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Lymphatic System
Chapter 21
Main Functions of Lymphatic System
Drains excess interstial fluid (3-4L / day)
Transports dietary lipids
Carries out immune responses
Lymphatic System
Lymphatic System works quietly and makes possible the continued operation of Circulatory System.
It brings back about 3-4L/day of fluids, blood cells, plasma proteins to venous system. It is also vital
for the 100% working of body defense.
Circulatory system is a 2-way system – heart to body tissues and from body tissues to heart. On the
other hand, lymphatic system operates only from tissues to heart. It is 1-way system. Lymphatic
system originates in peripheral tissues as lymph capillaries and vessels and ends at venous
connections.
Lymphatic System
Lymphatic system consists of
Lymphatic capillaries, lymphatic vessels, lymphatic trunks and lymphatic ducts
Lymphoid tissues – tonsils, vermiform appendix and intestinal lymphatic follicles (Peyer’s Patch)
Lymphoid organs are of 2 types:
Primary: Red bone marrow and Thymus
Secondary: Spleen and Lymph nodes.
Lymph – blood plasma, with lower % of proteins and white blood cells, filters out of blood capillaries
and becomes Tissue Fluid = Interstial Fluid (ISF). ISF enters lymphatic capillaries and becomes lymph.
Lymphatic Capillaries and Vessels
Peripheral tissues  Lymphatic capillaries  lymphatic collecting vessels  lymphatic trunks 
lymphatic duct  opens into subclavian vein. Kidney shaped Lymph nodes are present, periodically
associated with lymphatic collecting vessels and trunks. Lymphatic vessels usually have more valves
and branch more frequently than veins. Like veins all 3 tunics are present in lymphatic vessels but
are thinner with more branches.
Flap-like mini-valves are present in lymphatic capillaries and help to collect tissue fluid.
Lacteals are special lymphatic capillaries present in finger like Villi of intestinal wall. These lacteals
collect milky white lymph, called Chyle, rich in fat products.
Lymphatic ducts
Lymphatic vessels join to become lymphatic trunks. Jugular, subclavian and bronchomediastinal
trunks respectively collect lymph from head, upper limb and chest. Lumbar trunks collect lymph
from lower limbs and intestinal trunks from intestine and other organs in the region.
Right Lymphatic duct – collects lymph from right arm, right side of head, neck and thorax. When
absent, the lymphatic trunks directly open into veins of the neck.
Thoracic Duct – collects lymph from rest of the body. It arises inferiorly as an extended sac –
Cisterna Chyli, in front of 1st and 2nd lumbar vertebrae. Right thoracic duct is not present in all
humans.
Lymphoid Cells
Lymphoid Cells – all lymph cells arise in bone marrow but get mature in different ways. B-cells
mature in bone marrow and T-cells mature in thymus gland.
B-Cells produce immunoglobulin proteins called Antibodies.
Helper T-cells stimulate B-cells to transform into Plasma Cells that produce antibodies on a massive
scale.
B-cells also transform into Memory Cells
T-Cells are of 2 types:
Cytotoxic cells 2. Helper T-cells
B – Cells and T – Cells
T-Cells
Cell Type
B-Cells
Mature inside
Bone marrow
Thymus gland
Responsible for
Humoral
Cellular immunity
Act by making
Antibodies
Cytotoxic cells and enzymes
Other types
Change to Plasma cells to produce huge
number of antibodies
Helper T-cells and Memory cells
(body fluids) immunity
Lymphoid Tissues
Lymphoid Tissue is mainly a kind of loose Reticular Connective Tissue. It provides site for storage
and proliferation of lymphocytes. These include tonsils and intestinal nodules.
Tonsils are several swellings of mucosa. These include Pharyngeal, Palatine, and Lingual Tonsils.
Pharyngeal tonsils lie close to opening of auditory tubes and prevent infection spreading to middle
ear. Palatine tonsils lie on palate and lingual tonsils lie on posterior part of tongue.
Thymus
Thymus is present in superior mediastinum between sternum and aorta.
It is a bilobed organ. Connective tissue capsule covers each lobe. Trabeculae arise from capsule and
divide each lobe into lobules.
Each lobule has outer cortex and inner medulla
Thymic medulla has characteristic Thymic (Hassal’s) corpuscles of unknown function.
It is best developed at the time of birth. It degenerates in middle age. It secretes thymosin
hormones required to convert immature pre T cells into mature T-cells.
Lymph Nodes
Lymph Nodes are bean shaped lymphatic organs associated with lymphatic vessels. About 600 in
body, mostly lie in clusters like axillary and inguinal lymphatic nodes.
Parts include outer fibrous capsule, partitions - trabeculae, outer cortex, inner cortex and inner
medulla.
Outer Cortex has germinal centers to produce lymphatic cells and inner Medulla has cords and
reticular fibers. Macrophages are associated with reticular fibers and destroy microorganisms and
debris.
Each lymph node receives many afferent lymphatic vessels and passes lymph into lesser number of
efferent lymphatic vessels.
Flow of lymph in lymph node: afferent lymphatic vv  subscapular sinus
 trabecular sinus 
medullary sinus
 efferent lymphatic vv
Spleen
Spleen lies in left hypochondriac region between diaphragm and stomach.
It has smooth superior surface but has indentations made by gastric impression, colic impression
and renal impression.
Stroma consists of capsule, Trabeculae, reticular fibers and fibroblasts.
Parenchyma has white and red pulps. White pulp has lymphocytes and macrophages around
branches of splenic artery. Macrophages eliminate worn out RBC in spleen.
Red pulp has venous sinuses and Splenic Cords (Billroth’s) made of RBC’s, macrophages, and
lymphocytes.
Lymphatic Nodules
Lymphatic nodules are egg shaped masses of lymphatic tissue lacking capsule.
Mucosa Associated Lymphatic Tissue (MALT): These lie in lamina propria (Areolar ct) of mucous
membranes of gastrointestinal, respiratory, urinary and reproductive systems.
Aggregated Lymphatic Follicles (Peyer’s Patch): are large clusters in small intestine and appendix.
Tonsils form a tonsilar (Waldeyer’s) ring at junction mouth and oropharynx, and nasal cavity and
nasopharynx. Pharyngeal tonsil (adenoid) lie in nasopharynx. Palatine tonsils lie laterally between
mouth and oropharynx. Lingual tonsils lie at base of tongue.
AIDS and role of Memory Cells
AIDS Virus attacks Helper T-cells and destroys the immune system. Then many opportunistic
diseases like Pneumonia attack and kill the person.
Memory T-cells live for long periods and alert the immune system when an invader enters the body
after 1st infection or vaccination.
Recap 1 Lymphatic System
1. Lymphatic system begins as a peripheral network of lymphatic vessels and ends at
connections to ------- --------.
2. Lymphatic ducts bring ----L of tissue fluid back to veins.
3. Lymphatic tissues are collections of loose connective tissue and lymphocytes. For example
--------and -------------------------.
4. Lymphatic organs are complex organs joined to lymphatic ducts. Examples include
----------,--------- and ----------------.
5. B-cells originate and mature in ---------------.
6. T-cells originate in --- and mature in ----. (mature in = differentiate)
7. ---- is a lymphatic organ attached to lateral side of stomach and ---- lies in chest superior to
heart.
8. Inflammation is brought by ---- cells of blood and ---- cells of connective tissues.
9. AIDS virus attack ------cells of immune system and compromise it.
10. Germinal centers lie in --- ---- and filtering center lies in ------- of lymph node.
11. -----includes capsule, trabeculae, reticular fibers and fibroblasts and ----- is functional part of
lymphatic organs like thymus, spleen and lymph nodes.