3. Objectives
At the end of this session, the learner will be able to:
• Define lymph & the lymphatic system
• Identify the organs of lymphatic system
• Describe the general functions of the lymphatic system
• Describe how lymph is formed
• Describe the lymph vessels & how lymph is returned to the blood
vessels
• Describe the structure and functions of the lymph nodes, nodules,
spleen and the thymus glands
4. Lymphatic system
• The lymphatic system is part of the vascular
system and an important part of the immune
system, comprising a large network of lymphatic
vessels that carry a clear fluid called lymph,
directionally towards the heart.
• The lymphatic system was first described in the
17th century independently by Olaus
Rudbeck and Thomas Bartholin.
6. Lymphatic system
• The lymphatic system is a network of tissues and
organs that help rid the body of toxins, waste and
other unwanted materials. The primary function
of the lymphatic system is to transport lymph, a
fluid containing infection-fighting white blood
cells, throughout the body.
7. Components of Lymphatic system
• It consist of :
– Lymph (Fluid)
– Lymphatic vessels (that transports Lymph)
– Structure: organs & lymphatic tissue
8. Lymph
Lymph is a clear and colorless fluid; the word "lymph" comes
from the Latin word lympha, which means "connected to
water," according to the National Lymphadema Network.
Return interstitial fluid and leaked plasma proteins back to
blood
Approximately 3L / day
Once interstitial fluid enters lymphatics, it is called lymph
9. Lymph
• Lymph returned to the blood is composed of:
– Water
– Blood cells
– Proteins
• Harmful materials that enter lymph vessels
– Bacteria
– Viruses
– Cancer cells
– Cell debris
11. Lymphatic Organs and Tissues
Primary Lymphatic Organs –the sites where B
and T lymphocytes are produced and trained.
• They are Bone marrow and Thymus gland.
Secondary Lymphatic Organs and tissues—the
sites where immune responses are carried out.
• Secondary organs are lymph nodes and spleen.
• While the tissues are lymph nodules.
• The aggregations of lymph nodules are called
tonsils.
13. Function of the lymphatic system
• It has three primary function
– Drain excess interstitial fluid
– Transports dietary lipids & lipid soluble vitamins
– Carries out immune responses
• Drain excess interstitial fluid: Lymphatic vessels drain excess
interstitial fluid from tissue space and return it to the blood
• This function closely links it with the cardiovascular system.
• Infact without this function, the maintenance of circulating blood
volume would not be possible
14. Cont….
• Transports dietary lipids: lymphatic vessels
transport lipids and lipid-soluble vitamins (A,D,E
and K) absorbed by the Gastrointestinal tract
• Carries out immune response: lymphatic tissue
initiates highly specific responses directed against
particular microbes or abnormal cells
15. How lymph is formed
• Most components of the blood plasma, such as
nutrients, gases and hormones filter freely
through the capillary wall to form interstitial
fluid but more fluid filter out of blood capillaries
than return to them by reabsorption.
• The excessive filtered fluid about 3 liter per day
drain into lymphatic vessels and become a lymph
16. Cont..
• Plasma leaves the body's cells once it has
delivered its nutrients and removed debris. Most
of this fluid returns to the venous circulation
through tiny blood vessels called venules and
continues as venous blood. The remainder
becomes lymph, according to the Mayo Clinic.
20. Lymphatic vessels
• Transport lymph
• Resemble small veins in structure but have thinner walls and
more valves
• At interval along the lymphatic vessels, lymph flow through
lymph nodes
• Lymphatic vessels lies in subcutaneous tissue and generally
flow the same routine as veins
21. Lymphatic Capillaries
• These origin as a blind end tubes in the
interstitial spaces
• Similar to blood capillaries, except
– Very permeable (take up proteins, cell debris,
pathogens, and cancer cells)
• Endothelial cells overlap loosely to form one-way
minivalves
22. Lymphatic capillaries
• Lacteals: specialized lymph capillaries present
in intestinal mucosa
– Absorb digested fat and deliver fatty lymph
(chyle) to the blood
25. Lymphatic Vessels
• Lymphatic collecting
vessels
– Collects lymph from
lymph capillaries
– Carries lymph to and away
from lymph nodes
– Returns fluid to circulatory
veins near the heart at the
right lymphatic duct or
thoracic duct
26. Lymphatic Collecting Vessels
• Similar to veins, except
– Have thinner walls, with more internal valves
– Anastomosis more frequently
• Collecting vessels in skin travel with superficial veins
• Deep vessels travel with arteries
• Nutrients supplied from branching vasa vasorum
27. Lymphatic Trunks
• As lymphatic vessels exit lymph nodes in a particular
region of the body, they unite to form lymph trunk
• The principle trunks are:
– Paired lumbar
– Paired bronchomediastinal
– Paired subclavian
– Paired jugular trunks
– Single intestinal trunk
28. Lymph Trunks and Ducts cont….
• Lumber Trunks (Rt and Lt)—drain lymph from
lower limbs, pelvis, kidneys, adrenal gland and
abdominal wall.
• Intestinal Trunk—drains lymph from the
stomach, intestines , pancreas, spleen, and liver.
• Bronchomediastinal Trunks—drain lymph from
the thoracic wall, lungs, and heart.
• Subclavian Trunks—drain the upper limbs.
• Jugular Trunks—drain the head and neck.
• These trunks open into larger vessels called
lymph ducts.
29. Lymphatic Ducts
• Lymph delivered into one of two large ducts
– Right lymphatic duct drains right upper arm and right
side of head and thorax
– Thoracic duct arises as cisterna chyli; drains rest of
body
• Each empties lymph into venous circulation at
junction of internal jugular and subclavian veins
on its own side of body
30. Internal
jugular vein
Entrance of
right lymphatic
duct into vein
Entrance of
thoracic duct
into vein
Thoracic
duct
Cisterna
chyli
Collecting
lymphatic
vessels
Regional
lymph
nodes:
Cervical
nodes
Axillary
nodes
Inguinal
nodes
Aorta
Drained by the right lymphatic duct
Drained by the thoracic duct
Lymphatic vessels and ducts
31. Right jugular trunk
Right lymphatic
duct
Right subclavian
trunk
Right subclavian
vein
Right broncho-
mediastinal trunk
Brachiocephalic
veins
Superior
vena cava
Azygos vein
Cisterna chyli
Right lumbar
trunk
Lymphatic Vessels
Anterior view of thoracic and abdominal wall.
Internal
jugular veins Esophagus
Trachea
Left jugular
trunk
Left subclavian
trunk
Left subclavian
vein
Entrance of
thoracic duct
into vein
Left broncho-
mediastinal
trunk
Ribs
Thoracic duct
Hemiazygos
vein
Left lumbar
trunk
Inferior vena cava
Intestinal trunk
32. Lymph Transport
• Lymph propelled by
– Contraction of skeletal muscle
– Pressure changes in thorax during breathing
– Valves to prevent backflow
– Pulsations of nearby arteries
– Contractions of smooth muscle in walls of lymphatics
33. Lymphoid Cells
• Lymphocytes main warriors of immune
system
– Arise in red bone marrow
• Mature into one of two main varieties
– T cells (T lymphocytes)
– B cells (B lymphocytes)
34. Lymphocytes
• T cells
– Manage immune response
– Attack and destroy infected cells
• B cells
– Produce plasma cells, which secrete antibodies
• Antibodies mark antigens for destruction by phagocytosis or
other means
35. Other Lymphoid Cells
• Macrophages phagocytize foreign substances;
help activate T cells
• Dendritic cells capture antigens and deliver them
to lymph nodes; activate
T cells
• Reticular cells produce reticular fiber stroma
that supports other cells in lymphoid organs
36. Figure 20.3 Reticular connective tissue in a human lymph node.
Macrophage
Reticular cells on
reticular fibers
Lymphocytes
Medullary sinus
Reticular fiber
37. Lymph Nodes
• Principal lymphoid organs of body
• Located along lymphatic vessels are about 600 bean-shaped
• Embedded in connective tissue, in clusters along lymphatic
vessels
• Scattered throughout the body, both superficially and deep.
• Large numbers of lymph nodes are present near the
mammary glands and in the axillae and groins.
38. Structure & Function of a Lymph
Node
• External fibrous capsule
• Trabeculae extend inward and divide node into
compartments, provide support and provide route for blood
vessels in to the anterior of a node
• Cortex: consist of outer part and deeper Para cortex
• Outer Cortex: inactivated B cells called follicles when
activated the germinal Centre.
39. Structure & Function of a Lymph
Node
• Para/Deep Cortex: consists of T cells.
• T cells circulate continuously among blood, lymph nodes, and
lymph.
• Medulla: Large blood vessels, sinuses & medullary cord.
• Medullary cords: extend inward from cortex and contain B
cells, macrophages, and plasma cells
• Lymph sinuses contain macrophages
40. Internal
jugular vein
Entrance of
right lymphatic
duct into vein
Entrance of
thoracic duct
into vein
Thoracic
duct
Cisterna
chyli
Collecting
lymphatic
vessels
Regional
lymph
nodes:
Cervical
nodes
Axillary
nodes
Inguinal
nodes
Aorta
Drained by the right lymphatic duct
Drained by the thoracic duct
Lymph node distribution
41. Figure 20.4 Lymph node.
Afferent
lymphatic
vessels
Cortex
• Lymphoid follicle
• Germinal center
• Subcapsular sinus
Efferent
lymphatic
vessels Follicles
Trabecula
Subcapsular
sinus
Capsule
Medullary
cords
Medullary
sinuses
Trabeculae
• Medullary
sinus
• Medullary
cord
Medulla
Hilum
Longitudinal view of the internal structure of a lymph
node and associated lymphatics
Photomicrograph of part of a lymph
node (72x)
Capsule
42. Lymph Nodes
• Functions
1. Filter lymph—To separate particulate matter.
2. Phagocytosis__ Of particulate matter.
3. Providing Immunity—T and B lymphocytes
43. Spleen
• Largest lymphoid organ
• Contain reticular and lymphatic tissue
• Location: It lies in the left hypochondriac region of the
abdominal cavity between the fundus of the stomach
and diaphragm
• Color: Reddish purple
• Measurement:12cm long, 7cm wide and 2.5 cm thick
• Weight: 200g
44. Structure of the spleen
• The spleen is slightly oval in shape with hilum on the
lower medial border
• The anterior surface is covered with peritoneum
• It is enclosed in fibroelastic capsules, that dips into the
organ forming traberculae
• The parenchyma of the spleen consists of two different
kind of tissue called white pulp & red pulp
45. Structure of the Spleen
• Splenic pulp
– White pulp is lymphatic tissue consisting of
• Lymphocytes & macrophages
• Destroying blood borne pathogen.
– Red pulp has three basic function.
1. Removal by macrophages of worn out blood cells
2. Storage of platelets up to 1/3rd of blood of body's supply
3. Production of blood cells during fetal life.
46. Function of spleen
• Phagocytosis
– Old and abnormal erythrocytes are mainly destroyed in the spleen, and
the breakdown products, bilirubin and irons are transported to the liver
via splenic and portal veins
– Other cellular materials e.g., leukocytes, platelets and bacteria are
phagocytosed in the spleen
– Unlike lymph node, the spleen has no afferent lymphatic entering , so it
is not exposed to disease spread by lymph
47. Function of spleen
• Storage of blood
– The spleen contain up to 350ml of blood and in response
to sympathetic stimulation can rapidly return most of
this volume to the circulation e.g. hemorrhage
• Immune response
– The spleen contain T and B lymphocytes which are
activated by the presence of antigens e.g. in infection
– Lymphocytes proliferation in serious infection can cause
enlargement of the spleen
48. Function of spleen
• Erythropoiesis
– The spleen and liver are the important sites of fetal
blood cell production and spleen can also fulfill
this function in adults in times of great needs.
51. Thymus
• Bilobed organ, located in mediastinum b/w
sternum & the aorta.
• Weight: At birth: 10-15 g
At puberty: 30-40 g
After puberty:10 g in adults
52. Structure of the Thymus
• Thymic lobules contain outer cortex and inner medulla
• Most thymic cells are lymphocytes
– Cortex contains rapidly dividing lymphocytes and scattered
macrophages
• Medulla contains fewer lymphocytes and thymic
corpuscles involved in regulatory T cell development
(prevent autoimmunity)
54. Function of thymus gland
• The thymus is an organ that is critically important to
the immune system which serves as the body's defense
mechanism providing surveillance and protection against
diverse pathogens, tumors, antigens and mediators of tissue
damage
• The thymus is as the „school“ of T-lymphocytes („T“ as in
„Thymus“), because it teaches this subgroup of lymphocytes
to differentiate between the body's own and alien immune
cells.
55. Mucosa-associated Lymphoid Tissue
(MALT)
• Lymphoid tissues in mucous membranes throughout
body
• Protects from pathogens trying to enter body
• Largest collections of MALT in tonsils, Peyer's
patches, appendix
• Also in mucosa of respiratory and genitourinary organs;
rest of digestive tract
56. Tonsils
• Simplest lymphoid organs
• Form ring of lymphatic tissue around pharynx
– Palatine tonsils—at posterior end of oral cavity
– Lingual tonsil—grouped at base of tongue
– Pharyngeal tonsil—in posterior wall of nasopharynx
– Tubal tonsils—surrounding openings of auditory tubes into pharynx
• Function:
– Gather and remove pathogens in food or air
– Trap and destroy bacteria and particulate matter
– Allow immune cells to build memory for pathogens
57.
58. Aggregates of Lymphoid Follicles
• Peyer's patches and appendix
– Clusters of lymphoid follicles
– Peyer's patches are located in your small intestine, usually
in the ileum or distal area. Similar structures are also
found in the appendix
– Destroy bacteria, preventing them from breaching intestinal
wall
– Generate "memory" lymphocytes
