THE LYMPHATIC SYSTEM LECTURE NOTES
Lymphatic System is a complex system of capillaries, vessels, valves, ducts nodes and
organs that helps to protect and maintain the internal fluid environment of the entire
body. It does so by producing, filtering, and conveying lymph and by producing various
blood cells.
The lymphatic system is closely related to the circulation of blood in the body and is in
reality an extension of the circulatory system with complementary functions. Both
systems transport vital fluids throughout the body and both have a system of vessels that
transport these fluids.
The lymphatic system is really a strange system has many lymphoid organs and vessels
derived from veins of the cardiovascular system. The lymphatic vessels keep the
cardiovascular system functional by maintaining blood volume. The lymphoid organs
help defend the body from pathogens by providing operating sites for phagocytes and
cells of the immune system.
The lymphatic system transports a fluid called lymph through special vessels called L.
capillaries and lymphatics. This lymph eventually gets returned to the blood from where
it originated. In addition to fluid control, our lymphatic system is essential to helping us
control and destroy a large number of microorganisms that can invade our bodies and
cause disease and even death.
STRUCTURE OF THE LYMPHATIC SYSTEM:
1. LYMPH
2. LYMPH VESSELS
3. LYMPH NODES
4. MAJOR LYMPH DUCTS
5. LYMPH ORGANS – 4 TOTAL
BREAKDOWN OF LYMPHATIC SYSTEM:
1. LYMPH
a. Name for interstitial fluid once it enters lymphatic capillary
b. Dynamic fluid that varies in appearance and composition depending on
location in the body, the health of the individual, diet and many other factors
c. Generally a clear, colorless fluid.
d. Milky in appearance in special L. vessels (LACTEALS) due to fat content.
(lacteals – specialized L. vessels found in villi of small intestine- whose role is
to absorb fats and transport them from GI tract to blood)
e. Differs from blood – lymph has no RBCs.
f. Resembles plasma in composition but contains less protein
g. Nearly identical to the interstitial fluid of the region of the body in which
lymph occurs
h. No pump to force movement – movement of lymph caused by breathing and
by contractions of the skeletal system
i. Moves slowly and in one direction due to one-way valves to prevent backflow
2. LYMPHATIC CAPILLARIES – LYMPHATIC VESSELS
L.Capillaries
a. Numerous, small, lymph vessels that form networks throughout the tissue s
spaces in the body.
b. Carry lymph from tissue spaces to larger lymphatic vessels
c. One end lies in a pool of tissue fluid - other end connects to larger lymph vessel
d. Like blood capillaries, lymph capillaries - one layer of flattened epithelial cells.
L. Vessels
a. Fine, transparent, thin walled, very permeable vessels that carry lymph
b. Like veins consist of three tissue layers and have valves to prevent backflow
c. Distributed throughout most tissues and have characteristic beaded appearance
due to lymph nodes found at various intervals
d. Convey lymph from L. capillaries to lymph nodes
e. Convey lymph from lymph nodes to lymphatic ducts
3. LYMPH NODES also known as LYMPH GLANDS
L. Nodes
a. Small, oval structures – resemble small seeds or almonds
b. Range in size from 1 – 25 mm in length (.04 to 1 inch)
c. Deep or superficial masses of lymphoid tissue found along L. system
d. Filters lymph
e. Keep substances such as bacteria from entering bloodstream – fight infection
f. Produce lymphocytes, monocytes and plasma cells
g. Lymph flows into nodes through AFFERENT L. vessels
h. Lymph flows out of nodes through EFFERENT L. vessels
i. Identified by their body location
MAJOR GROUPS OF LYMPH NODES: Isolate vital organ of the trunk from
the head and the extremities. The purpose of the isolation is to prevent infections from
spreading to the vital organs. Major lymph nodes provide an increased level of protection
against infections that can begin – nose, mouth, ears, eyes.
1. CERVICAL NODES
2. AXILLARY NODES
3. INGUINAL NODES
1. Cervical nodes
a. Located on either side of neck
b. Nodes on right side of neck drain into RIGHT LYMPHATIC DUCT
c. Nodes on left side of neck drain into THORACIC DUCT
d. Swelling of cervical L nodes = “swollen glands” – Ex.= Strep throat
2. Axillary nodes
a. Located in right and left arm pits
b. Nodes in right thorax and arm drain into RIGHT LYMPHATIC DUCT
c. Nodes in left thorax and arm drain into THORACIC DUCT
3. Inguinal nodes
a. Located in the region of the groin
b. Nodes drain the lower extremities and external genital organs into THORACIC
DUCT
Lymph nodules are tiny, densely packed spherical nodes or group of lymph cells
embedded mainly in tonsils, spleen and thymus.
4. MAJOR LYMPHATIC DUCTS:
1. RIGHT LYMPHATIC DUCT
a. Major lymphatic vessel that conveys lymph from RUQ (right upper quadrant)
b. Includes head, neck, thorax and upper extremity of the body’s right side
c. Conveys lymph to RIGHT SUBCLAVIAN VEIN
2. THORACIC DUCT
a. Common trunk of ALL lymphatic vessels in body except those on RUQ
b. Begins in abdomen – travels through thorax – ascends into neck – over
the clavicle – into LEFT SUBCLAVIAN VEIN
5. MAJOR LYMPHATIC ORGANS:
1. TONSILS
a. Small, rounded masses of lymphoid tissue
b. Four major groups of tonsils: palatine, pharyngeal, lingual, intestinal
1. Palatine – back of the mouth on lateral walls of pharynx - tonsils
2. Pharyngeal – roof of posterior wall of pharynx/behind nose - adenoids
3. Lingual – near the root of the tongue
4. Intestinal tonsils – L nodules forming a single layer in mucous
membrane of ileum – Peyer’s Patches, oval, ½ inch wide. Contain
macrophages to destroy bacteria and protect intestinal wall.
2. THYMUS GLAND
a. Bi-lobed mass of glandular, lymphoid tissue
b. Located in the mediastinum – along the trachea, behind the sternum
c. Reaches maximum size in puberty, then decreases and is replaced by
connective tissue and fat.
d. Produces lymphocytes (T cells)
e. Secretes thymosin – needed for maturing T cells, lymphoid tissue growth
f. Involved in immunity – protect against foreign substances and harmful
microorganisms
3. SPLEEN
a. Highly vascular organ located in LUQ behind the stomach
b. Largest mass of lymphoid tissue in body
c. Soft, spongy and purplish in color
d. Produces erythrocytes in a fetus
e. Produces leukocytes, monocytes, lymphocytes and plasma cells
f. Stores blood cells – stores about 12 cubic inches of blood that can be
returned to bloodstream in case of hemorrhage or other emergency
g.
h.
i.
j.
Filters out and destroys bacteria
Filters out worn-out RBCs
Filters cancer cells and other particulate matter
Can be removed because liver and bone marrow can perform splenic
functions.
4. PEYER’s PATCHES – aggregated lymphatic follicles
a. Resemble tonsils
b. Found in walls of small intestines
c. Macrophages destroy bacteria – prevent intestinal walls from bacterial
infection and penetration
LYMPHATIC CIRCULATION:
1. Plasma of blood filtered by capillaries
2. Plasma passes into interstitial spaces between tissue cells – becomes
interstitial fluid
3. Interstitial fluid passes from interstitial spaces into lymph capillaries –
becomes lymph fluid ( water with plasma solutes of ions, gases, nutrients,
proteins and substances from tissue cells such as hormones, enzymes and
waste products).
4. Lymph drained by L capillaries passed to lymphatic vessels
5. Lymph heads toward lymph nodes via afferent L vessels
6. Lymph passes through L nodes
7. L node identifies substances – immune response activated
8. Lymphocytes produces and are released into lymph
9. Lymph head towards major lymphatic duct (RLD, TD) via efferent L vessels
10. The thoracic duct empties all of its lymph into the left subclavian vein and the
right lymphatic duct empties all of its lymph into the right subclavian vein
11. Lymphocytes reach blood and produce antibodies against microorganisms
12. Macrophages remove dead microorganisms and foreign substances by
phagocytosis
MAINTAINING HOMEOSTASIS:
1. INTEGUMENTARY – L vessels drain interstitial fluid from dermis of skin
preventing edema
2. SKELETAL – Lymphocytes are produced in red bone marrow
3. MUSCULAR – Contractions of muscles compresses lymphatics and helps
push the flow of lymph toward the right and left lymphatic ducts
4. NERVOUS – Undue stress may suppress the immune response. Nervous
system innervates large L vessels and helps regulate immune response
5. ENDOCRINE – Thymus produces T cells and secretes thymosin
6. CARDIOVASCULAR – Blood plasma is the source of interstitial fluid which
becomes lymph when drained by L capillaries. The Lymphatic system returns
this fluid to the bloodstream via the right and left subclavian veins, connecting
with the right and left lymphatic ducts
7. DIGESTIVE – Lacteals in villi of small intestine absorb fats. Hydrochloric
acid in gastric juice destroys most pathogens. Digests and absorbs nutrients
for lymphatic tissues. Peyer’s patches in wall of small intestine destroy
bacteria.
8. RESPIRATORY – Breathing and contraction of respiratory system maintain
lymph flow. Immune systems cells receive oxygen and get rid of carbon
dioxide waste via the respiratory system
9. URINARY – Regular amount of extracellular fluid. Blood homeostasis
maintained by urinary system for lymphoid tissue function. Urine can flush
out microorganisms from body
10. REPRODUCTIVE – Acid environment of external genitalia prevent bacterial
growth. In female reproductive tract, immune system does not attach male
sperm as foreign body ensuring possibility of fertilization.
COMMON DISORDERS AND ABNORMALITIES OF LYMPHATIC SYSTEM:
1. SPLENOMEGALY – Enlargement of spleen that is associated with various
conditions including infection and hypertension
Can be from – scarlet fever, syphilis, typhoid fever
Can be from – blood fluke worm “schistosoma” – eggs of parasite lodge in
spleen causing irritation.
2. LYMPHEDEMA or LYMPHADENITIS – Disorder characterized by
swelling and by accumulation of lymph in soft tissue and caused by
inflammation, obstruction or removal of lymph channels
3. LYMPHANGITIS – Inflammation of one or more lymphatic vessels due to
infection of one of the extremities. Red streaks visible in skin.
4. LYMPHOMA – Tumor involving lymphatic tissue, begins as enlarged mass
of lymph nodes – usually no pain – nodes compress surrounding structures
causing complications – immune response becomes depressed – person
susceptible to opportunistic infections.
Hodkin’s Lymphoma – a malignant disorder of unknown origin often
appearing first in cervical or axillary nodes. Usually seen age 20 -30, more
common in men than women. Tx – drugs and radiation.
Most lymphomas are non Hodgkin’s lymphoma and are more widespread
throughout the lymphatic system
5. TONSILLITIS – Infection of a tonsil
6. AIDS – acquired immune deficiency syndrome – caused by infection with the
human immunodeficiency virus (HIV). Attacks T cells, invades T cells and
replicates more virus, eventually destroys T cells.