The lymphatic system carries excess tissue fluid called lymph throughout the body and returns it to the bloodstream. It is made up of lymph nodes, lymph vessels, and lymphatic organs. The lymphatic system has four main functions: returning excess lymph to the bloodstream, filtering lymph in lymph nodes to remove bacteria and foreign particles, transporting waste from the intestines, and producing lymphocytes and antibodies for immunity. It contains diffuse lymphatic tissue in various organs, nodular tissue in lymph nodes and organs like the spleen and thymus gland. Lymph flows through a network of vessels and is filtered through lymph nodes located throughout the body in specific lymph centers.

1. THE LYMPHATIC
SYSTEM
By
Dr. Luay Obed Hamza

2. What is the Lymphatic System?
• The lymphatic system is a network of: capillaries, vessels, ducts, nodes and tissues
• It is part of the circulatory system
• It carries excess tissue fluid (lymph) back to the circulating blood
• It is found in all regions of the body except the central nervous system and bone marrow
• It produces lymphocytes, which in turn produce antibodies – so technically, it has a role in
immunity
• The lymphatic system includes the lymphatic tissue and the lymphatic vessels.
• Lymphatic vessels include the lymph, capillaries and lymph vessels which anastomosis with
venous channels.

3. Components of the Lymphatic System

4. 4 Functions of the Lymphatic System
1. Return excess lymph to the circulating blood
2. Filter lymph to remove bacteria and other foreign particles.This takes places in
the lymph nodes
3. Transport waste materials – the products of fat digestion and fat-soluble
vitamins from the lacteals of the intestinal villi to the circulation
4. To produce lymphocytes, which in turn make antibodies

5. Types of lymphatic tissue
1- Diffuse lymphatic tissue
2- Nodular lymphatic tissue
2- Lymphatic organ

6. A- Lymphatic tissue and organs
1- Diffuse lymphatic tissue:
occurs in the mucous
membranes of the visceral
body systems. In the intestine,
there are called (Payers
patches) similar accumulations
occur in the greater omentum
(milk spot) and in the pia
matter (arachnoid cell
accumulations).

7. A- Lymphatic tissue and organs
2-Tonsils : are sub epithelial
accumulations of lymphatic
tissue i n the pharynx.The
major ones form a ring at the
entrance to the esophagus and
larynx where they contact
potential pathogens.

8. A- Lymphatic tissue and organs
3-Lymph nodes:
• are encapsulated collections of lymphatic tissue located along the course of
lymphatic vessels.
• Lymph nodes are located around the body and some are superficial so can be
palpitated.
• Several afferent lymphatic vessels enter the convex margin of the node and one or
two efferent vessels leave a depressed hilus.
• Within the lymph nodes of most domestic mammals the lymphatic nodules are
concentrated peripherally in the cortex, but in the pig, they are centrally located.
• Lymph flow is also reversed in the lymph nodes of pigs (the afferent vessels enter at
the hilus and the efferent vessels leave through the other parts of the capsule).

9. Lymph nodes
• Lymph nodes are named according to their
location, and these are relatively constant
among the different domestic species.
Functionally, analogous groups of lymph
node (i.e. those which receive afferent
vessels from approximately the same
region in the various species) are termed
lymph centers. There are 19 lymph centers
in the body: 5 in the head and neck, 5 in the
thorax and thoracic limb, 4 in the abdomen,
and 5 in the pelvis and pelvic limb.

10. Lymph nodes

14. A- Lymphatic tissue and organs
4-Hemal nodes:
• differ from regular lymph nodes in that they filter blood instead of lymph.
• Among the domestic mammals they are found only in the ruminants.
• Hemal nodes are found mainly in the cephalic and cervical regions as well as in
the thoracic, abdominal and pelvic cavities. They are often found near regular
lymph nodes.
• They are easily distinguished from the lymph node, however, by their reddish
brown- (vs. blue-grey) color.

15. A- Lymphatic tissue and organs
5-Spleen:
• the largest lymphoid organ in the body.
• It -is a flat, elongated structure interposed in the blood stream located next to
the left abdominal wall.
• In the fetus it produces red blood cells. In the adult it stores red blood cells that
can be squeezed back into circulation when needed.
• It also produces lymphocytes, stores iron, and destroys worn out red blood
cells.
• The hilus is the area where vessels and nerves enter the spleen. It is a long
groove in the carnivores, horse and pig, and a small indentation in ruminants.

17. A- Lymphatic tissue and organs
6-Thymus:
• The thymus develops from the ventral diverticulae of
the third pharyngeal pouches. In early development,
these diverticuli elongate into a tube-like structure
which contacts the pericardium caudally.
• At birth, the fully developed, generalized thymus
consists of cervical lobes (left and right) an
intermediate lobe and the thoracic lobe.
• In the carnivores and horse, only the thoracic lobe is
developed. The cervical lobes are prominent in
ruminants and the pig, and these are connected to the
thoracic lobe by an unpaired intermediate lobe.

18. B-Lymphatic vessels
Lymphatic vessels have a similar
structure to veins.
Lymph flow is mainly passive and
relies on the contractions of
surrounding muscles to move the
lymph along.
The valves prevent the backflow
and pooling of lymph in the vessels.

19. B-Lymphatic vessels

20. B-Lymphatic vessels
• Lymphatic vessels are found throughout the entire body.
• The fluid which they carry is termed lymph, and it varies in composition according to the
activity of the animal and the part of the body from which it originates.
• The larger lymphatic channels include the following:
1- Left and right jugular trunks (tracheal duct) course parallel to the trachea.The right one
may unite with the axillary lymphatic channels to form the right lymphatic duct.The left
jugular trunk may unite directly with the thoracic duct near the venous angle.
2-The thoracic duct is the large lymphatic channel which conveys lymph from the cysterna
chyli to the left venous angle. Its origin from the cysterna chyli is single in ruminants and
pigs, but in dogs and horses it is double (sometimes even triple in dogs).The thoracic duct
traverses the diaphragm through the aortic hiatus in all species except the ruminants where
it courses independently through the musculature of the lumbar part of the diaphragm.

21. B-Lymphatic vessels
The cysterna chyli lies on the right, dorsal side of the aorta, between the
origins of the diaphragmatic crura. It extends from the second lumbar vertebra to
the last thoracic vertebra.The cysterna chyli receives the following lymphatic
channels:
a- Lumbar trunks (left and right)
b- Celiac trunk
c- Intestinal trunk
d- Colic trunk
e- Jejunal trunk
f- Gastric trunk
g- Hepatic trunk

23. Lymph nodes of the head
1- Parotid lymph center:
The parotid lymph center consists
of one or more parotid lymph
nodes at the base of the ear close
to the temporomandibular joint
and covered by the parotid gland
or the masseter muscle. The
afferent lymphatic drains the
dorsal half of the head, the orbit
and the masticatory muscles.

24. Lymph nodes of the head
2- Mandibular lymph center:
The mandibular lymph center comprises a number of lymph
nodes located between the hemi mandibles, in close proximity to
the greater sublingual salivary gland and the mandibular salivary
gland.They can be easily identified on palpation ( Fig. 13.8,9 and 12).

25. Lymph nodes of the head
3- Retropharyngeal lymph center:
The retropharyngeal lymph center is divided into a medial and
a lateral group ( Fig. 13.8,9 and 12). In the horse the lateral
retropharyngeal lymph node drains from the guttural pouch. All
lymph from the head passes through the medial retropharyngeal
lymph nodes before it drains into the tracheal (jugular) trunk (Fig.
13.12).

29. Lymph nodes of the neck
The lymph nodes of the neck are organized in two groups:
• Superficial cervical lymph center
• Deep Cervical lymph center
1- Superficial cervical lymph center:
The superficial cervical lymph center is located cranial to the
shoulder joint, covered by the brachiocephalic and the
omotransversarius muscles.The lymph nodes of the superficial cervical
lymph center include the dorsal, middle and ventral superficial cervical
lymph nodes, with species specific variation (Fig. 13.8 and 12).

30. Lymph nodes of the neck
2- Deep Cervical lymph center:
The deep cervical lymph center comprises several groups of
lymph nodes which are located along the trachea (Fig. 13.9 and 12).
They consist of cranial , middle and caudal deep cervical lymph
nodes. There is great variation in the distribution of these lymph
nodes, and the middle one may be absent in some species.

34. Lymph nodes of the thoracic limb
Lymph from the superficial and proximal parts of the fore limb
drains to the superficial cervical lymph center , lymph from the of the
limb drains to the axillary lymph center (Fig. 13.12).
Axillary lymph center:
The axillary lymph center lies within the axilla, medial to the
shoulder joint , where the axillary artery bifurcates to form the
subscapular and the brachial arteries. In addition to the proper axillary
lymph node, there may be an accessory axillary lymph node caudal to
it and the lymph node of the first rib cranial to it. In the horse and the
sheep a more distal group may be located on the medial aspect of the
elbow joint.

36. Lymph nodes of the thorax
The walls of the thorax are drained by the:
1- Dorsal thoracic lymph center
2-Ventral thoracic lymph center
The organs within the thoracic cavity are drained by the:
1- Mediastinal lymph center
2- Bronchial lymph center
3- Dorsal thoracic lymph center
4-Ventral thoracic lymph center

37. Lymph nodes of the thorax cavity
1- Dorsal thoracic lymph center:
The dorsal thoracic lymph center comprises two groups of lymph nodes,
the intercostal lymph nodes and the thoracic aortic lymph nodes (Fig. 13.10
and 12). As indicated by their names, the intercostal lymph nodes are located
within the upper part of some of the intercostal spaces, and nodes of the
thoracic aortic are dispersed along the aorta. They are inconsistent in number
between species.
Ruminant often have hemal nodes in this region. Hemal nodes have a similar
architecture to lymph node, but differ from lymph nodes in that their sinuses
do not contain lymph, but blood and are connected to the blood vessels
instead of lymph vessels.

38. Lymph nodes of the thorax cavity
2-Ventral thoracic lymph center:
The lymph nodes of the ventral thoracic lymph center are located dorsal
to the sternum and lateral to the transverse thoracic muscle. They are
grouped in a cranial set in all domestic species, with ruminant and some cats
having a second set ventral thoracic lymph nodes (Fig. 13.10 and 12).
3- Mediastinal lymph center:
The mediastinal lymph center comprises cranial , middle and caudal lymph
nodes, which are located in the like-named part of the mediastinum. The
caudal set is missing in the dog and cat, although in 25% of cats a phrenic
lymph node is present next to the caval foramen. In ruminants the caudal
mediastinal lymph nodes from a relatively large mass on the dorsal aspect of
the esophagus (Fig. 13-10). Enlargement of these lymph nodes can cause
obstruction of the esophagus in these species.

41. Lymph nodes of the thorax cavity
3- Bronchial lymph center:
The bronchial lymph center consists of the tracheobronchial (some times
called bifurcational) lymph nodes located above the bifurcation of the
trachea (Fig. 13-10). These are grouped into a right, middle and the left set of
lymph nodes. In ruminant and pigs a tracheal bronchus, there is an additional
cranial tracheobronchial group. Small pulmonary lymph nodes may be
present within the lung tissue along the main bronchi. These lymph nodes are
important for lymphatic drainage of the lungs. In the horse the left
tracheobronchial group is of special important with regards to the
pathogenesis of the paralysis of the left recurrent laryngeal nerve. It is
hypothesized that inflammation of these lymph nodes could spread to the
adjacent nerve or that enlargement of the lymph nodes could mechanically
damage the nerve, thus leading to the clinical condition of laryngeal
hemiplegia (roaring).

43. Lymph nodes of the abdomen
The abdominal cavity and its organ are drained by
several group of lymph nodes along the abdominal
aorta, located in the lumbar region and at the origin of
the intestinal arteries. The three lymph centers
associated with the drainage of the abdominal viscera
have tributary territories broadly corresponding to
those of the celiac, cranial mesenteric and caudal
mesenteric arteries. The efferent vessels of theses
centers converge to form the cisterna chyli.

44. Lymph nodes of the abdomen
1- Lumbar Lymph center
The lumber lymph center consist of the lumbar aortic and renal lymph nodes. The
lumbar aortic lymph nodes lie either side of the aorta, between the transverse
processes of the lumbar vertebrae (Fig. 13-12). Hemal nodes may also be present in
the same location in ruminants.
The lumbar lymph nodes receive afferent lymph vessels from the abdominal roof and
from efferent vessels of more caudally located lymph nodes. The lymph drainage from
the lumbar lymph center is received by cisterna chyli.
2- Coeliac Lymph center
The coeliac lymph center includes the lymph nodes located within the region supplied
by the coeliac artery. These are the coeliac, splenic, gastric and pancreaticoduodenal
lymph nodes (Fig. 13-12). In ruminant the gastric lymph nodes are subdivided in
ruminal, reticular, omasal and abomasal lymph nodes.

46. Lymph nodes of the abdomen
3- Cranial mesenteric lymph center
The cranial mesenteric lymph center includes the cranial mesenteric,
jejunal, caecal and colic lymph nodes. They show considerable
interspecies variation with regard to number, form and location (Fig.
13-12 and 13). These nodes drain the small and large intestine as far
distally as the transverse colon.
4- Caudal mesenteric lymph center
Consist of the caudal mesenteric lymph nodes, which receive the
lymph from the descending colon (Fig. 13-12 ). Its efferent vessels from
the caudal mesenteric trunk, which opens into the cisterna chyli.

48. Lymph nodes of the pelvic cavity and pelvic limb
1- Iliosacral lymph center
It comprises the :
• Medial iliac lymph nodes
• Lateral iliac lymph nodes
• Internal iliac lymph nodes
• Sacral lymph nodes
• Anorectal lymph nodes
The medial iliac lymph nodes are the main group of the iliosacral lymph center and are
located at the quadrification of the aorta (Fig. 13.14). The lateral iliac lymph nodes are
lacking in the dog and not consistently present in the in the other domestic mammals.
When present they are found at the bifurcation of the deep circumflex ilial artery. Other
lymph nodes belonging to the iliosacral center are found ventral to the sacrum (sacral
lymph nodes), lateral to the rectum (anorectal lymph nodes) and at internal iliac
nodes (internal iliac lymph nodes) (Fig. 13.14).

50. Lymph nodes of the pelvic cavity and pelvic limb
2- Iliofemoral lymph center
It comprises nodes located the course of the external iliac artery or femoral continuation
(in the cat and horse) (Fig. 13.14).
3- Inguinofemoral lymph center
It comprises the following lymph nodes
• Superficial Inguinal lymph nodes also called scrotal or mammary lymph nodes
• Sub iliac lymph nodes ( missing in the dog, rare in the cat)
• Coxal lymph nodes
• Lymph node of the Para lumbar fossa
• Epigastric lymph nodes
The inguinofemoral lymph center drains the flank, the caudoventral part of the
abdominal wall, the scrotum and the mammary glands (Fig. 13.14).

52. Lymph nodes of the pelvic cavity and pelvic limb
4- Ischial lymph center
It consist of the ischial lymph node, which is located on the lateral
aspect of the sacrosciatic ligament close to the ischial tuberosity.
This lymph node is not present in dog.
5- Popliteal lymph center
Is the most distal center of the pelvic limb and comprises
superficial and deep popliteal lymph nodes, which are located
within the popliteal fossa caudal to the stifle. In dog and cat the
superficial popliteal nodes are easily palpable through the skin (Fig.
13.12).