LYMPHATIC
SYSTEM
Mr. Godfrey R Mathews
M. Pharm (Pharmacology)
Immunity
Immunity or Resistance is the ability of
body to ward off damage or disease
through our defenses.
 Two general types of immunity:
 Innate
 Adaptive

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Two general types of Immunity

Innate:
 Defense present by birth.
 First line defense – Physical and
Chemical barrier of skin.
 Second line defense – Antimicrobial
agent, NK cells, Phagocytes.
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Cont…

Adaptive:
 Defense involves specific recognition of
microbe.
 Adaptive
immunity
involves
Lymphocytes called T lymphocytes (T
cells) and B lymphocytes (B cells)
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LYMPHATIC SYSTEM
Essentially a
drainage system
accessory to venous
system
larger particles that
escape into tissue fluid can
only be removed via
lymphatic system
Components of the Lymphatic System
246 
Lymph
 Lymphatic Vessels
 Lymphatic
Capillaries
 Lymphatic Vessels
 Lymphatic Trunks
 Lymphatic Ducts

Lymphatic Organs
 Thymus
 Lymph
Nodes
 Spleen
 Tonsils

Lymphatic cells
LYMPH

What is lymph ?
Tissue fluid (interstitial fluid) that enters
the lymphatic vessels
Lymphatic Capillaries
249
Features of structure:




Blind end
Single layer of overlapping endothelial cells
More permeable than that of blood capillary
Absent from avascular structures, brain, spinal cord and bone
marrow
Lymphatic Capillaries – Lacteals
2410



The small intestine contains special types of
lymphatic capillaries called lacteals.
Lacteals pick up not only interstitial fluid, but
also dietary lipids and lipid-soluble vitamins.
The lymph of this area has a milky color due
to the lipid and is also called chyle.
Lymphatic Vessels
2411
Features of structure
 Three layered wall but
thinner than vein,
 More numerous valves
than in vein
 Interposed by lymph
nodes at intervals
 Arranged in superficial
and deep sets
LYMPH TRUNKS
 right and left jugular trunks
 right and left subclavian trunks
 right and left bronchomediastinal
trunks
 right and left lumbar trunks
 intestinal trunk
LYMPHATIC DUCTS
2413
Right lymphatic duct

Formed by union of right
jugular, subclavian, and
bronchomediastinal trunks

Ends by entering the right
venous angle
LYMPHATIC DUCTS
Thoracic duct




Begins in front of L1 as a
dilated sac, the cisterna chyli,
formed by left and right
lumbar trunks and intestinal
trunk
Enter thoracic cavity &
ascends
Travels upward, veering to
the left at the level of T5
THORACIC DUCT…..
15
At the root of the neck, it
turns laterally
 arches forwards and
descends to enter the left
venous angle
 before termination, it
receives the left jugular,
Subclavian and bronchomediastinal trunk

FORMATION AND TRANSPORT OF
TISSUE FLUID
Cont…
•Like veins, lymphatic vessels contain valves, which
ensure the one-way movement of lymph.
•Proteins (large molecules) leaves blood capillaries
which cannot return back (due to concentration
gradient).
•Lymph drains into venous blood through the right
lymphatic duct and the thoracic duct at the junction of
the internal jugular and subclavian veins.
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The sequence of fluid flow
Blood capillaries (blood)
Interstitial spaces (interstitial fluid)
Lymphatic capillaries (lymph)
Lymphatic vessels (lymph)
Lymphatic ducts (lymph)
Junction of the internal jugular and subclavian
veins (blood)
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Two Pumps Aid return of venous blood to
heart
•Respiratory Pump
Pressure change occurs during inhalation (breathing
in)
Lymph flows from abdominal region to thoracic region
After the pressure reverses (during exhalation)
Backflow of the lymph is prevented by valves present
in the lymphatic vessels
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Two Pumps Aid return of venous
blood to heart
•Skeletal Muscle Pump
Milking action of skeletal
muscles compresses lymphatic
vessels
Forces lymph toward internal
jugular and subclavian veins
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Functions of the Lymphatic System
2421

Reabsorbs excess interstitial fluid:
 returns
it to the venous circulation
 maintain blood volume levels
 prevent interstitial fluid levels from rising out of control.

Transport dietary lipids:
 transported
through lacteals
 drain into larger lymphatic vessels
 eventually into the bloodstream.

lymphocyte development, and the immune response.
Lymphatic Cells
2422
Also called lymphoid cells.
 Located in both the lymphatic system and the
cardiovascular system.
 Work together to elicit an immune response.
 Types of lymphatic cells are:

 macrophages
 epithelial
cells
 dendritic cells
 lymphocytes
LYMPHATIC ORGANS
Primary Lymphatic organs (Sites where stem cells divide
and become immunocompetent)
 Red bone marrow
 Thymus gland
Secondary Lymphatic organs
Lymph nodes
 Lymph nodules
 Spleen

THYMUS
24
Features

Bilobed organ located in mediastinum between sternum and aorta.

A connective tissue capsule seperates the two lobes.

Extensions of the capsule, called trabeculae, penetrate inward and divide
each lobe into lobules.

Each thymic lobule consists of a deeply staining outer cortex and light
staining inner cortex.

The cortex composed of large no's of T cells, and scattered dendritic cells,
epithelial cells, and macrophages.

Thymic hormones (thymosin & thymopoietin aid in maturation of T cells).
Cont…
Dendritic cells: which are derived from monocytes, and so
named because they have long, branched projections that
resemble the dendrites of a neuron, assist the maturation process.
Epithelial cells in the cortex has several long processes that
surround and serve as a framework as many as 50 T-cells, These
epithelial cells help “educate” the pre-T cells in a process known
as positive selection
Macrophages help clear out the debris of dead and dying cells.
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Cont…




Only about 2% of developing T cells survive in the
cortex. The remaining cells die via apoptosis.
Thymic macrophages help clear out the debris of
dead and dying cells.
The surviving T cells enter the medulla.
The medulla consists of widely scattered, more
mature T cells, epithelial cells, dendritic cells, and
macrophages.
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Lymph Nodes
2427





Small, round or oval
located along the pathways of
lymph vessels.
length from 1 - 25 millimeters
Typically found in clusters
receive lymph from many body
regions.
Lymph nodes are also found
individually throughout the
body tissues.
Lymph node
Features
 Bean-shaped bodies
 With afferent vessels (entering
at the periphery) and efferent
lymph vessels(emerging at the
hilus)
 Arranged in groups, along the
blood vessels or the flexural
side of the joint
 Divided into superficial and
deep groups
Germinal Layer of Lymph Node
In the germinal center are B cells, follicular
dendritic cells (a special type of dendritic cell), and
macrophages.
When follicular dendritic cells “present” an antigen
(described later in the chapter), B cells proliferate
and develop into antibody-producing plasma cells
or develop into memory B cells.
Memory B cells persist after an initial immune
response and “remember” having encountered a
specific antigen.
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Cont…
B cells that do not develop properly undergo
apoptosis (programmed cell death) and are
destroyed by macrophages.
The region of a secondary lymphatic nodule
surrounding the germinal center is composed of
dense accumulations of B cells that have migrated
away from their site of origin within the nodule.
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Lymph nodes function :
As lymph enters one end of a lymph node, foreign substances are
trapped by the reticular fibers within the sinuses of the lymph
node.
•
Then macrophages destroy some foreign substances by
phagocytosis while lymphocytes destroy others by immune
responses.
The filtered lymph then leaves the other end of the lymph node.
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Spleen
33
 Location
 Left epigastric region

Largest lymphatic organ in the body.

Can vary considerably in size and weight.



The parenchyma of the spleen consists of two
different kinds of tissue called white pulp and
red pulp.
White pulp is lymphatic tissue, consisting
mostly of lymphocytes and macrophages
arranged around branches of splenic artery.
The red pulp consists of blood-filled venous
sinuses and cords of splenic tissue called
splenic (Billroth’s) cords.
Cont…



Blood flowing into the spleen through the splenic artery
enters the central arteries of the white pulp.
Within the white pulp, B cells and T cells carry out immune
functions, similar to lymph nodes, while spleen macrophages
destroy blood-borne pathogens by phagocytosis.
Within the red pulp, the spleen performs three functions
related to blood cells
(1)removal by macrophages of ruptured, worn out, or
defective blood cells and platelets;
(2) storage of platelets, up to one-third of the body’s
supply;
(3)production of blood cells (hemopoiesis) during fetal life.
Lymphatic Nodules
2435
 Oval
clusters of lymphatic cells with some extracellular
matrix that are not surrounded by a connective tissue
capsule.


Filter and attack antigens.
In some areas of the body, many lymphatic nodules group
together to form larger structures.
 mucosa-associated lymphatic tissue (MALT) or tonsils
 very prominent in the mucosa of the small intestine,
primarily in the ileum
 Peyer patches
 also present in the appendix
MALT (Mucosa Associated
Lymphoid Tissue)
37
Tonsils
2438
clusters of lymphatic cells and extracellular matrix
not completely surrounded by a connective tissue
capsule.
 Consist of multiple germinal centers and crypts


Several groups of tonsils form a protective ring
around the pharynx.
 pharyngeal tonsils (or adenoids) in nasopharynx
 palatine tonsils in oral cavity
 lingual tonsils along posterior one-third of the
tongue
Innate Immunity




Innate immunity includes the external physical and
chemical barriers provided by the skin and mucous
membranes.
It also includes various internal defenses, such as
antimicrobial substances, natural killer cells, phagocytes,
inflammation, and fever.
First line of defense: Skin and Mucous membrane
Ex: - Skin
- Mucous membrane
- Lacrimal apparatus
- Defecation and vommiting
- Vaginal secretions and flow of urine
Cont…





Second line of defense: Internal defense
When pathogens penetrate the physical and chemical barriers
of the skin and mucous membranes, they encounter a second
line of defense: internal antimicrobial substances, phagocytes,
natural killer cells, inflammation, and fever.
There four main types of anti-microbial substances:
-Interferons, -iron-binding proteins, and antimicrobial proteins.
Phagocytosis
Inflammation
Adaptive Immunity
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Thank
You