lymphatic System
of tissue fluid formed in the
The removal by mononuclear
phagocytic series cells of cell debris and foreign matter (e.g. bacteria) and the prevention
of bacterial and foreign material from entering the blood
Production of lymphocytes and control of the
Lymphatic capillaries form plexuses in tissue spaces.
These have much wider meshes than those of adjacent blood capillaries.
They often begin as dilated lymphatics with blind endings.
The endothelium of lymphatic capillaries is permeable to much larger molecules
than blood capillaries (e.g., cell debris, bacteria and colloidal material).
- Lymph from most tissues is clear and colourless.
- However, lymph from the small intestine (duodenum, jejunum and ileum)
is milky due to the absorption
of fat globules (chylomicrons) and is called chyle.
- The terminal lymph capillaries from this region are
- Lymphatic capillaries are absent from avascular structures (e.g. epidermis,
cornea, articular cartilage)
and from the CNS and bone marrow.
- Deep lymphatic channels (trunks) in the adult often accompany
the other vessels.
The Flow of Lymph Fluid
aid the flow of lymph fluid
from tissue spaces to lymph nodes
and finally to the venous bloodstream:
- "Filtration pressure" in tissue
spaces, generated by filtration of fluid under pressure from the haemal
- Contraction of neighbouring muscles
compresses the lymph vessels, moving lymph in the direction determined by the arrangement
- Pulsation of adjacent arteries;
- Respiratory movements and the low blood pressure
in the brachiocephalic vein during inspiration.
- Smooth muscle in the walls of lymphatic trunks is most marked proximal
to their valves. Stimulation of sympathetic
nerves causes their contraction. Pulsatile contractions in the thoracic
duct are known to occur also.
There are several important roles performed by lymph
- Provision of a labyrinth of channels of large surface area and volume
through which lymph slowly percolates;
- Trapping of foreign material in lymph nodes
and exposure to nodal macrophages;
- Production of lymphocytes and a pool of stem cells to become antibody-producing B
lymphocytes and mature T lymphocytes;
- Interaction between antigen-bearing mononuclear
phagocytes and lymphocytes to produce immune responses;
- Re-entry of blood-borne lymphocytes into lymphatic channels and thence to the haemal circulation;
- Humoral antibody production and its addition to lymph and ultimately the
- A normal young adult body contains about 400 to 450 lymph nodes.
- The limbs and superficial body
wall have relatively few.
- The arm and superficial
thoracoabdominal wall (down to the umbilicus) contain about 30
- The leg, superficial buttock,
infraumbilical abdominal wall and perineum
contain only about 20 nodes.
- The head and neck
carry about 60 to 70 nodes.
- The thorax has up to 100 nodes
in its deep walls and contents.
- The abdomen and pelvis have 230 or more nodes in
its deep walls and contents.
Major Lymphatic Channels
The Thoracic Duct
This is the largest lymphatic channel in the body (38 to 45 cm in length).
It extends from the 1st lumbar vertebra to the root of the neck.
This lymphatic channel drains lymph from the left arm, left neck and head, left thorax, left upper abdomen (to umbilicus), both
sides of the abdomen below the umbilicus and both lower limbs.
- It arises either from the confluence
of several lymph channels on the posterior abdominal wall, or in
some individuals (20%), these lymph channels drain into a dilated
sac known as the cisterna chyli.
- The cisterna chyli when present lies anterior
to the L1 and L2.
- When it reaches the level of the T5
it inclines to the left until it finally
terminates either into the junction of the left internal jugular and subclavian
veins or one of those veins only.
- In 50% of people it has a terminal
dilatation or ampulla.
- Before it terminates, it receives the left jugular (draining lymph from left head and neck) and left subclavian (from left arm) trunks.
The Right Lymphatic Duct
On the right side of the body:
- Lymph from the right head and neck,
right arm is drained by the right
- The right thorax is drained by the right
- The abdomen (down to the convex
surface of the liver) is drained by the right bronchomediastinal trunk.
- In 20% of people these join
into a single channel, the right
- This drains into the junction
of the right internal jugular and right
subclavian veins or each of these veins separately.
Lymphatic Drainage of the Head and Neck
Nodes in the head and neck may be divided into a terminal group
related to the carotid sheath (deep
cervical), and outlying groups.
The deep cervical nodes drain into the jugular trunk, which enters the thoracic
duct on the left and the right
lymphatic duct or jugulo-subclavian junction
on the right.
The Deep Cervical Lymphatic Nodes
These nodes are divided into superior
and inferior groups.
- The superior group lies adjacent
to the upper internal jugular vein, usually deep to the sternocleidomastoid muscle.
- The inferior group lies adjacent
to the lower internal jugular vein.
Superficial Groups of Lymph Nodes
In the head: occipital,
retroauricular (mastoid), parotid,
In the neck: submandibular,
submental, anterior cervical,
- Efferent lymph vessels from these nodes drain to the
Lymphatic Drainage of the Thorax
The left and right
bronchomediastinal trunks drain into the thoracic duct
and the right lymphatic duct respectively;
- Parietal nodes:
- Visceral nodes:
- Tracheobronchial (superior and inferior)
Lymphatic Drainage of the
Abdomen and Pelvis
The lymph drainage of the abdomen is mainly via the thoracic duct.
Three terminal groups of lumbar nodes are
identified; preaortic, lateral aortic, retroaortic:
Preaortic Lymph Nodes
Preaortic lymph nodes consist of:
- Coeliac nodes, draining gastric, hepatic, pancreaticosplenic nodes;
- Superior mesenteric nodes, draining nodes in
- Inferior mesenteric nodes, draining nodes in
- These are associated with the appropriate
- Efferent lymph vessels from these nodes form intestinal
trunks, which enter the abdominal confluence
of the lymph trunks and then the thoracic duct.
Lateral Aortic Lymph Nodes
The efferent lymph vessels of these form paired lumbar trunks.
The structures whose lymph vessels drain into the lateral aortic lymph nodes are:
- Suprarenal glands;
- Abdominal ureter;
- Posterior abdominal wall;
- Testis and ovary;
- Uterus and uterine tube.
- Several other named groups of nodes are known:
- Common iliac nodes;
- External iliac nodes;
- Internal iliac nodes.
Retroaortic Lymph Nodes
These nodes drain the posterior abdominal wall.
They may actually be peripheral nodes of the lateral group.
The thymus is responsible for the production of thymus-processed
It also has humoral secretory functions (producing
thymulin, thymopoietin, thymosin alpha I and thymosin beta 4).
These regulate lymphocyte production, differentiation and activities within the
thymus as well as throughout the body's lymphoid tissue.
It may thus be regarded as an endocrine organ.
- At birth it weighs about 10 to 15 g, growing until puberty when it weighs 30 to 40 g.
- After puberty it gradually diminishes in size, being
replaced by fatty tissue, and weighs only about 10 g during middle age.
- In early life it consists of two
unequal pyramidal lobes connected by loose connective
- It lies in the superior and
- The thymus extends inferiorly as far as the 4th costal cartilage.
- It extends superiorly, tapering
into the neck as far as the inferior
poles of the thyroid gland.
The Tonsils and Waldeyer's Ring
Waldeyer's ring consists of nasopharyngeal, lingual and palatine tonsils.
Together, these form a protective ring at the entrances of the nasal and oral cavity into the pharynx.
The spleen lies in the left hypochondrium, to the left of the stomach
It consists of a capsule surrounding white
and red pulp.
- The red pulp contains sinuses
filled with blood, while the white pulp
consists of lymphoid tissue: reticular
fibres and lymphocytes (both T and B).
- The spleen is involved in phagocytosis of foreign debris in the blood, immune responses, haemopoiesis
and erythrocyte storage.
- Although it is of great importance in the defence of the body, it is not
- Many of its functions may be taken
over by other lymphoid tissue or the liver if the spleen is removed.