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The tissues and organs that produce, store, and carry
white blood cells that fight infections and other
This system includes the
Development starts by the end of the fifth week of
The lymphatic system begins as a series of sacs 108 at
the points of junction of certain of the embryonic
The lining walls of its vessels are always endothelial.
These lymph-sacs are developed by the confluence
of numerous venous capillaries, which at first lose
their connections with the venous system, but
subsequently, on the formation of the sacs, regain
Development in Human Embryo
In human embryo the lymph sacs from which the
lymphatic vessels are derived are six in number.
Two paired Jugular Lymph sac
At the junction of the internal jugular and subclavian veins.
Retroperitoneal Lymph sac
At the root of the mesentery of the intestine. develops from
the primitive vena cava and mesonephric veins
Posterior Lymph sacs
Develop from the iliac veins
Lymphatic System Components
Lymphatic system components includes :
Lymph means clear water and it is basically the
colorless fluid and protein that has been squeezed out
of the blood.
Lymph is a fluid similar in composition to blood
Changes in plasma composition will change lymph
Protein concentration of lymph is lower than in
plasma and varies inversely proportional to rate of
formation that varies from tissue to tissue.
Lymph flow rate
Lymph flow rate is usually low. It is influenced
primarily by the rate of lymph formation.
The flow rate is affected by compression of
lymphatics by negative intrathoracic pressure
Valves in the lymph vessels prevent retrograde flow
similar to those in veins.
Formation of lymph
ISF forms at the arterial (coming from the heart) end
of the capillaries because of higher pressure of blood,
Most of it returns to its venous ends and venules; the
rest (10—20%) enters the lymph capillaries as lymph.
Thus lymph formed is a watery clear liquid with the
same composition as the ISF.
As it flows through the lymph nodes, however, it
comes in contact with blood and tends to accumulate
more cells (particularly lymphocytes) and proteins.
An organ that is characterized by clusters of
lymphocytes and other cells, such as macrophages,
enmeshed in a framework of short, branching
connective tissue fibers.
The lymphocytes originate in the red bone marrow
with other types of blood cells and are carried in the
blood from the bone marrow to the lymphatic organs.
Types of Lymphatic organs
Primary lymphatic organs
Secondary lymphatic organs
Encapsulated diffuse lymphoid tissue
includes the spleen and lymph nodes.
Unencapsulated diffuse lymphoid tissue
includes gut-associated lymphoid tissues and
One of a number of small swellings found at intervals
along the lymphatic system.
They are widely distributed throughout the body
along the lymphatic pathways.
Lymph nodes are not present in the central nervous
Composed of lymphoid tissue.
Structure of lymph nodes
Small bean-shaped structures
Usually less than 2.5 cm (1 inch) in length.
Three superficial regions where lymph nodes tend to
Inguinal nodes in the groin
Axillary nodes in the armpit
Cervical nodes in the neck
Function of Lymph nodes
Filter the lymph before it is returned to the blood
Preventing foreign particles from entering the
They also produce lymphocytes
Waxing, Waning of Lymph Nodes
Waxing and waning terms used to describe transient or
short-term fluctuations in the size of lymph nodes
that could be accounted
Response to treatment
Immune activation against lymphoma
Collapsing of necrotic areas in lymph nodes may
explain a sudden decrease in a large lymph node.
Lymph nodes may enlarge when immune cells react
to pathogen such as virus or bacteria.
Cluster of lymphatic tissue just under the mucous
membranes that line the nose, mouth, and pharynx
(throat) called tonsils.
There are three groups of tonsils.
1. Pharyngeal tonsils
2. Palatine tonsils
3. Lingual tonsils
Provide protection against harmful substances and
pathogens that may enter the body through the nose
Function of Spleen
Primary lymphatic organ in the body; it is located
over the heart and/or in the neck area, anterior to the
ascending aorta and posterior to the sternum.
The thymus consists of two lobes enclosed in a
capsule and is further divided internally
Function of the thymus is the processing and
maturation of special lymphocytes (white blood cells)
called T-lymphocytes or T-cells, which are associated
with antibody production.
Tubular vessels transport back lymph to the blood
ultimately replacing the volume lost from the blood
during the formation of the interstitial fluid.
The two main lymph ducts are:
Structure of lymphatics is based on that of blood
Inner lining of single flattened endothelial cells
Smooth muscles arranged in a circular fashion
around endothelial cells
Outermost layer consists of fibrous tissue
Specialized form of reticular connective tissue that
contains various types of white blood cells enmeshed
In it, most numerous being the lymphocytes.
Lymphoid tissue can be of three types depending
upon the stage of lymphocyte development and
Primary(central) lymphoid tissue
Secondary(peripheral) lymphoid tissue
Tertiary lymphoid tissue
Function of Lymphoid Tissues
Makes up the spleen, the thymus, and the tonsils, as
well as visceral nodes, and lacteals which are all
associated with mucous membranes of the gastrointestinal tract.
Concerned with immune functions in defending the
body against the infections and spread of tumors.
Functions of Lymphatic System
Draining fluid into the bloodstream
Filtering the blood
helps fight infection in many ways such as
Helping to make special white blood cells
(lymphocytes) that produce antibodies
Having other blood cells called macrophages
inside the lymph nodes which swallow up and kill any